JPH09251658A - Optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable even optical disks different from each other in the thickness of a substrate to be correctly reproduced with one optical pickup by providing a polarizing hologram element transmitting one component among the component of the ordinary ray and the component of the extraordinary ray of light beams heading to an optical disk and diffracting other component. SOLUTION: When an optical disk D of a thick substraste is reproduced, light beams emitted from a semiconductor laser element 11 transmit a beam splitter 12 to be converted into parallel light rays by a collimating lens 15. The component becoming an ordinary ray in regard to the optical axis of a polarizing hologram element 16 among the light beams from the lens 15 does not receive the action of the hologram surface 16a and is made incident on an objective lens 13. These light beams are correctly focused on the signal recording surface D1 of the optical disk D. Besides, when a second optical disk of a thin substrate is reproduced, the component becoming an extraordinary ray in regard to the optical axis of the element 16 receives the action of the surface 16a and the light beams are correctly focused on the recording surface D2 of the optical disk D.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup used in an optical disk reproducing apparatus for recording and / or reproducing information by irradiating an optical disk with light and detecting return light. It is.

[0002]

2. Description of the Related Art Conventionally, an optical pickup for recording and / or reproducing such an optical disc is constructed as shown in FIG. In the figure, an optical pickup 1 includes a semiconductor laser element 2, a beam splitter 3,
It has an objective lens 4, a photodetector 5, and the like.

The beam splitter 3 has a reflection surface 3a inclined at 45 degrees with respect to the optical axis of the objective lens 4 so that the light beam emitted from the semiconductor laser element 2 and the signal recording surface of the optical disk 6 are recorded. To separate the return light from
That is, the light beam from the semiconductor laser element 2 is reflected by the reflection surface 3a of the beam splitter 3, and the return light from the optical disk 6 passes through the beam splitter 3.

[0004] The objective lens 4 is a convex lens, and applies the light beam reflected by the beam splitter 3 to the optical disk 6.
It is converged on a desired track on the signal recording surface. Further, the objective lens 4 is supported by a biaxial actuator (not shown) so as to be movable in a biaxial direction, that is, a focusing direction indicated by an arrow FCS and a tracking direction indicated by an arrow TRK in the drawing.

[0005] The photodetector 5 is configured to have a light receiving portion for a return light beam that enters through the beam splitter 3.

According to the optical pickup 1 having such a configuration, the light beam emitted from the semiconductor laser element 2 is
The light is reflected by the reflecting surface 3a of the beam splitter 3, and further converged to a certain point on the signal recording surface of the optical disc 6 via the objective lens 4.

The return light beam reflected on the signal recording surface of the optical disk 6 again enters the beam splitter 3 via the objective lens 4. Here, the return light beam passes through the beam splitter 3 and enters the light receiving unit of the photodetector 5. Thereby, the information recorded on the signal recording surface of the optical disk 6 is reproduced based on the detection signal output from the photodetector 5.

[0008]

In recent years, the density of optical discs has been increasing as an auxiliary storage device of a computer and a package medium of audio / video information. There is a method in which the numerical aperture NA of the objective lens is made larger than the numerical aperture NA of the objective lens in the conventional optical pickup for a compact disk. However, if the numerical aperture NA is increased, the allowable range for the tilt of the optical disk is reduced. There's a problem.

The optical disk has a predetermined disk substrate thickness (generally, 1.2 mm for a compact disk or the like).
mm), the signal recording surface is provided via the transparent substrate. If the optical disk is inclined with respect to the optical axis of the objective lens of the optical pickup, a wavefront aberration occurs, and the RF
The signal reproduction will be affected. At this time, regarding the wavefront aberration, the third-order coma which occurs in proportion to the cube of the numerical aperture and the first power of the skew angle θ is dominant. Therefore, an optical disc provided with a transparent substrate made of polycarbonate or the like that is mass-produced at low cost has a skew angle θ of, for example, plus or minus 0.5 to plus or minus 1 degree, and the semiconductor of the optical pickup 1 is affected by the above wavefront aberration. The converging spot from the laser element 2 to the optical disk 6 becomes asymmetrical, and intersymbol interference significantly increases, which makes it impossible to accurately reproduce the reproduction signal (RF signal).

