JP2892944B2 - Optical head device and optical information device - Google Patents

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 used for irradiating a target object with a light beam and detecting the positional relationship between the focal position of the light beam and the target object. In an optical information device, the present invention is suitable for an optical head device for recording or reproducing information on an information carrier such as an optical disk.

[0002] The present invention also relates to an optical information device for recording, erasing or reproducing information on an information carrier such as an optical disk using the optical head device.

[0003]

2. Description of the Related Art A hologram is used to simplify the optical system of an optical head.
There is one shown in FIG. 7 described in Japanese Patent No. 88032. This will be described below as a first conventional example.

In FIG. 7, reference numeral 2 denotes a semiconductor laser light source.
The outward light beam 3 emitted from the light source 2 passes through the hologram 8 and enters the objective lens 110, and is converged on the optical disk 4. The return light beam reflected by the optical disk follows the original light path in reverse and enters the hologram 8. The diffracted light 6 generated from the hologram by the light beam on the return path enters the detector 7.

The diffracted light 6 is designed to have an astigmatic wavefront, and the objective lens 1
With 10 defocus or just focus,
The shape changes as shown in FIG. In FIG. 8, (b) shows the just-focused state, and (a) and (c) show the defocused state. 9 is a diffraction light for focus error signal detection.

Accordingly, the focus error signal FE is obtained by the following operation: FE = (S1 + S4)-(S2 + S3) (1)

Next, as another conventional example, there is a configuration as shown in FIG. 9 disclosed in, for example, Japanese Patent Application No. 60-72732 (Japanese Patent Application Laid-Open No. 61-233439). This will be described below as a second conventional example.

An object of this conventional example is to provide a small-sized, low-cost, differential detection type optical pickup of a magneto-optical disk signal by forming two light splitters each having a diffractive structure. To get the equipment.

In FIG. 1, after the light is emitted from the light source 2,
The light beam converged on the disk 4 by the objective lens 246 and reflected from the disk 4 is again transmitted to the objective lens 246.
, And is split by the first light splitter 243 into diffracted light 247 and transmitted light. The diffracted light 247 is transmitted to the first light splitter 24.
3 and reaches the optical sensor 250 through the polarizing plate 249 while being totally reflected by the upper surface and the lower surface. On the other hand, the transmitted light is incident on the second diffraction structure 242 via the low refractive index layer 244, and the diffracted light 248 similarly passes through the polarizing plate 249 and the light sensor-2.
Reach 50.

The second light splitter 242 and the first light splitter 2
A low-refractive layer 244 having a lower refractive index than the base of the light splitter is provided between the light splitter 43 and the second light splitter 242 or the first light splitter 243. A phase adjustment film 251 is provided. The phase difference between the P-polarized light component and the S-polarized light component at the time of reflection is made 180 ° by the phase adjusting film 251, and the polarization plane of the diffracted light beam is rotated by 90 °. For this reason,
The diffracted light beam 248 and the diffracted light beam 247 have their polarization planes at 90 ° to each other.

These diffracted light beams 247 and 248 reach the optical sensor while being reflected in the light splitter on which the diffraction structure is formed. FIG. 10A shows the diffraction portion of the diffraction structure.
The configuration is as follows. By receiving the diffracted light beams 247 and 248 by the optical sensor 250 shown in FIG. 10B and calculating the output of the optical sensor 250, a focusing signal, a tracking signal, and a magneto-optical signal can be obtained.

[0012] Further, as another conventional example, for example,
FIG. 11 is disclosed in Japanese Unexamined Patent Publication No. 61-195534.
This will be described below as a third conventional example. This conventional example
Arranged diffraction means in the optical path of incident light and reflected light
One-sided optical means with lens action
Adjustment work is easy,
Space can be reduced and weight and size can be reduced.
And the diffraction means are arranged in the optical path of the incident light and the reflected light.
Integrated on one side of optical means with lens action
It is formed.

The diffractive means is a phase type diffractive plate, and the depth of the groove is set to の of the wavelength λ of the light, so that only + 1st-order diffracted light and -1st-order diffracted light are generated from the diffractive means. . For example, the + 1st-order diffracted light is converged on the disc without aberration by the objective lens, the -1st-order diffracted light has astigmatism, and the -1st-order diffracted light is received by the detector to obtain a focus error signal.

