JPH03165337A - Optical head - Google Patents

Abstract

PURPOSE:To obtain the optical head which can be reduced in size and weight and decreased in the number of its components without any deterioration in detection accuracy by providing a condenser lens which has a transmission part and a light shield part and a 1st and a 2nd photodetector which have two photodetection surfaces. CONSTITUTION:Only the light component of 0th order in the projection light from an optical path changing means (22-24) is made incident on the condenser lens 26 principally, its diameter is smaller than the diameter of the projection light, and the center of the diameter is positioned on the optical axis of the optical path changing means; and the transmission part 26a which converges the projection light is formed on one side of a border line passing the center and the light shield part 26b is formed on the other side. A photodetector 28 consists of the 1st photodetector 31 having 1st and 2nd photodetection surfaces 31a and 31b divided by a division line which is nearly parallel to the border line and positioned at the focus of the transmission part and the 2nd photodetector 32 having 3rd and 4th photodetecting surfaces 32a and 32b arranged nearby on both sides of the detector 31 about the track direction of a disk; and the detector 31 detects the defocusing of the transmission part and the detector 32 detects a deviation in the intensity distribution of ring belt light.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is used for consumer optical video or optical audio disks, image file devices, etc., and is used to optically store information recorded on optical disks, magneto-optical disks, etc. An optical head for recording or recording and reproducing information, especially an optical system for an optical head that performs servo such as focusing and tracking using reflected light from an optical disk or magneto-optical disk, etc. It is related to.

(Prior art) In an optical head installed in an optical disk device, a magneto-optical disk device, etc., a light beam emitted from a light source such as a laser is transmitted to the optical head in order to record or reproduce information. It is necessary to constantly irradiate a minute spot with a diameter of, for example, about 1 μm onto the tracks of the disk using an optical system. At this time, as the disk rotates, the direction perpendicular to the rotation direction, that is, the direction perpendicular to the disk surface (
This may cause surface runout in the focus direction or eccentricity in the radial direction. Therefore, in the optical head,
In order to correct these two amounts of deviation, there are focus control (also called focus servo) that makes the light spot follow the movement of the surface, and tracking control (also called track servo) that makes the light spot follow the movement of eccentricity. say)
We are doing this.

Conventionally, this type of optical head was developed by Japanese Patent Application Laid-Open No. 59-19
There was one described in Publication No. 5330. The configuration will be explained below using figures.

FIG. 2 is a diagram showing an example of the configuration of the conventional optical head described in the above-mentioned document.

This optical head has a beam splitter 1 provided in an output optical path of output light L1 emitted from a semiconductor laser or the like. A quarter-wave plate 2 and an objective lens 3 are arranged in the reflected optical path of reflected light L2 obtained by reflecting the emitted light L1 by the beam splitter 1. The reflected light L3 from the disk 4 is irradiated with the reflected light L2 converged by the objective lens 3. In the reflected optical path of the reflected light L3, there is a beam splitter 2 through which the reflected light L3 passes through the objective lens 3 and the quarter-wave plate 2.
A splitting prism 5 for splitting the reflected light L3 into split light L4 and split light L5 is provided in contact with the exit surface of the splitting prism 9.
A photodetector 6 for detecting a track error signal is arranged in the output optical path of the divided light L4, and a condenser lens 7 and a light detector 6 for detecting a focus error signal are arranged in the output optical path of the divided light L5. A detector 8 is arranged. The photodetector 8 is arranged so that the focal point of the condenser lens 7 is located on its surface.

The optical head configured as described above detects a focus error signal and a tracking error signal as follows.

The objective lens 3 is in focus on the track 4a of the disk 4, and the reflected light L2 is irradiated onto the disk 4.
When the light L3 correctly follows the track 4a of the disk 4, the reflected light L3 from the disk 4 becomes substantially parallel light. The left half of the reflected light L3 becomes almost parallel divided light L4 that passes through the dividing prism 5, and the right half becomes divided light L5 that is totally reflected by the dividing prism 5 and emitted in a direction almost orthogonal to the divided light L4. Each is divided. The divided light L4 is irradiated onto the photodetector 6, and the divided light L5 is focused on the photodetector 8 by the lens action of the condensing lens 7.

When the focus of the objective lens 3 shifts from the surface of the track 4a of the disk 4 in the focus direction, the focus of the condenser lens 7 shifts from the surface of the photodetector 8 in a direction perpendicular to the surface, and this shift is detected. A focus error signal is detected based on the output of the photodetector 8.

When the reflected light L2 that follows the track 4a deviates from the track 4a in the radial direction (tracking direction), the image formation pattern on the photodetector 6 due to the divided light L4 changes, and the photodetector 6 that detects this change changes. A track error signal is detected based on the output.