Therefore, paying attention to the fact that the third-order coma is proportional to the disk substrate thickness of the optical disk, the third-order coma is reduced by half by reducing the thickness of the disk substrate by half to 0.6 mm. It is possible to In this case, as an optical disc, two standards having different characteristics,
That is, the disk substrate thickness is relatively thick (for example, 1.2 mm)
And a disk substrate having a relatively small thickness (for example, 0.6
mm) are mixed.

By the way, for example, a disk substrate thickness of 0.6 m
When an optical disc such as a compact disc having a disc substrate thickness of 1.2 mm, a write-once optical disc, or a magneto-optical disc is reproduced by using an objective lens corresponding to the m optical disc, the difference in disc substrate thickness causes Since the fourth-order spherical aberration occurs, the tolerance of the error in the thickness of the disc substrate that the optical pickup can deal with is greatly exceeded. Therefore, there is a problem that a signal cannot be correctly detected from the return light from the optical disk. Thus, there is a problem that the conventional optical pickup cannot reproduce both types of optical disks.

In view of the above points, the present invention provides an optical pickup and an optical disk reproducing apparatus using the same so that the reproduction of the optical disk can be performed correctly even if the optical disks have different substrate thicknesses. Has an aim.

[0013]

According to the present invention, the above object is to provide a light source which emits a light beam, a light beam which is emitted from the light source and is focused on a signal recording surface of the optical disc, and the optical disc. Light separating means for separating the return light from the light separating means, light detecting means for guiding the returning light from the light separating means, and one of the ordinary light component and the extraordinary light component of the light beam traveling from the light separating means to the optical disc. Penetrate the ingredients,
This is achieved by an optical pickup that includes a polarizing hologram element that diffracts and converges or diverges the other component.

According to the above construction, of the light beam from the light separating means, the component which becomes the ordinary ray with respect to the optical axis of the polarizing hologram element is transmitted, so that a predetermined lens effect is obtained when transmitting through the objective lens, for example. It is added and correctly converged on the signal recording surface of the first type optical disc. On the other hand, of the light beam from the light separation element, the component that becomes extraordinary light with respect to the optical axis of the polarizing hologram element is diffracted when it enters this polarizing hologram element, and moreover, it is necessary by this polarizing hologram element. Due to such a lens effect, it is converged on the signal recording surface of the second type optical disc having a substrate thickness different from the substrate thickness of the first optical disc. In addition, the polarization hologram element, if it is made to selectively diffract the component that becomes ordinary light or extraordinary light,
Either the ordinary light component or the extraordinary light component may be diffracted, and may be converged or diverged.

[0015]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. The embodiment described below is a preferred specific example of the present invention, and thus various technically preferable limitations are added. However, the scope of the present invention particularly limits the present invention in the following description. The embodiment is not limited to these embodiments unless otherwise stated.

FIG. 10 shows an embodiment of an optical disk (playback) device incorporating the optical pickup according to the embodiment of the present invention. In the figure, an optical disk device 1
Reference numeral 10 includes a spindle motor 112 for driving the optical disc D to rotate, and an optical pickup 113. Here, the spindle motor 112 is driven and controlled by an optical disk drive controller 114 and a servo control circuit, and is rotated at a predetermined rotation speed. As the optical disk D, a user or the like can select and reproduce a plurality of types of optical disks such as a first type optical disk and a second type optical disk described later, for example.

The optical pickup 113 irradiates the signal recording surface of the rotating optical disc D with light to record a signal or to detect a return light from the signal recording surface. A reproduction signal based on the return light is output to the demodulator 115.

As a result, the recording signal demodulated by the signal demodulator 115 is error-corrected by the error correction 116 and sent to an external computer, audio equipment or the like via the interface 117, for example. Thus, an external computer or audio device can receive a signal recorded on the optical disc D as a reproduction signal.

The optical pickup 113 includes:
For example, a head access control unit 118 for moving to a predetermined recording track on the optical disc D is connected. Further, at this moved predetermined position, the servo circuit 1 for moving the objective lens in the focusing direction and the tracking direction with respect to the biaxial actuator holding the objective lens of the optical pickup 113.
19 are connected.

