JP2000057595A - Optical head device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head device capable of generating a focus error signal that is less affected by the diffraction of a pit, a recording mark or a groove on an optical disk with respect to the positional shifting of an optical element. SOLUTION: An optical beam emitted from a light source 1 is converged and illuminated to an optical disk by an objective lens. A reflection light from the optical disk is guided through a diffraction type optical element to a photodetector 9, the diffraction type optical element 8 having two diffraction areas divided along an area dividing line extended in parallel or vertical to a track on the optical disk, and the photodetector 9 having two light receiving surfaces respectively having dividing lines extended in parallel or vertical to the track on the optical disk and composed of 4 divided areas for respectively detecting a +1st order diffracting light and a -1st order diffracting light. From output signals corresponding to these two light receiving surfaces of the photodetector 9, a computing circuit 13 generates a focus error circuit to cancel the positional shifting effect of the diffraction type optical element 8 or the photodetector 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device for recording and / or reproducing information by irradiating an optical recording medium such as an optical disk or an optical card with a light beam. Without being affected by noise due to diffraction from pits or recording marks on the recording surface, and without being affected by noise due to diffraction from grooves when the light beam crosses the track of the recording medium; and The present invention relates to an optical head device capable of detecting a focus error with high light use efficiency.

[0002]

2. Description of the Related Art In an optical head device for recording / reproducing information using an optical disk, the focal position of an objective lens is made coincident with the recording surface in order to focus and irradiate a light beam from a light source onto the recording surface of the optical disk. This is very important. For this purpose, a control (focusing servo) for detecting a focus error of the objective lens with respect to the recording surface and moving the objective lens in the optical axis direction based on the error is performed. As a focus error detection method in an optical head device, many methods are known, and an astigmatism method is well known as a general method.

FIG. 22 shows a focus error detection system based on the astigmatism method. The optical beam from the light source 1 is irradiated as a minute spot on the optical disk 6 via the collimator lens 2, the beam shaping prism 3, the beam splitter 4, and the objective lens 5, and the reflected light from the optical disk 6 is guided to the cylindrical lens 14 to After the astigmatism is given, it is arranged at a position where the beam cross section of the astigmatism optical system becomes circular at the time of focusing (when the optical disk 6 is at the focal position of the objective lens 5).
The output from the photodetector 15 is input to the arithmetic circuit 13 via the current-voltage conversion amplifier array 12 and
(A + C) −
The focus error signal is obtained by performing the calculation of (B + D).

[0004]

In a conventional focus error detection system based on the astigmatism method, if the optical system is an ideal optical system having no displacement of the optical element, the focus error signal is always zero during focusing. However, it is practically impossible to attach the optical element to the optical head device without displacement. When such a displacement of the optical element exists, the focus error signal does not become zero even during focusing due to the influence of diffraction from the pits or recording marks, and it becomes difficult to perform stable focusing servo. is there.

FIG. 23 shows the intensity distribution of the light beam on the light receiving surface of the photodetector shown in FIG. In FIG. 23A, reference numerals 151 to 153 denote light receiving surfaces of the four-divided photodetector 15, the middle circles represent light beams incident on the photodetector 15, and the black parts represent pits or recording marks on the optical disk 6. 2 schematically shows a diffraction image. FIG.
(B), dashed circles 171 to 173 indicate light spots on the optical disk 6, and 16 indicates pits or recording marks.

When a pit or a recording mark 16 on the optical disk 6 is scanned by a light beam focused by the objective lens 5 as shown by spots 171, 172, and 173 in FIG. The light intensity distribution above is represented by 151, 152, 153 in FIG.
It changes like Here, the black portions in the figure correspond to the darkened portions due to the diffraction from the pits or the recording marks 16.

As shown in FIG. 23, when there is a displacement in the four-divided photodetector 15, the focus error signal F = (A + C)-(B + D) is not detected even during focusing. Positive (+) when the light intensity distribution on the vessel 15 is 151,
In the case of 152, it fluctuates to zero, and in the case of 153, it fluctuates to negative (-), indicating that it is difficult to perform correct focusing control.

Further, as a second problem, there is a case where not only diffraction from a pit mark or a recording mark but also diffraction from a groove is affected.

That is, in a conventional focus error detection system based on the astigmatism method, if the optical system is an ideal optical system having no displacement of the optical element, the focus error signal is always zero at the time of focusing. However, it is practically impossible to attach the optical element to the optical head device without displacement.
When such a displacement of the optical element exists, there is a problem that the focus error signal does not become zero even during focusing due to the influence of the diffraction from the groove, and stable focusing servo becomes difficult.

FIG. 27 shows a light beam intensity distribution on the light receiving surface of the photodetector of FIG. Also, FIG. 27A shows the light receiving surfaces 251 to 253 of the four-divided photodetector 15, wherein the circle inside is the light beam incident on the photodetector 15, and the black part is the diffraction image of the groove on the optical disk 6. This is schematically shown. In FIG. 23 (b),
Light spots on the optical disc 6 indicated by circles df,
Groove 116 is shown.

The light beam focused on the groove 116 on the optical disk 6 by the objective lens 5 is used as shown in FIG.
When scanning as shown by spots d, e, f of
The light intensity distribution on the split photodetector 15 changes like light receiving surfaces 251 to 253 in FIG. Here, a black part in the figure corresponds to a part that is darkened by the influence of the diffraction from the groove 116.

As shown in FIG. 27, when the four-divided photodetector 15 is misaligned, the focus error signal F = (A + C)-(B + D) is not detected even when focusing. The light intensity distribution on the detector 15 fluctuates to positive (+) in the case of the light receiving surface 151, zero in the case of the light receiving surface 152, and negative (-) in the case of the light receiving surface 153, making it difficult to perform correct focusing control. You can see that there is.

The present invention has been made in order to solve the above two problems. Even when the optical element is misaligned, the effect of diffraction of pits and recording marks on an optical disk, and furthermore, the effect of a groove. It is an object of the present invention to provide an optical head device that can obtain a focus error signal that is less affected by diffraction.

[0014]

In order to solve the above-mentioned problems, an optical head device according to the present invention comprises: a light source for emitting a light beam; and a light beam emitted from the light source, which is focused and irradiated on a recording medium. An objective lens for transmitting reflected light from the recording medium, and a plurality of divided areas divided by a dividing line along a direction parallel to a track on the recording medium in a plane perpendicular to the optical axis of the reflected light. Having a light receiving surface, a photodetector having the light receiving surface arranged such that the paired divided regions are arranged at symmetrical positions with respect to the optical axis, and with respect to the optical axis of the reflected light. In a plane perpendicular to the recording medium, the reflected light is divided along a direction parallel to the track on the recording medium and a direction perpendicular to the track, and + N-order diffracted light (N is one or more) at each divided portion of the reflected light. Any integer) and -N
Next-order diffracted light (N is an arbitrary integer of 1 or more) is received by the divided regions of the light receiving surface arranged at positions symmetrical to each other with respect to the optical axis, and mutually diffracted along a direction parallel to the track. Diffraction that diffracts the reflected light so that the + N-order diffracted lights and the −N-order diffracted lights in the adjacent divided portions are received by the divided areas located on the opposite sides of the dividing line on the light receiving surface. And a calculating means for calculating a focus error signal from an output signal of the photodetector for both the + N-order diffracted light and the -N-th diffracted light.

More specifically, a first optical head device according to the present invention comprises: a light source for emitting a light beam; a light beam emitted from the light source being focused and irradiated on a recording medium; A diffraction lens having an objective lens that transmits reflected light and two diffraction regions arranged at a position where the reflected light is incident and divided along a region division line extending in a direction parallel to a track on the recording medium; An optical element and a first and a fourth divided area divided by a dividing line extending in a direction parallel to and perpendicular to a track on the recording medium in a plane perpendicular to the optical axis of the reflected light. A photodetector having a second light receiving surface, wherein the first and second light receiving surfaces are arranged such that the paired divided regions are arranged at symmetrical positions with respect to the optical axis; From the output signal of the photodetector, the recording medium Comprising a calculating means for generating the operation a focus error signal indicating a focus error of said objective lens with respect.

In the arithmetic means, an output signal corresponding to the first and second light receiving surfaces from the photodetector is added to a sum signal of signals corresponding to predetermined two divided areas having a diagonal positional relationship. Find the difference signal from the sum signal of the signals corresponding to the other two divided areas in a diagonal positional relationship,
Further, a focus error signal is generated by obtaining a sum signal of these two difference signals.

That is, by equally dividing the influence of diffraction of pits and recording marks in the diffraction area divided in parallel with the track direction, it is possible to cancel the influence and reduce the influence of diffraction on the focus error signal. it can. That is, since the diffraction of pits and recording marks is distributed in the track direction, if the dividing line of the diffraction area is parallel to the track direction,
No matter where the pit position is, there is no difference in the effect of diffraction (the amount of shadow in the light spot) between the two diffraction regions, and therefore no adverse effect on the focus error signal.

In the second optical head device according to the present invention, the operation of the arithmetic means in the first optical head device is simplified, and the output signal corresponding to the first light receiving surface from the photodetector is recorded on a recording medium. The difference signal between the signals corresponding to the first and second divided areas adjacent to each other in the direction parallel to the upper track is determined, and the output signal from the photodetector corresponding to the second light receiving surface is recorded on a recording medium. Signals corresponding to third and fourth divided areas which are adjacent to each other in a direction parallel to the upper track and which are different from the first and second divided areas in a direction perpendicular to the track on the recording medium. Find the difference signal of
Further, a focus error signal is generated by obtaining a sum signal of these two difference signals.

A third optical head device according to the present invention comprises a light source for emitting a light beam, and an objective for focusing and irradiating the recording medium with the light beam emitted from the light source and transmitting reflected light from the recording medium. A lens, a diffractive optical element disposed at a position where the reflected light is incident, and having two diffractive regions divided along a region dividing line extending in a direction parallel to a track on the recording medium; In a plane perpendicular to the optical axis of light, the first and second light receiving surfaces divided into four divided regions by dividing lines extending in a direction parallel to and perpendicular to the track on the recording medium are defined. A photodetector having the first and second light receiving surfaces such that the paired divided regions are arranged at positions symmetrical with respect to the optical axis, and an output signal of the photodetector. From the object to the recording medium Comprising a calculating means for generating the operation a focus error signal indicating a focus error of the lens.

In the arithmetic means, the output signals from the photodetector corresponding to the first and second light receiving surfaces and the output signals corresponding to the third and fourth light receiving surfaces pass through the optical axis and pass through the optical axis. The sum signal of signals corresponding to two predetermined divided regions in a non-symmetrical positional relationship with respect to an axis extending in a direction parallel to the track, and the sum of signals corresponding to the other two divided regions in a non-symmetrical positional relationship. A focus error signal is generated by calculating a difference signal between the two signals and a sum signal of the two difference signals.

In the third optical head device, two divided regions of the first and second light receiving surfaces or the third and fourth light receiving surfaces of the photodetector which are in a non-linear symmetric positional relationship are connected to each other. With this configuration, a part of the calculation of the calculation means may be performed on the photodetector.

In the first to third optical head devices, for example, when the objective lens is in focus on the recording medium, the diffractive optical element reflects the light projected on the photodetector surface. When the spot shape of the light exhibits a line-symmetric shape, and is deviated from the in-focus state, the spot shape is configured to have a characteristic of deviating from the line symmetry according to the deviation amount. Further, specifically, this diffractive optical element is configured such that one diffraction region has a pin-shaped diffraction grating and the other diffraction region has a barrel-shaped diffraction grating.

A fourth optical head device according to the present invention comprises a light source for emitting a light beam, and an object for focusing and irradiating the recording medium with the light beam emitted from the light source and transmitting reflected light from the recording medium. A lens and 4 divided along an area dividing line that is disposed at a position where the reflected light is incident and extends in a direction parallel to and perpendicular to a track on the recording medium.
A diffractive optical element having two diffraction regions, and in a plane perpendicular to the optical axis of the reflected light, each having a dividing line along a direction parallel to a track on the recording medium,
First, second, third, and fourth light receiving surfaces including two divided regions for respectively detecting + N-order diffracted light from four diffraction regions of the diffractive optical element, and -1st order from the diffraction regions Fifth, sixth, seventh and eighth light receiving surfaces each composed of two divided regions for detecting a folded light, respectively, and the paired divided regions are arranged at positions symmetrical with respect to the optical axis. And a calculation for generating a focus error signal indicating a focus error of the objective lens with respect to the recording medium from an output signal of the photodetector having the first to eighth light receiving surfaces. Means.

In the arithmetic means, the output signal corresponding to the first, second, third, and fourth light receiving surfaces from the photodetector is added to the sum signal of the signal corresponding to any one of the divided areas. A difference signal from the sum signal of the signals corresponding to the other divided area is obtained, and any one of the output signals corresponding to the fifth, sixth, seventh, and eighth light receiving surfaces from the photodetector is determined. The difference signal between the sum signal of the signal corresponding to the region and the sum signal of the signal corresponding to the other divided region is obtained, and the focus error signal is generated by obtaining the sum signal of these two difference signals.

Further, in the fifth optical head device, of the first, second, third and fourth light receiving surfaces or the fifth, sixth, seventh and eighth light receiving surfaces of the photodetector, A part of the calculation by the calculation means may be performed on the photodetector by connecting and configuring two divided areas adjacent to each other in a direction parallel to the track on the medium.

The diffractive optical element in the fifth optical head device, specifically, for example, when the objective lens is in focus on the recording medium, reflects the reflected light projected on the photodetector surface. When the eight spots are located on one area of each of the first, second, third, fourth, fifth, sixth, seventh, and eighth light receiving surfaces and are out of focus, Eight spots increase according to the shift amount, and four spots among the eight spots correspond to the first, second, third, fourth, fifth, sixth, seventh and seventh spots according to the shift direction. It is configured to have a characteristic of moving to one region of each of the eight light receiving surfaces.

The optical head device according to the present invention further comprises means for generating, from the output signal of the photodetector, a tracking error signal indicating the positional deviation of the light beam with respect to the track on the recording medium in the track width direction by calculation. May be.

The optical head device according to the present invention has a beam splitter for separating the light beam emitted from the light source from the reflected light reflected by the recording medium and passing through the objective lens. The element may be arranged between the objective lens and the beam splitter, and when tracking is performed by moving the objective lens in the track width direction, the diffractive optical element may be simultaneously moved in the track width direction.

In the optical head device of the present invention thus configured, even if there is a displacement of the photodetector or the diffractive optical element, the influence of diffraction from pits or recording marks on the recording surface of the recording medium. The fluctuation of the focus error signal generated in the above is canceled by the assumption of the calculation, so that a stable focus error can be detected.

Further, according to the present invention, there is provided an optical disk device using the above-described optical head device.

Further, the present invention is not limited to the diffraction effect from a pit or a recording mark on a recording surface, but also includes a diffractive optical element for avoiding the effect of diffraction from a groove when a light beam crosses a track of a recording medium. The optical element is not limited to the direction parallel to the tracking direction of the recording medium, and it is possible to use a diffractive optical element having two diffraction regions divided along a region dividing line extending in the vertical direction.

The eleventh aspect specifies the two types of optical head devices by not limiting the direction of the area dividing line. That is, the present invention provides a light source that emits a light beam, an objective lens that focuses and irradiates a light beam emitted from the light source onto a recording medium, and transmits reflected light from the recording medium, and an optical axis of the reflected light. In a plane perpendicular to the optical axis, the light receiving surface is divided into a plurality of divided regions by a dividing line in a predetermined direction, and the paired divided regions are arranged at symmetrical positions with respect to the optical axis. A photodetector having a light-receiving surface, and the reflected light in a plane perpendicular to the optical axis of the reflected light in a direction parallel to a track on the recording medium and in a direction perpendicular to the track. Split
+ N-order diffracted light (N is an arbitrary integer of 1 or more) and −N-order diffracted light (N is an integer of 1 or more) in each divided portion of the reflected light are arranged at positions symmetrical to each other with respect to the optical axis. The light is received by the divided area of the light receiving surface,
The + N-order diffracted lights and the −N-order diffracted lights in the divided portions adjacent to each other along the predetermined direction are received by the divided regions located on the opposite sides with respect to the division line of the light receiving surface, respectively. A diffractive optical element that diffracts the reflected light;
An optical head device comprising: arithmetic means for calculating a focus error signal from an output signal of the photodetector for both Nth-order diffracted lights.

An optical head device provided to reduce the influence of groove diffraction is further provided.
An object of the present invention is to provide an optical head device in which a dividing line for dividing a diffraction region of a diffractive optical element is perpendicular to a tracking direction of a recording medium.

That is, by equally dividing the effect of the groove diffraction in the diffraction region divided perpendicularly to the track direction, this effect can be canceled out and the effect of the groove diffraction on the focus error signal can be reduced. . That is, since the diffraction of the groove is distributed in the direction perpendicular to the track direction, if the dividing line of the diffraction area is perpendicular to the track direction, the influence of diffraction between the two diffraction areas (shading of the shadow in the light spot) ) Does not occur, and therefore does not adversely affect the focus error signal.

The optical head device according to the present invention having such a diffraction region focuses and irradiates a light source for emitting a light beam and a recording medium having a groove (guide groove) with the light beam emitted from the light source. An objective lens for transmitting the reflected light from the recording medium, and a plurality of divided areas divided by a dividing line along a direction perpendicular to a track on the recording medium in a plane perpendicular to the optical axis of the reflected light. Having a light receiving surface, a photodetector having the light receiving surface arranged such that the paired divided regions are arranged at symmetrical positions with respect to the optical axis, and with respect to the optical axis of the reflected light. In a plane perpendicular to the recording medium, the reflected light is divided along a direction parallel to the track on the recording medium and a direction perpendicular to the track, and + N-order diffracted light (N is one or more) at each divided portion of the reflected light. Any integer) and -Nth order diffracted light N is 1 or more arbitrary integer). However,
+ N-order diffracted lights and -N-order diffracted lights in the divided portions adjacent to each other along the direction perpendicular to the track while being received by the divided regions of the light receiving surface arranged at positions symmetrical to each other with respect to the optical axis. Are diffractive optical elements for diffracting the reflected light so as to be received by the divided areas located on opposite sides of the light receiving surface with respect to the division line, the + N-order diffracted light and the-
Calculating means for calculating a focus error signal from an output signal of the photodetector for both of the N-order diffracted lights.

More specifically, a first optical head device according to the present invention having a plurality of diffraction regions divided vertically to a track comprises a light source for emitting a light beam, and a light beam emitted from the light source. An objective lens for focusing and irradiating a recording medium having a groove (guide groove) and transmitting reflected light from the recording medium; and an objective lens disposed at a position where the reflected light is incident, in a direction perpendicular to a track on the recording medium. A diffractive optical element having two diffraction regions divided along an extended region dividing line, and a direction parallel to and perpendicular to a track on the recording medium in a plane perpendicular to an optical axis of the reflected light. Has a first and a second light receiving surface divided into four divided regions by a dividing line extending in the direction of, and the paired divided regions are arranged at symmetrical positions with respect to the optical axis. 1st and 1st A photodetector formed by arranging the light-receiving surface,
Calculating means for generating, by calculation, a focus error signal indicating a focus error of the objective lens with respect to the recording medium from the output signal of the photodetector.

In the arithmetic means, the output signal corresponding to the first and second light receiving surfaces from the photodetector is summed with the sum signal of the signals corresponding to the two predetermined diagonally positioned divided areas. Find the difference signal from the sum signal of the signals corresponding to the other two divided areas in a diagonal positional relationship,
Further, a focus error signal is generated by obtaining a sum signal of these two difference signals.

In the second optical head device according to the present invention having a plurality of diffraction areas vertically divided into tracks, the operation of the arithmetic means in the first optical head device is simplified.
For an output signal corresponding to the first light receiving surface from the photodetector, a difference signal between signals corresponding to the first and second divided areas which are adjacent to each other in the direction perpendicular to the track on the recording medium is obtained. The output signal from the photodetector corresponding to the second light receiving surface is adjacent to the track on the recording medium in a direction perpendicular to the track, and the first and second divided areas correspond to the track on the recording medium. Third, where the position in the vertical direction is different,
A focus error signal is generated by obtaining a difference signal between the signals corresponding to the fourth divided region and further obtaining a sum signal of these two difference signals.

A third optical head device having a plurality of diffraction regions vertically divided into tracks according to the present invention comprises a light source for emitting a light beam and a groove (guide groove) for transmitting the light beam emitted from the light source. An objective lens that focuses and irradiates a recording medium having the same and transmits reflected light from the recording medium, and an area dividing line that is disposed at a position where the reflected light is incident and extends in a direction perpendicular to a track on the recording medium. A diffractive optical element having two diffractive regions divided along a plane extending in a direction parallel to and perpendicular to a track on the recording medium in a plane perpendicular to the optical axis of the reflected light First and second divided into four divided areas by lines
The first and second light receiving surfaces are arranged such that the paired divided regions are arranged at positions symmetrical with respect to the optical axis.
And a calculation means for calculating a focus error signal indicating a focus error of the objective lens with respect to the recording medium from an output signal of the photodetector.

In the arithmetic means, the output signals corresponding to the first and second light receiving surfaces and the output signals corresponding to the third and fourth light receiving surfaces from the photodetector pass through the optical axis. The sum signal of signals corresponding to two predetermined divided regions in a non-symmetrical positional relationship with respect to an axis extending in the direction perpendicular to the track, and the sum of signals corresponding to the other two divided regions in a non-symmetrical positional relationship. A focus error signal is generated by calculating a difference signal between the two signals and a sum signal of the two difference signals.