(Problems to be Solved by the Invention) However, the optical head having the above configuration has the following problems.

Split light L4. Since the light beams L5 are emitted in directions shifted by approximately 90 degrees from each other, the photodetector 6 and the photodetector 8 are placed apart from each other, which increases the size of the optical head.
It is necessary to provide separate devices for processing the outputs of the photodetectors 6.8, which increases the number of parts. Moreover, the devices must be adjusted separately, increasing adjustment time.

The present invention provides an optical head that solves the problems of the prior art, such as an increase in the size of the optical head, an increase in the number of parts, and an increase in adjustment time.

(Means for Solving the Problems) In order to solve the above problems, the first invention changes the optical path of light from the disk using an optical path changing means, and after receiving the light with a photodetector, based on the output of the photodetector. In an optical head that detects a focus error signal and a track error signal, a condensing lens configured as below is provided, and
The photodetector is constructed as follows.

That is, the condensing lens mainly receives only the O-order light component included in the light emitted from the optical path changing means, has a diameter smaller than the aperture of the emitted light, and the center of the diameter is aligned with the optical path. A transmitting part for converging the emitted light is formed on one side and a light shielding part is formed on the other side of the boundary line that is located on the optical axis of the changing means and passes through the center.

The photodetector includes a first photodetector for detecting a focus error signal, and has first and second light receiving surfaces that are substantially parallel to the boundary line and are separated by a dividing line located at the focal point of the transparent section. a second photodetector for detecting a track error signal, the second photodetector having third and fourth light-receiving surfaces disposed close to each other on both sides of the first photodetector with respect to the track direction of the disk; It consists of

According to the second invention, in the optical head which changes the optical path of the light from the disk by the optical path changing means, receives the light by the photodetector, and then detects the focus error signal and the track error signal based on the output of the photodetector, A condensing lens and a wedge prism configured as below are provided, and the photodetector is configured as follows.

That is, the condensing lens mainly receives only the zero-order light component included in the light emitted from the optical path changing means, converges the emitted light, and has a diameter smaller than the aperture of the emitted light. It is something.

The wedge prism has a ridge line that divides the convergent light converged by the condensing lens into a first divided light that connects a first focus and a second divided light that connects a second focus, and It is configured to have approximately the same aperture as the optical lens.

The photodetector includes a first light receiving surface for detecting a focus error signal, and has first and second light receiving surfaces divided by a first dividing line that is substantially parallel to the ridgeline and located at the first focal point. a detector, a detector substantially parallel to the ridgeline and the second
a third divided by a second dividing line located at the focal point of
and a second photodetector for detecting a focus error signal having a fourth light-receiving surface, and disposed close to both sides of the first and second photodetectors with respect to the track direction of the disk. and a third photodetector for detecting a track error signal having fifth and sixth light receiving surfaces.

(Function) According to the first invention, since the optical head is configured as described above, the condensing lens converts the emitted light from the optical path changing means into the convergent light converged by the lens action of the transmission part and the condensed light. It works to separate the annular light that does not pass through the lens. 1st
The second photodetector works to detect a shift in focus of the transmission part, and the second photodetector works to detect a change in the intensity distribution of the annular light in the annular zone.

According to the second invention, the condenser lens functions to separate the light emitted from the optical path changing means into convergent light that is converged by the entire surface of the condenser lens and annular light that does not pass through the condenser lens. . The wedge prism functions to split the convergent light into a first split light and a second split light. The first photodetector is operative to detect the first defocus and the second photodetector is operative to detect the second defocus. The third photodetector serves to detect changes in the intensity distribution in the annular zone of the annular light.

Therefore, the above problem can be solved.

(Example) FIG. 1 is a schematic configuration diagram showing an example of the configuration of an optical head showing a first example of the present invention.

This optical head is installed, for example, in an optical disk device, and is emitted from a light source 21 composed of a semiconductor laser or the like in a direction substantially parallel to the y-axis direction (laser light) L21.
A polarizing beam splitter 22, a 1/4 wavelength plate 23, and an objective lens 24, which are optical path changing means, are provided in the output optical path. This polarizing beam splitter 22, quarter wavelength plate 23, and objective lens 24 are configured to provide a reflection optical path of reflected light L23 from a group (groove) forming a track 25a on an optical disk 25 disposed close to the objective lens 24. It is arranged to be located inside. track 2
5a and is totally reflected by the polarizing beam splitter 22 in a direction parallel to the X-axis direction, the reflected light L23 is emitted from the optical path changing means.
and a photodetector 28 are arranged. The condensing lens 26 has a diameter that is smaller than the diameter of the reflected light L23 and made as small as possible so that only the 0th-order light component of the reflected light L23 mainly enters (without disturbing the ±1st-order light, etc. as much as possible). ing. The center of its diameter is located on the optical axis of the polarizing beam splitter 22, and the condensing lens 26 is divided into two in the y-axis direction by a boundary line 27 that passes through the center and is approximately parallel to the Z-axis. A transparent part 26a is formed, and a light shielding part 2 is formed in the other region.
6b is formed. The photodetector 28 has a transmission section 26a.
is placed on the focal point.