FIG. 1 shows an embodiment of an optical pickup according to the present invention. In FIG. 1, an optical pickup 10 includes a semiconductor laser element 11 as a light source, a grating 18 as a diffracting means, a beam splitter 12 as a light separating means, an objective lens 13, and a photodetector (photodetector) 14 as a light detecting means. A collimator lens 15 and a polarizing hologram element 16 arranged between the beam splitter 12 and the objective lens 13 are provided. Here, since the semiconductor laser element 11, the beam splitter 12, the objective lens 13, and the photodetector 14 have the same configurations as those described in FIG. 11, duplicate description will be omitted and different configurations will be mainly described. To do.

The grating 18 is a diffraction grating, and converts a light beam emitted from the semiconductor laser device 11 into a light beam.
It diffracts into at least three light beams perpendicular to the plane of FIG. Thus, on the signal recording surface of the optical disk D, a main spot and two side spots are formed on both sides of the main spot by being shifted by a half track.

The collimator lens 15 converts a light beam transmitted through the beam splitter 12 and traveling toward the optical disk D into a parallel light beam. Polarizing hologram element 16
Is, for example, as shown in FIG. 1, lithium niobate (Li
As shown in FIG. 3, a concentric lattice is formed on the surface of the NbO ₃ ) substrate 16a by a proton exchange method, and a dielectric film is formed on the lattice to impart predetermined polarization characteristics and lens characteristics. .

FIG. 3 is a view of the exit surface of the polarizing hologram element 16 as viewed from above.
A light beam shown at 16d comes in from the semiconductor laser device 11. Then, the optical axis 1 of the polarizing hologram element 16
Regarding 6c, the ordinary light component of the light beam 16d that passes through the beam splitter 16 and is incident, and the extraordinary light component diffracts and converges. That is,
FIG. 4 shows the exit surface of the polarizing hologram element 16 of FIG. 1 when viewed from above. In the figure, the light beam L1 is
It is an ordinary light component having a polarization direction in a direction orthogonal to the optical axis 16c of the hologram element shown in FIG. FIG. 5 is a view of the hologram element 16 seen from above in FIG. 1, and the light beam L2 is an extraordinary light component having a polarization direction in a direction orthogonal to the ordinary light component L1. Therefore, in the hologram element 16, the dielectric film cancels the phase difference generated when the ordinary light component L1 passes through the proton exchange region, and the transmittance of the ordinary light component L1 is set to 1. Then, the extraordinary light component L2
This extraordinary light component L2 is diffracted, and is made to converge as shown by the dotted line in FIG.

The optical disk D is conceptually shown in FIG. 1, and corresponds to a first optical disk D1 and a second optical disk D2 having different signal recording surface positions corresponding to the difference in the thickness of the transparent substrate. The information recorded on both optical disks is read by the optical pickup 10.

The return light separated by the half mirror surface 12a of the beam splitter 12 is incident on the cylindrical lens 17, and the return light is given astigmatism to the photodetector 14 as light detecting means.

The photodetector 14 is constructed, for example, as shown in FIG. That is, the photodetector 14 is arranged at the center and has a light receiving portion 17a having four divided light receiving portions A, B, C, and D, and a side beam vertically separated from the light receiving portion 17a. Light receiving sections 17b and 17 arranged so as to receive
c.

Thus, the light beam from the semiconductor laser element 11 is separated into three light beams in the tracking direction by the grating 18, and the main beam of the return light beam reflected on the signal recording surface of the optical disk D is received at the center. The light is incident on the portion 17a, and two side beams are incident on the light receiving portions 17b and 17c, respectively.

Each of the light receiving sections 17b and 17c and the light receiving section 17
The output currents from the divided light receiving portions A, B, C, and D of a are converted into voltages by the amplifiers 21d to 21e, are sent to the amplifiers 22 and 23, and are processed as described below to obtain optical signals. A servo signal necessary for fine movement control of the objective lens 13 of the pickup 10 can be obtained. A focus error signal based on the astigmatism method is obtained in the light receiving unit 17a where the main beam of the return light enters the cylindrical lens 17 with astigmatism added thereto. That is, the focusing error signal FCS is

[Equation 1] Given in.