As another conventional example, there is FIG. 12 disclosed in, for example, Japanese Patent Application Laid-Open No. 61-112246. This will be described below as a fourth conventional example. The purpose of this conventional example is to arrange a diffraction grating between the light source and the converging lens, split the return light from the record carrier by the diffraction grating, and guide it to the photodetector, which has symmetry and a reduced number of parts. The present invention is to reduce the size, weight, and cost as much as possible, and its configuration is as follows.

That is, the light emitted from the light source 2 is collimated by the collimating lens 224 and then transmitted through the diffraction grating 223, and the zero-order light is transmitted to the recording surface 22 of the disk 4.
The laser beam advances in a direction orthogonal to 1 and is converged by the objective lens 222 to irradiate the recording surface 221.

The irradiated light is modulated at a recording information portion on the disk 4, collected by an objective lens 222, and then diffracted by a diffraction grating 223. The light diffracted by the diffraction grating 223 is transmitted to the collimating lens 22.
4, the information is converged on the detectors 226a and 226b, and the information on the disk 4 can be reproduced. As a result, symmetry of the pickup is realized, and reduction in size, weight, and cost can be realized.

In this field, for example, Japanese Patent Application No. Sho 6
No. 2-219712 (JP-A-64-62838)
There is FIG. This will be described below as a fifth conventional example. (A) is a front view,
(B) is a side view. An object of the present invention is to provide a focusing means and a hologram element while maintaining a constant relative position so as to prevent a tracking deviation from occurring. The configuration is as follows.

The light condensing means 213 and the hologram element 212 are provided while maintaining a constant relative position. At the time of the tracking operation, the focusing means 213 and the hologram element 212 move at the same time. Accordingly, there is almost no relative displacement between the hologram element and the reflected light beam incident through the light condensing means. Thereby, a good tracking servo signal can be obtained. For example, even when the condensing unit is moved so that the convergent spot follows the deviation of the information recording area of the recording medium, the relative position between the condensing unit and the hologram element does not shift.

[0019]

However, according to the first and second prior art optical system configurations, when the objective lens is moved by the action of the tracking servo mechanism (tracking following), the beam enters the hologram surface. The position moves as indicated by the dotted line in FIG. 14 (however, here, a part of the optical system and the light beam from the light source to the optical disk are omitted).

Therefore, as shown by a dotted line in FIG. 15, there is a problem that the diffracted light on the detector moves, thereby deteriorating the characteristics of the focus error signal. Such a problem also occurs in, for example, an optical system using a lens or a half mirror employed in an optical head device currently commercialized.

Further, in the configuration of the second conventional example, FIG.
, The divided areas 243b and 24 of the first light splitter 243
3c is received by G or H of the optical sensor 250, and the divided area 242b of the second light splitter 242 is received.
Light diffracted from the optical sensor 250
And D, and the outputs of these are calculated to obtain a tracking error signal.

However, when the objective lens is moved by tracking following in this configuration, the incident position of the beam on the light splitter surface is moved, so that the amount of light incident on each divided area (243b and 243c and 242b and 242c) changes. In addition, there is a problem that an offset occurs in the tracking error signal, and accurate tracking cannot be performed.

Further, in the configuration of the second conventional example, as is apparent from FIG. 9, since the optical sensor 250 is provided at the end of the optical splitter, the light source 2 and the optical sensor 250 must be arranged close to each other. Can not. For this reason, there is a problem that the signal is easily deteriorated due to a temperature change or a temporal distortion. That is, when the light source 2 or the collimating lens 5 is displaced due to a change in temperature or distortion over time, the incident angle of the light to the light splitter changes, and the diffracted light 247, 2
There is a problem that the position of 48 is shifted and the signal is easily deteriorated.

Further, in the configuration of the second conventional example, since it is necessary to generate diffracted light at a very large diffraction angle by the light dividing means, the pitch of the diffraction grating of the light dividing means becomes very small, making fabrication difficult. In addition, there is a problem that it becomes expensive.

In the third to fifth conventional examples, since the diffractive means and the objective lens are maintained in a fixed positional relationship, even if the objective lens moves due to tracking, the incident position of the beam on the diffractive means is not changed. Does not move. However, it has the following problems.