FIG. 3 is a front view of the photodetector of FIG. 1.

This photodetector 28 includes a two-split photodetector 31, which is a first photodetector, and a two-split photodetector 32, which is a second photodetector.
The track direction of the optical disc 25 is y.
It is arranged almost parallel to the axial direction.

The two-split photodetector 31 is approximately parallel to the Z-axis direction and has a transparent section 2.
The light-receiving surface 31a is a first light-receiving surface and the light-receiving surface 31b is a second light-receiving surface, which are divided into two in the y-axis direction by the dividing line 31c. ing.

The two-split photodetector 32 has a light-receiving surface 32a, which is a third light-receiving surface, and a light-receiving surface, which is a fourth light-receiving surface, which are arranged close to both sides of the two-split photodetector 31 with respect to the track direction. 3
2b.

A circuit for detecting a focus error signal and a tracking error signal based on the output of the photodetector 28 is shown in FIG.

FIG. 4 is a configuration block diagram showing an example of the configuration of the signal detection circuit in FIG. 1.

This signal detection circuit is a two-split photodetector 31a.

31b, 32a, and 32b, respectively, and has amplifiers 41, 42, 44, 45 that convert changes in current output from the two-split photodetectors 31a to 32b into voltage changes. Amplifier 41.4 is connected to the output side of amplifier 41.42.
An amplifier 43 is connected which calculates the difference between the two outputs and outputs a focus error signal Ef. An amplifier 46 is connected to the output side of the amplifiers 44, 45, which calculates the difference between the amplifiers 44, 45 and outputs a track error signal Et.

Next, the operation will be explained.

Output light L21 emitted from the light source 21 passes through the polarizing beam splitter 22 and the quarter-wave plate 23, is converged into convergent light L22 by the objective lens 24, and is irradiated onto the track 25a of the optical disc 25. Truck 25a
The reflected light L23 passes through the objective lens 24 and the quarter-wave plate 23, and is totally reflected by the polarizing beam splitter 22 in a direction parallel to the X-axis direction. As shown in FIG. 5, since the surface of the optical disk 25 has an uneven shape due to the groups 25b forming the tracks 25a, the reflected light L23 includes an O-order light component L23- which is reflected along the same path as the convergent light L22. 0 and ±1st order photoacid L23-1 etc. (hereinafter, ±2nd order photoacid, ±
tertiary photoacid (not shown) is included. The reflected light L23 totally reflected by the polarizing beam splitter 22 is separated by the condensing lens 26 into a convergent light L24 and an annular light L25. At this time, as shown in FIG.
5 includes the 0th-order light component L23-0 of the reflected light L23 and the ±1st-order photoacid L23-1. The convergent light L24 is irradiated onto the dividing line 31c of the two-split photodetector 31 to connect the focal point S1, and part of the annular light L25 irradiates the same area on the light receiving surface 32a and the light receiving surface 32b.

The two-split photodetector 31 that receives the convergent light L24 detects the focus error signal Ef in the following manner.

Figure 7 (a>, (b), (c) shows the convergent light L2 in Figure 1.
4, in which (a) is an image when the image is in focus, and (b) and (c) are images when the image is out of focus.

(2) In the case of FIG. 7(a), the objective lens 24 is in focus on the track 25a, and at this time, the convergent light L24 focuses S1 on the dividing line 31c, so the light receiving surface 31a.

There is no output from 31b, and no focus error signal Ef is output.

(2) In the case of FIG. 7(b), the track 25a has moved away from the focal point of the objective lens 24, and at this time, the convergent light L24 is irradiated onto the light receiving surface 31b. At this time, the light receiving surface 31a is not irradiated with the convergent light L24. Therefore, current flows from the light-receiving surface 31b to the amplifier 42, but no current flows from the light-receiving surface 31a, so that the amplifier 43 outputs a focus error signal Ef.

■ In the case of FIG. 7(c), the track 25a is too close to the objective lens 24 than the focal point of the objective lens 24, and at this time, the convergent light L24
is irradiated onto the light receiving surface 31a. At this time, the light receiving surface 31b is not irradiated with the convergent light L24.

Therefore, current flows from the light-receiving surface 31a to the amplifier 41, but no current flows from the light-receiving surface 31b, so the amplifier 43
A focus error signal Ef is output from.