In the light receiving sections 17b and 17c where the side spot of the return light is incident, a tracking error signal based on a so-called three-beam method is obtained. That is, the tracking error signal TRK is

[Equation 2] Will be given by The reproduction signal is transmitted to the light receiving unit 17.
a. That is, the reproduction signal RF is

(Equation 3) And given.

The optical pickup 10 of this embodiment is configured as described above. First, a case of reproducing a first type optical disc having a thick substrate (for example, substrate thickness = 1.2 mm) will be described. In FIG. 6, a portion indicated by a solid line is an optical path used when reproducing the first type optical disc D having a relatively large substrate thickness. The light beam emitted from the semiconductor laser element 11 is transmitted to a beam splitter 12.
And is converted by the collimator lens 15 into a parallel light beam. The light beam from the collimator lens 15 enters the polarizing hologram element 16. In this light beam, the polarization hologram element 1
With respect to the optical axis of No. 6, the ordinary light component is transmitted through the hologram surface 16a without being affected by the hologram surface 16a as shown by the solid line.
The light enters the objective lens 13.

The objective lens 13 is given an appropriate NA in advance corresponding to the substrate thickness of the first optical disc D, and appropriately focuses the ordinary light component on the signal recording surface D1 of the optical disc D. Therefore, since the spherical aberration is suppressed to a low level, the light beam based on the ordinary component is correctly focused on the signal recording surface D1 of the optical disc D having a thick disc substrate.

The return light beam reflected by the signal recording surface D1 of the optical disc D returns through the optical elements of the objective lens 13, the polarizing hologram element 16 and the collimator lens 15, and is reflected by the half mirror surface 12a of the beam splitter 12. Has been done. This return light is emitted from the cylindrical lens 17
Then, astigmatism is given to the light and the light enters the photodetector 14. As a result, the photodetector 14 obtains the focusing error signal FCS, the tracking error signal TRK, and the reproduction signal RF by being processed as described above. In this case, the component that becomes an extraordinary ray with respect to the optical axis of the hologram element 16 is focused on the signal recording surface corresponding to the optical disc having a thin substrate, and as a result, even in the returning light, it is more than in the light receiving surface of the photodetector 14. It will focus on the back. Therefore, there is no influence on the reproduction signal RF.

On the other hand, when reproducing the second type of optical disc having a thin substrate (for example, substrate thickness = 0.6 mm), it is performed as shown in FIG. In FIG. 7, a portion indicated by a dotted line is an optical path used when reproducing the second type optical disc D having a relatively small substrate thickness. The light beam emitted from the semiconductor laser device 11 passes through the half mirror surface 12a of the beam splitter 12, and is converted by the collimator lens 15 into a parallel light beam. The light beam from the collimator lens 15 enters the polarizing hologram element 16. The component of the light beam that becomes abnormal light with respect to the optical axis of the polarizing hologram element 16 is affected by the hologram surface 16a as shown by a dotted line. As a result, the extraordinary light component of the light beam is diffracted, converged, and enters the objective lens 13.

Further, the light beam is generated by the objective lens 13
Is further converged by being subjected to a lens effect. Thereby, the spherical aberration due to the difference in the substrate thickness from the first optical disc is corrected, and the extraordinary light component is properly converged on the signal recording surface D2 of the optical disc D. Therefore, also in this case, since the spherical aberration is suppressed to a low level, the light beam based on the extraordinary light component is correctly focused on the signal recording surface of the optical disc D having a thin disc substrate thickness.

The extraordinary light component of the return light beam reflected by the signal recording surface D2 of the optical disc D is the objective lens 13,
The polarization hologram element 16 and the collimator lens 15 return to the respective optical elements and are reflected by the half mirror surface 12 a of the beam splitter 12. This return light is given astigmatism by the cylindrical lens 17 and enters the photodetector 14. As a result, the photo detector 1
4, the focusing error signal FCS and the tracking error signal TR are processed as described above.
K, a reproduction signal RF is obtained. In this case, the component that becomes an ordinary ray with respect to the optical axis of the hologram element 16 will be focused on the signal recording surface corresponding to the optical disc having a thick substrate, and as a result, even in the returning light, the light receiving surface of the photodetector 14 will be greater than that. It will focus on you. Therefore, there is no influence on the reproduction signal RF.