First, in the third conventional example, only the + 1st-order diffracted light and the -1st-order diffracted light are generated from the diffraction means. For example +
The first-order diffracted light is converged on the disc without aberration by the objective lens, and the -1st-order diffracted light has astigmatism.

However, since the -1st-order diffracted light includes not only astigmatism but also unnecessary aberrations such as spherical aberration, FIG.
An ideal focal line as shown in (a) and (c) cannot be obtained. This is because the diffraction means cannot freely design the diffracted light on the return path with the main focus. For this reason, there is a problem that an offset of the focus error signal is easily generated, the differential sensitivity is low, and an offset occurs due to crosstalk to the focus error signal at the time of crossing the groove.

If the wavelength of the light source deviates from the designed value or the relative position between the hologram and the lens deviates at the time of fabrication, +1
There is also a problem that aberration occurs in the next-order diffracted light, and good convergence characteristics cannot be obtained on the information medium.

Further, since there is no freedom to create a diffraction means region for generating diffracted light for detecting a tracking error signal, no method for obtaining a tracking error signal is disclosed. Except for a concentric pattern having a common center with the center of the lens, it is technically difficult to directly produce an arbitrary curved grid pattern on the optical lens as shown in FIG. There is a problem of fear.

The fourth conventional example has the following problems. That is, the diffraction grating 223 is a so-called simple diffraction grating, and is a diffraction grating formed of straight lines and having an equal pitch. This is apparent from the description of the fourth conventional example that "for the first time in a finite optical system in which the collimating lens 224 is omitted, astigmatism occurs in diffracted light".

On the other hand, the diffracted light generated when the convergent light is obliquely incident on the simple diffraction grating contains not only astigmatism but also unnecessary aberrations such as spherical aberrations.
An ideal focal line as shown in (a) and (c) cannot be obtained. For this reason, there is a problem that an offset of the focus error signal is easily generated, the differential sensitivity is low, and an offset occurs due to crosstalk to the focus error signal at the time of crossing the groove.

Further, a method for obtaining a tracking error signal is not disclosed. Further, the light source 2 and the light detector 226
a and 226 b are fixed to the objective lens 222 by the housing 225. Here, it is necessary to move the objective lens 222 at high speed by a focusing servo or tracking servo mechanism.
Since a and 226b and the housing 225 which must be enlarged to support them are connected, there is a problem that it is difficult to move at high speed.

Further, since the photodetectors 226a and 226b are arranged as separate components on the housing 225, there is a problem that the number of components is large and the cost is increased.

The fifth conventional example has the following problems. That is, the fifth conventional example is a device for detecting a tracking error signal, but does not disclose a method for detecting a focus error signal. Also, the photodetector 2
17 and 218 are arranged as separate parts, and there is a problem that the number of parts is large and causes an increase in cost. The hologram element 212 outputs data from the light source 2.
Diffraction also occurs in the optical path on the way to disk 4
However, this diffracted light is transmitted from the hologram element 212 to the imaging lens 2.
13 so that most of the imaging lens 213
The light reaches disk 4 and reflects off disk 4
The light enters the detector 217 or the light detector 218. here
In the fifth embodiment, as is apparent from FIG.
The hologram element 212 has no lens action and diffracted light is coupled
Focused only by the lens action of the lens 213
You. Therefore, the above-mentioned diffracted light on the outward path also converges on the disk 4.
Of the part that is different from the
The information is read and incident on the photodetector. That is, the book
Incoming reproduction information becomes noise and the reproduction signal quality deteriorates.
There is also a problem of making it.

[0035]

According to the present invention, in order to solve the above-mentioned problem, a hologram is linked to the lens so that all of the reflected light from the optical disk, which has passed through the objective lens, is fixed to a certain portion of the hologram. Incident on

More specifically, a light source, a refraction type objective lens for receiving a light beam emitted from the light source and converging the light beam on a target object, and transmitting the first light beam reflected on the target object through the objective lens A hologram to be received, and a detector for receiving diffracted light generated from the hologram and generating an output in accordance with the amount of light, wherein the hologram is positioned at a fixed relative position with respect to the refraction type objective lens using coupling means. And a 0th-order diffracted light beam, out of the light beam emitted from the light source, which is not subjected to diffraction of the hologram, in a forward optical path until the light beam emitted from the light source is converged on a target object. Is converged on the target object by the refraction type lens, and the returning light beam reflected from the target object by the first light beam is formed by an objective lens. Diffracted light that is generated when transmitted and incident on the hologram has at least two different wavefronts that connect either the focal point or a focal line extending in substantially the same direction at different convergence distances, or a wavefront that has only astigmatism. It is a configuration including.

