JP2000235715A - Optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the stable read-out of an information signal while hardly being affected even in the case becoming the defocussed state, in the optical head for reading out the information signal from an optical recording medium whereon the information signal is recorded by the displacement of the wall surface of a groove. SOLUTION: The optical head 1 is provided with a light splitting means for splitting the return light from the optical recording medium 5 to plural luminous fluxes, a 1st photodetecting means for detecting any one among the plural luminous fluxes, and a 2nd photodetecting means for detecting any one of the luminous fluxes other than the luminous fluxes to be detected by the 1st photodetecting means. Then, the return light is detected by the 1st photodetecting means to produce a tangential push-pull signal, and also by the 2nd photodetecting means, the return light is detected to produce a focus error signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium in which a groove is formed in a substrate along a recording track and an information signal is recorded by displacement of a wall surface of the groove, and a return light therefrom. The present invention relates to an optical head that reads out an information signal by detecting an optical signal.

[0002]

2. Description of the Related Art CDs, DVDs, and the like have been put into practical use as optical recording media. Conventionally, these optical recording media record information signals as pits. On the other hand, as a recording method capable of reducing errors during signal reproduction rather than recording as pits and achieving higher density, a groove is formed in a substrate along a recording track, A method of recording an information signal by displacement of the wall surface of the groove has been devised (Japanese Patent Application Nos. 10-124342 and 10-124).
No. 180829). In the following description, the groove formed in this manner is referred to as a groove, and the hill-shaped portion between the grooves is referred to as a land.

When an information signal is read from an optical recording medium on which an information signal is recorded due to a displacement of a groove wall surface, the optical head is irradiated with light by an optical head to detect the return light. I do.

Specifically, as shown in FIG. 34, light is applied to an optical recording medium such that a light spot S is located on a groove wall surface 200 (ie, a portion between the groove G and the land L). . The light spot S does not always completely follow the groove wall 200 in which the center of the light spot S is displaced so as to correspond to the information signal.
It moves along the average center line 201 of the groove wall surface 200.

[0005] Then, the light irradiated on the groove wall 200 is reflected by the optical recording medium, and the returned light is detected. At this time, the return light of the portion A located on the front side with respect to the track direction is received and detected, and the return light of the portion B located on the rear side with respect to the track direction is received and detected, and the difference between them is taken. . The difference signal thus obtained is called a tangential push-pull signal.

That is, the tangential push-pull signal TPP is obtained by receiving the return light of the portion A located on the front side in the track direction and detecting the return light as a. When the result of receiving and detecting the return light is represented by b, it is expressed by the following equation (1-1).

TPP = ab (1-1) In general, the amount of light returned from the groove G and the amount of light returned from the land L are different. Therefore,
When the relative positional relationship between the center of the light spot S and the groove wall surface 200 changes, the tangential push-pull signal changes depending thereon. That is, the tangential push-pull signal changes according to the displacement of the groove wall surface 200.

For example, in the example of FIG. 35, in the light spot S1, the portion A1 on the front side in the track direction has a small portion on the land L and a large portion on the groove G. . On the other hand, for the portion B1 on the rear side with respect to the track direction, the land L
The portion of the groove G is large, and the portion of the groove G is small.

In the example of FIG. 35, the light spot S
In No. 2, the portion A2 on the front side in the track direction has a large portion on the land L and a small portion on the groove G. On the other hand, the portion B2 on the rear side in the track direction has a small portion on the land L and a large portion on the groove G.

Therefore, the obtained tangential push-pull signal differs between the light spot S1 and the light spot S2.

As described above, the tangential push-pull signal changes according to the displacement of the groove wall surface 200. Therefore, by detecting the tangential push-pull signal, an information signal recorded as the displacement of the groove wall surface 200 can be read.

FIG. 36 shows an example of an optical head used to read an information signal from an optical recording medium on which an information signal has been recorded by the displacement of the groove wall 200 as described above.

An optical head 210 shown in FIG. 36 performs focus servo (focusing of light applied to the optical recording medium 211) by an astigmatism method, and performs tracking servo (spot position of light applied to the optical recording medium 211). Is controlled by a three-beam method.

The optical head 210 is used for the optical recording medium 21.
When the information signal is read from No. 1, the laser light is emitted from the laser light source 212. This laser beam is diffracted by the diffraction grating 213 to perform tracking servo by the three-beam method, and is separated into a main beam and two sub-beams.
In FIG. 36, illustration of the two sub-beams is omitted. Thereafter, the laser light is applied to the beam splitter 21.
4, the light enters the objective lens 215 and is focused on the signal recording surface of the optical recording medium 211 by the objective lens 215.

The light collected on the signal recording surface of the optical recording medium 211 is reflected by the optical recording medium 211 and returns. This return light passes through the objective lens 215 again, enters the beam splitter 214, and is reflected by the beam splitter 214.

The return light reflected and extracted by the beam splitter 214 is incident on a photodetector 217 via a cylindrical lens 216, and is received and detected by the photodetector 217. here,
The cylindrical lens 216 is for giving astigmatism to the return light in order to perform focus servo by the astigmatism method.

FIG. 37 shows the configuration of the light receiving section of the photodetector 217 and the light spots on those light receiving sections. In addition, 45 ° by the cylindrical lens 216
Of the photodetector 217
The light spot on the optical recording medium 211 is rotated by 90 ° with respect to the light spot on the optical recording medium 211.

As shown in FIG. 37, the photodetector 2
Reference numeral 17 denotes a first light receiving unit 218 that detects return light of a principal ray out of laser light diffracted by the diffraction grating 213.
And a second light receiving section 21 for detecting return light of one of the sub-beams
9 and a third light receiving unit 2 for detecting return light of the other sub-light beam
20. The first light receiving portion 218 has a light receiving surface divided into four, and the first to fourth light receiving portions 2
18a, 218b, 218c, and 218d.

Here, the detection amount at the first light receiving unit 218a constituting the first light receiving unit 218 is A, the detection amount at the second light receiving unit 218b is B, and the detection amount at the third light receiving unit 218c is Is the detection amount of C and the detection amount of the fourth light receiving unit 218d is D, the focus error signal FE is given by the following equation (1-2).
And the tangential push-pull signal TPP is obtained by performing the operation shown in the following equation (1-3).

FE = A + C−B−D (1-2) TPP = A + D−B−C (1-3)

[0021]

When a tangential push-pull signal is detected by the optical head 210 shown in FIG. 36, if the focus position of the light applied to the optical recording medium 211 is in the correct focus state, , A good tangential push-pull signal is obtained. However, when the focus position of the light irradiated on the optical recording medium 211 is shifted and the optical recording medium 211 is defocused, a large distortion occurs in the tangential push-pull signal.

FIG. 38 (b) shows the spot shape of the return light incident on each of the light receiving sections 218, 219 and 220 of the photodetector 217 in the case of the just focus state, and FIG. 38 (a) and FIG. c)
FIG. 7 shows the spot shape of the return light incident on each of the light receiving sections 218, 219, and 220 of the photodetector 217 in the case of the defocus state.

In the optical head 210, in order to perform focus servo by the astigmatism method, astigmatism is given to the return light by the cylindrical lens 216. Therefore, when the optical head 210 is in a defocused state, FIG. a)
38 (c), the photodetector 217
The spot shape of the return light incident on each of the light receiving portions 218, 219, 220 becomes elliptical.

As a result, the tangential push-pull signal represented by the above equation (1-3) is greatly distorted due to astigmatism in the defocus state. In this case, the information signal recorded on the optical recording medium 211 cannot be correctly read.

As described above, in the conventional optical head 210, when the information signal is read from the optical recording medium on which the information signal is recorded due to the displacement of the groove wall surface, the tangential push-pull signal is greatly distorted. And the information signal cannot be read stably.

The present invention has been proposed in view of the above-described conventional circumstances, and irradiates light to an optical recording medium on which an information signal is recorded by displacement of a groove wall surface.
It is an object of the present invention to provide an optical head for reading out an information signal by detecting the return light and capable of stably reading out an information signal without being significantly affected by a defocused state. And

[0027]

According to a first optical head of the present invention, a groove is formed on a substrate along a recording track, and an information signal is recorded by displacement of a wall surface of the groove. The optical head reads out information signals from an optical recording medium by irradiating light and detecting return light.
And a light splitting means for splitting the return light into a plurality of light fluxes, a first light detecting means for detecting any one of the plurality of light fluxes, and a first light detecting means for detecting the first light flux among the plurality of light fluxes. Second light detecting means for detecting any one of the light fluxes other than the light flux detected by the means.

The first light detecting means includes a first light receiving section for receiving and detecting a portion of the light beam to be detected located on the front side in the track direction, and a first light receiving section on the rear side in the track direction. A second light receiving unit for receiving and detecting a portion located at a position, and generating a tangential push-pull signal by taking a difference between a light amount detected by the first light receiving unit and a light amount detected by the second light receiving unit. . Further, the second light detecting means adjusts the focal position of light applied to the optical recording medium based on a result of detecting any one of the light fluxes other than the light flux detected by the first light detecting means. To generate a focus error signal.

In the first optical head according to the present invention as described above, the return light is split into a plurality of light beams by the light splitting means. Then, a tangential push-pull signal is generated by detecting any one of the plurality of light beams by the first light detection means, and a light beam other than the light beam detected by the first light detection means is detected. A focus error signal is generated by detecting one of them by the second light detecting means.

Therefore, in this optical head, the first light detecting means for generating the tangential push-pull signal and the second light detecting means for generating the focus error signal are independent optical systems. Therefore, in this optical head, even if, for example, astigmatism is given to the return light in order to obtain a focus error signal, it does not affect the tangential push-pull signal.

Further, the second optical head according to the present invention comprises:
A groove is formed in the substrate along the recording track, and the optical signal is recorded on the optical recording medium on which the information signal is recorded by the displacement of the wall surface of the groove, and the return light is detected to detect the information signal from the optical recording medium. Is an optical head for reading out. And it has a tangential push-pull signal generating means for generating a tangential push-pull signal, and a focus error signal generating means for generating a focus error signal.

The tangential push-pull signal generating means includes a first light receiving section for receiving and detecting a portion of the return light located on the front side in the track direction, and a first light receiving section located on the rear side in the track direction. And a second light receiving unit that receives and detects a portion to be detected. Then, a tangential push-pull signal is generated by taking the difference between the amount of light detected by the first light receiving unit and the amount of light detected by the second light receiving unit. Further, the focus error signal generating means detects the return light by dividing it into a plurality of light beams, and based on the detection results,
A focus error signal is generated for adjusting the focal position of light applied to the optical recording medium.

In the second optical head according to the present invention as described above, the return light is divided into a plurality of light beams by the focus error signal generating means and detected, and based on the detection result, the light is recorded on the optical recording medium. A focus error signal for adjusting the focal position of the irradiation light is generated. Therefore, this optical head can obtain a focus error signal without giving astigmatism or the like to the return light. Therefore, in this optical head, it is possible to avoid such a problem that a large distortion occurs in the tangential push-pull signal due to the effect of astigmatism given for focus servo.

[0034]

Embodiments of the present invention will be described below in detail with reference to the drawings.

The optical head described below as an example irradiates light onto an optical recording medium on which an information signal is recorded by displacement of a groove wall surface, and detects the return light thereof, whereby the optical recording medium can be used. This is for reading recorded information signals. Note that a method of recording an information signal by displacement of a groove wall surface is described in, for example, Japanese Patent Application No. Hei 10-1.
No. 24342, Japanese Patent Application No. 10-180829, and the like.