Thus, according to the optical pickup 10 of this embodiment, the polarization directions of the light from the semiconductor laser element 11 are orthogonal to each other for the first type optical disc and the second type optical disc having different substrate thicknesses. The components can be applied to each type of optical disc. As a result, with respect to the two types of optical disks having different substrate thicknesses, it is possible to accurately reproduce both of them without causing adverse effects on the reproduction signal due to spherical aberration.

FIG. 9 shows another embodiment of the optical pickup. In the figure, the optical pickup 30 is
The light emitting / receiving element 37 having a light emitting portion as a light source and a light receiving portion integrally formed, a collimator lens 15, a polarizing hologram element 16, and an objective lens 13 are provided.

In this optical pickup 30, the collimator lens 15, the polarizing hologram element 16, the objective lens 13, and the optical disk D have the same configurations as those described with reference to FIG.

The light emitting / receiving element 37 has a first substrate 38 and a second substrate 39 mounted on one end side of the first substrate 38.
have. Photodetectors 34 and 36 as light detecting means are formed on the upper surface of the first substrate 38, and the trapezoidal prism 3 made of an isotropic material such as glass is formed on the upper surface.
5 is placed. Note that a semi-transmissive film is provided on the upper surface of the photodetector 34.

On the second substrate 39, the semiconductor laser element 31 is arranged with the emitting end face of the laser light facing the prism 35 side. Opposed to the emission end face of the semiconductor laser element 31, the prism 35 is formed with a slope inclined at approximately 45 degrees. On this slope, a beam splitter 32 as a light splitting means composed of a half mirror surface is provided. Is formed. On the upper surface of the prism 35, a total reflection surface 33 made of a total reflection mirror coat is provided.

Therefore, in this optical pickup 30, the light beam emitted from the semiconductor laser element 31 is
It goes to the beam splitter 32, is reflected by the half mirror surface thereof, and the optical path is bent by 90 degrees in FIG. This light beam enters the collimator lens 15 and becomes a parallel light beam, and enters the polarization hologram element 16.
In this polarizing hologram element 16, the light beam receives the same operation as that of the optical pickup of FIG. As a result, the component of ordinary light with respect to the optical axis of the polarization hologram element 16 is transmitted as it is, and is converged by the objective lens 13 onto the signal recording surface D1 of the first type optical disc having a relatively thick substrate.

On the other hand, the component that becomes extraordinary light with respect to the optical axis of the polarization hologram element 16 is the polarization hologram element 16.
Is diffracted and converged by the hologram surface 16a of the second optical disc 16 and passes through the objective lens 13 and is converged on the signal recording surface D2 of the second type optical disc having a relatively thin substrate as shown by a dotted line.

As described above, depending on the type of the optical disc D to be reproduced, the light beam which is then converged on the signal recording surface D1 or D2 of the optical disc is reflected to become return light, and the objective lens 13 and the polarizing hologram element are used. 16, passing through the half mirror surface of the beam splitter 32 through the collimator lens 15 and entering the prism 35.

Part of the return light that has entered the prism 35 enters the photodetector 34, and the rest is reflected, reflected by the total reflection film 33 on the upper surface of the prism 35, and enters the photodetector 36. Therefore, by processing the output signals of the photo detectors 34 and 36 by known means, the servo signals of the tracking error signal and the focus error signal and the reproduction signal RF can be obtained.

As described above, also in the optical pickup 30, with respect to the first type optical disc and the second type optical disc having different substrate thicknesses, the components in which the polarization directions of the light from the semiconductor laser element 11 are orthogonal to each other are respectively generated. It can be applied to optical discs of As a result, with respect to the two types of optical disks having different substrate thicknesses, it is possible to accurately reproduce both of them without causing adverse effects on the reproduction signal due to spherical aberration. Further, since the light-emitting element and the light-receiving element are integrally formed, one optical pickup that records information of at least two types of optical discs can be made compact.

In the above embodiment, the optical disk has a disk substrate thickness of, for example, 1.2 mm and 0.6.
For the mm type, the light beam is focused on the signal recording surfaces of the optical disc having a relatively thin disc substrate thickness and the optical disc having a relatively thick disc substrate thickness.
The present invention is not limited to this. For example, the present invention can be applied to a case where a bonded optical disk in which two substrates are bonded and a normal optical disk are reproduced.