Alternatively, the target object has a track structure,
The light beam on the return path passes through the hologram to generate a diffraction light for focus error signal detection and a diffraction light for tracking error signal detection, and the detector receives the diffraction light for focus error detection and the diffraction light for tracking error detection. The configuration is preferable for, for example, an information recording medium.

Further, it is preferable that a detector for receiving the diffraction term for detecting the focus error signal and a detector for receiving the diffracted light for detecting the tracking error signal are provided on the same substrate.

It is preferable that the objective lens having the hologram fixedly connected to the light source be relatively movable.

Further, the hologram is divided and used, and as a wave front to be written therein, in order to obtain a focus error signal, an astigmatic wave front or a spherical wave having a focal point before and after the reference surface is used. It is also preferable to make a configuration.

In the case where a hologram area for generating a diffracted light for detecting a tracking error signal is also formed, of the beam incident on the hologram, the light beam on the optical disk in the direction perpendicular to the tracking is used. It is preferable to create a part that changes most sensitively according to the movement.

[0042]

By using the objective lens of the present invention in which the holograms are connected and fixed, regardless of the movement of the objective lens due to the tracking follow-up, the returning light beam is incident on a certain portion of the hologram. Does not move on the detector.

Further, if the hologram is divided and used to add multifunctionality, the number of parts can be reduced.
In particular, when a wavefront for obtaining a tracking error signal is created on a hologram, a very stable tracking servo can be realized because the distribution of the far field pattern incident on the hologram does not depend on the movement of the objective lens.

As a method for obtaining a focus error signal, an ideal astigmatism or one or more sets of spherical waves having a focal point before and after a reference surface are used, so that a focus servo can be performed with a simple optical system. realizable.

Further, by forming all the detectors for servo signal detection on one substrate, the number of parts is reduced and the cost is reduced.

Further, by making the objective lens relatively movable with respect to the light source, the objective lens can be reduced in weight and driven at a high speed.

Further, an optical information device constituted by using this optical head device is a highly reliable, inexpensive and compact optical information device because no defocus occurs due to tracking.

[0048]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of a lens to which a hologram, which is a key of the present invention, is connected and fixed. In FIG. 1, a hologram 102 is linked to a refraction type optical lens 101 by using a connecting means 103.

That is, if the hologram 102 and the refraction type lens 101 are separately formed and connected using the connection means 103, a lens with a hologram can be realized more easily.

In particular, as described later, the hologram 10
In order to freely design the grid pattern 2 and obtain a focus error signal and a tracking error signal with good characteristics, it is necessary to produce an arbitrary curve as the grid pattern. Although it is technically difficult to directly fabricate the optical lens on the optical lens as shown in FIG. 11 and may increase the cost, the hologram 102 and the refraction-type lens 101 are separated from each other as in the present invention.
If they are made separately and connected using the connecting means 103, there is a practical effect that a lens with a hologram can be realized simply and inexpensively.

FIG. 2 is a diagram for explaining in principle the configuration of an embodiment of the optical head of the present invention. The light source 2 may include an optical system for wavefront correction in some cases, but is not directly related to the present invention, and a description thereof will be omitted.

The outgoing light beam 3 emitted from the light source 2 passes through the collimator lens 5 to become parallel light, and is converged on the optical disk 4 by the objective lens 1 to which the hologram is connected and fixed. The returning light beam reflected by the information recording / reproducing surface of the optical disk having the protective film 401 and the base material 402 is again incident on the objective lens 1 to which the hologram is connected and fixed. For example, as shown in FIG. 2, + 1st-order diffracted light (or −1st-order diffracted light) 6 diffracted by the hologram is condensed by the collimator lens 5, and is incident on a detector 7 arranged near the light source 2.

Here, by arranging the detector 7 close to the light source 2, the optical head optical system is arranged in a group near one optical axis, and the temperature change and the time-dependent change There is an effect that various signals can be detected stably without being affected by displacement of components due to distortion.

Further, by disposing the detector 7 close to the light source 2, the light source 2 and the detector 7 can be easily assembled with accurate relative positions.