In the third optical head device, two divided regions having a non-symmetrical positional relationship among the first and second light receiving surfaces or the third and fourth light receiving surfaces of the photodetector are connected to each other. With this configuration, a part of the calculation of the calculation means may be performed on the photodetector.

In the first to third optical head devices, for example, when the objective lens is in focus on the recording medium, the diffractive optical element reflects the reflected light projected onto the photodetector surface. When the spot shape of the light exhibits a line-symmetric shape, and is deviated from the in-focus state, the spot shape is configured to have a characteristic of deviating from the line symmetry according to the deviation amount. Further, specifically, this diffractive optical element is configured such that one diffraction region has a pin-shaped diffraction grating and the other diffraction region has a barrel-shaped diffraction grating.

A fourth optical head device having a plurality of diffraction regions vertically divided into tracks according to the present invention is a light source for emitting a light beam, and the light beam emitted from the light source is focused and irradiated on a recording medium. An objective lens that transmits reflected light from the recording medium, and an objective lens that is disposed at a position where the reflected light is incident, and is divided along an area dividing line extending in a direction parallel to and perpendicular to a track on the recording medium. A diffractive optical element having four diffractive regions, and a dividing line along a direction perpendicular to a track on the recording medium in a plane perpendicular to the optical axis of the reflected light, First, second, third, and fourth light receiving surfaces each including two divided regions for detecting + N-order diffracted light from four diffraction regions of the diffractive optical element, respectively, and-from the diffraction regions.
Fifth, sixth, seventh, and eighth light receiving surfaces each including two divided regions for detecting the first-order diffracted light, and the paired divided regions are arranged at positions symmetrical with respect to the optical axis. A photodetector provided with the first to eighth light receiving surfaces so as to generate a focus error signal indicating a focus error of the objective lens with respect to the recording medium from an output signal of the photodetector. Calculation means for performing the calculation.

Then, in the calculating means, the output signal corresponding to the first, second, third and fourth light receiving surfaces from the photodetector is summed with the sum signal of the signal corresponding to any one of the divided areas. A difference signal from the sum signal of the signals corresponding to the other divided area is obtained, and any one of the output signals corresponding to the fifth, sixth, seventh, and eighth light receiving surfaces from the photodetector is determined. The difference signal between the sum signal of the signal corresponding to the region and the sum signal of the signal corresponding to the other divided region is obtained, and the focus error signal is generated by obtaining the sum signal of these two difference signals.

Further, in a fifth optical head device having a plurality of diffraction regions vertically divided into tracks, the first, second, third, and fourth light receiving surfaces of the photodetector or the fifth, sixth, and fifth light receiving surfaces are provided. By combining two divided areas of the seventh and eighth light receiving surfaces which are adjacent to each other in the direction perpendicular to the track on the recording medium, a part of the calculation of the calculation means can be performed by the photodetector. You may go on.

The diffractive optical element in the fifth optical head device having a plurality of diffraction regions vertically divided into tracks is as follows:
Specifically, for example, when the objective lens is in focus with respect to the recording medium, eight spots of the reflected light projected on the photodetector surface are first, second, third, fourth, and fourth spots. The eight light spots are located on one region of each of the fifth, sixth, seventh, and eighth light receiving surfaces, and when out of focus, the eight spots are increased according to the amount of shift, and the directions in which the spots are shifted Of the eight spots move to one of the first, second, third, fourth, fifth, sixth, seventh, and eighth light receiving surfaces in accordance with the first, second, third, fourth, fifth, sixth, seventh, and eighth light receiving surfaces. It is configured as follows.

In the optical head device according to the present invention, a tracking error signal indicating a displacement of a light beam with respect to a track on a recording medium in a track width direction is generated from an output signal of a photodetector by a push-pull method or a phase difference method. It may further have means for performing.

Further, the optical head device according to the present invention has a beam splitter for separating the light beam emitted from the light source from the reflected light reflected by the recording medium and passing through the objective lens. The element may be arranged between the objective lens and the beam splitter, and when tracking is performed by moving the objective lens in the track width direction, the diffractive optical element may be simultaneously moved in the track width direction.

In the optical head device of the present invention thus configured, even if the photodetector and the diffractive optical element are misaligned, they are generated due to the diffraction from the groove on the recording surface of the recording medium. Since the fluctuation of the focus error signal is canceled in the course of the calculation, stable focus error detection becomes possible.

Further, according to the present invention, there is provided an optical disk device using an optical head device having a plurality of diffraction regions which are vertically divided into tracks as described above.

[0051]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 shows a configuration of a main part of an optical head device according to a first embodiment of the present invention. This optical head device includes a light source 1, a collimator lens 2, a beam shaping prism 3, a beam splitter 4, an objective lens 5, a condenser lens 7, a diffractive optical element 8, a photodetector 9, and an amplifier array having a current-voltage conversion function. 12 and an operation circuit 13.

The light source 1 is, for example, a semiconductor laser. Light emitted from the light source 1 is converted into a parallel light beam by a collimator lens 2. The light that has exited from the collimator lens 2 enters a beam splitter 4 after the beam shape is shaped by a beam shaping prism 3. The light transmitted through the beam splitter 4 is transmitted to a CD-ROM or DVD by the objective lens 5.
Optical disk 6 consisting of (Digital Versatile Disk)
Is focused and irradiated as a minute spot.

The reflected light from the optical disk 6 passes through the objective lens 5 in the opposite direction to the light incident on the optical disk 6 and enters the beam splitter 4. The reflected light from the optical disk 6 that has entered the beam splitter 4 is reflected by the beam splitter 4, is then condensed by a condenser lens 7, and is incident on a diffractive optical element 8.

FIG. 2 shows a configuration example of the diffraction optical element 8. The diffractive optical element 8 has two diffraction regions 8A and 8B composed of a curve group as shown in FIG. Specifically, the diffraction area 8A is a pin-shaped diffraction grating, and the diffraction area 8B is a barrel-shaped diffraction grating. These diffraction regions 8A and 8B are defined as straight lines that pass through the optical axis (z axis in FIG. 1) of the reflected light from the optical disk 6 and are parallel to the tracks on the optical disk 6 (x axis in FIG. 1). It is divided as a division line L1. The diffraction areas 8A and 8B diffract the reflected light from the optical disc 6 into 0th-order diffracted light and ± 1st-order diffracted light, respectively. The grating pitch of the diffraction areas 8A and 8B has a spatial frequency necessary for separating and detecting the 0th-order diffracted light, the + 1st-order diffracted light, and the -1st-order diffracted light in the vicinity of the focal plane of the condenser lens 7, and the + 1st order diffracted light. A spatial change is given to transform the folded light and the -1st-order diffracted light into a spot shape necessary for detecting a focus error near the focal plane of the condenser lens 7.

The grating pattern shape of the diffractive optical element 8 shown in FIG. 2A is such that the distance between the diffractive optical element 8 and the photodetector 9 is 20 mm and the beam diameter on the diffractive optical element 8 is 2 mm.
In the case of (1), the separation distance between the 0th-order diffracted light and the ± 1st-order diffracted light from the diffraction area 8A of the diffractive optical element 8 near the focal plane of the condensing lens 7 is 0.6 mm. This is an example designed so that the separation distance between the 0th-order diffracted light and ± 1st-order diffracted light from the diffraction region 8B of the element 8 is 0.4 mm. Further, in order to distribute the first-order diffracted light equally to ±, the cross-sectional shape of the diffraction regions 8A and 8B is a step-like shape in which the ratio of the grating width D2 to the grating pitch D1 is 1/2 as shown in FIG. It is desirable to use a phase grating. The light detector 9 is arranged to detect the diffracted light from the diffractive optical element 8.

FIG. 3 shows a configuration example of the photodetector 9. The photodetector 9 has first and second light receiving surfaces 10 and 11 divided into four parts. The first light receiving surface 10 is divided into four divided regions 10 by a dividing line in the same direction as the image of the region dividing line L1 of the diffractive optical element 8 and a dividing line orthogonal thereto.
a to 10d. Similarly, the second light receiving surface 1
1 is divided into four divided regions 11a to 11d by a dividing line in the same direction as the image of the region dividing line L1 of the diffractive optical element 8 and a dividing line orthogonal to the dividing line.

Then, as shown in FIG.
a, 10b are +1 from the area 8A of the diffractive optical element 8
The second-order diffracted light is received, and the divided areas 10c and 10d receive the + 1st-order diffracted light from the area 8B of the diffractive optical element 8. The divided areas 11c and 11d are formed in the area 8A of the diffractive optical element 8.
-1st-order diffracted light from the first and second divided regions 11a and 11b
Receives the -1st-order diffracted light from the area 8B of the diffractive optical element 8. The signal current corresponding to each of the divided areas 10a to 10d and 11a to 11d of the light receiving surfaces 10, 11 of the photodetector 9 is converted into a voltage signal by the current-voltage conversion amplifier array 12, and is amplified to an appropriate level. After that, it is input to the arithmetic circuit 13.

The operation circuit 13 generates the focus error signal F by the operation shown in the following equation (1). F = (S10a + S10c)-(S10b + S10d) + (S11b + S11d)-(S11a + S11c) (1) where S10a, S10b, S10c, S10
d represents a signal corresponding to each of the divided areas 10a, 10b, 10c, and 10d among output signals corresponding to the light receiving surface 10, and S11a, S11b, S11c, S
11d represents a signal corresponding to each of the divided areas 11a, 11b, 11c, 11d among output signals corresponding to the light receiving surface 11.

That is, in the present embodiment, in the arithmetic circuit 13, the output signal corresponding to the light receiving surface 10 from the photodetector 9 is divided into two diagonally divided areas 10.
a, 10c (S10a + S1)
0c) and the sum signal (S10b) of the signals corresponding to the other two divided regions 10b and 10d which are also in a diagonal positional relationship.
+ S10d) (S10a + S10c).
− (S10b + S10d), and further, regarding the output signal corresponding to the light receiving surface 11 from the photodetector 9, the sum signal (S11b + S11d) of the signals corresponding to the two divided regions 11b and 11d having a diagonal positional relationship. And the other two divided areas 11a and 11 also having the same diagonal positional relationship.
c (S11a + S11c)
)-(S11b + S11d)-(S11b)
a + S11c), and the sum signal of these two difference signals is obtained to generate the focus error signal F.

FIG. 5 is a spot diagram showing a spot shape change on the light receiving surface of the photodetector 9 of the light beam diffracted by the diffractive optical element 8 when the relative position between the objective lens 5 and the optical disk 6 changes. Indicated by In the figure, the light beam spot is represented by a set of dots. FIG. 5A shows a state where the objective lens 5 is close to the optical disc 6. FIG. 5B shows a case where the optical disk 6 is in focus with the focal plane of the objective lens 5 positioned, and the light beam spot has a substantially line-symmetric shape. FIG.
5A shows a state when the objective lens 5 is separated from the optical disk 6, and the light beam spot shape changes in the opposite direction to that in FIG.

Accordingly, by performing the calculation of the equation (1) in the calculation circuit 13 as described above, the amount of the shift from the focal position of the objective lens 5 is zero when the focus state shown in FIG. A focus error signal whose magnitude and polarity change in accordance with the direction of. FIG. 6 shows a change in the focus error signal F with respect to the focus error.

According to the present embodiment, even if the diffractive optical element 8 or the photodetector 9 is displaced due to, for example, an error in the assembly of the optical head or aging, the conventional astigmatism method is used. It is possible to reduce the fluctuation of the focus error signal which occurs remarkably in the focus error detection. Hereinafter, this effect will be described in detail with reference to FIGS.

FIGS. 7 to 9 show the intensity distribution of the light beam incident on the diffractive optical element 8 during focusing and the light beam on the light receiving surface of the photodetector 9 after being diffracted by the diffractive optical element 8. 3 shows the intensity distribution of. Hereinafter, FIGS.
And (ii) when the photodetector 9 has a misalignment, and (iii) when the diffractive optical element 8 has a misalignment. Each case will be described.

(I) In the case where there is no displacement between the diffractive optical element 8 and the photodetector 9 The light intensity at the time of focusing with an ideal optical system where there is no displacement between the diffractive optical element 8 and the photodetector 9 The distribution is shown in FIG. In FIG. 7A, reference numerals 91 to 93 denote light receiving surfaces of the photodetector 9, and black portions schematically show diffraction images of pits or recording marks on the optical disk 6. 81 in FIG. 7B
Numerals 83 indicate the surface of the diffractive optical element 8, wherein a circle schematically shows a light beam incident on the diffractive optical element 8, and a black portion schematically shows a diffraction image of a pit or a recording mark. FIG.
The dashed circles 191 to 193 in (c) are light beam spots on the optical disk 6 and indicate pits or recording marks 18 on the optical disk 6.

The pits or recording marks 18 on the optical disk 6 are formed by the light beam focused by the objective lens 5 as shown in FIG.
When scanning like (191), (192) and (193) in (c),
The intensity distribution of the light incident on the diffractive optical element 8 changes as indicated by 81, 82, and 83 in FIG. At this time, the intensity distribution of the + 1st-order diffracted light and the -1st-order diffracted light from the diffractive optical element 8 on the light receiving surface of the photodetector 9 is indicated by 91 and 91 in FIG.
The intensity distribution changes as indicated by 92 and 93, and the intensity distribution between the + 1st-order diffracted light and the -1st-order diffracted light is symmetric with respect to the origin (the intersection between the optical axis and the light receiving surface). Therefore, if the pits or the recording marks 18 on the optical disk 6 are scanned with the light beam as shown in FIG. 7, the light receiving intensity of each light receiving surface of the photodetector 9 changes even at the time of focusing. ), The focus error signal F
Is calculated, (S10a + S10 in Expression (1))
c)-(S10b + S10d), (S11b +
Since both S11d)-(S11a + S11c) become zero, the focus error signal F always becomes zero.

(Ii) When the photodetector 9 is misaligned Next, the photodetector 9 is provided with a region dividing line L1 of the diffractive optical element 8.
FIG. 8 shows the light intensity distribution at the diffractive optical element 8 and the photodetector 9 at the time of focusing when there is a displacement in the direction orthogonal to the image of FIG. As in FIG. 7, reference numerals 94 to 96 in FIG. 8A denote light receiving surfaces of the photodetector 9, and a black portion schematically shows a diffraction image of a pit or a recording mark on the optical disk 6. 8B, reference numerals 84 to 86 denote surfaces of the diffractive optical element 8, and circles indicate light beams incident on the diffractive optical element 8,
The black portion schematically shows a diffraction image of a pit or a recording mark. 8C indicate light beam spots on the optical disc 6, and indicate pits or recording marks 18 on the optical disc 6.

In this case, when the pit or the recording mark 18 on the optical disk 6 is scanned by the light beam, the light detector 9 is scanned.
Although the light receiving intensity of each light receiving surface changes, the light amount deviation on the photodetector 9 can be canceled out by calculating the focus error signal F according to the equation (1), and the light amount deviation significantly occurs in the conventional astigmatism method. The fluctuation of the focus error signal F that has been occurring can be reduced. That is, also in this case, similarly to the case of (i), (S10a + S10c) −
(S10b + S10d), (S11b + S11d)
)-(S11a + S11c) are both zero, so that the focus error signal F is always zero.

(Iii) When the Diffractive Optical Element 8 is Displaced Further, in the present embodiment, even if the diffractive optical element 8 is displaced, the fluctuation of the focus error signal can be reduced. FIG. 9 shows the intensity distribution on the diffractive optical element 8 and the photodetector 9 at the time of focusing when the diffractive optical element 8 has a displacement in the direction orthogonal to the region dividing line L1 of the diffractive optical element 8. Show. As in FIGS. 7 and 8, FIG.
Reference numerals 97 to 99 denote light receiving surfaces of the photodetector 9, and black portions schematically show diffraction images of pits or recording marks on the optical disk 6. In FIG. 9B, reference numerals 87 to 89 denote the surfaces of the diffractive optical element 8; circles schematically show the light beam incident on the diffractive optical element 8, and black portions schematically show the diffraction images of the pits or recording marks. . The dashed circle 1 in FIG.
Numerals 91 to 193 denote light beam spots on the optical disk 6, such as pits or recording marks 18 on the optical disk 6.
Is shown.

In this case, since the amounts of light incident on the two diffraction regions 8A and 8B of the diffractive optical element 8 are different, the beam size on the photodetector 9 becomes unbalanced.
By calculating the focus error signal F by
The light amount deviation on the photodetector 9 can be canceled out, and even if the pit or the recording mark 18 is scanned with the light beam, the fluctuation of the focus error signal F which has been significantly generated by the conventional astigmatism method can be reduced. it can.

That is, in this case, (S10a + S10c)-(S10b + S10) in the equation (1)
d), (S11b + S11d)-(S11a +
The two difference signals of S11c) have a certain value, but since these difference signals have the same magnitude and opposite polarities, they are canceled out by the operation of equation (1), and the focus error signal F is always zero. Becomes

As described above, according to the present embodiment, even when the diffractive optical element 8 and the photodetector 9 are misaligned, the focus error can be correctly detected without being affected by these misalignments. Become.

As a modification of the present embodiment, the focus error signal F can be calculated by the following equation (2) or (3) instead of the equation (1). F = (S10d−S10a) + (S11c−S11b) (2) F = (S10c−S10b) + (S11d−S11a) (3) That is, according to the equation (2), the light receiving surface from the photodetector 9 is obtained. For the output signal corresponding to 10, a difference signal (S10d-S10a) between signals corresponding to the divided areas 10d and 10a having an adjacent positional relationship in the direction of the area dividing line L1 (the direction parallel to the track on the optical disc 6) is obtained. , Photodetector 9
Output signals corresponding to the light receiving surface 11 from the region 1 are adjacent to each other in the direction of the region dividing line L1 and
The difference signals (S11c-S11b) of the signals corresponding to the divided regions 11c and 11b having different positions in the direction perpendicular to the region division line L1 from the regions 0d and 10a are obtained, and these two difference signals (S10d-S10a) and (S11c) are obtained. −
The focus error signal F is generated by obtaining the sum signal of S11b).

Similarly, in the equation (3), the output signal corresponding to the light receiving surface 10 from the photodetector 9 is divided by the region dividing line L1
The difference signal (S10c-S10b) between the signals corresponding to the divided regions 10c and 10b having the adjacent positional relationship in the direction of (1) is obtained. Is adjacent to
Further, a difference signal (S11d-S11a) of signals corresponding to the divided regions 11d and 11a having different positions in the direction perpendicular to the region dividing line L1 from the divided regions 10c and 10b is obtained, and these two difference signals (S10c-S10b) are obtained. ,
The focus error signal F is generated by obtaining the sum signal of (S11d-S11a).

Even if the focus error signal F is generated according to the equation (2) or (3), the light detector 9 shown in FIG.
As is clear from the light intensity distributions on the light receiving surfaces 94 to 96 when there is a positional deviation, if the focus error signal F is calculated by the equation (2) or (3), the light quantity deviation on the photodetector 9 Can be cancelled, and the fluctuation of the focus error signal F, which has been significantly generated by the conventional astigmatism method, can be reduced.

As is apparent from the light intensity distribution on the light receiving surfaces 97 to 99 when the diffractive optical element 8 shown in FIG. 9 has a positional shift, the focus error is calculated by the equation (2) or (3). By calculating the signal F, the light amount deviation on the photodetector 9 can be canceled out, and the fluctuation of the focus error signal F which has been conspicuously generated by the conventional astigmatism method can be reduced.

Further, in the optical head device of the present embodiment,
From the output signal of the photodetector 9, not only the focus error signal F but also the tracking error signal T can be obtained at the same time. For example, a push-pull method for obtaining a tracking error signal from irregularities indicating a continuous track such as a groove on the optical disk 6 or a phase difference method for obtaining a tracking error signal from a continuous pit row recorded on the optical disk 6. .

In the push-pull method, the operation of the photodetector 9 differs between the case where the direction of the dividing line of the diffractive optical element 8 shown in FIG. 2 is the tangential direction of the optical disk 6 and the case where it is the radial direction. The calculation may be performed on the output signals corresponding to the respective light receiving surfaces 10 and 11 of the photodetector 9 in FIG. 3 so that the light beam is split into two in the tangential direction of the optical disk 6.

For example, when the direction of the dividing line of the diffractive optical element 8 is the tangential direction of the optical disk 6, the tracking error signal T can be calculated according to one of the following equations (4), (5), and (6). . T = (S10a + S10b)-(S10c + S10d) (4) T = (S11c + S11d)-(S11a + S11b) (5) T = (S10a + S10b)-(S10c + S10d) + (S11c + S11b) 6) That is, the tracking error signal T by the push-pull method can be obtained by using any of the above three equations (4), (5), and (6).

On the other hand, in the tracking error detection method by the phase difference method, the light receiving surface of the photodetector 9 is arranged so that the light beam returned from the optical disk 6 is divided with the tangential direction and the radial direction of the optical disk 6 as axes. It should just be. For example, a tracking error signal T by the phase difference method is a signal T1 obtained by the following equations (7) and (8).
It is obtained by detecting the phase difference of T2. T1 = S10a + S10c (7) T2 = S10b + S10d (8) Similarly, the tracking error signal T is obtained by the phase difference method.
Is a method of detecting the phase difference between the signals T3 and T4 obtained by the following equations (9) and (10). T3 = S11a + S11c (9) T4 = S11b + S11d (10) Further, as another method for obtaining the tracking error signal T by the phase difference method, the phase difference between the signals T5 and T6 obtained by the following equations (11) and (12) is obtained. There is a way to detect T5 = S10a + S10c + S11a + S11c (11) T6 = S10b + S10d + S11b + S11d (12) In the present embodiment, any of the three tracking error detection methods described above may be used, and similar results are obtained.