Further, in the above-described embodiment, the polarization hologram element diffracts and converges the extraordinary light component, and irradiates the signal recording surface of the optical disc with a thin substrate. However, the present invention is not limited to this, and in a polarization hologram, the extraordinary light component is not diffracted, but is irradiated onto the signal recording surface of an optical disc with a relatively large substrate thickness, and the ordinary light component is diffracted to produce a signal recording surface of an optical disc with a thin substrate thickness. May be converged to. Further, either a component of the ordinary light or the component of the extraordinary light may be diverged by using the polarization hologram element, and the component may be irradiated on the signal recording surface of the corresponding optical disc. That is, the present invention is applied to a polarizing hologram element as long as it selectively has a lens function with respect to ordinary light and extraordinary light.

[0048]

As described above, according to the present invention, it is possible to correctly reproduce information recorded on an optical disk by using a single optical pickup, even if the optical disk has a different disk substrate thickness.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an optical pickup according to the present invention.

FIG. 2 is a diagram showing an example of a lattice pattern of a polarizing hologram element of the optical pickup of FIG.

FIG. 3 is a diagram showing a relationship between an optical axis of a polarizing hologram element of the optical pickup of FIG. 1 and incident light.

FIG. 4 is a diagram showing a relationship between an optical axis of a polarizing hologram element of the optical pickup of FIG. 1 and an ordinary light component.

FIG. 5 is a diagram showing a relationship between an optical axis of a polarizing hologram element of the optical pickup of FIG. 1 and an extraordinary light component.

FIG. 6 is a diagram for explaining the operation of the optical pickup of FIG. 1;

FIG. 7 is a diagram for explaining the operation of the optical pickup of FIG.

8 is a diagram showing a configuration example of a light detection means of the optical pickup of FIG.

FIG. 9 is a diagram showing a second embodiment of the optical pickup of the present invention.

FIG. 10 is a block diagram showing a configuration example of an optical disc device using the optical pickup of the present invention.

FIG. 11 is a diagram showing a position example of a conventional optical pickup.

[Explanation of symbols]

10, 30: optical pickup, 11: semiconductor laser element (light source), 12: beam splitter, 1
2a: half mirror surface, 13: objective lens, 1
4 ... Photodetector, 15 ... Collimator lens, 16 ... Polarizing hologram element, D ... Optical disk, D1, D2 ... Signal recording surface

Claims (5)

[Claims] 1. A light source that emits a light beam, a light beam emitted from the light source and condensed on a signal recording surface of an optical disc, and a light splitting device that splits the return light from the optical disc. A light detecting means for guiding the return light from the light separating means, and one of the ordinary light component and the extraordinary light component of the light beam traveling from the light separating means to the optical disc, and the other component is diffracted and converged or An optical pickup comprising a polarizing hologram element for diverging. 2. One of the ordinary component and the extraordinary component of the light beam passing through the hologram element is the first component.
Is converged on the signal recording surface of the optical disc, and the other component is
A second substrate having a substrate thickness different from that of the first optical disc
The optical pickup according to claim 1, wherein the optical pickup converges or diverges toward a signal recording surface of the optical disc. 3. The optical pickup according to claim 1, wherein the light beam heading from the light separating means toward the optical disc passes through a collimator lens to become parallel light, and then enters the hologram element. 4. The optical pickup according to claim 1, wherein at least the light source, the light separating means, and the light detecting means are integrally formed. 5. An optical pickup having means for rotating and driving the optical disk, and light detecting means for irradiating the rotating optical disk with light through an objective lens to detect return light from the optical disk; The optical pickup includes a signal processing circuit that generates a reproduction signal based on a detection signal, and the optical pickup emits a light beam, and light emitted from the light source and condensed on the signal recording surface of the optical disc. Beam separating means for separating the return light from the optical disk, light detecting means for guiding the returning light from the light separating means, and an ordinary light component and an abnormal light component of the light beam traveling from the light separating means to the optical disk. An optical disk device comprising a polarizing hologram element that transmits one of the components and diffracts and converges or diverges the other component. .