<First Embodiment> FIG. 1 shows a first embodiment of an optical head according to the present invention.

The optical head 1 includes a laser light source 2 composed of a semiconductor laser or the like that emits a laser beam having a predetermined wavelength,
A first beam splitter 3 arranged on the optical path of the laser light, a second beam splitter 4 arranged on the optical path of the laser light, and condensing the laser light on the signal recording surface of the optical recording medium 5 The objective lens 6, a first photodetector 7 for detecting the return light reflected and extracted by the second beam splitter 4, and astigmatism in the return light reflected and extracted by the first beam splitter 3. Cylindrical lens 8 to be provided and cylindrical lens 8
And a second photodetector 9 for detecting return light to which astigmatism has been added.

When an information signal is read from the optical recording medium 5 by the optical head 1, the optical recording medium 5 is driven to rotate, and a laser beam is emitted from the laser light source 2 of the optical head 1. This laser light passes through the first beam splitter 3 and the second beam splitter 4 and is incident on the objective lens 6, and is condensed on the signal recording surface of the optical recording medium 5 by the objective lens 6. At this time, the light spot on the signal recording surface of the optical recording medium 5 moves along the average center line of the groove wall surface as the optical recording medium 5 rotates.

The laser light focused on the signal recording surface of the optical recording medium 5 is reflected by the optical recording medium 5 and returns. This return light passes through the objective lens 6 again and enters the second beam splitter 4.

The second beam splitter 4 divides the return light into a first light flux and a second light flux by reflecting a part of the return light and transmitting the rest. As explained below,
The first light beam obtained by splitting the return light by the second beam splitter 4 is detected by the first photodetector 7, and the second light beam obtained by splitting the return light by the second beam splitter 4 is , Are detected by the second photodetector 9.

As described above, the second beam splitter 4
Reflects a part of the return light. The return light reflected and extracted by the second beam splitter 4 is incident on the first photodetector 7.

Here, as shown in FIG. 2, the first photodetector 7 has a light receiving surface divided into two and has two light receiving portions 7a and 7b. That is, the first photodetector 7 receives and detects the portion of the return light reflected and extracted by the second beam splitter 4 that is located on the front side with respect to the track direction of the optical recording medium 5 and detects it. It includes a light receiving section 7a and a second light receiving section 7b for receiving and detecting a portion located on the rear side of the optical recording medium 5 in the track direction.

In the optical head 1, the difference between the amount of light detected by the first light receiving portion 7a of the first photodetector 7 and the amount of light detected by the second light receiving portion 7b of the first photodetector 7 is calculated. To generate a tangential push-pull signal. That is, the detection amount at the first photodetector 7a of the first photodetector 7 is A, the second photodetector 7 is
Assuming that the detection amount at b is B, the tangential push-pull signal TPP is obtained by performing the calculation shown in the following equation (2-1). That is, in this optical head 1,
The tangential push-pull signal is generated by performing the calculation shown in the following equation (2-1) from the detection results of the light receiving units 7a and 7b.

TPP = AB (2-1) On the other hand, the return light transmitted through the second beam splitter 4 is:
The light enters the first beam splitter 3 and is reflected by the first beam splitter 3. The return light reflected and extracted by the first beam splitter 3 is incident on the second photodetector 9 after being provided with astigmatism by passing through the cylindrical lens 8.

The second photodetector 9 is for generating a focus error signal by an astigmatism method. As shown in FIG. 3, the second photodetector 9 has a light-receiving surface divided into four parts. And four light receiving sections 9
a, 9b, 9c, 9d.

Here, the first photodetector 9
A is the detection amount at the light receiving portion 9a, B is the detection amount at the second light receiving portion 9b, C is the detection amount at the third light receiving portion 9c, and D is the detection amount at the fourth light receiving portion 9d. Then, the focus error signal FE is obtained by performing the calculation represented by the following equation (2-2). That is, in the optical head 1, the focus error signal is generated by performing the calculation represented by the following equation (2-2) from the detection results of the light receiving units 9a, 9b, 9c, and 9d.

FE = A + C-BD (2-2) In the optical head 1 as described above, the return light is split by the second beam splitter 4 into a first light beam and a second light beam. ing. Then, a tangential push-pull signal is generated by detecting the first light beam with the first photodetector 7, and a focus error signal is generated by detecting the second light beam with the second photodetector 9. I am trying to do it.

In the optical head 1, the return light is given astigmatism by the cylindrical lens 8 in order to obtain a focus error signal. But,
The astigmatism is given to the second beam splitter 4
Is a second light flux obtained by splitting the return light by
No astigmatism is given to the luminous flux. And
The generation of the tangential push-pull signal is performed by detecting a first light beam to which no astigmatism is given.

Therefore, in the optical head 1, it is difficult for the astigmatism given to the return light to generate the focus error signal by the astigmatism method to affect the tangential push-pull signal. Absent.

Therefore, the optical head 1 can detect a tangential push-pull signal without being affected by astigmatism, and is not greatly affected by a defocused state even if it is in a defocused state.
Reading of an information signal can be performed stably.

In the above description, the tracking servo for controlling the spot position of the light applied to the optical recording medium 5 is not particularly mentioned.
For example, a tracking servo by a push-pull method, a tracking servo by a sample servo method, and the like are applicable.

<Second Embodiment> FIG. 4 shows a second example of an optical head according to the present invention.

The optical head 10 has a laser light source 11 composed of a semiconductor laser or the like which emits laser light of a predetermined wavelength.
A first beam splitter 12 disposed on the optical path of the laser light, a second beam splitter 13 disposed on the optical path of the laser light, and a laser beam collected on the signal recording surface of the optical recording medium 14. The objective lens 15 that emits light, the first photodetector 16 that detects the return light extracted through the second beam splitter 13, and the return light reflected and extracted by the first beam splitter 12 are astigmatism. A cylindrical lens 17 for giving aberration and a second photodetector 18 for detecting return light to which astigmatism is given by the cylindrical lens 17 are provided.

The optical recording medium 14 is
When reading an information signal from the optical head 10, the optical recording medium 14 is driven to rotate, and a laser beam is emitted from the laser light source 11 of the optical head 10. At this time, the laser light is emitted substantially parallel to the signal recording surface of the optical recording medium 14.

The laser beam passes through the first beam splitter 12 and then enters the second beam splitter 13, is reflected by the second beam splitter 13 and enters the objective lens 15. That is, the second beam splitter 13 guides the laser light emitted substantially parallel to the signal recording surface of the optical recording medium 14 to the objective lens 15 arranged to face the optical recording medium 14. It functions as a so-called startup mirror.

The laser light reflected by the second beam splitter 13 and incident on the objective lens 15 is focused on the signal recording surface of the optical recording medium 14 by the objective lens 15. At this time, the light spot on the signal recording surface of the optical recording medium 14 moves along the average center line of the groove wall surface as the optical recording medium 14 rotates.

The laser light focused on the signal recording surface of the optical recording medium 14 is reflected by the optical recording medium 14 and returns. This return light passes through the objective lens 15 again and enters the second beam splitter 13.

The second beam splitter 13 transmits a part of the return light and reflects the rest, thereby splitting the return light into a first light flux and a second light flux. As described below, the first light flux obtained by splitting the return light by the second beam splitter 13 is detected by the first photodetector 16, and the return light is split by the second beam splitter 13. The second light beam is detected by the second photodetector 18.

As described above, the second beam splitter 1
3 transmits a part of the return light. The return light transmitted through the second beam splitter 13 and extracted is
To the photodetector 16.

Here, the first photodetector 16
First photodetector 7 of optical head 1 shown in FIG.
Similarly to the above, the light receiving surface is divided into two and has two light receiving sections. That is, the first photodetector 16 of the optical head 10 receives a portion of the return light transmitted through the second beam splitter 13 and located on the front side in the track direction of the optical recording medium 14. There is provided a first light receiving portion for detecting, and a second light receiving portion for receiving and detecting a portion located on the rear side of the optical recording medium 14 in the track direction. Also in this optical head 10, similarly to the optical head 1 shown in FIG. 1, the light amount detected by the first light receiving portion of the first photodetector 16 and
A tangential push-pull signal is generated by taking the difference from the light amount detected by the second light receiving unit of the first photodetector 16.

On the other hand, the return light reflected by the second beam splitter 13 enters the first beam splitter 12 and is reflected by the first beam splitter 12. The return light reflected and extracted by the first beam splitter 12 is incident on the second photodetector 18 after being given astigmatism by transmitting through the cylindrical lens 17.

This second photodetector 18 is for generating a focus error signal by the astigmatism method. Like the second photodetector 9 of the optical head 1 shown in FIG. It is divided and has four light receiving sections. Then, in the optical head 10, as in the optical head 1 shown in FIG. 1, a focus error signal is generated from the detection result of each light receiving unit of the second photodetector 18.

In this optical head 10, as in the optical head 1 shown in FIG. 1, the astigmatism given to the return light for generating the focus error signal by the astigmatism method is changed by the tangential push-pull signal. There is no effect on

Therefore, this optical head 10 is also provided in FIG.
As in the case of the optical head 1 shown in (1), the tangential push-pull signal can be detected without being affected by astigmatism. Signal reading can be performed stably.

In the optical head 10, the laser beam is emitted substantially parallel to the signal recording surface of the optical recording medium 14, and the second beam splitter 13 is caused to function as a rising mirror. To the objective lens 15 arranged so as to face the optical recording medium 14. Therefore, the optical head 10 has a short optical path in the direction perpendicular to the signal recording surface of the optical recording medium 14 and is very suitable for reducing the thickness.

In the above description, the tracking servo for controlling the spot position of the light applied to the optical recording medium 14 is not particularly mentioned. However, in the optical head 10, for example, the tracking servo by the push-pull method is used. Alternatively, a tracking servo using a sample servo method or the like can be applied.

<Third Embodiment> FIG. 5 shows a third embodiment of the optical head according to the present invention.

The optical head 20 has a laser light source 21 composed of a semiconductor laser or the like which emits a laser beam of a predetermined wavelength.
And a diffraction grating 22 disposed on the optical path of the laser light, and a first beam splitter 2 disposed on the optical path of the laser light.
3, a second beam splitter 24 disposed on the optical path of the laser beam, an objective lens 26 for condensing the laser beam on the signal recording surface of the optical recording medium 25, and reflected by the second beam splitter 24. A first photodetector 27 for detecting the return light extracted and taken out, a cylindrical lens 28 for giving astigmatism to the return light reflected and taken out by the first beam splitter, and an astigmatism caused by the cylindrical lens 28. A second photodetector 29 for detecting the provided return light.

The optical recording medium 25 is
When reading an information signal from the optical head 20, the optical recording medium 25 is driven to rotate, and a laser beam is emitted from the laser light source 21 of the optical head 20. This laser light first enters the diffraction grating 22. The diffraction grating 22 separates laser light into three beams in order to perform tracking servo by a three-beam method. That is, the laser light incident on the diffraction grating 22 is diffracted by the diffraction grating 22 and separated into a principal ray and two sub-rays. In FIG. 5, illustration of the two sub-beams is omitted.