Next, the principle of focus error detection in the present invention will be described in more detail with reference to FIG. Although the configuration of the first embodiment is basically used here, the principle is the same in the embodiment described later.

FIG. 10 is a diagram for explaining the relationship between the diffractive optical element 8 and the photodetector 9 shown in FIG. 4, and in order to make the description easy to understand, a direction parallel to the tracks on the optical disc 6 is shown. Semi-circular reflected light 101 divided along
This reflected light 101 is used as a diffraction area 8A of the diffraction optical element 8.
The divided areas 10a and 10b of the first light receiving surface 10 of the photodetector 9 and the divided areas 11d and 11d of the second light receiving surface 11 on which the diffracted light generated by the diffraction at (8Aa, 8Ab) is incident. Only 11c is shown.

As shown in FIG. 10, a semicircular reflected light 1
01 is diffracted by the diffraction area 8A of the diffractive optical element 8, and +
First-order diffracted light 103a, 104a and -1st-order diffracted light 103
b, 104b occur. Here, the diffracted lights 103a, 103
Reference numeral 3b denotes a diffracted light at a position approximately intermediate between the diffractive optical element 8 and the photodetector 9. The diffracted light beams 104a and 104b are diffracted light beams on the photodetector 9, and have a focused beam shape in which the optical disk 6 is located at the focal position of the objective lens 5. In FIG. 10, in order to detect a focus error, the grating pattern of the diffractive optical element 8 is such that + 1st-order diffracted light from the areas 8Aa and 8Ab of the diffractive optical element 8 is applied to the divided areas 10b and 10a of the photodetector 9, respectively. It is designed so that the -1st-order diffracted light from the areas 8Aa and 8Ab reaches the divided areas 11d and 11c of the photodetector 9, respectively.

That is, the + 1st-order diffracted light and the -1st-order diffracted light of the divided reflected light obtained by dividing the reflected light 101 in a direction parallel to the track on the optical disk 6 and in a direction perpendicular to the direction are:
The light is received by divided regions (for example, divided regions 10b and 11d of the light beam 9) of the light receiving surface of the photodetector arranged at positions symmetrical to each other with respect to the optical axis of the reflected light. Therefore, the divided portions adjacent to each other along the Y axis (for example, the diffraction region 8
Aa and reflected light incident on the diffraction region 8Ab).
The N-order diffracted lights and the −N-order diffracted lights are separated from each other with respect to the X-axis.
0b and 10a and the divided areas 11a and 11c). The diffractive optical element 8 is designed based on the above concept.

This is because, as can be seen from the cross sections of the diffracted lights 103a and 103b on the way from the diffractive optical element 8 to the photodetector 9, the + 1st-order diffracted light moves counterclockwise in the traveling direction, The grating pattern of the diffractive optical element 8 is designed so that the -1st-order diffracted light having a conjugate relationship with the folded light travels clockwise in the traveling direction in the xy plane in the z-axis direction.

At the time of focusing, the divided areas 10a, 10a
The beam shape of the + 1st-order diffracted light 104a on b and the beam shape of the -1st-order diffracted light 104b on the divided regions 11d and 11c are respectively symmetric with respect to the x-axis.

On the other hand, the objective lens 5 is
When the focus shift occurs, the light detector 9 is moved in the same manner as in FIG.
Since the symmetry of the beam shape is lost above the x-axis, the arithmetic circuit 13 calculates Equation (1), Equation (2), or Equation (3).
By performing the above calculation, the focus error signal F is obtained.

Even when the photodetector 9 and the diffractive optical element 8 are misaligned as described in the above (ii) and (iii), the diffraction image 202 of the pits on the optical disk 6 is shown in FIG.
As shown in (1), since it appears in the divided regions arranged at positions symmetrical with respect to the z-axis, according to the above-described calculations, the effect of reducing the fluctuation of the focus error signal F due to these positional deviations can be obtained.

That is, by detecting the focus error using the output signal of the photodetector 9 regarding both the + 1st-order diffracted light and the -1st-order diffracted light of the reflected light, the focus error signal F due to the influence of the diffraction image such as pits is detected. Fluctuations can be reduced.

Note that the beam shapes on the photodetector 9 are different between FIG. 5 and FIG. This is an example in which the diffractive optical element 8 is designed so as to reduce the reflected light in the x-axis direction irrelevant to the focus error detection in FIG. 5, whereas in FIG. 10, the description is simplified. Depending on the case.

The grating pattern of the diffractive optical element 8 shown in FIG.
+ 1st-order diffracted light from the photodetector 9 is divided into
However, it is also possible to design the + 1st-order diffracted light from the diffraction regions 8Aa and 8Ab to reach the divided regions 10a and 10b of the photodetector 9, respectively. In this case, the first-order diffracted light from the diffraction areas 8Aa and 8Ab of the diffractive optical element 8 has a conjugate relationship with the + 1st-order diffracted light.
c and 11d, respectively, and the same effect as in the case described above is obtained.

Further, when the distance between the diffractive optical element 8 and the photodetector 9 becomes short, when the grating pattern of the diffractive optical element 8 is designed by optimizing only the + 1st-order diffracted light,-
Since the first-order diffracted light is distorted, the effect of reducing the fluctuation of the focus error signal F due to the influence of a diffraction image such as a pit is weakened. Therefore, the grating pattern of the diffractive optical element 8 is designed to be optimized for ± 1st-order diffracted light. It is desirable to do. Specifically, for example, the + 1st-order diffracted light from the diffraction regions 8Aa and 8Ab of the diffraction optical element 8 reaches the divided regions 10b and 10a of the photodetector 9, respectively. The -1st-order diffracted light from the diffraction regions 8Aa and 8Ab of the element 8 is divided into the divided regions 11d and 11d of the photodetector 9.
What is necessary is just to design so that each may reach c.

When the tracking error is detected by the phase difference method, the reflected light from the optical disk 6 may be divided into four parts. In this embodiment, when the reflected light is focused, the diffractive optical element 8 and the photodetector are used. Since it will be divided into 4 by 9
Depending on the direction of rotation of the diffracted light from the diffractive optical element 8, the divided area on the photodetector 9 to which the diffracted light reaches changes. The tracking error signal by the phase difference method is basically obtained by detecting a diagonal light beam centered on the optical axis of the light beam divided into four in the tangential direction and the radial direction of the optical disk 6 as described above. From the signal, for example, in the present embodiment, it is obtained by the calculation of Expressions (7) to (12).

Although the description has been made using the ± 1st-order diffracted light, the present invention is not limited to this, and ± Nth-order diffracted light (where N is 1)
The same effect can be obtained by using any of the above integers).

(Second Embodiment) FIG. 11 shows a diffraction optical element 8 and a photodetector 9 of a detection optical system according to a second embodiment of the present invention. The diffractive optical element 8 has two diffraction regions 8C and 8D as in the first embodiment, and these diffraction regions 8C and 8D pass through the optical axis of the condenser lens 7,
Further, the optical disk 6 is divided by an area dividing line L1 which is a straight line parallel to the track. The diffraction areas 8C and 8D are
The light reflected from the optical disk 6 is diffracted into ± first-order diffracted light.

The photodetector 9 has four light receiving surfaces 21, 22, 23, and 24, each of which is divided into two.
Each of two divided areas 21 of 1, 22, 23, and 24
a, 21b, 22a, 22b, 23a, 23b, 24
The paired divided regions are arranged such that a and b are point-symmetric with respect to the z-axis which is the optical axis of the reflected light. In other words, the light receiving surfaces 21, 22, 23, 24
Are parallel to the x-axis, and the two divided light receiving surfaces 21 and 24, 22 and 23 corresponding to the ± 1st-order diffracted light, respectively.
Is located so as to be point-symmetric with respect to the z-axis.

In this case, the pattern of the diffractive optical element 8 is such that when the objective lens 7 is at the focal position, the + 1st-order diffracted light from the area 8c1 of the diffractive optical element 8 is applied to the area 21b of the photodetector. The next-order diffracted light respectively reaches the region 24a of the photodetector, and +
The first-order diffracted light reaches the photodetector region 21a, the -1st-order diffracted light reaches the photodetector region 24b, and the + 1st-order diffracted light from the region 8d1 of the diffractive optical element 8 is the photodetector region. 22a, the -1st-order diffracted light is in the photodetector region 23b, the + 1st-order diffracted light in the region 8d2 of the diffractive optical element 8 is in the photodetector region 22b, and the -1st-order diffracted light is in the photodetector region 23a. To reach it, the diffracted light beam is basically designed to rotate. Furthermore, the pattern of the diffractive optical element 8 has four light receiving surfaces 21, 22, 23, and 4 whose central axes at which the intensity distribution of the light spot on the photodetector 9 is symmetric when the objective lens 7 is at the focal position. It is designed to coincide with each of the 24 dividing lines.

With such a configuration, the light receiving surface 21 is a + 1st-order diffracted light from the region 8C of the diffractive optical element 8, the light receiving surface 22 is a + 1st order diffracted light from the region 8D of the diffractive optical element 8, and the light receiving surface 23 is diffracted. From the area 8D of the mold optical element 8
The first-order diffracted light and the light receiving surface 24 are in the area 8C
-1st-order diffracted light from the light source is received.

That is, in the first embodiment, the divided regions 10a and 10b for receiving the + 1st-order diffracted light from the region 8A of the diffractive optical element 8 and the divided regions 10c and 10d for receiving the + 1st-order diffracted light from the region 8B. The divided regions 11c and 11d that are arranged in the x-axis direction and receive the -1st-order diffracted light from the region 8A of the diffractive optical element 8 and the divided regions 10a and 10b that receive the -1st-order diffracted light from the region 8B are the x-axis. Lined up in the direction.

On the other hand, in this embodiment, the divided area 2 for receiving the + 1st-order diffracted light from the area 8C of the diffractive optical element 8
1a, 21b and divided regions 22a, 22b for receiving + 1st-order diffracted light from region 8D are arranged in the y-axis direction, and divided regions 23a, 23b for receiving -1st-order diffracted light from region 8D of diffractive optical element 8 And the divided regions 24a and 24b that receive the -1st-order diffracted light from the region 8E are arranged in the y-axis direction.

Each light receiving surface 21, 22, 23,
The signal current corresponding to each of the 24 divided regions is converted into a voltage signal by the current-voltage conversion amplifier array 12 and amplified to an appropriate level as shown in FIG. You. Then, as shown in equations (1a), (2a), and (3a), the first
The focus error signal F is calculated by the same calculation as any one of the equations (1), (2), and (3) in the embodiment. Thereby, the influence of diffraction due to pits and marks on the optical disk 6 can be reduced.

F = (S21a + S22b)-(S21b + S22a) + (S23b + S24a)-(S23a + S24b) (1a) F = (S22a-S21a) + (S24b-S23b) (2a) F = (S22b-S21) + (S24a-S23a) (3a) In this case, S10a, S1 in equations (1) to (8)
0b, S10c, S10d, S11a, S11
b, S11c, and S11d correspond to divided areas 21a, 21b, 22, 22a, 23a, and 23a, respectively.
Signals S21 respectively corresponding to 23b, 24b and 24a
a, S21b, S22b, S22a, S23a
, S23b, S24b, and S24a. That is, in the arithmetic circuit 13, the output signals corresponding to the first and second light receiving surfaces 21 and 22 and the output signals corresponding to the second light receiving surfaces 23 and 24 from the photodetector 9 are line-symmetric with respect to the X axis. A focus error signal F is generated by obtaining a difference signal between each of the sum signals of the signals corresponding to the two divided regions having a positional relationship and a sum signal of these two difference signals.

Further, as for the tracking error signal T, similarly to the first embodiment, the following equations (4a) and (5a) are obtained.
According to any of (6a) or the following equation (7a)
The phase difference between the signals T1 and T2 obtained by (8a) or the signal T3 obtained by the following equations (9a) and (10a)
It can be calculated by detecting the phase difference of T4 or the phase difference of signals T5 and T6 obtained by the following equations (11a) and (12a).

T = (S21a + S21b)-(S22b + S22a) (4a) T = (S24b + S24a)-(S23a + S23b) (5a) T = (S21a + S21b)-(S22b + S22a) + (S24a) + (S24a) + S23b) (6a) T1 = S21a + S22b (7a) T2 = S21b + S22a (8a) T3 = S23a + S24b (9a) T4 = S23b + S24a (10a) T5 = S21a + S22b + S23a + S24b (11a) T6 = S21b + S22a + S23b + S24a (12a Note that the four light receiving surfaces 2 in the present embodiment are divided into two.
1, 2, 23, and 24 may be arranged in any manner as long as they are symmetrical with respect to the optical axis by two. FIG.
In 1, the two light receiving surfaces 21 and 22, 23 above and below the x axis
And 24 are in contact with each other, but need not be in contact.

(Third Embodiment) FIG. 12 shows a third embodiment of the present invention, in which the photodetector 9 of the second embodiment is changed to calculate the focus error signal F. An example in which a part is performed on the photodetector 9 will be described. In this case, the + 1st-order diffracted light by the regions 8C and 8D of the diffractive optical element 8 in FIG.
Receiving surface for receiving one of the second order diffracted lights, for example, -1
Regarding the light receiving surfaces 23 and 24 that receive the next-order diffracted light, one of the divided regions, that is, divided regions 23a and 24
b, 23b and 24a are connected to each other to form light receiving surfaces 25 and 26, respectively.

As a result, as the output signal corresponding to the light receiving surface 25, the sum (S23a + S24b) of the output signals corresponding to the divided areas 23a and 24b in FIG. 11 is obtained. , The sum of the output signals corresponding to the divided areas 23b and 24a in FIG. 11 (S23
b + S24a) are obtained. That is, equation (1a)
(S23b + S24a) and (S23a
Since the calculation of + S24b) is performed on the photodetector 9, the calculation is simplified and the number of light receiving surfaces can be reduced.

The light receiving surface 2 for receiving + 1st-order diffracted light by the regions 8C and 8D of the diffractive optical element 8 in FIG.
1 and 22 each other, that is, 21
a and 22b and 21b and 22a may be connected to each other. In this case, (S23b
+ S24a) and (S23a + S24b) are calculated on the photodetector 9.

In this case, as for the tracking error signal T, the output signal corresponding to the light receiving surface on which the calculation is not performed on the photodetector 9, for example, in the example of FIG. The corresponding output signals (S21a, S2
1b, S22a, S22b), for example, according to equation (4a) or by detecting the phase difference between signals T1 and T2 obtained by equations (7a) and (8a).

The light receiving surface 2 for receiving the + 1st-order diffracted light by the regions 8C and 8D of the diffractive optical element 8 in FIG.
One of the divided areas 21a and 22 respectively
b, 21b and 22a are respectively combined to obtain the formula (1)
a) (S21a + S22b) and (S21b +
When the calculation of S22a) is performed on the photodetector 9, the output signal (S23) corresponding to the light receiving surfaces 23 and 24 is provided.
a, S23b, S24a, S24b) alone, for example, according to equation (5a) or (9a) (1
The tracking error signal T is obtained by detecting the phase difference between the signals T3 and T4 respectively obtained by Oa).

(Fourth Embodiment) FIG. 13 shows a diffraction optical element 8 and a photodetector 9 of a detection optical system according to a fourth embodiment of the present invention. In the present embodiment, one of the ± 1st-order diffracted lights by the diffractive optical element 8, for example, only the -1st-order diffracted light, is detected by the photodetector 9, and the focus error signal F is generated. A similar technique is disclosed in Japanese Unexamined Patent Publication No.
As described in Japanese Patent No. 64231, in this embodiment, a diffractive optical element 8 having four diffraction regions 8E, 8F, 8G, and 8H and a photodetector 9 having four divided light receiving surfaces are provided. The configuration consists of Such a configuration is advantageous for tracking error detection by the phase difference method.

That is, when a tracking error signal is detected by the phase difference method, it is necessary to accurately divide the reflected light from the optical disk into four parts. In a conventional configuration, a small light beam is divided into four parts on a photodetector. In order to be
It is necessary to accurately adjust the center line of the light beam intensity distribution on the photodetector to the dividing line of the light receiving surface of the photodetector, and there is a problem that this adjustment is troublesome. In contrast,
In the present embodiment, since the reflected light from the optical disk 6 is divided into four by a large light beam on the diffractive optical element 8, there is an advantage that the adjustment accuracy may be coarse and the adjustment is easy.

In FIG. 13, the diffractive optical element 8 has four diffraction regions 8 divided by a region division line L1 and a vertical region division line L2 parallel to the track on the optical disk 6.
E, 8F, 8G, and 8H. The grating patterns of these diffraction regions 8E, 8F, 8G, and 8H have the 0th-order diffracted light, the + 1st-order diffracted light, and the -1st-order diffracted light near the focal plane of the condenser lens 7.
In order to have a spatial frequency necessary for separating and detecting the second-order diffracted light and to transform the + 1st-order diffracted light and the -1st-order diffracted light into a spot shape necessary for detecting a focus error near the focal plane of the condenser lens 7. Is given a spatial change.

In this case, the pattern of the diffractive optical element 8 is such that, when the objective lens 7 is at the focal position, the -1st-order diffracted light of the area 8E of the diffractive optical element 8 is reflected by the area 33 of the photodetector.
a, so that the -1st-order diffracted light of the area 8F of the diffractive optical element 8 reaches the area 31a of the photodetector, and the -1st-order diffracted light from the area 8H of the diffractive optical element 8 is It was designed such that the -1st-order diffracted light from the region 8G of the diffractive optical element 8 reaches the region 34a of the photodetector in the region 33a. Although the present embodiment is different from the first to third embodiments, diffracted light from a region adjacent to the track of the diffractive optical element 8 in the direction parallel to the track on the optical disk 6 is shifted with respect to the x-axis. Are designed so as to reach the divided regions located on the opposite sides of each other, so that the characteristics are basically the same as those of the first to third embodiments.

In this example, the photodetector 9 is arranged so as to detect the -1st-order diffracted light by the diffractive optical element 8, and each of the four light receiving surfaces 31, 32, 33, and 34 is divided into two.
Having. These light receiving surfaces 31, 32, 33, 34
The diffraction areas 8F, 8H, 8 of the diffractive optical element 8, respectively.
-1st order diffracted light from E and 8G is received respectively. Each of the two divided areas 3 of the light receiving surfaces 31, 32, 33, and 34
1a, 31b, 32a, 32b, 33a, 33b, 34
The output signals of the photodetector 9 corresponding to a and b are respectively S31a, S31b, S32a, S32b,
Assuming that S33a, S33b, S34a, and S34b, the arithmetic circuit 13 of FIG. 1 generates the focus error signal F by the following equation. F = (S31a + S32a + S33b + S34b)-(S31b + S32b + S33a + S34a) (13) That is, in the present embodiment, the first to fourth light receiving surfaces 31, 32, 33, 3 from the photodetector 9 in the arithmetic circuit 13 in the present embodiment.
4, the sum signal (S31a + S32a + S33b + S34b) of the signals corresponding to any one of the divided areas 31a, 32a, 33b, and 34b.
) And the other divided areas 31b, 32b, 33a, 34a
Signal (S31b + S32b + S)
33a + S34a) to obtain a difference signal,
A focus error signal F is generated.

FIG. 14 is a spot diagram showing a change in the shape of the light beam diffracted by the diffractive optical element 8 on the light receiving surface of the photodetector 9 when the relative position between the objective lens 5 and the optical disk 6 changes. . FIG. 14A shows the optical disk 6.
2 shows a state when the objective lens 5 is close to the object.
FIG. 14B shows an optical disc 6 on the focal plane of the objective lens 5.
Is focused and the light beam spot is 2
Each of the divided light receiving surfaces 31, 32, 33, and 34 is located in only one region. FIG.
14A shows a state when the objective lens 5 is separated from the optical disk 6, and the light beam spot changes in the opposite direction to that in FIG. 14A.

Therefore, by the calculation of the equation (11), FIG.
The focus error signal F, which is zero in the in-focus state shown in FIG. 3B and whose magnitude and polarity change in accordance with the amount of displacement from the focal position of the objective lens 5 and the direction of the displacement, can be obtained.

The tracking error signal T is obtained by a push-pull method for obtaining a tracking error signal from irregularities indicating continuous tracks such as grooves on an optical disk, or a tracking error signal from a continuous pit train recorded on an optical disk. Is possible.

In the push-pull method, the direction of the x-axis division line of the diffractive optical element 8 shown in FIG.
The operation of the photodetector 9 differs between the case of the tangential direction and the case of the radial direction.
The operation may be performed on the output signal corresponding to each light receiving surface in FIG. 13 so that the light beam is divided into two in the tangential direction.