Further, by arranging the detector 7 close to the light source 2, the diffraction angle of the diffracted light on the hologram 102 becomes small, so that the pitch of the grating pattern of the hologram 102 becomes large (rough). Therefore, there is an effect that the production of the hologram 102 is facilitated and the production cost is reduced.

The signal intensity of each divided area of the detector obtained from the diffracted light incident on the detector 7 changes according to the focus state, and thus a focus error signal is obtained from this signal. In particular, when astigmatism is used as a method of obtaining a focus error signal, a hologram or a four-divided detector similar to the conventional example such as the above-mentioned Japanese Patent Application Laid-Open No. 62-188032 may be used.

In the embodiment of the present invention using astigmatism as a method for obtaining a focus error signal, ideal astigmatism is used, and a change in the shape of diffracted light in two directions with respect to an orthogonal dividing line is used. As a result, the focus error signal having a high differential sensitivity can be obtained, and the (signal) / (noise) ratio of the focus error signal to circuit noise can be further increased. . In addition, since the diffracted light is not converged and is a large spot, the position of the detector can be set with a sufficient margin when assembling the optical head device.

Therefore, the tolerance of the detector position shift,
That is, there is an effect that the assembly cost of the detector can be reduced without requiring high accuracy as the assembly accuracy of the detector.

When diffracted light having a focal point in front of or behind the reference surface is used as the diffracted light used to obtain the focus error signal, the hologram is formed by combining an off-axis Fresnel zone plate or a Fresnel zone plate. become. In other words, the hologram grid pattern is
It consists of curves with varying pitch.

In this case, the state of the diffracted light on the detector is as shown in FIG. FIGS. 7A to 7C show changes in the shape of the diffracted light on the detector surface due to a change in the positional relationship between the hologram-coupled fixed lens 1 and the information carrier 4 in the optical axis direction. FIG. 7B shows a state of just focus, and FIGS. 7A and 7C show a state of defocus.

At this time, the focus error signal FE is given by FE = (S10 + S30-S20)-(S40 + S60)
-S50)... (2).

As shown in FIG. 2, FIG. 3, FIG. 6, etc., the number of parts can be reduced by forming all the detectors for servo signal detection on one substrate.
There is an effect that the price can be reduced.

According to the present invention, the focus error signal is detected from the hologram by using light beams having focal points respectively on the rear side and the front side of the detector.
For example, as shown in FIG. 3B, when the two diffracted lights 6 have the same size in the direction perpendicular to the dividing lines 601 to 604, the sizes are equal to the detectors S20 and S5.
It can be designed to be larger than the width of zero. By designing the size of the diffracted light 6 to be large as described above, the position of the detector can be set with a sufficient margin when assembling the optical head device. In particular, as shown in FIG.
Are parallel, the displacement of the detector in the direction of the dividing lines 601 to 604 has no effect on the focus error signal. Therefore, a particularly large detector displacement can be allowed. That is, there is an effect that the assembly cost of the detector can be reduced without requiring high accuracy as the assembly accuracy of the detector.

In FIG. 3, the two diffracted light beams 6 are drawn as spherical waves converging at one point for simplicity, and the following description is made in accordance with the drawing, but the FE signal using FIG. As is apparent from the detection method, the FE signal detection of the present invention is such that the size of the diffracted light according to the focus state of the light beam emitted from the lens 101 on the information carrier 4 is equal to the division lines 601 to 604 of the detector. It takes advantage of changing in the vertical direction. Accordingly, when the diffracted light 6 is viewed from the direction in which the dividing lines 601 to 604 of the detectors S10 to S60 extend (that is, from the surface of the detector),
It is necessary that the light beams have focal lines (focus as a special example of a spherical wave) converged on the rear side and the front side of the detectors S10 to S60, respectively. Absent.

As described above, the hologram is designed to generate two kinds of spherical waves having different curvatures or a wavefront having ideal astigmatism as the first-order diffracted light, and the focus error signal can be detected. . Such a hologram can be easily realized by recording interference fringes of light as is well known, or by a method called a computer generated hologram (a computer generated hologram). The explanation for is omitted.