After that, the laser beam passes through the first beam splitter 23 and the second beam splitter 24 and is incident on the objective lens 26, and is condensed on the signal recording surface of the optical recording medium 25 by the objective lens 26. Is done. At this time,
On the signal recording surface of the optical recording medium 25, the light spot of the principal ray is positioned on the groove wall surface. Also,
The light spot moves along the average center line of the groove wall surface as the optical recording medium 25 rotates.

The laser light focused on the signal recording surface of the optical recording medium 25 is reflected by the optical recording medium 25 and returns. This return light passes through the objective lens 26 again and enters the second beam splitter 24.

The second beam splitter 24 splits the return light into a first light beam and a second light beam by reflecting a part of the return light and transmitting the rest. As described below, the first light flux obtained by splitting the return light by the second beam splitter 24 is detected by the first photodetector 27, and the return light is split by the second beam splitter 24. The second light flux is detected by the second photodetector 29.

As described above, the second beam splitter 2
4 reflects a part of the return light. The return light reflected and extracted by the second beam splitter 24 enters the first photodetector 27.

Here, the return light is converged light by returning through the objective lens 26. The first photodetector 27 is disposed at a position sufficiently separated from the second beam splitter 24,
As shown in FIG. 6, the light receiving portions 27a and 27b are provided sufficiently small. Thereby, as shown in FIG. 6, the light receiving sections 27a and 27 of the first photodetector 27 are formed.
Only the return light of the principal ray diffracted by the diffraction grating 22 is incident on b, and the return light of the sub-ray diffracted by the diffraction grating 22 is prevented from entering.

Here, the first photodetector 27
The light receiving surface is divided into two, and the two light receiving portions 27a, 27
b. That is, the first photodetector 2
Reference numeral 7 denotes a first light receiving portion 27a for receiving and detecting a portion of the return light reflected and extracted by the second beam splitter 24, which is located on the front side with respect to the track direction of the optical recording medium 25; A second light receiving unit 27b for receiving and detecting a portion of the recording medium 25 located on the rear side in the track direction. Also, in the optical head 20, similarly to the optical head 1 shown in FIG. 1, the light amount detected by the first light receiving portion 27a of the first photodetector 27 and the second light receiving portion of the first photodetector 27 2
A tangential push-pull signal is generated by taking the difference from the light amount detected in 7b.

On the other hand, the return light transmitted through the second beam splitter 24 enters the first beam splitter 23,
The light is reflected by the first beam splitter 23. The return light reflected and extracted by the first beam splitter 23 is incident on the second photodetector 29 after being provided with astigmatism by transmitting through the cylindrical lens 28.

The second photodetector 29 is for generating a tracking servo signal by the three-beam method and generating a focus error signal by the astigmatism method. This second photodetector 29 is configured as shown in FIG.
As shown in FIG.
The light receiving device includes first and second light receiving portions 29a and 29b for receiving return light of two sub-lights, respectively, and a third light receiving portion 29c for receiving return light of the main light. Further, the third light receiving portion 29c for receiving the return light of the principal ray has a light receiving surface divided into four, and the first to fourth light receiving portions 30a, 30b, 30
c, 30d.

Here, the detection amount of the second photodetector 29 in the first light receiving portion 29a is A, and the second light receiving portion 29b
Assuming that the amount of detection at B is B, the tracking error signal TE for controlling the spot position of the light applied to the optical recording medium 25 can be obtained by performing the calculation represented by the following equation (2-3). That is, the optical head 20 calculates the following equation (2−2) based on the detection results of the light receiving sections 29a and 29b.
The tracking error signal is generated by performing the calculation shown in 3).

TE = AB (2-3) The third light receiving section 29 of the second photodetector 29
Among the light receiving units constituting c, the detection amount at the first light receiving unit 30a is A, the detection amount at the second light receiving unit 30b is B, the detection amount at the third light receiving unit 30c is C, Fourth light receiving unit 30d
When the detection amount at D is D, the focus error signal FE
Is obtained by performing the calculation shown in the following equation (2-4). That is, the optical head 20 generates a focus error signal by performing the calculation represented by the following equation (2-4) from the detection results of the light receiving units 30a, 30b, 30c, and 30d.

FE = A + C−B−D (2-4) As with the optical head 1 shown in FIG. 1, the optical head 20 also generates a focus error signal by the astigmatism method. The astigmatism given to the return light does not affect the tangential push-pull signal.

Therefore, this optical head 20 is also provided in FIG.
As in the case of the optical head 1 shown in (1), the tangential push-pull signal can be detected without being affected by astigmatism. Signal reading can be performed stably.

In the optical head 20, tracking servo for controlling the spot position of the light applied to the optical recording medium 25 is performed by a three-beam method.
When the tracking servo is performed by the three-beam method, when detecting the tangential push-pull signal, there is a possibility that a sub-beam for performing the tracking servo by the three-beam method interferes and the tangential push-pull signal is deteriorated. is there.

However, in the optical head 20, a first signal for detecting a tangential push-pull signal is used.
The light receiving units 27a and 27b of the photodetector 27 of
The return light of the sub beam for performing the tracking servo by the three-beam method does not enter, and only the return light of the main beam enters.

Therefore, in this optical head 20, 3
The sub-beam for performing the tracking servo by the beam method does not affect the detection of the tangential push-pull signal. Therefore, the optical head 20 can obtain a good tangential push-pull signal while employing the tracking servo by the three-beam method.

<Fourth Embodiment> FIG. 8 shows a fourth example of an optical head according to the present invention.

The optical head 40 has a laser light source 41 composed of a semiconductor laser or the like for emitting a laser beam of a predetermined wavelength.
A diffraction grating 42 disposed on the optical path of the laser light; and a first beam splitter 4 disposed on the optical path of the laser light.
3, a second beam splitter 44 disposed on the optical path of the laser light, an objective lens 46 for condensing the laser light on the signal recording surface of the optical recording medium 45, and reflected by the second beam splitter 44 The first photodetector 47 for detecting the return light extracted and taken out, the pinhole 48 disposed between the second beam splitter 44 and the first photodetector 47, and the light reflected by the first beam splitter 43. A cylindrical lens 49 for providing astigmatism to the extracted return light, and a second for detecting the return light to which astigmatism is added by the cylindrical lens 49.
And a photodetector 50.

An optical recording medium 45 is formed by the optical head 40.
When reading an information signal from the optical head 40, the optical recording medium 45 is driven to rotate, and a laser beam is emitted from the laser light source 41 of the optical head 40. This laser light first enters the diffraction grating 42. The diffraction grating 42 separates laser light into three beams in order to perform tracking servo by a three-beam method. That is, the laser light incident on the diffraction grating 42 is diffracted by the diffraction grating 42 and separated into a principal ray and two subsidiary rays. In FIG. 8, illustration of the two sub-beams is omitted.

Thereafter, the laser beam passes through the first beam splitter 43 and the second beam splitter 44 and is incident on the objective lens 46, and is condensed on the signal recording surface of the optical recording medium 45 by the objective lens 46. Is done. At this time,
On the signal recording surface of the optical recording medium 45, the light spot of the principal ray is positioned on the groove wall surface. Also,
The light spot moves along the average center line of the groove wall surface as the optical recording medium 45 rotates.

The laser light focused on the signal recording surface of the optical recording medium 45 is reflected by the optical recording medium 45 and returns. This return light again passes through the objective lens 46 and enters the second beam splitter 44.

The second beam splitter 44 splits the return light into a first light beam and a second light beam by reflecting a part of the return light and transmitting the rest. As described below, the first light flux obtained by splitting the return light by the second beam splitter 44 is detected by the first photodetector 47, and the return light is split by the second beam splitter 44. The second light flux is detected by the second photodetector 50.

As described above, the second beam splitter 4
4 reflects a part of the return light. Then, the return light reflected and extracted by the second beam splitter 44 enters the first photodetector 47 via the pinhole 48.

Here, the return light is converged by returning through the objective lens 46. Then, this return light is once focused, and then enters the first photodetector 47 in a state of being diffused light again. The pinhole 48 is arranged at a position where the return light of the chief ray is focused. Therefore, the return light of the sub-light beam diffracted by the diffraction grating 42 is blocked without passing through the pinhole 48, and the first photodetector 47 outputs the main light beam of the light beams separated by the diffraction grating 42. Only the return light of the light beam enters.

Here, the first photodetector 47 is
First photodetector 7 of optical head 1 shown in FIG.
Similarly to the above, the light receiving surface is divided into two and has two light receiving sections. That is, the first photodetector 47
A first light receiving section for receiving and detecting a portion of the return light reflected and extracted by the second beam splitter 44, which is located on the front side in the track direction of the optical recording medium 45; 45, a second light receiving unit for receiving and detecting a portion located on the rear side with respect to the track direction. Also in the optical head 40, similarly to the optical head 1 shown in FIG. 1, the light amount detected by the first light receiving portion of the first photo detector 47 and the light amount detected by the second light receiving portion of the first photo detector 47 are different. A tangential push-pull signal is generated by taking the difference from the detected light quantity.

On the other hand, the return light transmitted through the second beam splitter 44 enters the first beam splitter 43,
The light is reflected by the first beam splitter 43. The return light reflected and extracted by the first beam splitter 43 is incident on the second photodetector 50 after being provided with astigmatism by transmitting through the cylindrical lens 49.

The second photodetector 50 is for generating a tracking servo signal by a three-beam method and a focus error signal by an astigmatism method. This second photodetector 50 is provided in FIG.
The second photodetector 29 of the optical head 20 shown in FIG.
Similarly to the first embodiment, there are provided first and second light receiving units for respectively receiving return light of two sub-beams diffracted by the diffraction grating 42, and a third light receiving unit for receiving return light of the main light beam. I have. Further, the third light receiving portion for receiving the return light of the principal ray has a light receiving surface divided into four and includes first to fourth light receiving portions. Then, in the optical head 40 as well, like the optical head 20 shown in FIG.

In the optical head 40, as in the optical head 1 shown in FIG. 1, the astigmatism given to the return light for generating the focus error signal by the astigmatism method is changed by the tangential push-pull signal. There is no effect on

Therefore, this optical head 40 is also provided in FIG.
As in the case of the optical head 1 shown in (1), the tangential push-pull signal can be detected without being affected by astigmatism. Signal reading can be performed stably.

In the optical head 40, tracking servo for controlling the spot position of the light irradiated on the optical recording medium 45 is performed by a three-beam method.
When the tracking servo is performed by the three-beam method, when detecting the tangential push-pull signal, there is a possibility that a sub-beam for performing the tracking servo by the three-beam method interferes and the tangential push-pull signal is deteriorated. is there.

However, in the optical head 40, a first signal for detecting a tangential push-pull signal is used.
The return light of the sub-light beam for performing the tracking servo by the three-beam method does not enter the light receiving portion of the photodetector 47, and only the return light of the main light beam enters.

Therefore, in this optical head 40, 3
The sub-beam for performing the tracking servo by the beam method does not affect the detection of the tangential push-pull signal. Therefore, the optical head 40 can obtain a good tangential push-pull signal while employing the tracking servo by the three-beam method.

<Fifth Embodiment> FIG. 9 shows a fifth embodiment of the optical head according to the present invention.

The optical head 60 has a laser light source 61 composed of a semiconductor laser or the like which emits a laser beam of a predetermined wavelength.
And a beam splitter 6 disposed on the optical path of the laser light.
2, an objective lens 64 for condensing a laser beam on a signal recording surface of an optical recording medium 63, a hologram element 65 disposed in an optical path of return light reflected and extracted by a beam splitter 62, and a hologram element A cylindrical lens 66 for providing astigmatism to the return light transmitted through 65
And a photodetector 67 that detects return light to which astigmatism has been given by the cylindrical lens 66.