For example, when the division line in the x direction of the diffractive optical element 8 is in the tangential direction of the optical disk 6, the tracking error signal T is obtained by the following equation. T = (S31a + S31b + S32a + S32b)-(S33a + S33b + S34a + S34b) (14) Further, the diffractive optical element 8 is so divided as to split the light beam returned from the optical disk 6 around the tangential direction and the radial direction of the optical disk 6. Are arranged, the tracking error signal F by the phase difference method becomes the following 2
It is obtained by detecting the phase difference between the signals obtained from the two equations. T7 = S31a + S31b + S34a + S34b (15) T8 = S32a + S32b + S33a + S33b (16) In the present embodiment, only the -1st-order diffracted light from the diffractive optical element 8 is incident on the photodetector 9, but the + 1st-order diffracted light Only the light may be incident on the photodetector 9, and the arithmetic circuit 13 performs the same operation to generate the focus error signal F and the tracking error signal T.

(Fifth Embodiment) FIG. 15 shows a diffraction optical element 8 and a photodetector 9 of a detection optical system according to a fifth embodiment of the present invention. The diffractive optical element 8 is the same as that of the fourth embodiment shown in FIG.
F, 8G, and 8H, and the lattice pattern thereof is composed of 0-order diffracted light, + 1-order diffracted light, and -1 near the focal plane of the condenser lens 7.
In order to have a spatial frequency necessary for separating and detecting the second-order diffracted light and to transform the + 1st-order diffracted light and the -1st-order diffracted light into a spot shape necessary for detecting a focus error near the focal plane of the condenser lens 7. Is given a spatial change.

On the other hand, the photodetector 9 has eight light-receiving surfaces 41 to 48 divided into two, and is arranged such that the respective division lines of the light-receiving surfaces 41 to 48 coincide with the x-axis. Further, the eight light receiving surfaces 41 to 48 are arranged so that two light receiving surfaces 41 to 48 are point-symmetrical with respect to the z axis.

The focus error detection method in the present embodiment is partially similar to the fourth embodiment, except that both the ± 1st-order diffracted lights are detected by the photodetector 9 as in the first embodiment. The difference from the fourth embodiment is that the detection is performed. Therefore, in the case of the present embodiment, since the focus error signal F is obtained from the signal based on the ± 1st-order diffracted light by calculation, the influence of the diffraction of the pits and marks on the optical disk 6 can be reduced.

In this case, when the objective lens 7 is at the focal position, the + 1st-order diffracted light from the area 8E of the diffractive optical element 8 is applied to the area 47b of the photodetector when the objective lens 7 is at the focal position. The first-order diffracted light reaches the photodetector region 43a, the + 1st-order diffracted light from the region 8F of the diffractive optical element 8 reaches the photodetector region 45b, and the -1st-order diffracted light reaches the photodetector region 41a. The + 1st-order diffracted light from the region 8H of the diffractive optical element 8 is placed in the photodetector region 46a, and the -1st-order diffracted light is placed in the photodetector region 42b.
The + 1st-order diffracted light in the area 8G of the diffractive optical element 8 is in the photodetector area 48a, and the -1st-order diffracted light is in the photodetector area 4a.
4b. This embodiment is different from the first to third embodiments, but is basically designed so that the diffracted light in the adjacent area of the diffractive optical element 8 is symmetric with respect to the x-axis. The first to third
It has the same characteristics as the embodiment.

In this embodiment, the light receiving surfaces 41, 4
2, 43, 44, 45, 46, 47, and 48, the respective divided areas 41a, 41b, 42a, 42b, 43a, 4
3b, 44a, 44b, 45a, 45b, 46a, 46
b, 47a, 47b, 48a, and 48b, output signals of the photodetector 9 are respectively S41a, S41b,
S42a, S42b, S43a, S43b, S
44a, S44b, S45a, S45b, S4
6a, S46b, S47a, S47b, S48
a, S48b, the arithmetic circuit 13 in FIG. 1 generates the focus error signal F by the following equation.

F = [(S41a + S42a + S43b + S44b)-(S41b + S42b + S43a + S44a)] + [(S45a + S46a + S47b + S48b)-(S45b + S46b + S47a in the embodiment, in the case of the (13) circuit in the embodiment, that is, in the case of the thirteenth embodiment) First to fourth light receiving surfaces 41, 42, 43, 4 from photodetector 9
4, the sum signal (S41a + S42a + S43b + S44b) of the signals corresponding to any one of the divided areas 41a, 42a, 43b, and 44b.
) And the other divided areas 41b, 42b, 43a, 44a
(S41b + S42b + S
43a + S44a), and the fifth to eighth light receiving surfaces 45, 46, 47, 48 from the photodetector 9 are obtained.
, The sum signal (S45a + S46a + S47b + S48b) of the signals corresponding to any one of the divided regions 45a, 46a, 47b, and 48b.
) And the other divided areas 45b, 46b, 47a, 48a
(S45b + S46b + S
47a + S48a), and a focus error signal F is generated by obtaining a sum signal of these two difference signals.

The tracking error can be detected by using a signal corresponding to only one of the + 1st-order diffracted light and the -1st-order diffracted light as in the fourth embodiment, but is similar to the first embodiment. It is also possible to use signals corresponding to all ± 1st-order diffracted lights. In this case, the tracking error signal T by the phase difference method is obtained by detecting the phase difference between the signals T11 and T12 obtained by the following equations (18) and (19).

T11 = S41a + S41b + S44a + S44b + S45a + S45b + S48a + S48b (18) T12 = S42a + S42b + S43a + S43b + S46a + S46b + S47a + S47b + S47T + push method, and push signal (19)
Is obtained by the following equation when the dividing line in the x-axis direction of the diffractive optical element 8 is in the tangential direction of the optical disc 6. T = (S41a + S41b + S42a + S42b + S45a + S45b + S46a + S46b)-(S43a + S43b + S44a + S44b + S47a + S47b + S48a + S48b) (Sixth Embodiment, Sixth Embodiment, Sixth Embodiment) An example is shown in which the photodetector 9 of the first embodiment is modified so that a part of the calculation for calculating the focus error signal F is performed on the photodetector 9. In this case, the + 1st-order diffracted light by the regions 8E, 8F, 8G, and 8H of the diffractive optical element 8 in FIG.
Receiving surface for receiving one of the second order diffracted lights, for example, -1
Of the light receiving surfaces 41, 42, 43, and 44 that receive the next-order diffracted light, one adjacent divided region of each of two adjacent light receiving surfaces 41 and 42, 43 and 44, that is, divided regions 41a and 42a, 41b and 42b, 43a and 44a, 43b and 4
4b are divided into divided areas 51a, 51b,
By forming the light receiving surfaces 5a and 52b,
1, 52.

As a result, the divided areas 51a of the light receiving surface 51,
As a signal corresponding to 51b, the divided area 41a in FIG.
(S41a + S42a)
), The sum of the signals corresponding to the divided areas 41b and 42b (S
41b + S42b), and as signals corresponding to the divided areas 52a and 52b of the light receiving surface 52,
Since the sum of the signals corresponding to the divided areas 43a and 44a (S43a + S44a) and the sum of the signals corresponding to the divided areas 43b and 44b (S43b + S44b) of FIG. 15 are obtained, a part of the calculation of the equation (17) is obtained. Photodetector 9
As described above, the calculation is simplified, and the number of light receiving surfaces can be reduced.

Further, of the light receiving surfaces 45, 46, 47 and 48 for receiving + 1st order diffracted light by the regions 8E, 8F, 8G and 8H of the diffractive optical element 8 in FIG. 15, two adjacent light receiving surfaces 45 and 46 are provided. , 47 and 48, that is, divided regions 45a and 46a and 45b.
And 46b, 47a and 48a, and 47b and 48b, respectively, to form a divided area to form two new light receiving surfaces. In this case also, a part of the calculation of the equation (17) is performed on the photodetector 9 Will be

In this case, the tracking error signal T is an output signal corresponding to the light receiving surface on which the calculation is not performed on the photodetector 9, for example, the light receiving surfaces 45 and 4 in the example of FIG.
6, 47, 48 divided areas 45a, 45b, 46a, 4
6b, 47a, 47b, 48a, 48b, output signals S45a, S45b, S46a,
S46b, S47a, S47b, S48a, S
Using only 48b, for example, it can be obtained by detecting the phase difference between the signals T11 and T12 obtained by the equations (18) and (19) or by performing the calculation of the equation (20).

(Seventh Embodiment) FIG. 17 shows a diffractive optical element 8 and a photodetector 9 of a detection optical system in an optical head device according to a seventh embodiment of the present invention. The diffractive optical element 8 is similar to the fourth to sixth embodiments shown in FIGS. 13 to 16 and has four diffraction regions 8E, 8F, 8G, and 8H, and its grating pattern is 0 near the focal plane of
It has a spatial frequency necessary to separate and detect the first-order diffracted light, the + 1st-order diffracted light and the -1st-order diffracted light, and detects the focus error near the focal plane of the condenser lens 7 for the + 1st-order diffracted light and the -1st-order diffracted light. Is given a spatial change for deforming to a spot shape required for the above.

On the other hand, the photodetector 9 for detecting light diffracted by the diffractive optical element 8 has eight light receiving surfaces 61 divided into two parts.
62, 63, 64, 65, 66, 67, and 68, but unlike the fifth embodiment, these light receiving surfaces 61, 6
2, 63, 64, 65, 66, 67, and 68 do not have their respective dividing lines on the x-axis, and are arranged in pairs at two point-symmetric positions about the z-axis. However, each light receiving surface is arranged such that the dividing line is parallel to the x-axis.

The focus error detection method in this embodiment is basically the same as that in the fifth embodiment. In this case, too, the focus error signal F is obtained from the signal based on the ± 1st-order diffracted light by calculation. The effect of diffraction of pits and marks can be reduced.

That is, in the present embodiment, the divided areas 61a, 61b, 62a, 62b, and 6 of the light receiving surfaces 61, 62, 63, 64, 65, 66, 67, and 68, respectively.
3a, 63b, 64a, 64b, 65a, 65b, 66
a, 66b, 67a, 67b, 68a, 68b, the output signals of the photodetector 9 are converted to S61a, S6, respectively.
1b, S62a, S62b, S63a, S63
b, S64a, S64b, S65a, S65b
, S66a, S66b, S67a, S67b
, S68a, S68b, the arithmetic circuit 13 of FIG. 1 generates the focus error signal F by the calculation of the following equation.

F = [(S61a + S62a)-(S65b + S66b)] + [(S63b + S64b)-(S67a + S68a)]-[(S61b + S62b)-(S65a + S66a)]-((S63a + S64b) (21) The tracking error detection may be the same as in the fifth embodiment. That is, the tracking error detection can be performed by using a signal corresponding to only one of the + 1st-order diffracted light and the -1st-order diffracted light as in the fourth embodiment, but similar to the first embodiment. It is also possible to use signals corresponding to all the ± first-order diffracted lights. In this case, the tracking error signal T by the phase difference method is given by the following equation (22).
It is obtained by detecting the phase difference between the signals T21 and T22 obtained by (23).

T21 = S61a + S61b + S63a + S63b + S65a + S65b + S67a + S67b (22) T22 = S62a + S62b + S64a + S64b + S66a + S66b + S68a This method is suitable for the tracking method. Configuration.

The tracking error signal T by the push-pull method is obtained by the following equation when the dividing line of the diffractive optical element 8 in the x-axis direction is in the tangential direction of the optical disc 6. T = (S61a + S61b + S62a + S62b + S67a + S67b + S68a + S68b)-(S63a + S63b + S64a + S64b + S65a + S65b + S66a + S66b) (Eighth Embodiment As an eighth embodiment of the present invention, an eighth embodiment will be described. An example is shown in which the photodetector 9 of the first embodiment is modified so that a part of the calculation for calculating the focus error signal F is performed on the photodetector 9. In this case, the + 1st-order diffracted light by the regions 8E, 8F, 8G, and 8H of the diffractive optical element 8 in FIG.
Receiving surface for receiving one of the second order diffracted lights, for example, -1
Of the light receiving surfaces 61, 62, 63, and 64 that receive the next-order diffracted light, one of the two divided light receiving surfaces 61 and 62, 63 and 64, that is, the divided regions 61a and 62a, 61b and 62b, 63a and 64a, 63b and 6
4b are respectively combined with divided areas 71a, 71b,
By forming the light receiving surfaces 7a and 72b,
1, 72.

As a result, the divided areas 71a of the light receiving surface 71,
As a signal corresponding to 71b, the divided area 61a of FIG.
(S61a + S62a)
), The sum of the signals corresponding to the divided areas 61b and 62b (S
61b + S62b), and as signals corresponding to the divided areas 72a and 72b of the light receiving surface 72,
Since the sum (S63a + S64a) of the signals corresponding to the divided areas 63a and 64a and the sum (S63b + S64b) of the signals corresponding to the divided areas 63b and 64b in FIG. 17 are obtained, a part of the calculation of the equation (21) is obtained. Photodetector 9
As described above, the calculation is simplified, and the number of light receiving surfaces can be reduced.

Further, of the light receiving surfaces 65, 66, 67, 68 for receiving + 1st-order diffracted light by the regions 8E, 8F, 8G, 8H of the diffractive optical element 8 in FIG. 17, two adjacent light receiving surfaces 65 and 66 are provided. , 67 and 68, ie, the divided regions 65a and 66a, 65b
And 66b, 67a and 68a, and 67b and 68b, respectively, to form a divided area to form two new light receiving surfaces. In this case as well, a part of the calculation of Expression (21) is performed on the photodetector 9 Will be

In this case, the tracking error signal T is an output signal corresponding to the light receiving surface on which the calculation is not performed on the photodetector 9, for example, the light receiving surfaces 65 and 6 in the example of FIG.
6, 67, 68 divided areas 65a, 65b, 66a, 6
6b, 67a, 67b, 68a, 68b, output signals S65a, S65b, S66a,
S66b, S67a, S67b, S68a, S
Using only 68b, for example, it can be obtained by detecting the phase difference between the signals T21 and T22 obtained by Expressions (22) and (23) or by performing the operation of Expression (24).

(Ninth Embodiment) FIG. 19 shows, as a ninth embodiment of the present invention, an operation for calculating a focus error signal F by further changing the photodetector 9 of the eighth embodiment. Another example is shown in which a part of is performed on the photodetector 9. In this case, each of the light receiving surfaces 71 and 72 in FIG. 18 has one of the divided regions, that is, 71a and 72b,
The light receiving surface 7 is newly added by combining each of 71b and 72a.
3, 74.

As a result, the output signals corresponding to the light receiving surface 73 include the divided areas 61a, 62a, and 6 in FIG.
3b, 64b (S61a + S62)
a + S63b + S64b is obtained, and as an output signal corresponding to the light receiving surface 74, the divided area 61 in FIG.
b, 62b, 63a, and 64a (S6
1b + S62b + S63a + S64a), so that a greater part of the operation of equation (21) is performed on the photodetector 9, which simplifies the operation and further reduces the number of light receiving surfaces. it can.

As for the tracking error signal T, the eighth
19, the output signal corresponding to the light receiving surface on which the calculation is not performed on the photodetector 9, for example, the divided areas 65a, 65 of the light receiving surfaces 65, 66, 67, 68 in the example of FIG.
b, 66a, 66b, 67a, 67b, 68a, 68b
Output signals S65a and S65 of the photodetector 9 corresponding to
b, S66a, S66b, S67a, S67b
, S68a, and S68b only, for example, the expression (2)
2) It can be obtained by detecting the phase difference between the signals T21 and T22 obtained by (23) or by performing the calculation of Expression (24).

(Tenth Embodiment) FIG. 20 shows the structure of an optical head device according to a tenth embodiment of the present invention. This optical head device includes a light source 1, a collimator lens 2, a beam shaping prism 3, a beam splitter 4, an objective lens 5, a diffractive optical element 8, and a photodetector 9, and further includes a mirror 17 and a wave plate 18 in an optical system. Equipped, and furthermore, FIG.
In the same manner as described above, an amplifier array having a current-voltage conversion function (not shown) and an arithmetic circuit are provided. In the present embodiment, the insertion position of the diffractive optical element 8 is different.

The light emitted from the light source 1 is converted into a parallel light beam by the collimator lens 2, and the light emitted from the collimator lens 2 enters the beam splitter 4 after the beam shape is shaped by the beam shaping prism 3. . The light transmitted through the beam splitter 4 is reflected by a mirror 17, changes its direction, passes through a diffractive optical element 8, and is focused and irradiated as a minute spot on an optical disk (not shown) by an objective lens 5 through a wave plate 18. .

The light reflected from the optical disk is
And diffracted by the diffractive optical element 8. The diffracted light passes through the mirror 17 and the beam splitter 4 and is condensed on the photodetector 9 by the condenser lens 7.

In the optical system of this embodiment, unlike FIG. 1, the beam splitter 4 is located between the diffractive optical element 8 and the photodetector 9.
And the condenser lens 7 enters. In this case, the states of the light beams on the diffractive optical element 8 and the photodetector 9 are first to ninth.
By design including the beam splitter 4 and the condenser lens 7 in the same manner as in the above-described embodiment, the same effects as in the above-described embodiments can be obtained. Here, the only elements inserted between the diffractive optical element 8 and the photodetector 9 are the beam splitter 4 and the condenser lens 7, but another optical element is inserted to add other functions. Even so, the pattern of the diffractive optical element 8 may be designed including the characteristics of the optical element.

Further, when considering a mechanism system for moving an objective lens to move a light beam on an optical disk by performing tracking control, the diffraction type optical element 8 and the wavelength plate 1 are considered.
When the objective lens 8 is moved together with the objective lens 5, an offset may not be easily generated particularly in a tracking error signal by the push-pull method. That is, in an optical system in which the diffractive optical element 8 is fixed, when the objective lens 5 moves to perform tracking control, the beam on the photodetector 9 moves greatly. And it is difficult to move the objective lens 5 too much for tracking control.

On the other hand, the diffractive optical element 8 and the wave plate 1
When the object 8 is moved together with the objective lens 5, the light beam hardly moves on the photodetector 9, and the reflected light from the optical disk is further divided into two in the tangential direction on the diffractive optical element 8. Since each of the divided light beams is independently detected, there is no problem even if the light beam slightly moves. For this reason, even if the objective lens 5 moves greatly during tracking, an accurate push-pull signal can be obtained.

Here, the mechanism for moving the objective lens 5 may be an electromagnetic drive system of a magnet and a coil, and the objective lens 5, the diffractive optical element 8 and the wave plate 18 are simultaneously substantially parallel to the radial direction of the disk 6. Basically, any configuration may be used as long as it can be moved to.

When a polarizing type is used as the diffractive optical element 8, the light source 1 is first activated by the effect of the wave plate 18.
Since the light beam coming from the optical disk is not diffracted by the diffractive optical element 8 and only the reflected light from the optical disk is diffracted,
The light use efficiency of the light source 1 can be increased. Regarding the focus error detection and the tracking error detection, the same effect can be obtained by using any diffractive optical element.

In the above embodiment, the ± 1st-order diffracted light is used by the diffractive optical element 8, but the present invention is not limited to this, and focus error detection may be performed by using the ± Nth-order diffracted light.

(Eleventh Embodiment) FIG. 21 shows an optical head device according to an eleventh embodiment of the present invention, which differs from the previous embodiments in that an objective lens 5 is a finite system lens. The same is true. In this case, the collimator lens 2, the beam shaping prism 3, and the condenser lens 7 in FIG.
Becomes unnecessary.

In the first to eleventh embodiments described above, recording is performed by using the diffractive optical element 8 provided with a plurality of diffraction regions 8A and 8B parallel to the track direction as shown in a part of FIG. 1 shows an example of an optical head device that performs stable focus control while avoiding noise due to diffraction from pits or recording marks on a recording surface of a medium. That is, these embodiments are optical head devices suitable for a case where pits and recording marks are continuously provided on a recording surface, such as a DVD-ROM.

On the other hand, by using the diffractive optical element 108 in which a plurality of diffraction regions 108A and 108B are formed by dividing lines perpendicular to the track direction, noise due to diffraction from grooves on the recording surface of the recording medium is reduced. Can be avoided. This is, for example, the DVD shown in part of FIG.
The land 101 as in the case of using the RAM 106, etc.
This is suitable when the spot moves between the land and the groove of the groove 102 and the groove. Optical disk 1
In the case of 01, the noise caused by the diffraction from the groove is more problematic than the noise caused by the diffraction from the bit or the recording mark. Therefore, a diffractive optical element 108 having two diffraction regions 108A and 108B divided along a region division line extending in the direction perpendicular to the track direction in which the groove is affected is used. Hereinafter, an optical head device of the present invention using the optical disk 106 and the diffractive optical element 108 will be described based on twelfth to twenty-second embodiments.

(Twelfth Embodiment) In a twelfth embodiment, a diffractive optical element 108 having two diffraction areas 108A and 108B divided along an area division line extending in the direction perpendicular to the track direction is used. The other configuration is basically the same as that of the first embodiment.

Therefore, the present embodiment will be described with reference to the configuration shown in FIG. In the following embodiments, the sign of the diffractive optical element 108 is referred to as the diffractive optical element 8, and the diffractive regions 108A and 108B are referred to as the diffractive regions 8A.
8B.