As described above, in the present invention, the size of the diffracted light for detecting the focus error signal is designed to be large, so that the position of the detector can be set with a margin when assembling the optical head device. This has the effect of reducing the cost of assembling and providing an inexpensive optical head device. In addition, by connecting and fixing the hologram to the objective lens using the connecting means, the diffracted light having a large spread generated from the hologram does not move on the detector regardless of the movement of the objective lens due to tracking. Therefore, a stable focus error signal can be obtained in parallel with tracking. Also, since the number of parts can be reduced, the size of the optical head device can be reduced,
Cost reduction can be realized.

Further, in the present invention, as shown in FIG. 2 and FIG. 5, the outward light beam 3 emitted from the light source passes through the hologram 102 and enters the lens 101, and the information medium 4
Converges on. The light reflected by the optical disk enters the hologram 102 as a return path that reverses the original optical path. At this time, the diffracted light generated from the hologram is received by the detector 7 to obtain a focus error signal FE.

As described above, according to the present invention, the hologram 102
The light beam on the outward path that has passed through the
Even if the wavelength of the light source deviates from the design value or the relative position of the hologram 102 and the lens 101 deviates at the time of fabrication, it does not affect the optical characteristics of the optical head device at all. There is an effect that good convergence characteristics can be obtained. In particular, since the lens 101 uses a refraction type lens, there is an effect that the lens 101 is not affected by deviation from the design value of the light source wavelength as compared with the hologram.

Furthermore, the grating pattern of the hologram 102 has no effect on the convergence characteristics on the information medium 4, so that it can be designed in an optimal form to obtain a servo signal such as a focus error signal. For this reason, for example, when a focus error signal is detected using astigmatism, a focus error signal is detected using a light beam having only astigmatism and having no unnecessary aberration such as coma. be able to. Therefore, it is possible to obtain a focus error signal of very high quality such that no offset of the focus error signal is generated, the differential sensitivity is high, and no offset is generated due to crosstalk to the focus error signal when crossing the groove. There is. Diffracted light generated from the hologram 102 is a detector
-7 with two focal points on the front and back of the light receiving surface
Or has astigmatism. This is
That is, the hologram 102 has a lens function.
And On the outgoing optical path from light source 2 to disk 4
Even if diffraction occurs due to the hologram 102,
Is diffracted by the lens function of the hologram 102.
On disk 4, it is defocused and greatly expanded
Become. Therefore, the diffracted light on the outward path is recorded on the disk 4.
Without reading out the information
Therefore, even if it enters the detector 7, the original reproduced information
Noise, and as a result, the original reproduced signal quality is improved.
It has the effect that it can be reduced.

The tracking error signal can also be obtained from the diffracted light for detecting the focus error signal.
For example, as shown in FIG.
The tracking error signal can be obtained by separating the diffracted light different from the diffracted light for detecting the focus error signal from the holograms of the portions 1021 and 1022. In the case of the configuration shown in FIG.
23, 1024 and 1025 can be obtained.

For example, if a wavefront for obtaining a tracking error signal is formed on a hologram as shown in FIG. 4, the return light beam incident on the hologram does not move depending on the movement of the objective lens. There is an effect that an extremely stable tracking servo can be realized without causing a tracking error signal offset due to the movement of the beam.

When a hologram region for generating a diffracted light for detecting a tracking error signal is also formed on the same hologram, the light beam in the direction perpendicular to the tracking on the optical disc among the beams incident on the hologram. It is preferable to create a portion that changes most sensitively in accordance with the movement of. That is, as clearly shown in FIG. 4, the tracking error signal detection diffracted light generation region is
If each area is less than half of the total area of the hologram, the ratio of the amplitude of the tracking error signal to the amount of light used for detecting the tracking error signal is increased, and the ratio of (signal amplitude) / (noise) is increased. There is an effect that a strong and stable tracking error signal can be obtained.

In particular, when the objective lens 1 to which the hologram is connected and fixed moves with respect to the light source 2 by tracking or the like, for example, when a semiconductor laser is used as the light source 2, the distribution of the light amount is not uniform. There is a possibility that the light quantity on the objective lens 1 to which the light is connected and fixed may become non-uniform and a tracking error signal offset may occur. However, in this embodiment, (signal amplitude) /
Since the (noise) ratio increases, there is an effect that the offset does not become a problem and a stable tracking error signal can be obtained.

When it is necessary to further reduce the size of the optical head of the present invention, for example, the structure shown in FIG.
Of course, it is also possible to omit the collimating (light collecting) lens 5.