The optical recording medium 63 is
When reading an information signal from the optical head 60, the optical recording medium 63 is driven to rotate, and a laser beam is emitted from the laser light source 61 of the optical head 60.

This laser beam enters the objective lens 64 via the beam splitter 62, and is focused on the signal recording surface of the optical recording medium 63 by the objective lens 64. At this time, the light spot on the signal recording surface of the optical recording medium 63 moves along the average center line of the groove wall surface as the optical recording medium 63 rotates.

The laser light focused on the signal recording surface of the optical recording medium 63 is reflected by the optical recording medium 53 and returns. This return light passes through the objective lens 54 again and enters the beam splitter 62.

The return light incident on the beam splitter 62 is reflected by the beam splitter 62 and extracted. The return light reflected and extracted by the beam splitter 62 is incident on a photodetector 67 via a hologram element 65 and a cylindrical lens 66.

Here, the hologram element 65 has the structure shown in FIG.
A hologram pattern as shown in FIG. That is, the hologram element 65 divides the return light into a part located on the front side in the track direction and a part located on the back side in the track direction to obtain a tangential push-pull signal. Two gratings 65a and 65b having different grating directions are formed.

The return light incident on the hologram element 65 is
The light is diffracted by the hologram element 65 and split into a plurality of light beams. The plurality of light beams are given astigmatism by transmitting through the cylindrical lens 66, and then enter the photodetector 67.

FIG. 11 shows the return light diffracted by the hologram element 65 and the arrangement of the light receiving portion of the photodetector 67. In FIG. 11, the cylindrical lens 6
6 is not shown.

As shown in FIG. 11, the photodetector 6
7 is one grating 65 of the hologram element 65
a first light receiving portion 67a for receiving the + 1st order light diffracted by the first light receiving portion 67a
And a second light receiving section 67b for receiving the -1st order light. The hologram element 65 further includes a third light receiving section 67c for receiving + 1st-order light diffracted by the other grating 65b, and a fourth light-receiving section 67d for receiving -1st-order light.

Here, the first and second light receiving portions 67a and 67b of the photodetector 67 receive and detect a portion of the return light located on the front side in the track direction.
Further, the third and fourth light receiving sections 6 of the photodetector 67
7c and 67d receive and detect the portion of the return light located on the rear side with respect to the track direction.

Therefore, the first photodetector 67
A is the detection amount at the light receiving portion 67a, B is the detection amount at the second light receiving portion 67b, C is the detection amount at the third light receiving portion 67c, and D is the detection amount at the fourth light receiving portion 67d. Then, the tangential push-pull signal TPP is calculated by the following equation (2-5).
Can be obtained by performing the operation shown in (1).

TPP = A + B−C−D (2-5) That is, the optical head 60 includes the photodetector 6
7, the first and second light receiving portions 67a and 67b receive and detect the return light of the portion located on the front side in the track direction, and the third and fourth light receiving portions 67c and 67d of the photodetector 67. , And receives and detects the return light of the portion located on the rear side with respect to the track direction. Then, the first and second light receiving units 6 of the photodetector 67
7a, 67b and the photodetector 67
A tangential push-pull signal is generated by taking the difference between the light amounts detected by the third and fourth light receiving sections 67c and 67d.

The photodetector 67 includes a fifth light receiving section 67e for receiving the zero-order light out of the light transmitted through the hologram element 65. This fifth light receiving section 6
7e has a light-receiving surface divided into four parts, and includes first to fourth light-receiving parts 68a, 68b, 68c, 68d. These light receiving sections 68a, 68b, 68c, 68d are for generating a focus error signal by an astigmatism method.

The fifth light receiving section 67 of the photo detector 67
e, the first light receiving unit 68a
A, the detection amount at the second light receiving unit 68b is B,
The detection amount at the third light receiving unit 68c is C, and the fourth light receiving unit 68
When the detection amount at d is D, the focus error signal F
E is obtained by performing the operation shown in the following equation (2-6). That is, in the optical head 60, based on the detection results of the light receiving sections 68a, 68b, 68c, 68d,
The focus error signal is generated by performing the calculation represented by the following equation (2-6).

FE = A + C-BD (2-6) In the optical head 60 as described above, the return light is divided into a plurality of light beams by the hologram element 65 so that the tangential push-pull signal can be detected. are doing. Further, in the optical head 60, in order to obtain a focus error signal, the return light is divided into a plurality of light beams by the hologram element 65, and then the return light is given astigmatism by the cylindrical lens 66. .

As described above, if the return light is divided into a plurality of light beams by the hologram element 65 and then astigmatism is given to the return light, the return light is used to generate a focus error signal by the astigmatism method. The astigmatism given to the light does not affect the tangential push-pull signal.

Therefore, the optical head 60 can detect a tangential push-pull signal without being affected by astigmatism, and even if it is in a defocused state, is not significantly affected by it. Reading of an information signal can be performed stably.

In the above description, the tracking servo for controlling the spot position of the light applied to the optical recording medium 63 has not been particularly mentioned. However, in the optical head 60, for example, the tracking servo by the push-pull method is used. Alternatively, a tracking servo using a sample servo method or the like can be applied.

<Sixth Embodiment> FIG. 12 shows a sixth embodiment of the optical head according to the present invention.

The optical head 70 detects a focus error signal by the Foucault method when reading an information signal from the optical recording medium 71, and comprises a semiconductor laser or the like which emits a laser beam of a predetermined wavelength. A laser light source 72, a beam splitter 73 disposed on the optical path of the laser light, an objective lens 74 for condensing the laser light on a signal recording surface of the optical recording medium 71, and a beam splitter 73
Prism 75 for dividing the return light reflected and extracted by the light into two light beams, and a Foucault prism 7
And a photodetector 76 for detecting the return light split into two light beams by the reference numeral 5.

The optical recording medium 71 is
When reading an information signal from the optical head 70, the optical recording medium 71 is driven to rotate, and a laser beam is emitted from the laser light source 72 of the optical head 70.

This laser light enters the objective lens 74 via the beam splitter 73, and is focused on the signal recording surface of the optical recording medium 71 by the objective lens 74. At this time, the light spot on the signal recording surface of the optical recording medium 71 moves along the average center line of the groove wall surface as the optical recording medium 71 rotates.

The laser light focused on the signal recording surface of the optical recording medium 71 is reflected by the optical recording medium 71 and returns. This return light passes through the objective lens 74 again and enters the beam splitter 73.

The return light incident on the beam splitter 73 is reflected by the beam splitter 73 and extracted. The return light reflected and extracted by the beam splitter 73 is
After being split into two light beams, the light beam enters the photodetector 76.

FIG. 13 shows the return light split into two light beams by the Foucault prism 75 and the photodetector 7.
6 shows the arrangement of the light receiving units. As shown in FIG. 13, the Foucault prism 75 is arranged such that its ridgeline 75a is in the tangential direction (the direction orthogonal to the track direction). As shown in FIG. 13, the photodetector 76 includes first to fourth light receiving units 76a, 76b, 76c, and 76d arranged in parallel with each other.

When the Foucault prism 75 and the photodetector 76 are just-focused (when the laser beam condensed by the objective lens 74 is focused on the signal recording surface of the optical recording medium 71), the Foucault prism 75 One of the light beams obtained by splitting the return light is focused on the boundary between the first light receiving portion 76a and the second light receiving portion 76b, and the other light beam obtained by splitting the return light by the Foucault prism 75 Is the third light receiving section 76
It is arranged so as to focus on the boundary between c and the fourth light receiving section 76d.

In the optical head 70, the Foucault prism 75 and the photodetector are arranged as described above, and a focus error signal is generated by the Foucault method. FIG. 14 shows the principle of focus error signal detection by the Foucault method.
This will be described with reference to FIG.

When the objective lens 74 is too close to the optical recording medium 71 and is in a defocused state, FIG.
As shown in (a), one of the two light beams obtained by splitting the return light by the Foucault prism 75 is incident on the second light receiving portion 76b, and the other is incident on the third light receiving portion 76c. In the case of the just-focused state, as shown in FIG. 14B, one of the luminous fluxes obtained by splitting the return light by the Foucault prism 75 is connected to the first light receiving unit 76a and the second light receiving unit 76a. The other light is focused on the boundary between the light receiving portion 76b and the other light is focused on the boundary between the third light receiving portion 76c and the fourth light receiving portion 76d. When the objective lens 74 is too far from the optical recording medium 71 and is in a defocused state, as shown in FIG. 14C, of the luminous flux obtained by splitting the return light by the Foucault prism 75, One enters the first light receiving section 76a, and the other enters the fourth light receiving section 76d.

Therefore, among the light receiving portions of the photodetector 76, the detection amount of the first light receiving portion 76a is A, the detection amount of the second light receiving portion 76b is B, and the detection amount of the third light receiving portion 76c is C, when the detection amount at the fourth light receiving unit 76d is D, the focus error signal FE is represented by the following equation (2-7).
Can be obtained by performing the operation shown in (1). That is, in the optical head 70, the light receiving sections 76a, 76b, 76
The focus error signal is generated by the Foucault method by performing the calculation represented by the following equation (2-7) from the detection results at c and 76d.

FE = A + DBC (2-7) In the optical head 70, the ridgeline 75a of the Foucault prism 75 is set in the tangential direction, and a tangential push-pull signal is detected. To be the dividing line.

Therefore, among the light receiving portions of the photodetector 76, the detection amount at the first light receiving portion 76a is A, the detection amount at the second light receiving portion 76b is B, and the detection amount at the third light receiving portion 76c is C, when the detection amount at the fourth light receiving unit 76d is D, the tangential push-pull signal TPP is obtained by performing the calculation shown in the following equation (2-8). That is, in the optical head 70, the light receiving portions 76
From the detection results at a, 76b, 76c, and 76d, a tangential push-pull signal is generated by performing an operation represented by the following equation (2-8).

TPP = A + B−C−D (2-8) In the optical head 70 as described above, the return light is transmitted to the Foucault prism 75 by the Foucault prism 75 so that the tangential push-pull signal and the focus error signal can be detected. Divided into two rays. And in this optical head 70,
The focus error signal is detected by the Foucault method without giving astigmatism to the return light. Therefore, a tangential push-pull signal can be detected without being affected by astigmatism. Therefore, even if the defocused state occurs, the information signal can be read stably without being significantly affected.

In the above description, the tracking servo for controlling the spot position of the light applied to the optical recording medium 71 is not particularly mentioned. However, in the optical head 70, for example, the tracking servo by the push-pull method is used. Alternatively, a tracking servo using a sample servo method or the like can be applied.

<Seventh Embodiment> FIG. 15 shows a seventh embodiment of the optical head according to the present invention.

The optical head 80 detects a focus error signal by a concentric circle method when reading an information signal from the optical recording medium 81, and is composed of a semiconductor laser or the like which emits a laser beam of a predetermined wavelength. The laser light source 81, the beam splitter 82 disposed on the optical path of the laser light, the objective lens 84 for condensing the laser light on the signal recording surface of the optical recording medium 81, and the light reflected and extracted by the beam splitter 83 A light receiving device 85 for receiving the return light.