FIG. 2 shows a configuration example of the diffraction optical element 8. The diffractive optical element 8 has two diffraction regions 8A and 8B composed of a curve group as shown in FIG. Specifically, the diffraction area 8A is a pin-shaped diffraction grating, and the diffraction area 8B is a barrel-shaped diffraction grating. These diffraction regions 8A and 8B are formed by forming a straight line on an axis (x-axis in FIG. 1) passing through the optical axis (z-axis in FIG. 1) of the reflected light from the optical disk 6 and perpendicular to the track on the optical disk 6. It is divided as a division line L1. The diffraction areas 8A and 8B diffract the reflected light from the optical disc 6 into 0th-order diffracted light and ± 1st-order diffracted light, respectively. The grating pitch of the diffraction areas 8A and 8B has a spatial frequency necessary for separating and detecting the 0th-order diffracted light, the + 1st-order diffracted light, and the -1st-order diffracted light in the vicinity of the focal plane of the condenser lens 7, and the + 1st order diffracted light. A spatial change is given to transform the folded light and the -1st-order diffracted light into a spot shape necessary for detecting a focus error near the focal plane of the condenser lens 7.

The grating pattern shape of the diffractive optical element 8 shown in FIG. 2A is such that the distance between the diffractive optical element 8 and the photodetector 9 is 20 mm, and the beam diameter on the diffractive optical element 8 is 2 mm.
In the case of (1), the separation distance between the 0th-order diffracted light and the ± 1st-order diffracted light from the diffraction area 8A of the diffractive optical element 8 near the focal plane of the condensing lens 7 is 0.6 mm. This is an example designed so that the separation distance between the 0th-order diffracted light and ± 1st-order diffracted light from the diffraction region 8B of the element 8 is 0.4 mm. Further, in order to distribute the first-order diffracted light equally to ±, the cross-sectional shape of the diffraction regions 8A and 8B is a step-like shape in which the ratio of the grating width D2 to the grating pitch D1 is 1/2 as shown in FIG. It is desirable to use a phase grating. The light detector 9 is arranged to detect the diffracted light from the diffractive optical element 8. Then, the photodetector 9 is provided with the condenser lens 7.
Is located at the focal position. Thus, the condenser lens 7
Since the photodetector 9 is arranged at the focal position of the
Has no power and can have only the function of changing the aberration component. For this reason, it is possible to realize an error detection optical system that is less affected by the wavelength fluctuation of light, and to stably detect an error signal.

FIG. 3 shows a configuration example of the photodetector 9. The photodetector 9 has first and second light receiving surfaces 10 and 11 divided into four parts. The first light receiving surface 10 is divided into four divided regions 10 by a dividing line in the same direction as the image of the region dividing line L1 of the diffractive optical element 8 and a dividing line orthogonal thereto.
a to 10d. Similarly, the second light receiving surface 1
1 is divided into four divided regions 11a to 11d by a dividing line in the same direction as the image of the region dividing line L1 of the diffractive optical element 8 and a dividing line orthogonal to the dividing line.

Further, as shown in FIG. 3, a signal having a good symmetry of a signal obtained by a detector having a detector surface symmetric with respect to the optical axis having a point object is obtained. However, it is not necessary to be point symmetric.

Then, as shown in FIG.
a, 10b are +1 from the area 8A of the diffractive optical element 8
The second-order diffracted light is received, and the divided areas 10c and 10d receive the + 1st-order diffracted light from the area 8B of the diffractive optical element 8. The divided areas 11c and 11d are formed in the area 8A of the diffractive optical element 8.
-1st-order diffracted light from the first and second divided regions 11a and 11b
Receives the -1st-order diffracted light from the area 8B of the diffractive optical element 8. The signal current corresponding to each of the divided areas 10a to 10d and 11a to 11d of the light receiving surfaces 10, 11 of the photodetector 9 is converted into a voltage signal by the current-voltage conversion amplifier array 12, and is amplified to an appropriate level. After that, it is input to the arithmetic circuit 13.

The operation circuit 13 generates the focus error signal F by the operation shown in the following equation (1). F = (S10a + S10c)-(S10b + S10d) + (S11b + S11d)-(S11a + S11c) (1) where S10a, S10b, S10c, S10
d represents a signal corresponding to each of the divided areas 10a, 10b, 10c, and 10d among output signals corresponding to the light receiving surface 10, and S11a, S11b, S11c, S
11d represents a signal corresponding to each of the divided areas 11a, 11b, 11c, 11d among output signals corresponding to the light receiving surface 11.

That is, in the present embodiment, in the arithmetic circuit 13, the output signal corresponding to the light receiving surface 10 from the photodetector 9 is divided into two diagonally divided areas 10
a, 10c (S10a + S1)
0c) and the sum signal (S10b) of the signals corresponding to the other two divided regions 10b and 10d which are also in a diagonal positional relationship.
+ S10d) (S10a + S10c).
− (S10b + S10d), and further, regarding the output signal corresponding to the light receiving surface 11 from the photodetector 9, the sum signal (S11b + S11d) of the signals corresponding to the two divided regions 11b and 11d having a diagonal positional relationship. And the other two divided areas 11a and 11 also having the same diagonal positional relationship.
c (S11a + S11c)
)-(S11b + S11d)-(S11b)
a + S11c), and the sum signal of these two difference signals is obtained to generate the focus error signal F.

FIG. 5 is a spot diagram showing a change in the spot shape on the light receiving surface of the photodetector 9 of the light beam diffracted by the diffractive optical element 8 when the relative position between the objective lens 5 and the optical disk 6 changes. Indicated by In the figure, the light beam spot is represented by a set of dots. FIG. 5A shows a state where the objective lens 5 is close to the optical disc 6. FIG. 5B shows a case where the optical disk 6 is in focus with the focal plane of the objective lens 5 positioned, and the light beam spot has a substantially line-symmetric shape. FIG.
5A shows a state when the objective lens 5 is separated from the optical disk 6, and the light beam spot shape changes in the opposite direction to that in FIG.

5B and FIG. 5D, the state when the objective lens 5 is separated from the optical disk 6 is shown, and the change in the light beam spot shape is also shown in FIG.
The direction is opposite to that of FIG.

5 (b) and 5 (d) show the transition state from FIG. 5 (c) to FIG. 5 (a) and the transition state from FIG. 5 (c) to FIG. 5 (e). Each is shown.

Therefore, by performing the calculation of the equation (1) in the calculation circuit 13 as described above, the amount of the shift from the focal position of the objective lens 5 is zero at the time of the focused state in FIG. A focus error signal whose magnitude and polarity change in accordance with the direction of. FIG. 6 shows the relationship between the focus error signal F and the focus shift amount.

According to the present embodiment, even if the diffractive optical element 8, the photodetector 9, and the like are displaced due to, for example, errors in assembling the optical head or aging, the conventional astigmatism method is used. It is possible to reduce the fluctuation of the focus error signal which occurs remarkably in the focus error detection. Hereinafter, this effect will be described in detail with reference to FIGS.

FIGS. 24 (a), 25 (a) and 26
24A shows the intensity distribution of the light beam on the light detection surface of the photodetector 9 at the time of focusing, and FIGS. 24B, 25B, and 26B show the time distribution at the time of focusing. The intensity distribution of the light beam incident on the diffraction optical element 8 is shown in FIGS.
(C) and FIG. 26 (c) show the intensity distribution of the light beam on the optical disk 6. Hereinafter, FIGS.
And (ii) when the photodetector 9 has a misalignment, and (iii) when the diffractive optical element 8 has a misalignment. Each case will be described.

(I) In the case where there is no displacement between the diffractive optical element 8 and the photodetector 9 The light intensity at the time of focusing in an ideal optical system where there is no displacement between the diffractive optical element 8 and the photodetector 9 The distribution is shown in FIG. In FIG. 24A, reference numerals 91 to 93 denote light receiving surfaces of the photodetector 9, and a black portion schematically shows a diffraction image of a groove on the optical disk 6. FIG. 24B shows the surfaces 181 to 183 of the diffractive optical element 8, wherein a circle schematically shows a light beam incident on the diffractive optical element 8, and a black portion schematically shows a diffraction image of a groove. The dashed circles d and e in FIG.
f is a light beam spot on the optical disk 6 and indicates a groove G on the optical disk 6.

The grooves G on the optical disk 6 are formed by the light beams condensed by the objective lens 5 into circles d, e, and c in FIG.
When scanning as shown in FIG. 24F, the intensity distribution of the incident light on the diffractive optical element 8 is affected by the diffraction caused by the groove G.
It changes like the surface 181,182,183 of (b).
At this time, the intensity distribution of the + 1st-order diffracted light and the -1st-order diffracted light from the diffractive optical element 8 on the light receiving surface of the photodetector 9 changes as shown in images 191, 192, and 193 in FIG. The intensity distribution between the + 1st-order diffracted light and the -1st-order diffracted light is symmetric with respect to the origin (the intersection between the optical axis and the light receiving surface). Accordingly, if the light beam scans the groove G on the optical disk 6 as shown in FIG. 24, the light receiving intensity of each light receiving surface of the photodetector 9 changes even at the time of focusing. When the error signal F is calculated, (S
10a + S10c)-(S10b + S10d),
(S11b + S11d)-(S11a + S11c)
) Are both zero, so that the focus error signal F is always zero.

(Ii) When the photodetector 9 is misaligned Next, the photodetector 9 is provided with a region dividing line L1 of the diffractive optical element 8.
FIG. 25 shows the light intensity distribution at the time of focusing when there is a displacement in the direction orthogonal to the image of FIG. Like FIG. 24, FIG.
The images 194 to 196 in (a) are the light receiving surfaces of the photodetector 9, and the black portions schematically show the diffraction images of the grooves on the optical disk 6. FIG. 25B shows images 184 to 186.
Is a surface of the diffractive optical element 8, a circle schematically shows a light beam incident on the diffractive optical element 8, and a black portion schematically shows a diffraction image of the groove. The broken circles 191 to 191 in FIG.
193 is a light beam spot on the optical disk 6.

In this case, when the light beam scans the groove G on the optical disk 6, the light receiving intensity of each light receiving surface of the photodetector 9 changes.
Is calculated, the light amount deviation on the photodetector 9 can be canceled, and the fluctuation of the focus error signal F which has been conspicuously generated by the conventional astigmatism method can be reduced. That is, also in this case, similarly to the case of (i), (S10a + S10c)-(S10b + S10) in Expression (1).
d), (S11b + S11d)-(S11a +
Since both S11c) are zero, the focus error signal F is always zero.

(Iii) In the case where the diffractive optical element 8 has a positional shift Further, in this embodiment, even if the diffractive optical element 8 has a positional shift, the fluctuation of the focus error signal can be reduced. FIG. 26 shows an intensity distribution at the time of focusing when the diffractive optical element 8 has a displacement in a direction orthogonal to the region dividing line L1 of the diffractive optical element 8. 24 and 25
26A, the images 197 to 199 in FIG.
The black portion schematically shows a diffraction image of a groove on the optical disc 6. Image 18 in FIG.
Reference numerals 7 to 189 denote surfaces of the diffractive optical element 8, wherein a circle schematically shows a light beam incident on the diffractive optical element 8, and a black portion schematically shows a diffraction image of the groove. 26 (c) are light beam spots on the optical disc 6.

In this case, since the amounts of light incident on the two diffraction regions 8A and 8B of the diffractive optical element 8 are different, the size of the beam on the photodetector 9 becomes unbalanced.
By calculating the focus error signal F by
The light amount deviation on the photodetector 9 can be canceled out, and even when the groove G is scanned by the light beam, the fluctuation of the focus error signal F which has been significantly generated by the conventional astigmatism method can be reduced.

That is, in this case, (S10a + S10c)-(S10b + S10) in equation (1)
d), (S11b + S11d)-(S11a +
The two difference signals of S11c) have a certain value, but since these difference signals have the same magnitude and opposite polarities, they are canceled out by the operation of equation (1), and the focus error signal F is always zero. Becomes

As described above, according to the present embodiment, even when the diffractive optical element 8 and the photodetector 9 are misaligned, it is possible to correctly detect a focus error without being affected by these misalignments. Become.

As a modification of the present embodiment, the focus error signal F can be calculated by the following equation (2) or (3) instead of equation (1). F = (S10d−S10a) + (S11c−S11b) (2) F = (S10c−S10b) + (S11d−S11a) (3) That is, according to the equation (2), the light receiving surface from the photodetector 9 is obtained. For the output signal corresponding to 10, a difference signal (S10d-S10a) of signals corresponding to the divided areas 10d and 10a having an adjacent positional relationship in the direction of the area dividing line L1 (the direction perpendicular to the track on the optical disc 6) is obtained. , Photodetector 9
Output signals corresponding to the light receiving surface 11 from the region 1 are adjacent to each other in the direction of the region dividing line L1 and
The difference signals (S11c-S11b) of the signals corresponding to the divided regions 11c and 11b having different positions in the direction perpendicular to the region division line L1 from the regions 0d and 10a are obtained, and these two difference signals (S10d-S10a) and (S11c) are obtained. −
The focus error signal F is generated by obtaining the sum signal of S11b).

Similarly, in the equation (3), the output signal corresponding to the light receiving surface 10 from the photodetector 9 corresponds to the region dividing line L1
The difference signal (S10c-S10b) between the signals corresponding to the divided regions 10c and 10b having the adjacent positional relationship in the direction of (1) is obtained. Is adjacent to
Further, a difference signal (S11d-S11a) of signals corresponding to the divided regions 11d and 11a having different positions in the direction perpendicular to the region dividing line L1 from the divided regions 10c and 10b is obtained, and these two difference signals (S10c-S10b) are obtained. ,
The focus error signal F is generated by obtaining the sum signal of (S11d-S11a).

Even if the focus error signal F is generated according to the equation (2) or (3), the focus error signal F is generated from the light intensity distribution on the light receiving surfaces 194 to 196 when the photodetector 9 shown in FIG. As is apparent, the light amount deviation on the photodetector 9 can be canceled out, and the fluctuation of the focus error signal F which has been significantly generated by the conventional astigmatism method can be reduced.

Further, as is apparent from the light intensity distribution on the light receiving surfaces 197 to 199 when the diffractive optical element 8 shown in FIG. 26 has a position shift, the focus error is calculated by the equation (2) or (3). By calculating the signal F, the light amount deviation on the photodetector 9 can be canceled out, and the fluctuation of the focus error signal F which has been conspicuously generated by the conventional astigmatism method can be reduced.

Further, in the optical head device of the present embodiment,
From the output signal of the photodetector 9, not only the focus error signal F but also the tracking error signal T can be obtained at the same time. For example, a push-pull method for obtaining a tracking error signal from irregularities indicating a continuous track such as a groove on the optical disk 6 or a phase difference method for obtaining a tracking error signal from a continuous pit row recorded on the optical disk 6. .

In the push-pull method, the operation of the photodetector 9 differs depending on whether the direction of the dividing line of the diffractive optical element 8 shown in FIG. 2 is the tangential direction of the optical disk 6 or the radial direction. The calculation may be performed such that the light beam is split into two in the tangential direction of the optical disk 6.

For example, when the direction of the dividing line of the diffractive optical element 8 is the radial direction of the optical disk 6, the tracking error signal T can be calculated according to one of the following equations (25), (26), and (27). T = (S10a + S10d)-(S10b + S10c) (25) T = (S11b + S11c)-(S11a + S11d) (26) T = (S10a + S10d)-(S10b + S10c) + (S11b + S11c) 27) That is, the tracking error signal T by the push-pull method can be obtained by using any of the above three equations (25), (26), and (27).

On the other hand, in the tracking error detection method by the phase difference method, the light receiving surface of the photodetector 9 is arranged so that the light beam returned from the optical disk 6 is divided around the tangential direction and the radial direction of the optical disk 6 as axes. It should just be. For example, a tracking error signal T by the phase difference method is a signal T1 obtained by the following equations (7) and (8).
It is obtained by detecting the phase difference of T2. T1 = S10a + S10c (7) T2 = S10b + S10d (8) Similarly, the tracking error signal T is obtained by the phase difference method.
Is a method of detecting the phase difference between the signals T3 and T4 obtained by the following equations (9) and (10). T3 = S11a + S11c (9) T4 = S11b + S11d (10) Further, as another method for obtaining the tracking error signal T by the phase difference method, the phase difference between the signals T5 and T6 obtained by the following equations (11) and (12) is obtained. There is a way to detect T5 = S10a + S10c + S11a + S11c (11) T6 = S10b + S10d + S11b + S11d (12) In the present embodiment, any of the three tracking error detection methods described above may be used, and similar results are obtained.

Next, the principle of focus error detection according to the present invention will be described in more detail with reference to FIG. Here, the configuration of the twelfth embodiment is basically used, but the principle is the same in the embodiment described later.

FIG. 10 is a diagram for explaining the relationship between the diffractive optical element 8 and the photodetector 9 shown in FIG. 4. In order to make the description easy to understand, the direction perpendicular to the tracks on the optical disk 6 is shown. Semi-circular reflected light 101 divided along
This reflected light 101 is used as a diffraction area 8A of the diffraction optical element 8.
The divided areas 10a and 10b of the first light receiving surface 10 of the photodetector 9 and the divided areas 11d and 11d of the second light receiving surface 11 on which the diffracted light generated by the diffraction at (8Aa, 8Ab) is incident. Only 11c is shown.

As shown in FIG. 10, a semicircular reflected light 1
01 is diffracted by the diffraction area 8A of the diffractive optical element 8, and +
First-order diffracted light 103a, 104a and -1st-order diffracted light 103
b, 104b occur. Here, the diffracted lights 103a, 103
Reference numeral 3b denotes a diffracted light at a position approximately intermediate between the diffractive optical element 8 and the photodetector 9. The diffracted light beams 104a and 104b are diffracted light beams on the photodetector 9, and have a focused beam shape in which the optical disk 6 is located at the focal position of the objective lens 5. In FIG. 10, in order to detect a focus error, the grating pattern of the diffractive optical element 8 is such that + 1st-order diffracted light from the areas 8Aa and 8Ab of the diffractive optical element 8 is applied to the divided areas 10b and 10a of the photodetector 9, respectively. It is designed so that the -1st-order diffracted light from the areas 8Aa and 8Ab reaches the divided areas 11d and 11c of the photodetector 9, respectively.

That is, the + 1st-order diffracted light and the -1st-order diffracted light of the divided reflected light obtained by dividing the reflected light 101 in a direction parallel to the track on the optical disk 6 and in a direction perpendicular to the direction are:
The light is received by divided regions (for example, divided regions 10b and 11d of the photodetector 9) of the light receiving surface of the photodetector arranged at positions symmetrical to each other with respect to the optical axis of the reflected light. Therefore, + N-order diffracted lights and -N-order diffracted lights in the divided reflected lights adjacent to each other along the Y-axis (for example, the reflected lights incident on the diffraction area 8Aa and the diffraction area 8Ab) are located on opposite sides with respect to the X-axis. The light is received by the divided regions (for example, the divided regions 10b and 10a and the divided regions 11a and 11c). The diffractive optical element 8 is designed based on the above concept.

This is because, as can be seen from the cross sections of the diffracted lights 103a and 103b on the way from the diffractive optical element 8 to the photodetector 9, the + 1st-order diffracted light moves counterclockwise in the traveling direction, The grating pattern of the diffractive optical element 8 is designed so that the -1st-order diffracted light having a conjugate relationship with the folded light travels clockwise in the traveling direction in the xy plane in the z-axis direction.

Here, at the time of focusing, the divided areas 10a, 10a
The beam shape of the + 1st-order diffracted light 104a on b and the beam shape of the -1st-order diffracted light 104b on the divided regions 11d and 11c are respectively symmetric with respect to the x-axis.

On the other hand, the objective lens 5 is
When the focus shift occurs, the light detector 9 is moved in the same manner as in FIG.
Since the symmetry of the beam shape is lost above the x-axis, the arithmetic circuit 13 calculates Equation (1), Equation (2), or Equation (3).
By performing the above calculation, the focus error signal F is obtained.

Further, even when the photodetector 9 and the diffractive optical element 8 are misaligned as described in the above (ii) and (iii), the diffraction image 202 of the groove on the optical disc 6 can be obtained as shown in FIG.
Since it appears in the divided areas arranged at positions symmetrical with respect to the z-axis as shown by 0, according to the above-described calculations, the effect of reducing the fluctuation of the focus error signal F due to these positional shifts can be obtained.

That is, by detecting the focus error using the output signal of the photodetector 9 regarding both the + 1st-order diffracted light and the -1st-order diffracted light of the reflected light, the fluctuation of the focus error signal F due to the influence of the diffraction image of the groove is obtained. Can be reduced.

Note that the beam shapes on the photodetector 9 are different between FIG. 5 and FIG. This is an example in which the diffractive optical element 8 is designed so as to reduce the reflected light in the x-axis direction irrelevant to the focus error detection in FIG. 5, whereas in FIG. 10, the description is simplified. 8 shows a case where the diffractive optical element 8 is not designed as shown in FIG.

The grating pattern of the diffractive optical element 8 shown in FIG.
+ 1st-order diffracted light from the photodetector 9 is divided into
However, it is also possible to design the + 1st-order diffracted light from the diffraction regions 8Aa and 8Ab to reach the divided regions 10a and 10b of the photodetector 9, respectively. In this case, the first-order diffracted light from the diffraction areas 8Aa and 8Ab of the diffractive optical element 8 has a conjugate relationship with the + 1st-order diffracted light.
c and 11d, respectively, and the same effect as in the case described above is obtained.