Also, for example, the hologram coupling fixed lens is moved independently of the light source 2 with respect to the light source 2 and the detector 7 as shown in FIG. 2 and FIG. There is an effect that the movement can be made faster.

When the focus error signal detection and the tracking error detection are performed using the hologram shown in FIG. 4, for example, as shown in FIG. 16, a focus error signal detection detector area 71 and a tracking error signal detection 2 Two detector areas 72 and 73
Is preferably provided separately for the same detector 7, because the number of parts is small, the cost required for the assembling process can be reduced, and the size can be reduced.

Finally, FIG. 6 shows an embodiment of an optical information device constituted by using the optical head device described above. The optical disk 4 is rotated by the drive mechanism 14. The optical head device 10 is roughly moved by the optical head device driving device 12 to a desired track on the optical disk. The optical head device 10 also sends a focus error signal and a tracking error signal to the electric circuit 11 according to the positional relationship with the optical disk. The electric circuit sends a signal for finely moving the objective lens to the optical head device in response to the signal. With this signal, the optical head performs focus servo and tracking servo on the optical disk,
Reading, writing, or erasing of information is performed on the optical disc 4.

[0078]

By using the objective lens of the present invention in which the holograms are connected and fixed, the diffracted light generated from the hologram does not move on the detector regardless of the movement of the objective lens following the tracking. Therefore, a stable focus error signal can be obtained in parallel with tracking.

Further, since the number of parts can be reduced,
The optical head device can be reduced in size and cost. This effect becomes more prominent when the hologram is divided and used.

Further, since the far field pattern of the beam incident on the hologram is stable, the tracking servo can be stabilized.

Furthermore, an optical information device constituted by using the optical head device of the present invention has high reliability because defocus does not occur due to tracking follow-up, and is inexpensive and small in size because of a small number of components. Become.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a hologram coupling lens which is a requirement of the present invention.

FIG. 2 is a schematic sectional view of an optical head device according to an embodiment of the present invention.

FIG. 3A is a plan view illustrating a state of a defocus state on a detector of a diffracted light for detecting a focus error signal according to another embodiment of the present invention. FIG. 3B is a plan view illustrating focus in the embodiment. FIG. 4C is a plan view showing a state of a just-focused state on a detector of diffracted light for detecting an error signal. FIG. 4C is a plane view showing a state of a defocus state on a detector of diffracted light for detecting a focus error signal in the embodiment. Figure

FIG. 4 is a plan view of a hologram used in another embodiment of the present invention.

FIG. 5 is a schematic sectional view of an optical head device according to another embodiment of the present invention.

FIG. 6 is a schematic sectional view of an optical information device according to an embodiment of the present invention.

FIG. 7 is a schematic sectional view of a conventional optical head device.

FIG. 8A is a plan view showing a state of a defocus state on a detector of a diffracted light for detecting a focus error signal of an optical head device according to an embodiment of the present invention and a conventional optical head device. FIG. FIG. 4C is a plan view showing a state of a just-focused state on a detector of diffracted light for detecting a focus error signal of the embodiment and the conventional optical head device. FIG. A plan view showing a state of a defocused state on a detector of a diffracted light for detection.

FIG. 9 is a schematic sectional view of a conventional optical head device.

10A is a plan view showing a diffractive portion of a diffractive structure of a light splitter of a conventional optical head device. FIG. 10B is a plan view showing an optical sensor of the conventional optical head device.

FIG. 11 is a schematic sectional view of a conventional optical head device.

FIG. 12 is a schematic sectional view of a conventional optical head device.

13A is a schematic sectional front view of a conventional optical head device, and FIG. 13B is a schematic face side view of the device.

FIG. 14 is a cross-sectional view showing a state of a return path of a light beam in a conventional optical head device.

FIG. 15 is a plan view showing how diffracted light moves on a detector in a conventional optical head device.

FIG. 16 is a conceptual configuration diagram of an embodiment of an optical head device according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 hologram connecting lens 101 lens 102 hologram 103 connecting means 2 light source 3 light beam 4 optical disk 5 collimating lens 7 detector 8 hologram 9 diffracted light for focus error signal detection 10 optical head device 12 optical head device driving device 14 optical disk driving mechanism 601 to 604 Detector dividing line

Continued on the front page (72) Inventor Makoto Kato 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. References JP-A-64-62838 (JP, A) JP-A-62-289933 (JP, A) JP-A-56-57013 (JP, A) Jpn.