The optical recording medium 81 is
When reading an information signal from the optical head 80, the optical recording medium 81 is driven to rotate, and a laser beam is emitted from the laser light source 82 of the optical head 80.

This laser light enters the objective lens 84 via the beam splitter 83, and is focused on the signal recording surface of the optical recording medium 81 by the objective lens 84. At this time, the light spot on the signal recording surface of the optical recording medium 81 moves along the average center line of the groove wall surface as the optical recording medium 81 rotates.

The laser light focused on the signal recording surface of the optical recording medium 81 is reflected by the optical recording medium 81 and returns. This return light again passes through the objective lens 84 and enters the beam splitter 83.

The return light that has entered the beam splitter 83 is reflected by the beam splitter 83 and extracted. The return light reflected and extracted by the beam splitter 83 enters the light receiving device 85.

As shown in FIG. 16, the light receiving device 85 includes a triangular prism-shaped first prism 86 and a parallelepiped-shaped second prism 87 joined to the first prism 86. Be arranged on top. Here, the joint surface 89 between the first prism 86 and the second prism 87 functions as a beam splitter that separates incident light into transmitted light and reflected light.

As shown in FIG. 17, on a substrate 88, a first photodetector 90 is disposed at a portion facing the first prism 86, and a second prism 87 is provided.
The second photodetector 91 is disposed in a portion facing the second photodetector 91.

The return light reflected and taken out by the beam splitter 83 first enters the second prism 87 as shown in FIG. Then, the light enters the joint surface 89 between the first prism 86 and the second prism 87, and is separated into reflected light and transmitted light at the joint surface 89. Then, the return light transmitted through the bonding surface 89 is incident on the first photodetector 90 formed on the substrate 88 via the first prism 86. On the other hand, the return light reflected by the joining surface 89 once becomes focused inside the second prism 87 and then becomes diffused light again. Then, the light is reflected toward the substrate by the inner surface of the second prism 87 and enters a second photodetector 91 formed on the substrate 88.

It is to be noted that the light receiving device 85 is used for the first photodetector 90 during just-focusing (when the laser beam condensed by the objective lens 84 is focused on the signal recording surface of the optical recording medium 81). The size of the light spot of the return light incident on the first photodetector 90 on the first photodetector 90 is substantially equal to the size of the light spot of the return light incident on the second photodetector 91 on the second photodetector 91. deep.

As shown in FIG. 17, the first photodetector 90 has a light-receiving surface divided into four sections, and first to fourth light-receiving sections 90a and 90 arranged in parallel with each other.
b, 90c and 90d. Similarly, the second photodetector 91 also has a light-receiving surface divided into four, and the first to fourth light-receiving units 91a and 91 arranged in parallel with each other.
b, 91c and 91d. Note that the first and second
In the photodetectors 90 and 91, the dividing line dividing the light receiving surface is set in the tangential direction (the direction orthogonal to the track direction).

The first and second light receiving portions 90a and 90b of the first photodetector 90 are provided on the front side in the track direction of the optical recording medium 81 in the return light reflected and taken out by the beam splitter 83. The part located at is received and detected. Further, the third and fourth light receiving units 90
c and 90d receive and detect a portion located on the rear side of the optical recording medium 81 with respect to the track direction.

On the other hand, the first photodetector 91
The second light receiving units 91a and 91b receive and detect a portion of the return light reflected and extracted by the beam splitter 83, which is located on the rear side in the track direction of the optical recording medium 81. Further, the third and fourth light receiving units 91
c and 91d receive and detect a portion located on the front side in the track direction of the optical recording medium 81.

In the optical head 80, the light amounts detected by the first and second light receiving portions 90a and 90b of the first photo detector 90 and the third and fourth light receiving portions 91c and 91d of the second photo detector 91 are determined by Third and fourth light receiving portions 90c and 90d of first photodetector 90 and first and second light receiving portions 91 of second photodetector 91
A tangential push-pull signal is generated by taking the difference from the light amount detected in steps a and b.

That is, the detection amount of the first light detector 90a of the first photodetector 90 is set to a1,
The detection amount at 0b is b1, the detection amount at the third light receiving unit 90c is c1, the detection amount at the fourth light receiving unit 90d is d1, and the first light receiving unit 91a of the second photodetector 91 is
A2, the detection amount at the second light receiving portion 91b is b.
2. Assuming that the detection amount at the third light receiving unit 91c is c2 and the detection amount at the fourth light receiving unit 91d is d2, the tangential push-pull signal TPP is calculated by the following equation (2-9). It is obtained by doing. That is, in the optical head 80, these light receiving sections 90a, 90b, 90c, 9
From the detection results at 0d, 91a, 91b, 91c, and 91d, a tangential push-pull signal is generated by performing an operation represented by the following equation (2-9).

TPP = (a1 + b1-c1-d1) + (c2 + d2-a2-b2) (2-9) Further, in the optical head 80, the light receiving device 85
To detect the return light, thereby generating a focus error signal by the concentric circle method. The principle of focus error signal detection by the concentric circle method will be described with reference to FIG.

When the objective lens 84 is too close to the optical recording medium 81 and is in a defocused state, FIG.
As shown in (a), the light spot on the first photodetector 90 becomes larger than the light spot on the second photodetector 91. In the case of the just-focused state, as shown in FIG. 18B, the size of the light spot on the first photodetector 90 and the size of the light spot on the second photodetector 91 are almost equal. Become equal. When the objective lens 84 is too far from the optical recording medium 81 and is in a defocused state, as shown in FIG. 18C, the light spot on the first photodetector 90 is changed to the second photodetector 90. It becomes smaller than the light spot on 91.

Therefore, the first photodetector 90
A1, the amount detected by the first light receiving unit 90a is a1, the amount detected by the second light receiving unit 90b is b1, the amount detected by the third light receiving unit 90c is c1, and the amount detected by the fourth light receiving unit 90d is Is d1,
Further, the first light receiving section 91 of the second photodetector 91
When the detection amount at a is a2, the detection amount at the second light receiving unit 91b is b2, the detection amount at the third light receiving unit 91c is c2, and the detection amount at the fourth light receiving unit 91d is d2, The focus error signal FE is obtained by performing an operation represented by the following equation (2-10). That is, in the optical head 80,
These light receiving sections 90a, 90b, 90c, 90d, 91
From the detection results at a, 91b, 91c, and 91d, a focus error signal is generated by the concentric method by performing the calculation represented by the following equation (2-10).

FE = (a1 + d1-b1-c1)-(a2 + d2-b2-c2) (2-10) In the optical head 80 described above, the tangential push-pull signal and the focus error signal The return light is split into two light beams inside the light receiving device 85 so that the light can be detected. The optical head 80 detects the focus error signal by the concentric method without giving astigmatism to the return light. Therefore, a tangential push-pull signal can be detected without being affected by astigmatism. Therefore, even if the defocused state occurs, the information signal can be read stably without being significantly affected.

In the above description, the tracking servo for controlling the spot position of the light applied to the optical recording medium 81 is not particularly mentioned. However, in the optical head 80, for example, the tracking servo by the push-pull method is used. Alternatively, a tracking servo using a sample servo method or the like can be applied.

<Eighth Embodiment> An eighth embodiment of the optical head according to the present invention is shown in FIG.

This optical head 100 is used for the optical recording medium 10.
When the information signal is read out from the laser light source 1, a focus error signal is detected by a concentric circle method, and a laser light source 102 composed of a semiconductor laser or the like that emits a laser beam of a predetermined wavelength is disposed on an optical path of the laser beam. Beam splitter 103, an objective lens 104 for condensing laser light on a signal recording surface of the optical recording medium 101, and a light receiving device 105 for receiving return light reflected and extracted by the beam splitter 103. I have.

The optical recording medium 1 is
When the information signal is read from the optical head 100, the optical recording medium 101 is driven to rotate, and the laser light is emitted from the laser light source 102 of the optical head 100.

This laser beam is applied to the beam splitter 103
To the objective lens 104 via the
The light is condensed on the signal recording surface of the optical recording medium 101 by 04. At this time, the light spot on the signal recording surface of the optical recording medium 101 moves along the average center line of the groove wall surface as the optical recording medium 101 rotates.

The laser light focused on the signal recording surface of the optical recording medium 101 is reflected by the optical recording medium 101 and returns. This return light passes through the objective lens 104 again and enters the beam splitter 103.

The return light that has entered the beam splitter 103 is reflected by the beam splitter 103 and extracted. The return light reflected and extracted by the beam splitter 103 enters the light receiving device 105.

As shown in FIG. 20, the light receiving device 105 comprises a first prism 106 having a triangular prism shape and a second prism 1 having a parallelepiped shape joined to the first prism 106.
07 is disposed on the substrate 108. Here, the joint surface 109 between the first prism 106 and the second prism 107 functions as a beam splitter that separates incident light into transmitted light and reflected light.

As shown in FIG. 21, a first photodetector 110 is provided on a portion of the substrate 108 facing the first prism 106, and is provided on a portion facing the second prism 107. Second photodetector 11
1 is arranged.

The return light reflected and extracted by the beam splitter 103 is, as shown in FIG.
The light enters the second prism 106. Then, the light enters the joint surface 109 between the first prism 106 and the second prism 107, and is separated into reflected light and transmitted light at the joint surface 109. Then, the return light transmitted through the bonding surface 109 is incident on the first photodetector 110 formed on the substrate 108 via the first prism 106.
On the other hand, the return light reflected by the bonding surface 109 once becomes focused inside the second prism 107 and then becomes diffused light again. Then, the substrate 10 is placed on the inner surface of the second prism 107.
8 reflected on the substrate 108 and formed on the substrate 108.
Incident on the photodetector 111.

It is to be noted that the light receiving device 105 is provided with the first photodetector 110 during just-focusing (when the laser beam condensed by the objective lens 104 is focused on the signal recording surface of the optical recording medium 101). The size of the light spot of the return light incident on the first photodetector 110 on the second photodetector 11
The size of the light spot on the second photodetector 111 of the return light incident on 1 is set to be substantially equal.

As shown in FIG. 21, the light receiving surface of the first photodetector 110 is divided into three by a dividing line parallel to the track direction, and the light receiving surface is divided into two by a dividing line parallel to the tangential direction. The light receiving surface is divided into six parts as a whole. That is, this first
The first to sixth photodetectors 110a, 110b, 110c, and 110c as shown in FIG.
d, 110e and 110f. In the second photodetector 111, the light receiving surface is divided into three by a dividing line parallel to the track direction, and the first to third light receiving units 111a, 111b, 111 arranged in parallel with each other.
c.

Then, the first to third light receiving portions 110a, 110b, 110c of the first photodetector 110
Receives and detects a portion of the return light reflected and extracted by the beam splitter 103, which is located on the front side with respect to the track direction of the optical recording medium 101. Further, the fourth to sixth light receiving units 110d, 110e, 110f are:
A portion located on the rear side of the optical recording medium 101 with respect to the track direction is received and detected.

In the optical head 100, the first to third light receiving sections 110a, 110a of the first photo detector 110
The light amounts detected by 10b and 110c and the fourth to sixth light receiving units 110d and 110 of the first photodetector 110
e, a tangential push-pull signal is generated by taking the difference from the light amount detected at 110f. That is, the detection amount of the first photodetector 110 at the first light receiving unit 110a is a1, the detection amount at the second light receiving unit 110b is b1,
The detection amount at the third light receiving unit 110c is c1, the detection amount at the fourth light receiving unit 110d is d, the detection amount at the fifth light receiving unit 110e is e, and the detection amount at the sixth light receiving unit 110f is Assuming that f, the tangential push-pull signal TPP is obtained by performing the calculation shown in the following equation (2-11). That is, in the optical head 100, these light receiving sections 1
10a, 110b, 110c, 110d, 110e, 1
A tangential push-pull signal is generated by performing an operation represented by the following equation (2-11) from the detection result at 10f.