Further, when the distance between the diffractive optical element 8 and the photodetector 9 is reduced, when the grating pattern of the diffractive optical element 8 is designed by optimizing only the + 1st-order diffracted light,-
Since the first-order diffracted light is distorted, the effect of reducing the fluctuation of the focus error signal F due to the influence of the diffraction image of the groove is weakened. Therefore, the grating pattern of the diffractive optical element 8 is designed to be optimized for the ± first-order diffracted light. It is desirable. Specifically, for example, the + 1st-order diffracted light from the diffraction regions 8Aa and 8Ab of the diffraction optical element 8 reaches the divided regions 10b and 10a of the photodetector 9, respectively. The -1st-order diffracted light from the diffraction regions 8Aa and 8Ab of the element 8 is divided into the divided regions 11d and 11d of the photodetector 9.
What is necessary is just to design so that each may reach c.

When the tracking error is detected by the phase difference method, the reflected light from the optical disk 6 may be divided into four parts. In this embodiment, when the reflected light is focused, the diffractive optical element 8 and the photodetector are used. Since it will be divided into 4 by 9
Depending on the direction of rotation of the diffracted light from the diffractive optical element 8, the divided area on the photodetector 9 to which the diffracted light reaches changes. The tracking error signal by the phase difference method is basically obtained by detecting a diagonal light beam centered on the optical axis of the light beam divided into four in the tangential direction and the radial direction of the optical disk 6 as described above. From the signal, for example, in the present embodiment, it is obtained by the calculation of Expressions (7) to (12).

Although the description has been made using ± 1st-order diffracted light, the present invention is not limited to this, and ± Nth-order diffracted light (N is 1
The same effect can be obtained by using any of the above integers).

(Thirteenth Embodiment) A thirteenth embodiment is directed to a diffractive optical element 8 having two diffraction regions 8A and 8B divided along a region division line extending in a direction perpendicular to the track direction. In this case, the other configuration is the same.

FIG. 11 shows a diffraction optical element 8 and a photodetector 9 of a detection optical system according to a thirteenth embodiment of the present invention. The diffractive optical element 8 has two diffraction regions 8C and 8D as in the first embodiment.
C and 8D are divided by an area dividing line L1 which is a straight line passing through the optical axis of the condenser lens 7 and perpendicular to a track on the optical disk 6. The diffraction areas 8C and 8D diffract the reflected light from the optical disc 6 into ± first-order diffracted lights, respectively.

The photodetector 9 has four light receiving surfaces 21, 22, 23, and 24 each of which is divided into two.
Each of two divided areas 21 of 1, 22, 23, and 24
a, 21b, 22a, 22b, 23a, 23b, 24
The paired divided regions are arranged such that a and b are point-symmetric with respect to the z-axis which is the optical axis of the reflected light. In other words, the light receiving surfaces 21, 22, 23, 24
Are parallel to the x-axis, and the two divided light receiving surfaces 21 and 24, 22 and 23 corresponding to the ± 1st-order diffracted light, respectively.
Is located so as to be point-symmetric with respect to the z-axis.

In this case, the pattern of the diffractive optical element 8 is such that when the objective lens 7 is at the focal position, the + 1st-order diffracted light from the area 8c1 of the diffractive optical element 8 is applied to the area 21b of the photodetector. The next-order diffracted light respectively reaches the region 24a of the photodetector, and +
The first-order diffracted light reaches the photodetector region 21a, the -1st-order diffracted light reaches the photodetector region 24b, and the + 1st-order diffracted light from the region 8d1 of the diffractive optical element 8 is the photodetector region. 22a, the -1st-order diffracted light is in the photodetector region 23b, the + 1st-order diffracted light in the region 8d2 of the diffractive optical element 8 is in the photodetector region 22b, and the -1st-order diffracted light is in the photodetector region 23a. To reach it, the diffracted light beam is basically designed to rotate. Furthermore, the pattern of the diffractive optical element 8 has four light receiving surfaces 21, 22, 23, and 4 whose central axes at which the intensity distribution of the light spot on the photodetector 9 is symmetric when the objective lens 7 is at the focal position. It is designed to coincide with each of the 24 dividing lines.

With such a configuration, the light receiving surface 21 is a + 1st-order diffracted light from the region 8C of the diffractive optical element 8, the light receiving surface 22 is a + 1st order diffracted light from the region 8D of the diffractive optical element 8, and the light receiving surface 23 is diffracted. From the area 8D of the mold optical element 8
The first-order diffracted light and the light receiving surface 24 are in the area 8C
-1st-order diffracted light from the light source is received.

That is, in the first embodiment, the divided regions 10a and 10b for receiving the + 1st-order diffracted light from the region 8A of the diffractive optical element 8 and the divided regions 10c and 10d for receiving the + 1st-order diffracted light from the region 8B. The divided regions 11c and 11d that are arranged in the x-axis direction and receive the -1st-order diffracted light from the region 8A of the diffractive optical element 8 and the divided regions 10a and 10b that receive the -1st-order diffracted light from the region 8B are the x-axis. Lined up in the direction.

On the other hand, in the present embodiment, the divided area 2 for receiving the + 1st-order diffracted light from the area 8C of the diffractive optical element 8
1a, 21b and divided regions 22a, 22b for receiving + 1st-order diffracted light from region 8D are arranged in the y-axis direction, and divided regions 23a, 23b for receiving -1st-order diffracted light from region 8D of diffractive optical element 8 And the divided regions 24a and 24b that receive the -1st-order diffracted light from the region 8E are arranged in the y-axis direction.

Each light receiving surface 21, 22, 23,
The signal current corresponding to each of the 24 divided regions is converted into a voltage signal by the current-voltage conversion amplifier array 12 and amplified to an appropriate level as shown in FIG. You. Then, as shown in equations (1a), (2a), and (3a), the first
The focus error signal F is calculated by the same calculation as any one of the equations (1), (2), and (3) in the embodiment. Thereby, the influence of diffraction by the groove on the optical disk 6 can be reduced.

F = (S21a + S22b)-(S21b + S22a) + (S23b + S24a)-(S23a + S24b) (1a) F = (S22a-S21a) + (S24b-S23b) (2a) F = (S22b-S21) + (S24a-S23a) (3a) In this case, S10a, S1 in equations (1) to (8)
0b, S10c, S10d, S11a, S11
b, S11c, and S11d correspond to divided areas 21a, 21b, 22, 22a, 23a, and 23a, respectively.
Signals S21 respectively corresponding to 23b, 24b and 24a
a, S21b, S22b, S22a, S23a
, S23b, S24b, and S24a. That is, in the arithmetic circuit 13, the output signals corresponding to the first and second light receiving surfaces 21 and 22 and the output signals corresponding to the second light receiving surfaces 23 and 24 from the photodetector 9 are line-symmetric with respect to the X axis. A focus error signal F is generated by obtaining a difference signal between each of the sum signals of the signals corresponding to the two divided regions having a positional relationship and a sum signal of these two difference signals.

Further, as for the tracking error signal T, similarly to the twelfth embodiment, the following equations (28) and (29)
According to any one of (30) or (7a)
The phase difference between the signals T1 and T2 obtained by (8a) or the signal T3 obtained by the following equations (9a) and (10a)
It can be calculated by detecting the phase difference of T4 or the phase difference of signals T5 and T6 obtained by the following equations (11a) and (12a).

T = (S21a + S22a)-(S21b + S22b) (28) T = (S23b + S24b)-(S23a + S24a) (29) T = (S21a + S22a)-(S21b + S22b) + (S23b + S24b) + S24a) (30) T1 = S21a + S22b (7a) T2 = S21b + S22a (8a) T3 = S23a + S24b (9a) T4 = S23b + S24a (10a) T5 = S21a + S22b + S23b + S23b + S23b + S23b + S23b + S23b + S23b + S23bS12bS12bS12aSbS12aSbS12aSbS12bS12aSbS12aSbS12aSbS12aSbS12aSbS12aSbS12aSbb Note that the four light receiving surfaces 2 in the present embodiment are divided into two.
1, 2, 23, and 24 may be arranged in any manner as long as they are symmetrical with respect to the optical axis by two. FIG.
In 1, the two light receiving surfaces 21 and 22, 23 above and below the x axis
And 24 are in contact with each other, but need not be in contact.

(Fourteenth Embodiment) In the fourteenth embodiment, as in the thirteenth embodiment, two diffraction regions 8A and 8B divided along a region division line extending in the direction perpendicular to the track direction. This shows a case where a diffractive optical element 8 having the following is used, and the other configuration is the same as that of the third embodiment.

FIG. 12 shows a fourteenth embodiment of the present invention, in which the photodetector 9 of the thirteenth embodiment is changed and a part of the calculation for calculating the focus error signal F is performed by the photodetector 9. Here is an example of the above operation. In this case, of the light-receiving surface of the photodetector 9, a light-receiving surface for receiving one of + 1st-order and -1st-order diffracted light by the regions 8C and 8D of the diffractive optical element 8 in FIG. Of the light receiving surfaces 23 and 24 for receiving light, the divided regions 23a and 24b, 23b and 2
The light receiving surfaces 25 and 26 are newly formed by connecting and forming the respective light receiving surfaces 4a.

As a result, as the output signal corresponding to the light receiving surface 25, the sum (S23a + S24b) of the output signals corresponding to the divided areas 23a and 24b in FIG. 11 is obtained, and as the output signal corresponding to the light receiving surface 26, , The sum of the output signals corresponding to the divided areas 23b and 24a in FIG. 11 (S23
b + S24a) are obtained. That is, equation (1a)
(S23b + S24a) and (S23a
Since the calculation of + S24b) is performed on the photodetector 9, the calculation is simplified and the number of light receiving surfaces can be reduced.

Further, the light receiving surface 2 for receiving + 1st-order diffracted light by the regions 8C and 8D of the diffractive optical element 8 in FIG.
1 and 22 each other, that is, 21
a and 22b and 21b and 22a may be connected to each other. In this case, (S23b
+ S24a) and (S23a + S24b) are calculated on the photodetector 9.

In this case, the tracking error signal T is output to the output signal corresponding to the light receiving surface on which the calculation is not performed on the photodetector 9, for example, in the example of FIG. The corresponding output signals (S21a, S2
1b, S22a, S22b), for example, according to equation (4a) or by detecting the phase difference between signals T1 and T2 obtained by equations (7a) and (8a).

Further, the light receiving surface 2 for receiving the + 1st-order diffracted light by the regions 8C and 8D of the diffractive optical element 8 in FIG.
One of the divided areas 21a and 22 respectively
b, 21b and 22a are respectively combined to obtain the formula (1)
a) (S21a + S22b) and (S21b +
When the calculation of S22a) is performed on the photodetector 9, the output signal (S23) corresponding to the light receiving surfaces 23 and 24 is provided.
a, S23b, S24a, S24b) alone, for example, according to equation (5a) or (9a) (1
The tracking error signal T is obtained by detecting the phase difference between the signals T3 and T4 respectively obtained by Oa). (Fifteenth Embodiment) The fifteenth embodiment is similar to the fourth embodiment.
In the embodiment, two diffraction regions 8A divided along an area division line extending in a direction perpendicular to the track direction,
The figure shows a case where the diffractive optical element 8 having 8B is used, and other configurations are the same.

FIG. 13 shows a diffractive optical element 8 and a photodetector 9 of a detection optical system according to a fifteenth embodiment of the present invention. In the present embodiment, one of the ± first-order diffracted lights by the diffractive optical element 8, for example, only the −1st-order diffracted light, is detected by the photodetector 9.
To generate a focus error signal F. In the present embodiment, the four diffraction regions 8E, 8
It has a configuration including a diffractive optical element 8 having F, 8G, and 8H and a photodetector 9 having four divided light receiving surfaces. Such a configuration is advantageous for tracking error detection by the phase difference method.

That is, when detecting a tracking error signal by the phase difference method, it is necessary to accurately divide the reflected light from the optical disk into four parts. In the conventional configuration, a small light beam is divided into four parts on a photodetector. In order to be
It is necessary to accurately adjust the center line of the light beam intensity distribution on the photodetector to the dividing line of the light receiving surface of the photodetector, and there is a problem that this adjustment is troublesome. In contrast,
In the present embodiment, since the reflected light from the optical disk 6 is divided into four by a large light beam on the diffractive optical element 8, there is an advantage that the adjustment accuracy may be coarse and the adjustment is easy.

In FIG. 13, the diffractive optical element 8 has four diffraction regions 8 divided by a region division line L1 and a region division line L2 parallel to a track on the optical disk 6.
E, 8F, 8G, and 8H. The grating patterns of these diffraction regions 8E, 8F, 8G, and 8H have the 0th-order diffracted light, the + 1st-order diffracted light, and the -1st-order diffracted light near the focal plane of the condenser lens 7.
In order to have a spatial frequency necessary for separating and detecting the second-order diffracted light and to transform the + 1st-order diffracted light and the -1st-order diffracted light into a spot shape necessary for detecting a focus error near the focal plane of the condenser lens 7. Is given a spatial change.

In this case, the pattern of the diffractive optical element 8 is such that, when the objective lens 7 is at the focal position, the -1st-order diffracted light of the area 8E of the diffractive optical element 8 is converted to the light detector area 33.
a, so that the -1st-order diffracted light of the area 8F of the diffractive optical element 8 reaches the area 31a of the photodetector, and the -1st-order diffracted light from the area 8H of the diffractive optical element 8 is It was designed such that the -1st-order diffracted light from the region 8G of the diffractive optical element 8 reaches the region 34a of the photodetector in the region 33a. Although the present embodiment is different from the twelfth to fourteenth embodiments, the diffracted light from the region of the diffractive optical element 8 adjacent to the track on the optical disc 6 in the direction perpendicular to the x-axis. Are designed so as to reach the divided regions located on the opposite sides from each other, so that the characteristics are basically the same as those of the twelfth to fourteenth embodiments.

In this example, the photodetector 9 is arranged so as to detect the -1st-order diffracted light by the diffractive optical element 8, and each of the four light receiving surfaces 31, 32, 33, and 34 is divided into two.
Having. These light receiving surfaces 31, 32, 33, 34
The diffraction areas 8F, 8H, 8 of the diffractive optical element 8, respectively.
-1st order diffracted light from E and 8G is received respectively. Each of the two divided areas 3 of the light receiving surfaces 31, 32, 33, and 34
1a, 31b, 32a, 32b, 33a, 33b, 34
The output signals of the photodetector 9 corresponding to a and b are respectively S31a, S31b, S32a, S32b,
Assuming that S33a, S33b, S34a, and S34b, the arithmetic circuit 13 of FIG. 1 generates the focus error signal F by the following equation. F = (S31a + S32a + S33b + S34b)-(S31b + S32b + S33a + S34a) (13) That is, in the present embodiment, the first to fourth light receiving surfaces 31, 32, 33, 3 from the photodetector 9 in the arithmetic circuit 13 in the present embodiment.
4, the sum signal (S31a + S32a + S33b + S34b) of the signals corresponding to any one of the divided areas 31a, 32a, 33b, and 34b.
) And the other divided areas 31b, 32b, 33a, 34a
Signal (S31b + S32b + S)
33a + S34a) to obtain a difference signal,
A focus error signal F is generated.

FIG. 14 is a spot diagram showing a change in the shape of the light beam diffracted by the diffractive optical element 8 on the light receiving surface of the photodetector 9 when the relative position between the objective lens 5 and the optical disk 6 changes. . FIG. 14A shows the optical disk 6.
2 shows a state when the objective lens 5 is close to the object.
FIG. 14B shows an optical disc 6 on the focal plane of the objective lens 5.
Is focused and the light beam spot is 2
Each of the divided light receiving surfaces 31, 32, 33, and 34 is located in only one region. FIG.
14A shows a state when the objective lens 5 is separated from the optical disk 6, and the light beam spot changes in the opposite direction to that in FIG. 14A.

Therefore, by the operation of equation (11), FIG.
The focus error signal F, which is zero in the in-focus state shown in FIG. 3B and whose magnitude and polarity change in accordance with the amount of displacement from the focal position of the objective lens 5 and the direction of the displacement, can be obtained.

The tracking error signal T is obtained by a push-pull method for obtaining a tracking error signal from irregularities indicating continuous tracks such as grooves on the optical disk, or a tracking error signal from a continuous pit train recorded on the optical disk. Is possible.

In the push-pull method, the direction of the dividing line in the x-axis direction of the diffractive optical element 8 shown in FIG.
The operation of the photodetector 9 differs between the case of the tangential direction and the case of the radial direction.
The operation may be performed on the output signal corresponding to each light receiving surface in FIG. 13 so that the light beam is divided into two in the tangential direction.

For example, when the dividing line in the x direction of the diffractive optical element 8 is in the radial direction of the optical disc 6, the tracking error signal T is obtained by the following calculation. T = (S31a + S31b + S33a + S33b)-(S32a + S32b + S34a + S34b) (31) Further, the diffractive optical element 8 is so divided as to split the light beam returned from the optical disk 6 around the tangential direction and the radial direction of the optical disk 6. Are arranged, the tracking error signal F by the phase difference method becomes the following 2
It is obtained by detecting the phase difference between the signals obtained from the two equations. T7 = S31a + S31b + S34a + S34b (15) T8 = S32a + S32b + S33a + S33b (16) In the present embodiment, only the -1st-order diffracted light from the diffractive optical element 8 is incident on the photodetector 9, but the + 1st-order diffracted light Only the light may be incident on the photodetector 9, and the arithmetic circuit 13 performs the same operation to generate the focus error signal F and the tracking error signal T.

(Sixteenth Embodiment) A sixteenth embodiment is directed to a diffractive optical element 8 having two diffraction regions 8A and 8B divided along a region division line extending in a direction perpendicular to the track direction. In this case, the other configuration is the same.

FIG. 15 shows a diffractive optical element 8 and a photodetector 9 of a detection optical system according to the fifth and sixteenth embodiments of the present invention. The diffractive optical element 8 is the same as that of the fourth embodiment shown in FIG. 13, and includes four diffraction regions 8E, 8F, 8
G, 8H, and the grating pattern has a spatial frequency necessary for separating and detecting the 0th-order diffracted light, the + 1st-order diffracted light, and the -1st-order diffracted light in the vicinity of the focal plane of the condenser lens 7, and the + 1st-order diffracted light. A spatial change is given to transform the folded light and the -1st-order diffracted light into a spot shape necessary for detecting a focus error near the focal plane of the condenser lens 7.

On the other hand, the photodetector 9 has eight light-receiving surfaces 41 to 48 divided into two, and is arranged such that the respective dividing lines of these light-receiving surfaces 41 to 48 coincide with the x-axis. Further, the eight light receiving surfaces 41 to 48 are arranged so that two light receiving surfaces 41 to 48 are point-symmetrical with respect to the z axis.

The focus error detection method in this embodiment is partially similar to the fifteenth embodiment, but both the ± 1st-order diffracted light is detected by the photodetector 9 as in the twelfth embodiment. The difference from the fifteenth embodiment is that the detection is performed. Therefore, in the case of the present embodiment, since the focus error signal F is calculated from the signal based on the ± 1st-order diffracted light,
The influence of the diffraction of the groove on the optical disk 6 can be reduced.

In this case, when the objective lens 7 is at the focal position, the + 1st-order diffracted light from the area 8E of the diffractive optical element 8 is applied to the area 47b of the photodetector when the objective lens 7 is at the focal position. The first-order diffracted light reaches the photodetector region 43a, the + 1st-order diffracted light from the region 8F of the diffractive optical element 8 reaches the photodetector region 45b, and the -1st-order diffracted light reaches the photodetector region 41a. In addition, the + 1st-order diffracted light from the region 8H of the diffractive optical element 8 is placed in the region 46a of the photodetector, and the -1st-order diffracted light is placed in the region 42b of the photodetector.
The + 1st-order diffracted light in the area 8G of the diffractive optical element 8 is in the photodetector area 48a, and the -1st-order diffracted light is in the photodetector area 4a.
4b. Although the present embodiment is different from the twelfth to fourteenth embodiments, since the diffracted light in the adjacent area of the diffractive optical element 8 is designed to be symmetric with respect to the x-axis, the basic structure is basically different. Has a twelfth
To the fourteenth embodiment.

In this embodiment, the light receiving surfaces 41, 4
2, 43, 44, 45, 46, 47, and 48, the respective divided areas 41a, 41b, 42a, 42b, 43a, 4
3b, 44a, 44b, 45a, 45b, 46a, 46
b, 47a, 47b, 48a, and 48b, output signals of the photodetector 9 are respectively S41a, S41b,
S42a, S42b, S43a, S43b, S
44a, S44b, S45a, S45b, S4
6a, S46b, S47a, S47b, S48
a, S48b, the arithmetic circuit 13 in FIG. 1 generates the focus error signal F by the following equation.

F = [(S41a + S42a + S43b + S44b)-(S41b + S42b + S43a + S44a)] + [(S45a + S46a + S47b + S48b)-(S45b + S46b + S47a in the embodiment, in the case of the (S45b + S46b + S47a + 13) circuit, in the embodiment, that is, in the case of the (13), that is, in the embodiment, in the case of (13), in the present embodiment, this is the circuit, the S13a in the embodiment, that is, in the present embodiment, the (13), that is, in the embodiment, the circuit is in the thirteenth embodiment) First to fourth light receiving surfaces 41, 42, 43, 4 from photodetector 9
4, the sum signal (S41a + S42a + S43b + S44b) of the signals corresponding to any one of the divided areas 41a, 42a, 43b, and 44b.
) And the other divided areas 41b, 42b, 43a, 44a
(S41b + S42b + S
43a + S44a), and the fifth to eighth light receiving surfaces 45, 46, 47, 48 from the photodetector 9 are obtained.
, The sum signal (S45a + S46a + S47b + S48b) of the signals corresponding to any one of the divided regions 45a, 46a, 47b, and 48b.
) And the other divided areas 45b, 46b, 47a, 48a
(S45b + S46b + S
47a + S48a), and a focus error signal F is generated by obtaining a sum signal of these two difference signals.