Claims (6)

(57) [Claims] A light source; a refraction type objective lens for receiving a light beam emitted from the light source and converging the light beam on a target object;
A hologram, comprising: a hologram that receives a first light beam reflected by the target object through the objective lens; and a detector that receives a diffracted light generated from the hologram and generates an output according to the amount of light. Is connected and fixed at a fixed relative position to the refraction type objective lens by using a connecting means, and the hologram is connected and fixed to the pair.
The object lens is relatively movable with respect to the light source and
0th-order diffracted light of the light beam emitted from the light source, which does not receive diffraction of the hologram, in the outward optical path until the light beam emitted from the light source converges to the target object, moving by tracking. A beam is converged on the target object by the refraction-type lens, and the hologram is formed of a curve having a change in pitch, has a lens effect, and returns light reflected by the target object on the first light beam. Diffracted light generated when the beam passes through the objective lens and is incident on the hologram includes at least two first and second diffracted lights, and the two diffracted lights are focused or focused in substantially the same direction. And the first diffracted light and the second diffracted light connect either the focal point or the focal line at different convergence distances, respectively. Head device. 2. A light source, and a refraction type objective lens that receives a light beam emitted from the light source and converges the light beam on a target object.
A hologram, comprising: a hologram that receives a first light beam reflected by the target object through the objective lens; and a detector that receives a diffracted light generated from the hologram and generates an output according to the amount of light. Is connected and fixed at a fixed relative position to the refraction type objective lens by using a connecting means, and the hologram is connected and fixed to the pair.
The object lens is relatively movable with respect to the light source and
0th-order diffracted light of the light beam emitted from the light source, which does not receive diffraction of the hologram, in the outward optical path until the light beam emitted from the light source converges to the target object, moving by tracking. A beam is converged on the target object by the refraction-type lens, and the hologram is formed of a curve having a change in pitch, has a lens effect, and returns light reflected by the target object on the first light beam. An optical head device, wherein diffracted light generated when a beam passes through an objective lens and enters the hologram includes a wavefront having at least astigmatism. 3. The method according to claim 2, wherein the target object has a track structure, and generates a focus error signal detection diffracted light and a tracking error signal detection diffracted light when the returning light beam passes through the hologram. 3. A diffractive light for tracking and a tracking error signal detecting diffracted light are received by a detector.
The optical head device according to any one of the above. 4. The detector according to claim 3, wherein the detector for receiving the diffraction light for detecting the focus error signal and the detector for receiving the diffraction light for detecting the tracking error signal are provided on the same substrate. Optical head device. 5. A far-field diffraction pattern portion of a return beam incident on a hologram, which changes sensitively in response to the position of a convergent beam in a direction perpendicular to the track on a target object having a track structure. The optical head device according to any one of claims 1 to 4, wherein a tracking error signal detection diffracted light is generated from a hologram portion on which the light beam enters. 6. A light source, a refraction-type objective lens for receiving a light beam emitted from the light source and converging the light beam on a target object having a track structure, and a first light beam reflected by the target object on the objective lens. A hologram that is transmitted and received; and a detector that receives diffracted light generated from the hologram and generates an output in accordance with the amount of light, wherein the hologram is fixed to the refraction type objective lens by using coupling means. Is connected and fixed to the relative position of
The fixed objective lens is fixed relative to the light source.
The light beam emitted from the light source does not undergo diffraction of the hologram in the outward light path until the light beam emitted from the light source is movable and converges on a target object. When the light beam of the next-order diffracted light is converged on the target object by the refraction type lens, and the light beam on the return path where the first light beam is reflected by the target object passes through the objective lens and enters the hologram. An optical head mechanism including two wavefronts connecting any of the wavefronts having only a focal line or astigmatism that extends only in at least different convergence distances and focuses at least different convergence distances, the driving mechanism of the target object, Focus servo mechanism using a focus error signal obtained by the optical head mechanism, tracking error obtained by the optical head mechanism Tracking servo mechanism, the focus servo mechanism and an optical information apparatus, characterized in that it comprises a tracking servo mechanism respective electrical circuits, and a connection portion between the electric circuit and the power supply or an external power supply using a No..