TPP = (a1 + b1 + c1)-(d + e + f) (2-11) Further, in the optical head 100, the light receiving is performed similarly to the optical head 80 shown in FIG. By detecting the return light by the device 105, a focus error signal is generated by the concentric circle method.

That is, the first photodetector 110
A1, the detection amount at the second light receiving unit 110b is b1, the detection amount at the third light receiving unit 110c is c1, and the detection amount at the fourth light receiving unit 110d is Is d, the detection amount at the fifth light receiving unit 110e is e, the detection amount at the sixth light receiving unit 110f is f, and the detection amount at the first light receiving unit 111a of the second photodetector 111 is a
2. Assuming that the amount detected by the second light receiving unit 111b is b2 and the amount detected by the third light receiving unit 111c is c2, the focus error signal FE is calculated by the following equation (2-12). Is obtained. That is, in the optical head 100, these light receiving units 110a, 110b, 110c, 1
10d, 110e, 110f, 111a, 111b, 1
The focus error signal is generated by the concentric method by performing the calculation represented by the following equation (2-12) from the detection result at 11c.

FE = (a2 + c2-b2)-(a1 + d + c1 + f-b1-e) (2-12) In the optical head 100 described above, the tangential push-pull signal and the focus The return light is split into two light beams inside the light receiving device 105 so that an error signal can be detected. The optical head 100 detects the focus error signal by the concentric circle method without giving astigmatism to the return light. Therefore, a tangential push-pull signal can be detected without being affected by astigmatism. Therefore, even if the defocused state occurs, the information signal can be read stably without being significantly affected.

In the above description, the optical recording medium 101
The tracking servo for controlling the spot position of the light to be applied to the optical head 100 is not particularly mentioned, but for the optical head 100, for example, a tracking servo by a push-pull method, a tracking servo by a sample servo method, or the like is applicable. .

<Ninth Embodiment> A ninth embodiment of the optical head according to the present invention is shown in FIG.

This optical head 120 is used for the optical recording medium 12.
When the information signal is read out from the laser light source 1, a focus error signal is detected by a concentric circle method, and a laser light source 122 composed of a semiconductor laser or the like that emits a laser beam of a predetermined wavelength is disposed on the optical path of the laser beam. Beam splitter 123, an objective lens 124 for condensing laser light on a signal recording surface of the optical recording medium 121, and a hologram for diffracting return light reflected and taken out by the beam splitter 123 and dividing it into a plurality of light fluxes. Element 125,
A photodetector 126 for detecting return light diffracted by the hologram element 125 and divided into a plurality of light fluxes.

[0174] The optical recording medium 1 is
When reading an information signal from the optical head 21, the optical recording medium 121 is driven to rotate, and a laser beam is emitted from the laser light source 122 of the optical head 120. This laser light enters the objective lens 124 via the beam splitter 123, and is focused on the signal recording surface of the optical recording medium 121 by the objective lens 124. At this time, the optical recording medium 12
1 on the signal recording surface of the optical recording medium 1
With the rotation of 21, it moves along the average center line of the groove wall surface.

The laser light focused on the signal recording surface of the optical recording medium 121 is reflected by the optical recording medium 121 and returns. This return light passes through the objective lens 124 again and enters the beam splitter 123. The return light that has entered the beam splitter 123 is reflected by the beam splitter 123 and extracted. The return light reflected and taken out by the beam splitter 123 enters the hologram element 125. FIG. 23 shows a hologram pattern of the hologram element 125. As shown in FIG. 23, the hologram element 125 is a part of a concentric grating. Then, the return light that has entered the hologram element 125 is diffracted by the hologram element 125 and split into a plurality of light rays, and then enters the photodetector 126.

FIG. 24 shows the return light diffracted by the hologram element 125 and the arrangement of the light receiving portion of the photodetector 126. As shown in FIG. 24, the photodetector 126 receives the + 1st-order light and the first light-receiving unit 127 among the return lights diffracted by the hologram element 125 and divided into a plurality of light beams. And a second light receiving unit 128 that performs the operation.

Here, the + 1st-order light obtained by diffracting the return light by the hologram element 125 is once focused and then becomes the diffused light again.
6 and enters the first light receiving section 127. The -1st-order light obtained by diffracting the return light by the hologram element 125 enters the second light receiving unit 128 of the photodetector 126 before focusing.

Further, the optical head 120 is capable of moving the first light of the photodetector 126 during just focus (when the laser light focused by the objective lens 124 is focused on the signal recording surface of the optical recording medium 121). The size of the light spot on the first light receiving portion 127 of the return light incident on the light receiving portion 127 of the second light receiving portion 127 and the second light receiving portion 1 of the return light incident on the second light receiving portion 128 of the photodetector 126
The size of the light spot on 28 is made substantially equal.

The first light receiving portion 127 of the photodetector 126 has a light receiving surface divided into four, and the first to fourth light receiving portions 127a and 127a are arranged in parallel with each other.
7b, 127c, and 127d. Similarly, the second light receiving section 128 of the photodetector 126 also has a light receiving surface divided into four, and includes first to fourth light receiving sections 128a, 128b, 128c, 128d arranged in parallel with each other. The dividing line dividing the light receiving surfaces of the first and second light receiving sections 127 and 128 of the photodetector 126 is set in the tangential direction (the direction orthogonal to the track direction).

The first and second light receiving sections 12 constituting the first light receiving section 127 of the photodetector 126
7a and 127b receive and detect a portion of the return light reflected and extracted by the beam splitter 123, which is located on the front side in the track direction of the optical recording medium 121. Also, the first light receiving unit 1 of the photo detector 126
27 and 27, the third and fourth light receiving units 127c, 1
27d receives and detects a portion of the optical recording medium 121 located on the rear side in the track direction.

On the other hand, the first and second light receiving sections 128 constituting the second light receiving section 128 of the photodetector 126
A and 128b receive and detect a portion of the return light reflected and extracted by the beam splitter 123, which is located on the rear side in the track direction of the optical recording medium 121. Further, the second light receiving unit 1 of the photodetector 126
28 and the third and fourth light receiving sections 128c, 1
28d receives and detects a portion of the optical recording medium 121 located on the front side in the track direction.

In the optical head 120, the first and second light receiving sections 127a and 127b forming the first light receiving section 127 of the photodetector 126 and the second light receiving section 128 of the photodetector 126 are formed. Third
And the amount of light detected by the fourth light receiving units 128c and 128d, and the third and fourth light receiving units 127c and 127d constituting the first light receiving unit 127 of the photodetector 126.
And first and second light receiving portions 128a and 128b constituting a second light receiving portion 128 of the photodetector 126.
A tangential push-pull signal is generated by taking the difference from the light amount detected in step (1).

That is, the first of the photodetector 126
Among the light receiving units constituting the light receiving unit 127, the amount detected by the first light receiving unit 127a is a1, the second light receiving unit 127
The detection amount at b is b1, the detection amount at the third light receiving unit 127c is c1, the detection amount at the fourth light receiving unit 127d is d1,
Further, among the respective light receiving units constituting the second light receiving unit 128 of the photodetector 126, the detection amount at the first light receiving unit 128a is a2, and the detection amount at the second light receiving unit 128b is b.
2. Assuming that the detection amount at the third light receiving unit 128c is c2 and the detection amount at the fourth light receiving unit 128d is d2, the tangential push-pull signal TPP is expressed by the following equation (2-13).
Can be obtained by performing the operation shown in (1). That is, in the optical head 120, the light receiving units 127a and 127
b, 127c, 127d, 128a, 128b, 128
The tangential push-pull signal is generated by performing the operation shown in the following equation (2-13) from the detection results at c and 128d.

TPP = (a1 + b1-c1-d1) + (c2 + d2-a2-b2) (2-13) In the optical head 120, the photodetector 1
By detecting the return light at 26, a focus error signal is generated by the concentric circle method.

In this optical head 120, when the objective lens 124 is too close to the optical recording medium 121 and is in a defocused state, the light spot on the first light receiving section 127 of the photodetector 126 is It becomes smaller than the light spot on the second light receiving section 128. In the case of the just focus state, the size of the light spot on the first light receiving unit 127 of the photodetector 126 is substantially equal to the size of the light spot on the second light receiving unit 128 of the photodetector 126. . When the objective lens 124 is too far from the optical recording medium 121 and is in a defocused state, the light spot on the first light receiving unit 127 of the photodetector 126 is shifted on the second light receiving unit 128 of the photodetector 126. Larger than the light spot at.

Therefore, of the light receiving sections constituting the first light receiving section 127 of the photodetector 126, the first
The detection amount at the light receiving unit 127a is a1, the second light receiving unit 12
7b, the detection amount at the third light receiving unit 127c is c1, the detection amount at the fourth light receiving unit 127d is d1, and the second light receiving unit 12 of the photodetector 126 is
8, the first light receiving unit 128
The detection amount at a is a2, the detection amount at the second light receiving unit 128b is b2, the detection amount at the third light receiving unit 128c is c2,
When the detection amount at the light receiving unit 128d is d2, the focus error signal FE is obtained by performing the calculation represented by the following equation (2-14). That is, the optical head 12
0, these light receiving sections 127a, 127b, 127
c, 127d, 128a, 128b, 128c, 128
The focus error signal is generated by the concentric circle method by performing the calculation represented by the following equation (2-14) from the detection result at d.

FE = (a1 + d1-b1-c1)-(a2 + d2-b2-c2) (2-14) In the optical head 120 as described above, the tangential push-pull signal and the focus error signal The return light is diffracted by the hologram element 125 and divided into a plurality of light beams so that the light can be detected. The optical head 120 detects the focus error signal by the concentric method without giving astigmatism to the return light. Therefore, a tangential push-pull signal can be detected without being affected by astigmatism. Therefore, even if the defocused state occurs, the information signal can be read stably without being significantly affected.

In the above description, the optical recording medium 121
The tracking servo for controlling the spot position of the light to be applied to the optical head 121 is not particularly mentioned, but for the optical head 121, for example, a tracking servo by a push-pull method, a tracking servo by a sample servo method, or the like is applicable. .

<Tenth Embodiment> FIG. 25 shows a tenth embodiment of the optical head according to the present invention.

This optical head 140 is used for the optical recording medium 14.
When an information signal is read from the laser light source 1, a focus error signal is detected by a concentric circle method, and a laser light source 142 composed of a semiconductor laser or the like that emits a laser beam of a predetermined wavelength is disposed on an optical path of the laser beam. Beam splitter 143, an objective lens 144 for condensing a laser beam on a signal recording surface of the optical recording medium 141, and a hologram for diffracting return light reflected and taken out by the beam splitter 143 and dividing it into a plurality of light fluxes. Element 145,
A photodetector 146 for detecting return light diffracted by the hologram element 145 and divided into a plurality of light fluxes.