As for tracking error detection, the fifteenth
Although it is possible to use a signal corresponding to only one of the + 1st-order diffracted light and the -1st-order diffracted light as in the embodiment of FIG.
As in the twelfth embodiment, it is also possible to use signals corresponding to all the ± 1st-order diffracted lights. The tracking error signal T by the phase difference method in this case is expressed by the following equations (18) and (19).
Is obtained by detecting the phase difference between the signals T11 and T12 obtained by

T11 = S41a + S41b + S44a + S44b + S45a + S45b + S48a + S48b (18) T12 = S42a + S42b + S43a + S43b + S46a + S46b + S47a + S47b + S47T + Push method, and push signal (19)
Is obtained by the following equation when the dividing line in the x-axis direction of the diffractive optical element 8 is in the radial direction of the optical disc 6. T = (S41a + S41b + S42a + S42b + S45a + S45b + S47a + S47b)-(S43a + S43b + S44a + S44b + S46a + S46b + S48a + S48b) (The 17th embodiment is a vertical direction in the 17th embodiment). This shows a case where a diffractive optical element 8 having two diffraction regions 8A and 8B divided along a region division line is used, and the other configuration is the same as that of the sixth embodiment.

FIG. 16 shows a seventeenth embodiment of the present invention, in which the photodetector 9 of the sixteenth embodiment is modified and a part of the calculation for calculating the focus error signal F is performed by the photodetector 9. Here is an example of the above operation. In this case, of the light receiving surface of the photodetector 9, a light receiving surface that receives one of the + 1st-order diffracted light and the -1st-order diffracted light by the regions 8E, 8F, 8G, and 8H of the diffractive optical element 8 in FIG. Of the light receiving surfaces 41, 42, 43, and 44 for receiving the -1st-order diffracted light, one divided region of each of two adjacent light receiving surfaces 41 and 42, 43 and 44, that is, the divided regions 41a, 42a, and 41b. 42b, 43a and 44a, 43b and 4
4b are divided into divided areas 51a, 51b,
By forming the light receiving surfaces 5a and 52b,
1, 52.

Thus, the divided areas 51a,
As a signal corresponding to 51b, the divided area 41a in FIG.
(S41a + S42a)
), The sum of the signals corresponding to the divided areas 41b and 42b (S
41b + S42b), and as signals corresponding to the divided areas 52a and 52b of the light receiving surface 52,
Since the sum of the signals corresponding to the divided areas 43a and 44a (S43a + S44a) and the sum of the signals corresponding to the divided areas 43b and 44b (S43b + S44b) of FIG. 15 are obtained, a part of the calculation of the equation (17) is obtained. Photodetector 9
As described above, the calculation is simplified, and the number of light receiving surfaces can be reduced.

Also, of the light receiving surfaces 45, 46, 47 and 48 for receiving the + 1st-order diffracted light by the regions 8E, 8F, 8G and 8H of the diffractive optical element 8 in FIG. 15, two adjacent light receiving surfaces 45 and 46 are provided. , 47 and 48, that is, divided regions 45a and 46a and 45b.
And 46b, 47a and 48a, and 47b and 48b, respectively, to form a divided area to form two new light receiving surfaces. In this case also, a part of the calculation of the equation (17) is performed on the photodetector 9 Will be

In this case, the tracking error signal T is an output signal corresponding to the light receiving surface on which the calculation is not performed on the photodetector 9, for example, the light receiving surfaces 45 and 4 in the example of FIG.
6, 47, 48 divided areas 45a, 45b, 46a, 4
6b, 47a, 47b, 48a, 48b, output signals S45a, S45b, S46a,
S46b, S47a, S47b, S48a, S
Using only 48b, for example, it can be obtained by detecting the phase difference between the signals T11 and T12 obtained by the equations (18) and (19) or by performing the calculation of the equation (20).

(Eighteenth Embodiment) In the eighteenth embodiment, as in the above embodiments, two diffraction regions 8 divided along an area division line extending in the direction perpendicular to the track direction are used.
This shows a case where a diffractive optical element 8 having A and 8B is used, and the other configuration is the same as that of the seventh embodiment.

FIG. 17 shows a diffraction optical element 8 of the detection optical system in the optical head device according to the eighteenth embodiment of the present invention.
And the photodetector 9. The diffractive optical element 8 is shown in FIGS.
As in the fifteenth to seventeenth embodiments shown in FIG.
The diffraction grating has two diffraction regions 8E, 8F, 8G, and 8H.
It has a spatial frequency necessary to separate and detect the first-order diffracted light and the -1st-order diffracted light, and has a + 1st-order diffracted light and a -1st-order diffracted light.
A spatial change is given to transform the next-order diffracted light into a spot shape necessary for detecting a focus error near the focal plane of the condenser lens 7.

On the other hand, the photodetector 9 for detecting the light diffracted by the diffractive optical element 8 has eight light receiving surfaces 61 divided into two parts.
Although there are 62, 63, 64, 65, 66, 67, and 68, unlike the sixteenth embodiment, these light receiving surfaces 61,
62, 63, 64, 65, 66, 67, and 68 do not have their respective dividing lines on the x-axis, and are arranged in pairs at two points symmetrical with respect to the z-axis. However, each light receiving surface is arranged such that the dividing line is parallel to the x-axis.

The focus error detection method in this embodiment is basically the same as that in the sixteenth embodiment. In this case, too, the focus error signal F
Is calculated, the influence of diffraction of the groove on the optical disk 6 can be reduced.

That is, in the present embodiment, the respective divided areas 61a, 61b, 62a, 62b, 6 of the light receiving surfaces 61, 62, 63, 64, 65, 66, 67, 68 are respectively.
3a, 63b, 64a, 64b, 65a, 65b, 66
a, 66b, 67a, 67b, 68a, 68b, the output signals of the photodetector 9 are converted to S61a, S6, respectively.
1b, S62a, S62b, S63a, S63
b, S64a, S64b, S65a, S65b
, S66a, S66b, S67a, S67b
, S68a, S68b, the arithmetic circuit 13 of FIG. 1 generates the focus error signal F by the calculation of the following equation.

F = [(S61a + S62a)-(S65b + S66b)] + [(S63b + S64b)-(S67a + S68a)]-[(S61b + S62b)-(S65a + S66a)]-[(S63a + S64b) (21) The tracking error detection may be the same as in the sixteenth embodiment. That is, the tracking error detection can be performed by using a signal corresponding to only one of the + 1st-order diffracted light and the -1st-order diffracted light, as in the fifteenth embodiment, but similar to the twelfth embodiment. It is also possible to use signals corresponding to all the ± first-order diffracted lights. In this case, the tracking error signal T by the phase difference method is expressed by the following equation (2)
2) It can be obtained by detecting the phase difference between the signals T21 and T22 obtained by (23).

T21 = S61a + S61b + S63a + S63b + S65a + S65b + S67a + S67b (22) T22 = S62a + S62b + S64a + S64b + S66a + S66b + S68a This method is suitable for the tracking method. Configuration.

The tracking error signal T obtained by the push-pull method is obtained by the following equation when the dividing line of the diffractive optical element 8 in the x-axis direction is in the radial direction of the optical disk 6. T = (S61a + S61b + S64a + S64b + S66a + S66b + S67a + S67b)-(S62a + S62b + S63a + S63b + S65a + S65b + S68a + S68b) (Embodiment 19 in the 19th embodiment) The figure shows a case where a diffractive optical element 8 having two diffraction regions 8A and 8B divided along a region division line extending in a direction perpendicular to the above is used, and other configurations are the same as those of the eighth embodiment. It is.

FIG. 18 shows a nineteenth embodiment of the present invention, in which the photodetector 9 of the eighteenth embodiment is changed and a part of the calculation for calculating the focus error signal F is performed by the photodetector 9. Here is an example of the above operation. In this case, of the light-receiving surface of the photodetector 9, a light-receiving surface for receiving one of the + 1st-order diffracted light and the -1st-order diffracted light by the regions 8E, 8F, 8G, and 8H of the diffractive optical element 8 in FIG. Of the light receiving surfaces 61, 62, 63, and 64 that receive the -1st-order diffracted light, one of the two adjacent light receiving surfaces 61 and 62, 63 and 64, that is, each of the divided regions 61a, 62a, and 61b. 62b, 63a and 64a, 63b and 6
4b are respectively combined with divided areas 71a, 71b,
By forming the light receiving surfaces 7a and 72b,
1, 72.

As a result, the divided areas 71a,
As a signal corresponding to 71b, the divided area 61a of FIG.
(S61a + S62a)
), The sum of the signals corresponding to the divided areas 61b and 62b (S
61b + S62b), and as signals corresponding to the divided areas 72a and 72b of the light receiving surface 72,
Since the sum (S63a + S64a) of the signals corresponding to the divided areas 63a and 64a and the sum (S63b + S64b) of the signals corresponding to the divided areas 63b and 64b in FIG. 17 are obtained, a part of the calculation of the equation (21) is obtained. Photodetector 9
As described above, the calculation is simplified, and the number of light receiving surfaces can be reduced.

Further, of the light receiving surfaces 65, 66, 67, 68 for receiving the + 1st-order diffracted light by the regions 8E, 8F, 8G, 8H of the diffractive optical element 8 in FIG. , 67 and 68, ie, the divided regions 65a and 66a, 65b
And 66b, 67a and 68a, and 67b and 68b, respectively, to form a divided area to form two new light receiving surfaces. In this case as well, a part of the calculation of Expression (21) is performed on the photodetector 9 Will be

In this case, the tracking error signal T is an output signal corresponding to the light receiving surface on which the calculation is not performed on the photodetector 9, for example, the light receiving surfaces 65 and 6 in the example of FIG.
6, 67, 68 divided areas 65a, 65b, 66a, 6
6b, 67a, 67b, 68a, 68b, output signals S65a, S65b, S66a,
S66b, S67a, S67b, S68a, S
For example, the phase difference is obtained by detecting the phase difference between the signals T21 and T22 obtained by the equations (22) and (23) or by performing the operation of the equation (24) using only the signal 68b.

(Twentieth Embodiment) The twentieth embodiment relates to a diffractive optical element 8 having two diffraction regions 8A and 8B divided along a region division line extending in a direction perpendicular to the track direction. This embodiment shows a case where the ninth embodiment is used, and the other configuration is the same as that of the ninth embodiment.

FIG. 19 shows a twentieth embodiment of the present invention, in which the photodetector 9 of the nineteenth embodiment is further modified.
Another example in which a part of the calculation for calculating the focus error signal F is performed on the photodetector 9 will be described. In this case, one of the divided areas of the light receiving surfaces 71 and 72 in FIG. 18, that is, 71 a and 72 b, 71 b and 72
The light receiving surfaces 73 and 74 are newly formed by combining the respective “a”.

As a result, the output signals corresponding to the light receiving surface 73 include the divided areas 61a, 62a, and 6 in FIG.
3b, 64b (S61a + S62)
a + S63b + S64b is obtained, and as an output signal corresponding to the light receiving surface 74, the divided area 61 in FIG.
b, 62b, 63a, and 64a (S6
1b + S62b + S63a + S64a), so that a greater part of the operation of equation (21) is performed on the photodetector 9, which simplifies the operation and further reduces the number of light receiving surfaces. it can.

With respect to the tracking error signal T, the first
Similarly to the ninth embodiment, an output signal corresponding to the light receiving surface on which no calculation is performed on the photodetector 9, for example, the divided areas 65a, 65 of the light receiving surfaces 65, 66, 67, 68 in the example of FIG.
b, 66a, 66b, 67a, 67b, 68a, 68b
Output signals S65a and S65b of the photodetector 9 corresponding to
, S66a, S66b, S67a, S67b
, S68a and S68b alone, for example, by detecting the phase difference between the signals T21 and T22 obtained by the equations (22) and (23) or by performing the calculation of the equation (24).

(Twenty-First Embodiment) In the twenty-first embodiment, a diffractive optical element 8 having two diffraction regions 8A and 8B divided along a region division line extending in a direction perpendicular to the track direction is used. This embodiment shows a case where the present embodiment is used, and the other configuration is the same as that of the tenth embodiment.

FIG. 20 shows the structure of an optical head device according to the twenty-first embodiment of the present invention. This optical head device includes a light source 1, a collimator lens 2, a beam shaping prism 3, a beam splitter 4, an objective lens 5, a diffractive optical element 8,
In addition to the photodetector 9, the optical system further includes a mirror 17 and a wavelength plate 18, and further includes an amplifier array having a current-voltage conversion function (not shown) and an arithmetic circuit, which are not shown in FIG. In the present embodiment, the insertion position of the diffractive optical element 8 is different from that of FIG.

The light emitted from the light source 1 is converted into a parallel light beam by a collimator lens 2, and the light emitted from the collimator lens 2 enters a beam splitter 4 after a beam shape is shaped by a beam shaping prism 3. . The light transmitted through the beam splitter 4 is reflected by a mirror 17, changes its direction, passes through a diffractive optical element 8, and is focused and irradiated as a minute spot on an optical disk (not shown) by an objective lens 5 through a wave plate 18. .

The reflected light from the optical disk is
And diffracted by the diffractive optical element 8. The diffracted light passes through the mirror 17 and the beam splitter 4 and is condensed on the photodetector 9 by the condenser lens 7.

In the optical system of this embodiment, unlike FIG. 1, the beam splitter 4 is located between the diffractive optical element 8 and the photodetector 9.
And the condenser lens 7 enters. In this case, the diffraction pattern of the diffractive optical element 8 including the beam splitter 4 and the condenser lens 7 is adjusted so that the states of the diffractive optical element 8 and the light beam are similar to those in the first to ninth embodiments. With this design, the same effects as those of the above embodiments can be obtained.
Here, the element inserted between the diffractive optical element 8 and the photodetector 9 is the beam splitter 4 and the condenser lens 7.
However, even if another optical element is inserted to add another function, the pattern of the diffractive optical element 8 may be designed including the characteristics of the optical element.

Further, when a mechanism for moving an objective lens for moving a light beam on an optical disk by performing tracking control is considered, the diffraction optical element 8 and the wavelength plate 1
When the objective lens 8 is moved together with the objective lens 5, an offset may not be easily generated particularly in a tracking error signal by the push-pull method. That is, in an optical system in which the diffractive optical element 8 is fixed, when the objective lens 5 moves to perform tracking control, the beam on the photodetector 9 moves greatly. And it is difficult to move the objective lens 5 too much for tracking control.

On the other hand, the diffraction optical element 8 and the wave plate 1
If the objective lens 8 is moved together with the objective lens 5, the objective lens hardly moves, so that an accurate push-pull signal can be obtained even if the objective lens 5 moves greatly during tracking.

Here, the mechanism for moving the objective lens 5 may be an electromagnetic drive system of a magnet and a coil, and the objective lens 5, the diffractive optical element 8 and the wave plate 18 are simultaneously substantially parallel to the radial direction of the disk 6. Basically, any configuration may be used as long as it can be moved to.

When a polarizing type is used as the diffractive optical element 8, the light source 1
Since the light beam coming from the optical disk is not diffracted by the diffractive optical element 8 and only the reflected light from the optical disk is diffracted,
The light use efficiency of the light source 1 can be increased. Regarding the focus error detection and the tracking error detection, the same effect can be obtained by using any diffractive optical element.

In the above embodiment, the ± 1st-order diffracted light is used by the diffractive optical element 8, but the present invention is not limited to this, and focus error detection may be performed using ± Nth-order diffracted light.

As described above, the objective lens 5 and the diffractive optical element 8 are moved integrally, and the ± N-order diffracted light of the diffractive element 8 is used, so that the focus error signal is less leaked and the push-pull An optical head having a small tracking shift due to an objective lens shift in the method can be realized.

(Twenty-second Embodiment) The twenty-second embodiment is different from the eleventh embodiment in that the two diffraction regions 8A and 8B divided along the region division line extending in the direction perpendicular to the track direction are used. The figure shows a case where a diffractive optical element 8 is used, and the other configuration is the same as that of the eleventh embodiment.

FIG. 21 shows an optical head device according to the twenty-second embodiment of the present invention, which is the same as the previous embodiments, except that a finite system lens is used for the objective lens 5. In this case, the collimator lens 2, the beam shaping prism 3, and the condenser lens 7 in FIG. 1 become unnecessary.

[0269]

As described above, according to the present invention, even if the optical element is displaced, the fluctuation of the focus error signal caused by the diffraction from the groove on the recording surface of the recording medium is suppressed. It becomes possible.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of a main part of an optical head device according to the present invention.

FIG. 2 is a plan view showing the configuration of the diffractive optical element according to the embodiment.

FIG. 3 is a diagram showing a configuration of a light receiving surface of the photodetector in the embodiment.

FIG. 4 is a view showing the relationship between the direction of diffraction of the diffracted light from the diffractive optical element and the light receiving surface of the photodetector in the embodiment.

FIG. 5 is a diagram showing a change in a light beam spot shape on a light receiving surface of a photodetector with respect to a focus error.

FIG. 6 is a view showing a focus error signal waveform in the embodiment.

FIG. 7 shows a photodetector 9 at the time of focusing in the embodiment.
FIG. 4 is a diagram showing an intensity distribution of a light beam on the light detection surface, an intensity distribution of a light beam incident on the diffractive optical element 8 at the time of focusing, and an intensity distribution of a light beam on the optical disk 6.

FIG. 8 shows the intensity distribution of the light beam on the light detection surface of the light detector 9 when the light detector has a displacement in the embodiment.
FIG. 4 is a diagram showing an intensity distribution of a light beam incident on the diffractive optical element 8 during focusing and an intensity distribution of a light beam on the optical disk 6.

FIG. 9 shows the intensity distribution of the light beam on the light detection surface of the photodetector 9 when the diffractive optical element is misaligned in the embodiment, and the intensity distribution of the light beam incident on the diffractive optical element 8 during focusing. FIG. 4 is a diagram showing an intensity distribution and an intensity distribution of a light beam on an optical disc 6.

FIG. 10 is a simplified diagram of FIG. 5 for explaining the principle of focus error detection in the present invention.

FIG. 11 is a diagram showing a configuration of a diffractive optical element and a photodetector according to second and thirteenth embodiments of the present invention.

FIG. 12 is a diagram showing a configuration of a diffractive optical element and a photodetector according to third and fourteenth embodiments of the present invention.

FIG. 13 is a diagram showing a configuration of a diffractive optical element and a photodetector according to fourth and fifteenth embodiments of the present invention.

FIG. 14 is a diagram illustrating a change in a light beam spot shape on a light receiving surface of a photodetector with respect to a focus error.

FIG. 15 is a diagram showing a configuration of a diffractive optical element and a photodetector according to fifth and sixteenth embodiments of the present invention.

FIG. 16 is a diagram showing a configuration of a diffractive optical element and a photodetector according to sixth and seventeenth embodiments of the present invention.

FIG. 17 is a diagram showing a configuration of a diffractive optical element and a photodetector according to seventh and eighteenth embodiments of the present invention.

FIG. 18 is a diagram showing a configuration of a diffractive optical element and a photodetector according to eighth and nineteenth embodiments of the present invention.

FIG. 19 is a diagram showing a configuration of a diffractive optical element and a photodetector according to ninth and twentieth embodiments of the present invention.

FIG. 20 is a diagram showing a configuration of a main part of an optical head device according to tenth and twenty-first embodiments of the present invention.

FIG. 21 is a diagram showing a configuration of a main part of an optical head device according to eleventh and twenty-second embodiments of the present invention.

FIG. 22 is a diagram showing a configuration of an optical head device including a focus error detection system using a conventional astigmatism method.

FIG. 23 is a diagram showing a light intensity distribution on a light receiving surface when the four-divided photodetector in FIG. 21 is displaced.

FIG. 24 shows the light intensity on the diffractive optical element when there is no displacement between the photodetector and the diffractive optical element in the embodiment having the diffractive optical element having a plurality of diffraction regions divided perpendicular to the track direction. The figure which shows distribution and the light intensity distribution on a photodetector.

FIG. 25 is a diagram showing a light intensity distribution on the diffractive optical element and a light intensity distribution on the photodetector when the photodetector has a position shift in the embodiment.

FIG. 26 is a diagram showing a light intensity distribution on the diffractive optical element and a light intensity distribution on the photodetector when the diffractive optical element has a position shift in the embodiment.

FIG. 27 is a diagram showing a light intensity distribution on a light receiving surface when the four-divided photodetector in FIG. 21 is displaced.

FIG. 28 is an explanatory diagram illustrating two types of the present invention.