The optical recording medium 1 is
When reading the information signal from the optical head 41, the optical recording medium 141 is driven to rotate, and the laser light is emitted from the laser light source 142 of the optical head 140. This laser light enters the objective lens 144 via the beam splitter 143, and is focused on the signal recording surface of the optical recording medium 141 by the objective lens 144. At this time, the optical recording medium 14
1 on the signal recording surface of the optical recording medium 1
With the rotation of 41, it moves along the average center line of the groove wall surface.

The laser light focused on the signal recording surface of the optical recording medium 141 is reflected by the optical recording medium 141 and returns. This return light passes through the objective lens 144 again and enters the beam splitter 143. The return light that has entered the beam splitter 143 is reflected by the beam splitter 143 and extracted. The return light reflected and extracted by the beam splitter 143 enters the hologram element 145. This hologram element 145 is a part of a concentric grating, like the hologram element 125 of the optical head 120 shown in FIG. Then, the hologram element 14
5 is diffracted by the hologram element 145 and divided into a plurality of light rays, and then enters the photodetector 146.

FIG. 26 shows the return light diffracted by the hologram element 145 and the arrangement of the light receiving section of the photodetector 146. As shown in FIG. 26, the photodetector 146 includes a first light receiving unit 147 that receives + 1st-order light and a first light-receiving unit that receives −1st-order light among return lights diffracted by the hologram element 145 and divided into a plurality of light beams. And a second light receiving section 148.

Here, the + 1st-order light obtained by diffracting the return light by the hologram element 145 once focuses, and then becomes the diffused light again.
6 is incident on the first light receiving section 147. The -1st-order light obtained by diffracting the return light by the hologram element 145 enters the second light receiving section 148 of the photodetector 146 before focusing.

Further, the optical head 140 is configured to perform the first focus of the photodetector 146 during just-focusing (when the laser beam condensed by the objective lens 144 is focused on the signal recording surface of the optical recording medium 141). The size of the light spot on the first light receiving portion 147 of the return light incident on the light receiving portion 147 of the second light receiving portion 147 and the second light receiving portion 1 of the return light incident on the second light receiving portion 148 of the photodetector 146
The size of the light spot on 48 is set to be substantially equal.

In the first light receiving portion 147 of the photodetector 146, the light receiving surface is divided into three by a dividing line parallel to the track direction, and the light receiving surface is divided into two by a dividing line parallel to the tangential direction. The light receiving surface is divided into six as a whole. That is, the first light receiving unit 147 of the photodetector 146 includes the first to sixth light receiving units 147a, 147b, 147c, 147d, and 147.
e, 147f. Photo detector 1
The second light receiving section 148 has a light receiving surface divided into three by a dividing line parallel to the track direction, and the first to third light receiving sections 148a, 148b, 1 arranged in parallel with each other.
48c.

Then, the first to third light receiving portions 14 constituting the first light receiving portion 147 of the photodetector 146
7a, 147b and 147c are the beam splitters 143
Of the return light reflected and extracted by the optical recording medium 141, a portion located on the front side in the track direction of the optical recording medium 141 is received and detected. Also, the first of the photodetectors 146
4th to 6th light receiving units 1 constituting the light receiving unit 147 of FIG.
47d, 147e, and 147f receive and detect portions located on the rear side of the optical recording medium 141 with respect to the track direction.

In the optical head 140, the first to third light receiving sections 147a, 147b, 147c constituting the first light receiving section 147 of the photodetector 146.
And the fourth to sixth light receiving units 147 constituting the first light receiving unit 147 of the photodetector 146.
A tangential push-pull signal is generated by taking the difference from the light amounts detected at d, 147e and 147f.

That is, the first of the photodetectors 146
Among the light receiving units constituting the light receiving unit 147, the amount detected by the first light receiving unit 147a is a1, the second light receiving unit 147
The detection amount at b is b1, the detection amount at the third light receiving unit 147c is c1, the detection amount at the fourth light receiving unit 147d is d, the detection amount at the fifth light receiving unit 147e is e, Light receiving section 147f
, The tangential push-pull signal TPP is obtained by performing the calculation shown in the following equation (2-15). That is, in the optical head 140, these light receiving sections 147a, 147b, 147c, 1
From the detection results at 47d, 147e, and 147f, a tangential push-pull signal is generated by performing an operation represented by the following equation (2-15).

TPP = (a1 + b1 + c1)-(d + e + f) (2-15) In the optical head 140, the photodetector 146 is provided in the same manner as the optical head 120 shown in FIG. To detect the return light, thereby generating a focus error signal by the concentric circle method.

Here, among the respective light receiving sections constituting the first light receiving section 147 of the photodetector 146, the detection amount at the first light receiving section 147a is a1, and the second light receiving section 147b
, The detection amount at the third light receiving unit 147d is c, the detection amount at the fourth light receiving unit 147d is d, the detection amount at the fifth light receiving unit 147e is e, the sixth light reception. The detection amount in the unit 147f is assumed to be f. Further, among the respective light receiving units constituting the second light receiving unit 148 of the photodetector 146, the detection amount at the first light receiving unit 148a is a2, and the second light receiving unit 1
It is assumed that the detection amount at 48b is b2 and the detection amount at the third light receiving unit 148c is c3. At this time, the focus error signal F
E is obtained by performing the operation shown in the following equation (2-16). That is, in the optical head 140, the light receiving sections 147a, 147b, 147c, 147d, 14
From the detection results at 7e, 147f, 148a, 148b, and 148c, a focus error signal is generated by the concentric method by performing the calculation shown in the following equation (2-16).

FE = (a2 + c2-b2)-(a1 + d + c1 + f-b1-e) (2-16) In the optical head 140 as described above, the tangential push-pull signal and the focus The return light is diffracted by the hologram element 145 and divided into a plurality of light beams so that an error signal can be detected. The optical head 140 detects the focus error signal by the concentric method without giving astigmatism to the return light. Therefore, a tangential push-pull signal can be detected without being affected by astigmatism. Therefore, even if the defocused state occurs, the information signal can be read stably without being significantly affected.

In the above description, the optical recording medium 141
The tracking servo for controlling the spot position of the light applied to the optical head 140 is not particularly mentioned. However, for the optical head 140, for example, a tracking servo by a push-pull method, a tracking servo by a sample servo method, or the like can be applied. .

<Comparison with Conventional Optical Head> For detection of a tangential push-pull signal, the optical system of the optical head is modeled and calculated, and the conventional optical head is compared with the optical head to which the present invention is applied. And examined the difference. Hereinafter, the results will be described.

FIG. 27 shows a calculation model. In the following calculations, the irregularities of the lands and grooves formed on the optical recording medium were considered as causing a phase change in the return light reflected by the optical recording medium and returned.

As shown in FIG. 27, the laser light emitted from the laser light source is focused on the optical recording medium 161 by the objective lens 160. Here, the light distribution of the laser light emitted from the laser light source on the objective lens 160 is represented by L
(x, y).

The laser light focused on the optical recording medium 161 is reflected by the optical recording medium 161. Here, the complex reflectance of the optical recording medium 161 is represented by R ₀ + R ₁ (p + Δ
p, q + Δq). Note that R ₀ is an average value of the reflectance of the optical recording medium 161, and R ₁ is a component that changes with the rotation of the optical recording medium 161, which is | R ₀ || R ₁ |. Further, (p, q) indicates a light irradiation position on the optical recording medium 161 and (Δp, Δq) indicates a moving amount of the light irradiation position when the optical recording medium 161 rotates.

The return light reflected by the optical recording medium 161 and returned through the objective lens 160 enters the return optical system 162, passes through the return optical system 162, and enters the photodetector 163. Here, the return optical system 16
The distribution of the complex transmittance of No. 2 is b (x, y). Note that the astigmatism generated in the return optical system 162 is considered as a change in the distribution of the phase of the return light, that is, a change in the wavefront of the return light.

The return light that has entered the photodetector 163 through the return optical system 162 is
63. Here, the shape of the photodetector 163 for detecting the return light is D (p, q), and the light amount detected by the photodetector 163 is I (Δp, Δq).
And

Since the light irradiation position on the optical recording medium 161 changes with the rotation of the optical recording medium 161 and the complex reflectance of the optical recording medium 161 changes, the amount of light I (Δp, Δq) detected by the photodetector 163 is changed. ) Changes with the rotation of the optical recording medium 161.

In the above system, the light emitted from the laser light source and condensed on the optical recording medium 161 by the objective lens 160 is given by Fourier transform of the light on the objective lens 160. The return light reflected by the optical recording medium 161 and returned is multiplied by the complex reflectance of the optical recording medium 161 with the light condensed on the optical recording medium 161 to perform an inverse Fourier transform. It can be obtained by: The light distribution of the light condensed on the photodetector 163 for detecting the return light is obtained by multiplying the return transmittance of the return optical system 162 by the complex transmittance b (x, y) and then performing the Fourier transform.

Therefore, the light amount I detected by the photodetector 163 is represented by the following equation (3-1). In the following equation (3-1), F represents a two-dimensional Fourier transform.

I (Δp, Δq) = | D (F (b (F ⁻¹ (F (L) (R ₀ + R ₁ ))))) | ² dpdq (3-1) where: Since | R ₀ | | R ₁ |, the photodetector 1
The light amount I detected by 63 can be approximated by the following equation (3-2). In the following formula (3-2), * indicates a complex conjugate.

I (Δp, Δq) = 2 Re (V ^* (p, q) U (p, q) R ₁ (p + Δp, q + Δq) dpdq) (3-2) where V = F (b ^* F ^-1 (D ² F (b F ^-1 (F (L) R ₀ ))))), U = F (L) Here, P ( p, q). At this time, the light amount I detected by the photodetector 163 becomes P (p, q), the reflectance R ₁ of the optical recording medium 161.
Multiplied and integrated.

P (p, q) = V ^* (p, q) · U (p, q) (3-3) P (p, q) detects a tangential push-pull signal with an optical head In this case, an equivalent light spot is shown. That is, the light distribution of the return light returning after being reflected by the optical recording medium having an in-plane distribution of the complex reflectivity by uneven pattern, such as lands and grooves are formed, the complex reflectivity is constant for R ₁ This is equal to the light distribution of the return light when the optical recording medium is irradiated with a light spot having a light distribution defined by P (p, q). In the following description, P (p,
The light spot having the light distribution defined in q) is called a virtual light spot.

When the information signal is read from the optical recording medium by detecting the tangential push-pull signal, even if the objective lens is in a defocused state, the light distribution of the virtual light spot is changed to a just-focused state. It is desirable to be almost the same as in the state. The fact that the light distribution of the virtual light spot changes when the objective lens enters the defocus state means that distortion and crosstalk occur in the tangential push-pull signal when the objective lens enters the defocus state. That is.

Then, it was examined how the light distribution of the virtual light spot changes according to the focus state of the objective lens, and a conventional optical head and an optical head to which the present invention was applied were compared. The results are shown in FIGS.

FIGS. 28 to 30 show the light distribution of the virtual light spot in the conventional optical head 210 shown in FIG. FIG. 28 shows that the objective lens 215 is in a defocused state and the defocus amount is +0.5 μm.
29, FIG. 29 shows that the objective lens 215 is in the just-focused state, and FIG. 30 shows that the objective lens 215 is in the defocused state.
This is at the time of 5 μm.

As can be seen from FIGS. 28 to 30, FIG.
In the conventional optical head 210 shown in FIG.
When 15 is in the defocused state, the virtual light spot is rotated, and the light distribution of the virtual light spot is significantly different from the case where the objective lens 215 is in the just-focused state. This is because the conventional optical head 210 shown in FIG.
This is because astigmatism is given to the return light. For this reason,
In the conventional optical head 210, when the objective lens 215 is in a defocused state, distortion and crosstalk occur in the tangential push-pull signal.