[Description of Signs] 1 ... Light source 2 ... Collimator lens 3 ... Beam shaping prism 4 ... Beam splitter 5 ... Objective lens 6 ... Optical disk 7 ... Condensing lens 8 ... Diffractive optical element 8A to 8H ... Diffraction area L1, L2 ... Area Division line 9 ... Photodetector 10, 11 ... Divided light receiving surface 10a-10d, 11a-11d ... Division area 12 ... Amplifier 13 ... Operation circuit 14 ... Cylindrical lens 15 ... 4 division photodetector 16 ... Pit or recording Mark 17: Mirror 18: Wave plate 21, 22, 23, 24 ... Light receiving surface 21a, 21b, 22a, 22b, 23a, 23b, 2 divided into two
4a, 24b: divided area 25, 26: light receiving surface 31, 32, 33, 34 ... light receiving surface 31a, 31b, 32a, 32b, 33a, 33b, 3 divided into two
4a, 34b ... divided areas 41, 42, 43, 44, 45, 46, 47, 48 ... 2
Divided light receiving surface 41a, 41b, 42a, 42b, 43a, 43b, 4
4a, 44b, 45a, 45b, 46a, 46b, 47
a, 47b, 48a, 48b... divided area 51, 52... divided light receiving surface 51a, 51b, 52a, 52b... divided area 61, 62, 63, 64, 65, 66, 67, 68.
Divided light receiving surface 61a, 61b, 62a, 62b, 63a, 63b, 6
4a, 64b, 65a, 65b, 66a, 66b, 67
a, 67b, 68a, 68b: divided areas 71, 72: divided light receiving surfaces 71a, 71b, 72a, 72b: divided areas 73, 74: light receiving surfaces 81, 82, 83, 84, 85, 86, 87, 88,8
9: Light intensity distribution on diffractive optical element 91, 92, 93, 94, 95, 96, 97, 98, 9
9: Light intensity distribution on photodetector surface 151, 152, 153: 4-split photodetector 171, 172, 173: Optical spot on optical disk 191, 192, 193: Optical spot on optical disk D1: Diffractive optical element Grating pitch of D2 ... Grating surface of diffractive optical element

Claims (24)

[Claims] A light source that emits a light beam; an objective lens that focuses and irradiates a light beam emitted from the light source onto a recording medium to transmit reflected light from the recording medium; and an optical axis of the reflected light. A light receiving surface divided into a plurality of divided areas by a dividing line along a direction parallel to the track on the recording medium in a plane perpendicular to the recording medium, and paired with each other at symmetrical positions with respect to the optical axis; A photodetector having the light receiving surface arranged such that the divided areas are arranged; and a plane parallel to a track on the recording medium in a plane perpendicular to an optical axis of the reflected light. + N-order diffracted light (N is any integer of 1 or more) in each of the divided portions of the reflected light.
And -Nth-order diffracted light (N is an arbitrary integer equal to or greater than 1) are received by the divided regions of the light receiving surface arranged at positions symmetrical to each other with respect to the optical axis, and in a direction parallel to the track. The + N-order diffracted lights and the −N-order diffracted lights in the divided portions adjacent to each other along the same are separated from each other by the reflected light so that they are received by the divided areas located on the opposite sides with respect to the divided line on the light receiving surface. An optical head device, comprising: a diffractive optical element for diffracting light; and arithmetic means for calculating a focus error signal from an output signal of the photodetector for both the + N-order diffracted light and the -N-th diffracted light. 2. A light source for emitting a light beam, an objective lens for converging and irradiating a light beam emitted from the light source onto a recording medium and transmitting reflected light from the recording medium, and a position where the reflected light is incident A diffractive optical element having two diffraction regions divided along a region division line extending in a direction parallel to a track on the recording medium; and a plane perpendicular to an optical axis of the reflected light. Wherein the first and second light receiving surfaces are divided into four divided regions by dividing lines extending in a direction parallel to and perpendicular to the track on the recording medium, and the positions are symmetric with respect to the optical axis. A photodetector having the first and second light receiving surfaces arranged such that the paired divided regions are arranged; and a focus of the objective lens on the recording medium from an output signal of the photodetector. Error Calculating means for generating a focus error signal by calculation, wherein the diffractive optical element includes + N-order diffracted light (N is an integer of 1 or more) and −N-order diffracted light (N is 1 The above-mentioned arbitrary integer is configured to be received by the divided region of the light receiving surface disposed at a position symmetrical with respect to the optical axis, and the arithmetic unit includes a first and a second signal from the photodetector. For the output signal corresponding to the light receiving surface, a sum signal of signals corresponding to two predetermined divided regions in a diagonal positional relationship and a sum signal of signals corresponding to the other two divided regions in a diagonal positional relationship, An optical head device, wherein the focus error signal is generated by obtaining a difference signal of the two, and further obtaining a sum signal of the two difference signals. 3. A light source for emitting a light beam, an objective lens for converging and irradiating a light beam emitted from the light source onto a recording medium and transmitting reflected light from the recording medium, and a position where the reflected light is incident A diffractive optical element having two diffraction areas divided along an area dividing line extending in a direction parallel to a track on the recording medium; and a plane perpendicular to an optical axis of the reflected light. Wherein the first and second light receiving surfaces are divided into four divided regions by dividing lines extending in a direction parallel to and perpendicular to the track on the recording medium, and the positions are symmetric with respect to the optical axis. A photodetector having the first and second light receiving surfaces arranged such that the paired divided regions are arranged; and a focus of the objective lens on the recording medium from an output signal of the photodetector. Error A diffractive optical element comprising: a + N-order diffracted light (N is an arbitrary integer of 1 or more) and a −N-order diffracted light (N is 1
The above-mentioned arbitrary integer is configured to be received by the divided region of the light receiving surface arranged at a position symmetrical with respect to the optical axis, and the calculating means includes: a first light receiving surface from the photodetector; , A difference signal between signals corresponding to the first and second divided areas having an adjacent positional relationship in a direction parallel to the track on the recording medium is obtained, and a second signal from the photodetector is obtained. The output signal corresponding to the light receiving surface has an adjacent positional relationship in a direction parallel to the track on the recording medium, and the first and second divided areas have positions in a direction perpendicular to the track on the recording medium. An optical head device for generating the focus error signal by obtaining a difference signal between signals corresponding to different third and fourth divided areas, and further obtaining a sum signal of the two difference signals. 4. A light source for emitting a light beam, an objective lens for converging and irradiating a light beam emitted from the light source onto a recording medium and transmitting reflected light from the recording medium, and a position where the reflected light is incident A diffractive optical element having two diffraction areas divided along an area dividing line extending in a direction parallel to a track on the recording medium; and a plane perpendicular to an optical axis of the reflected light. , Each of which has a dividing line extending in a direction parallel to a track on the recording medium, and receives + N-order diffracted light (N is an arbitrary integer of 1 or more) from two diffraction regions of the diffractive optical element, respectively. First and second light receiving surfaces each composed of two divided areas for detection and two divided areas for detecting -N-th order diffracted light (N is any integer of 1 or more) from the two diffraction areas, respectively. Third and fourth consisting of A photodetector having a light-receiving surface, the first to fourth light-receiving surfaces arranged such that the paired divided regions are arranged at positions symmetrical with respect to the optical axis, and the light detector Calculating means for calculating a focus error signal indicating a focus error of the objective lens with respect to the recording medium from the output signal of the recording medium, wherein the diffractive optical element includes + N-order diffracted light from each of the diffraction areas and -N The second-order diffracted light is configured to be received by the divided area of the light receiving surface arranged at a position symmetrical with respect to the optical axis, and the arithmetic unit includes a first and a second light receiving surface from the photodetector. The corresponding output signal and the output signals corresponding to the third and fourth light receiving surfaces are divided into two predetermined divided regions having a non-linear symmetric positional relationship with respect to an axis passing through the optical axis and extending in a direction parallel to the track. Corresponding signal The focus error signal is calculated by calculating the difference signal between the sum signal and the sum signal of the signals corresponding to the other two divided regions in a non-linear symmetric positional relationship, and further calculating the sum signal of these two difference signals. An optical head device characterized by generating. 5. A non-symmetric line with respect to an axis extending in a direction parallel to said track through said optical axis, of said first and second light receiving surfaces or third and fourth light receiving surfaces of said photodetector. 5. The optical head device according to claim 4, wherein two divided regions having a positional relationship are connected to each other. 6. A light source for emitting a light beam, an objective lens for converging and irradiating a light beam emitted from the light source onto a recording medium and transmitting reflected light from the recording medium, and a position where the reflected light is incident And a diffractive optical element having four diffraction regions divided along a region division line extending in a direction parallel to and perpendicular to a track on the recording medium, and with respect to an optical axis of the reflected light. + N-th order diffracted light (N is one or more arbitrary ones) from four diffraction regions of the diffractive optical element, each having a division line along a direction parallel to a track on the recording medium in a plane perpendicular to the recording medium. First, second, third, and fourth light receiving surfaces each composed of two divided areas for detecting an integer) and -1st-order diffracted light (N is an arbitrary integer of 1 or more) from the diffraction area, respectively. Two to detect Fifth consisting split regions, sixth, has a light receiving surface of the seventh and eighth, first to eighth as the divided regions are arranged to be paired with each other at symmetrical positions with respect to optical axis
A light detector provided with a light receiving surface of the above, and a calculation means for generating a focus error signal indicating a focus error of the objective lens with respect to the recording medium from the output signal of the light detector by calculation, the diffraction The type optical element is configured such that + N-order diffracted light and -N-order diffracted light from the respective diffraction areas are received by the divided areas of the light receiving surface arranged at positions symmetrical with respect to the optical axis; Are the first, second, and third signals from the photodetector.
And a difference signal between a sum signal of a signal corresponding to one of the divided areas and a sum signal of a signal corresponding to the other divided area is determined for the output signal corresponding to the fourth light receiving surface. Of the output signals corresponding to the fifth, sixth, seventh, and eighth light receiving surfaces from the sum signal of the signal corresponding to any one of the divided regions and the sum signal of the signal corresponding to the other divided region An optical head device for generating the focus error signal by obtaining a difference signal and obtaining a sum signal of these two difference signals. 7. A track on the recording medium among the first, second, third and fourth light receiving surfaces or fifth, sixth, seventh and eighth light receiving surfaces of the photodetector. 7. The optical head device according to claim 6, wherein two divided regions having an adjacent relationship in a parallel direction are connected to each other. 8. The apparatus according to claim 1, further comprising means for calculating a tracking error signal indicating a displacement of the light beam in a track width direction with respect to a track on the recording medium from an output signal of the photodetector. Item 8. The optical head device according to any one of Items 1 to 7. 9. The method according to claim 1, wherein the diffractive optical element is arranged near the objective lens, and when the objective lens is moved in the track width direction, the diffractive optical element is simultaneously moved in the track width direction. The optical head device according to any one of claims 1 to 8, wherein 10. The optical head device according to claim 1, further comprising means for converging light reflected from the recording medium on the photodetector. 11. An optical disk device comprising the optical head device according to claim 1. Description: 12. A light source for emitting a light beam, an objective lens for converging and irradiating a light beam emitted from the light source onto a recording medium and transmitting reflected light from the recording medium, and an optical axis of the reflected light. In a plane perpendicular to the optical axis, the light receiving surface is divided into a plurality of divided regions by a dividing line in a predetermined direction, and the paired divided regions are arranged at symmetrical positions with respect to the optical axis. A photodetector provided with a light receiving surface; and, in a plane perpendicular to the optical axis of the reflected light, the reflected light is directed along a direction parallel to a track on the recording medium and a direction perpendicular to the track. + N-order diffracted light in each divided part of the reflected light (N is an arbitrary integer of 1 or more)
And -Nth-order diffracted light (N is an arbitrary integer of 1 or more) are received by the divided areas of the light receiving surface arranged at positions symmetrical to each other with respect to the optical axis, and are mutually separated along the predetermined direction. Diffraction that diffracts the reflected light so that the + N-order diffracted lights and the −N-order diffracted lights in the adjacent divided portions are received by the divided areas located on the opposite sides of the dividing line on the light receiving surface. 1. An optical head device comprising: a mold optical element; and a calculating means for calculating a focus error signal from an output signal of the photodetector for both the + N-order diffracted light and the -N-order diffracted light. 13. A light source for emitting a light beam, an objective lens for converging and irradiating a light beam emitted from the light source onto a recording medium and transmitting reflected light from the recording medium, and an optical axis of the reflected light. A light receiving surface divided into a plurality of divided areas by a dividing line along a direction perpendicular to a track on the recording medium in a plane perpendicular to the recording medium, and paired with each other at positions symmetrical with respect to the optical axis; A photodetector having the light receiving surface arranged such that the divided areas are arranged; and a plane parallel to a track on the recording medium in a plane perpendicular to an optical axis of the reflected light. + N-order diffracted light (N is any integer of 1 or more) in each of the divided portions of the reflected light.
And -N-th order diffracted light (N is an arbitrary integer of 1 or more) are received by the divided areas of the light receiving surface arranged at positions symmetrical to each other with respect to the optical axis, and in a direction perpendicular to the track. The + N-order diffracted lights and the −N-order diffracted lights in the divided portions adjacent to each other along the same are separated from each other by the reflected light so that they are received by the divided areas located on the opposite sides with respect to the divided line on the light receiving surface. An optical head device comprising: a diffractive optical element for diffracting light; and arithmetic means for calculating a focus error signal from an output signal of the photodetector with respect to both the + N-order diffracted light and the -N-order diffracted light. 14. A light source for emitting a light beam, an objective lens for converging and irradiating a light beam emitted from the light source onto a recording medium and transmitting reflected light from the recording medium, and a position where the reflected light is incident A diffractive optical element having two diffraction regions divided along a region division line extending in a direction perpendicular to a track on the recording medium, and a plane perpendicular to the optical axis of the reflected light Wherein the first and second light receiving surfaces are divided into four divided regions by dividing lines extending in a direction parallel to and perpendicular to the track on the recording medium, and the positions are symmetric with respect to the optical axis. A photodetector having the first and second light receiving surfaces arranged such that the paired divided regions are arranged; and a focus of the objective lens on the recording medium from an output signal of the photodetector. Error A diffractive optical element comprising: a + N-order diffracted light (N is an arbitrary integer of 1 or more) and a −N-order diffracted light (N is 1 The above-mentioned arbitrary integer is configured to be received by the divided region of the light receiving surface disposed at a position symmetrical with respect to the optical axis, and the arithmetic unit includes a first and a second signal from the photodetector. For the output signal corresponding to the light receiving surface, a sum signal of signals corresponding to two predetermined divided regions in a diagonal positional relationship and a sum signal of signals corresponding to the other two divided regions in a diagonal positional relationship, An optical head device, wherein the focus error signal is generated by obtaining a difference signal of the two, and further obtaining a sum signal of the two difference signals. 15. A light source for emitting a light beam, an objective lens for converging and irradiating a light beam emitted from the light source onto a recording medium and transmitting reflected light from the recording medium, and a position where the reflected light is incident A diffractive optical element having two diffraction regions divided along a region division line extending in a direction perpendicular to a track on the recording medium, and a plane perpendicular to the optical axis of the reflected light Wherein the first and second light receiving surfaces are divided into four divided regions by dividing lines extending in a direction parallel to and perpendicular to the track on the recording medium, and the positions are symmetric with respect to the optical axis. A photodetector having the first and second light receiving surfaces arranged such that the paired divided regions are arranged; and a focus of the objective lens on the recording medium from an output signal of the photodetector. Error A diffractive optical element comprising: a + N-order diffracted light (N is an arbitrary integer of 1 or more) and a −N-order diffracted light (N is 1
The above-mentioned arbitrary integer is configured to be received by the divided region of the light receiving surface arranged at a position symmetrical with respect to the optical axis, and the calculating means includes: a first light receiving surface from the photodetector; Is obtained, a difference signal between signals corresponding to the first and second divided areas which are adjacent to each other in the direction perpendicular to the track on the recording medium in the direction perpendicular to the track on the recording medium, and the second signal from the photodetector is obtained. The output signal corresponding to the light receiving surface is adjacent to the track on the recording medium in a direction perpendicular to the track, and the first and second divided areas have positions in a direction parallel to the track on the recording medium. An optical head device for generating the focus error signal by obtaining a difference signal between signals corresponding to different third and fourth divided areas, and further obtaining a sum signal of the two difference signals. 16. A light source for emitting a light beam, an objective lens for converging and irradiating a light beam emitted from the light source onto a recording medium and transmitting reflected light from the recording medium, and a position where the reflected light is incident A diffractive optical element having two diffraction regions divided along a region division line extending in a direction perpendicular to a track on the recording medium, and a plane perpendicular to the optical axis of the reflected light And + N-order diffracted light (N is an integer of 1 or more) from two diffraction regions of the diffractive optical element, each having a dividing line extending in a direction perpendicular to a track on the recording medium. First and second light receiving surfaces each composed of two divided areas for detection and two divided areas for detecting -N-th order diffracted light (N is any integer of 1 or more) from the two diffraction areas, respectively. The third, consisting of A photodetector having the first to fourth light receiving surfaces such that the paired divided regions are arranged at positions symmetrical with respect to the optical axis; Calculating means for calculating a focus error signal indicating a focus error of the objective lens with respect to the recording medium from the output signal of the recording medium, wherein the diffractive optical element includes + N-order diffracted light from each of the diffraction areas and- The N-th order diffracted light is configured to be received by the divided area of the light receiving surface disposed at a position symmetrical with respect to the optical axis, and the arithmetic unit includes a first and a second light receiving surface from the photodetector. And the output signals corresponding to the third and fourth light-receiving surfaces, two predetermined divided regions having a non-linear symmetrical positional relationship with respect to an axis passing through the optical axis and extending in a direction perpendicular to the track. Corresponding to The difference signal between the sum signal of the two signals and the sum signal of the signals corresponding to the other two divided regions in a non-linear symmetric positional relationship is obtained, and the sum signal of these two difference signals is obtained. An optical head device for generating an optical head. 17. A non-symmetric line of the first and second light receiving surfaces or the third and fourth light receiving surfaces of the photodetector, the axis extending through the optical axis and perpendicular to the track. 17. The optical head device according to claim 16, wherein two divided regions having a positional relationship are connected to each other. 18. A light source for emitting a light beam, an objective lens for converging and irradiating a light beam emitted from the light source onto a recording medium and transmitting reflected light from the recording medium, and a position where the reflected light is incident And a diffractive optical element having four diffraction regions divided along a region division line extending in a direction parallel to and perpendicular to a track on the recording medium, and with respect to an optical axis of the reflected light. + N-order diffracted light (N is one or more arbitrary ones) from four diffraction regions of the diffractive optical element, each having a division line along a direction perpendicular to a track on the recording medium in a plane perpendicular to the recording medium. First, second, third, and fourth light receiving surfaces each composed of two divided areas for detecting an integer) and -1st-order diffracted light (N is an arbitrary integer of 1 or more) from the diffraction area, respectively. Two to detect Fifth consisting divided regions, sixth, has a light receiving surface of the seventh and eighth, first to eighth as the divided regions are arranged to be paired with each other at symmetrical positions with respect to optical axis
A light detector provided with a light receiving surface of the above, and a calculation means for generating a focus error signal indicating a focus error of the objective lens with respect to the recording medium from the output signal of the light detector by calculation, the diffraction The type optical element is configured such that + N-order diffracted light and -N-order diffracted light from the respective diffraction areas are received by the divided areas of the light receiving surface arranged at positions symmetrical with respect to the optical axis; Are the first, second, and third signals from the photodetector.
And a difference signal between a sum signal of a signal corresponding to one of the divided areas and a sum signal of a signal corresponding to the other divided area is determined for the output signal corresponding to the fourth light receiving surface. From the output signal corresponding to the fifth, sixth, seventh and eighth light receiving surfaces from the sum signal of the signal corresponding to any one of the divided regions and the sum signal of the signal corresponding to the other divided region An optical head device for generating the focus error signal by obtaining a difference signal and obtaining a sum signal of these two difference signals. 19. A track on the recording medium among the first, second, third, and fourth light receiving surfaces or fifth, sixth, seventh, and eighth light receiving surfaces of the photodetector. 19. The optical head device according to claim 18, wherein two divided regions having an adjacent relationship in a vertical direction are connected to each other. 20. Further, there is further provided a means for generating a tracking error signal indicating a positional shift of the light beam in a track width direction with respect to a track on the recording medium from an output signal of the photodetector by a push-pull method or a phase difference method. The optical head device according to any one of claims 12 to 19, wherein: 21. The diffractive optical element is arranged near the objective lens, and when the objective lens is moved in the track width direction, the diffractive optical element is simultaneously moved in the track width direction. The optical head device according to any one of claims 12 to 20, wherein 22. The optical head device according to claim 12, further comprising means for converging light reflected from said recording medium to said photodetector. 23. An optical disk device comprising the optical head device according to claim 12. 24. An objective lens for converging a light beam emitted from a light source on a recording medium, and at a position perpendicular to an optical axis of reflected light from the recording medium and symmetric with respect to the optical axis. It has a plurality of light receiving surfaces arranged, and these light receiving surfaces are configured to be divided into a plurality of division regions by a plurality of division lines including a division line along a direction parallel to at least a track on the recording medium. A light detector, disposed upstream of the optical path of the photodetector, and in a plane perpendicular to the optical axis of the reflected light, reflects the reflected light at least along a direction parallel to a track on the recording medium. The reflected light is divided into + N-shaped diffracted light (N is any integer of 1 or more) and -Nth-order diffracted light (N is any integer of 1st or more) on the light receiving surface with respect to the optical axis. Said divisions arranged in symmetrical positions A diffractive optical element that diffracts the reflected light so that the reflected light is separately received in an area, and the optical axis of the objective lens from an output signal of the photodetector regarding both the + N-order diffracted light and the −N-order diffracted light. An optical head device comprising: an arithmetic unit for calculating an error signal regarding a position in a direction; and a driver for generating a signal for positioning the objective lens based on the error signal.