On the other hand, FIGS. 31 to 33 show the light distribution of the virtual light spot in the optical head 1 according to the present invention shown in FIG. FIG. 31 shows that the objective lens 6 is in a defocused state and the defocus amount is +0.5.
32, FIG. 32 shows that the objective lens 6 is in the just-focus state, and FIG. 33 shows that the objective lens 6 is in the defocus state, and the defocus amount is -0.5 μm.
It is time.

As can be seen from FIGS. 31 to 33, in the optical head 1 to which the present invention is applied, even when the objective lens 6 is in the defocused state, the light distribution of the virtual light spot is such that the objective lens 6 is in the just-focused state. Is almost the same as in Therefore, in the optical head 1 to which the present invention is applied, even if the objective lens 6 is in the defocus state, distortion and crosstalk hardly occur in the tangential push-pull signal, and reading of the information signal is stable. You can do it.

In FIGS. 31 to 33, the light distribution of the virtual light spot in the optical head 1 according to the present invention shown in FIG. 1 is shown.
0, 20, 40, 60, 70, 80, 100, 120,
Also at 140, the light distribution of the virtual light spot is the same as in FIGS. That is, these optical heads 10, 20, 40, 60, 70, 80, 100, 12
Even at 0 and 140, even if the objective lens is in the defocused state, distortion and crosstalk hardly occur in the tangential push-pull signal.
Information signals can be read stably.

[0223]

As described above in detail, in the optical head according to the present invention, the optical recording medium on which the information signal is recorded by the displacement of the groove wall surface is irradiated with light, and the return light is detected. As a result, even when the information signal is read, even if the defocus state occurs, the signal is not much affected by the defocus state, and the tangential push-pull signal hardly causes distortion or crosstalk. Therefore, it is possible to stably read the information signal from the optical recording medium.

Further, by using the optical head according to the present invention, it is possible to obtain a high-quality reproduction signal with less crosstalk from an adjacent track, so that the track density of the optical recording medium can be increased, and as a result, It is possible to construct a higher density optical recording system.

Further, even if the track density is the same, a high-quality reproduced signal with little crosstalk and distortion can be obtained by using the optical head according to the present invention. In this case, the linear recording density can be further increased, and as a result, a higher-density optical recording system can be constructed.

In the optical head according to the present invention, a better reproduction signal can be obtained than in the conventional optical head. Therefore, for example, in the case where the signal quality is equivalent to that of the conventional optical head, it is possible to reduce the component accuracy and the adjustment accuracy at the time of manufacturing the optical head, and as a result,
It is possible to provide a cheaper optical recording system.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a first example of an embodiment of an optical head to which the present invention has been applied.

FIG. 2 is a diagram showing a light receiving section of a first photodetector of the optical head shown in FIG.

FIG. 3 is a diagram showing a light receiving section of a second photodetector of the optical head shown in FIG.

FIG. 4 is a diagram showing a second example of the embodiment of the optical head to which the present invention is applied.

FIG. 5 is a diagram showing a third example of the embodiment of the optical head to which the present invention is applied.

6 is a diagram showing a light receiving section of a first photodetector of the optical head shown in FIG.

FIG. 7 is a diagram showing a light receiving section of a second photodetector of the optical head shown in FIG.

FIG. 8 is a diagram showing a fourth example of the embodiment of the optical head to which the present invention is applied.

FIG. 9 is a diagram showing a fifth example of the embodiment of the optical head to which the present invention is applied.

10 is a diagram schematically showing a hologram pattern of a hologram element of the optical head shown in FIG.

FIG. 11 is a diagram showing the return light diffracted by the hologram element and the arrangement of the light receiving section of the photodetector in the optical head shown in FIG. 9;

FIG. 12 is a diagram showing a sixth example of the embodiment of the optical head to which the invention is applied.

FIG. 13 is a diagram illustrating the return light divided into two light beams by the Foucault prism in the optical head shown in FIG.
FIG. 3 is a diagram illustrating an arrangement of a light receiving unit of the photo detector.

14A and 14B are diagrams for explaining the principle of focus error signal detection by the Foucault method. FIG. 14A illustrates a case where the objective lens is too close to the optical recording medium and is in a defocused state. FIG. 14B is a diagram showing a case where the objective lens is in the just focus state, and FIG. 14C is a diagram showing a case where the objective lens is too far from the optical recording medium and is in the defocus state.

FIG. 15 is a diagram showing a seventh example of the embodiment of the optical head to which the invention is applied.

16 is a diagram showing a configuration of a light receiving device of the optical head shown in FIG.

17 is a diagram illustrating a photodetector arranged on a substrate of the light receiving device illustrated in FIG. 16;

18A and 18B are diagrams for explaining the principle of focus error signal detection by the concentric circle method. FIG. 18A illustrates a case where the objective lens is too close to the optical recording medium and is in a defocused state. FIG. 18B is a diagram showing a case where the objective lens is in the just focus state, and FIG. 18C is a diagram showing a case where the objective lens is too far from the optical recording medium and is in the defocus state.

FIG. 19 is a diagram illustrating an eighth example of the embodiment of the optical head to which the invention is applied.

20 is a diagram showing a configuration of a light receiving device of the optical head shown in FIG.

21 is a diagram illustrating a photodetector arranged on a substrate of the light receiving device illustrated in FIG. 20;

FIG. 22 is a diagram showing a ninth embodiment of the optical head according to the present invention.

23 is a diagram schematically showing a hologram pattern of a hologram element of the optical head shown in FIG.

FIG. 24 is a diagram illustrating return light diffracted by a hologram element and an arrangement of a light receiving unit of a photodetector in the optical head illustrated in FIG. 22;

FIG. 25 is a diagram showing a tenth example of an optical head according to an embodiment of the present invention;

26 is a diagram showing the return light diffracted by the hologram element in the optical head shown in FIG. 25 and the arrangement of the light receiving section of the photodetector.

FIG. 27 is a diagram showing a calculation model when performing calculations by modeling the optical system of the optical head.

FIG. 28 is a diagram showing a light distribution of a virtual light spot when a defocus amount of an objective lens is +0.5 μm in a conventional optical head.

FIG. 29 is a diagram showing a light distribution of a virtual light spot when an objective lens is in a just-focus state in a conventional optical head.

FIG. 30 is a diagram illustrating a light distribution of a virtual light spot when a defocus amount of an objective lens is −0.5 μm in a conventional optical head.

FIG. 31 is a diagram showing a light distribution of a virtual light spot when a defocus amount of an objective lens is +0.5 μm in an optical head to which the present invention is applied.

FIG. 32 is a diagram showing a light distribution of a virtual light spot when the objective lens is in a just-focus state in the optical head to which the present invention is applied.

FIG. 33 is a diagram showing a light distribution of a virtual light spot when the defocus amount of the objective lens is -0.5 μm in the optical head to which the present invention is applied.

FIG. 34 is a diagram showing a state in which light is applied to an optical recording medium so that a light spot is located on a groove wall surface.

FIG. 35 is a diagram for explaining that when the relative positional relationship between the center of the light spot and the groove wall surface changes, the tangential push-pull signal changes accordingly.

FIG. 36 is a diagram illustrating an example of a conventional optical head.

FIG. 37 is a diagram showing a light receiving section of the photodetector of the optical head shown in FIG.

38 is a diagram showing a spot shape of return light incident on each light receiving portion of the photodetector in the optical head shown in FIG. 36, and FIG. ) And FIG. 38 (c) are diagrams showing a case in a defocused state.

[Explanation of symbols]

Reference Signs List 1 optical head, 2 laser light source, 3 first beam splitter, 4 second beam splitter, 5 optical recording medium, 6 objective lens, 7 first photodetector, 8 cylindrical lens, 9 second photodetector

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toshihiro Horigo 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo F-term in Sony Corporation (reference) 5D118 AA13 BA01 BB01 CF03 CF16 CG04 DA03 DA17 DA20 DA35 DB12 5D119 AA09 BA01 BB01 BB04 EA02 EA03 EC07 EC41 JA24 JA43 JC07 KA04 KA17

Claims (8)

[Claims] 1. An optical recording medium in which a groove is formed in a substrate along a recording track and an information signal is recorded by displacement of a wall surface of the groove, and return light is detected by detecting the return light. An optical head for reading an information signal from a recording medium, comprising: a light splitting unit that splits the return light into a plurality of light fluxes; a first light detection unit that detects any one of the plurality of light fluxes; And a second light detecting means for detecting any one of the light fluxes other than the light flux detected by the first light detecting means, among the light fluxes, wherein the first light detecting means comprises: A first light receiving unit for receiving and detecting a portion located on the front side with respect to the track direction, and a second light receiving unit for receiving and detecting a portion located on the rear side with respect to the track direction; The light amount detected by the first light receiving unit and the light amount detected by the second light receiving unit The second light detection means generates a tangential push-pull signal by taking a difference from the detected light quantity, based on a result of detecting one of the light fluxes other than the light flux detected by the first light detection means. An optical head for generating a focus error signal for adjusting a focal position of light applied to the optical recording medium. 2. The optical head according to claim 1, wherein said second light detecting means generates a focus error signal by an astigmatism method. 3. An optical diffraction means for diffracting light applied to an optical recording medium to separate the light into a principal ray and at least two sub rays, performing tracking servo by a three-beam method, and performing the first light detection. 2. The device according to claim 1, wherein the return light of the sub-light beam does not enter the first and second light receiving portions of the means, but only the return light of the main light beam enters. Optical head. 4. The optical head according to claim 1, wherein the light splitting unit splits the return light into a plurality of light beams by a diffractive optical element. 5. An optical recording medium in which a groove is formed in a substrate along a recording track and an information signal is recorded by displacement of a wall surface of the groove, and the return light is detected to detect light. An optical head for reading out an information signal from a recording medium, comprising: a first light receiving section for receiving and detecting a portion of the return light located on the front side in the track direction; A second light receiving portion for receiving and detecting a portion to be changed, and generating a tangential push-pull signal by taking a difference between the light amount detected by the first light receiving portion and the light amount detected by the second light receiving portion. An initial push-pull signal generating means, detecting the return light by dividing the return light into a plurality of light beams, and, based on a result of the detection, generating a focus error signal for performing a focus position adjustment of the light applied to the optical recording medium. The optical head is characterized in that it comprises a focus error signal generating means for forming. 6. The focus error signal generating means,
6. The optical head according to claim 5, wherein the return light is divided into a plurality of light beams by a diffractive optical element. 7. The focus error signal generating means according to claim 1,
The return light is converted into a first light beam and a second light beam by a Foucault prism.
And a focus error signal is generated by the Foucault method by detecting each of them by the light detecting means. The light detecting means used for generating the focus error signal by the Foucault method is the first light detecting means. 6. The photodetector according to claim 5, wherein the photodetector also serves as the first and second light receiving portions.
The optical head as described. 8. The focus error signal generating means,
The return light is divided into a first light beam and a second light beam, and the light beams are respectively detected by light detecting means to generate a focus error signal by a concentric circle method, which is used to generate a focus error signal by the concentric circle method. 6. The optical head according to claim 5, wherein said light detecting means serves also as first and second light receiving portions of said first light detecting means.