The two-split photodetector 32 that receives the annular light L25 detects the track error signal Et in the following manner.

8(a>, (b), and (c) show the light-receiving surface 32 of FIG. 3.
It is an intensity distribution diagram of the annular light L25 irradiated to a and 32b, and the figure (a>, (c) is an intensity distribution diagram when the light receiving surfaces 32a and 32b are asymmetrical, and the figure (b) is the intensity distribution diagram when the light receiving surfaces 32a and 32b are asymmetric. 32a, 3
2b is an intensity distribution diagram in the case of symmetry.

■ In the case of FIG. 8(b), for example, if information is held on the bottom surface of the group 25b forming the track 25, the optical axis of the objective lens 24 should be located at the center of the group 25a in the radial direction. The position of the objective lens 24 is controlled. When this position control is performed normally, the cross-sectional shape in the radial direction of the track 25a to which the convergent light L22 is irradiated is symmetrical, so the reflected light L23 is also symmetrical in the radial direction with respect to its optical axis. be. Therefore, the light receiving surface 32a.

The intensity distribution of the annular light L25 received by the ring 32b is symmetrical. In this case, since the amounts of current flowing from the light receiving surfaces 32a and 32b are the same and the output voltages of the amplifiers 44 and 45 are the same, the amplifier 46 does not output the track error signal Et.

(2) In the case of FIGS. 8(a) and 8(c) When the optical axis of the objective lens 24 is shifted from the center of the group 25b in the radial direction, the intensity distribution of the annular light L25 is no longer symmetrical. In this case, the light receiving surfaces 32a, 32b
Since the amounts of current output from the amplifiers 44 and 45 are different and the output voltages of the amplifiers 44 and 45 are different, the amplifier 46 outputs a track error signal Et.

This embodiment has the following advantages.

(The reflected light L23 from the polarized beam splitter 22 is converted into an annular light L25 and an annular light L25 by a condenser lens 26.
The convergent light L24 traveling inside the light beam L25 is separated from the convergent light L24. Therefore, the two-split photodetector 32 for detecting a track error signal, which is irradiated with the annular light L25, and the two-split photodetector 31, which is used for detecting a focus error signal, and which is irradiated with the convergent light L24, can be placed close to each other. . Therefore, the optical head shown in FIG. 1 can be smaller, lighter, and have fewer parts than the optical head shown in FIG. 2.

(■) Since the two-split photodetectors 31 and 32 can be placed close to each other, the output of the two-split photodetectors 31 and 32 can be processed by a single signal detection circuit, etc., as in the conventional example shown in Fig. 2. The configuration can be simplified compared to the case where two devices are required to process the output of the photodetector 6.8. Furthermore, since the signal detection circuit and the like can be configured as a single unit, the adjustment time can be shortened.

(III) The diameter of the condensing lens 26 is configured to be as small as possible so as to mainly contain only the zero-order light component L23-0 of the reflected light L23. Therefore, the ±1st-order light L23-1 and the like generated when the spot of the convergent light L22 is irradiated onto the uneven portion formed by the group 25b of the track 25a is not included in the convergent light L24 converged by the transmitting portion 26a. Therefore, the convergent light L2 due to the mixture of ±1st order light L23-1 etc.
4 is removed, and the focus error signal E
The detection accuracy of f is improved.

(IV) The position adjustment of the photodetector 28 can be performed easily and with high precision by simply aligning the focal point S1 of the transmitting section 26a on the dividing line 31c.

(V) The condensing lens 26 is configured by providing a transmitting part 26a and a light blocking part 26b with the boundary line 27 as a boundary.

Therefore, the focus error signal Ef can be easily detected in addition to detecting the shift of the focal point S1 of the transparent portion 26a.

FIG. 9 is a schematic configuration diagram showing an example of the configuration of an optical head showing a second embodiment of the present invention. In FIG. 9, common elements with those in FIG. 1 are given the same reference numerals.

This optical head differs from the optical head shown in FIG. 1 in the following points. That is, in the output optical path of the reflected light L23 from the polarizing beam splitter 22, instead of the condensing lens 26,
Condenser lens 47 that converges reflected light L23 into convergent light L26
, a wedge prism 48 , and a photodetector 50 in place of the photodetector 28 .

The condensing lens 47 is smaller than the aperture of the reflected light L23,
In addition, it has a diameter set as small as possible so that only the zero-order light component L23-0 of the reflected light L23 is mainly incident thereon.

The wedge prism 48 converts the convergent light L26 into divided light L28, which is a first divided light, and divided light L29, which is a second divided light.
It has a ridge line 48a that is arranged approximately parallel to the two axial directions to divide the lens into two parts, and has approximately the same diameter as the condenser lens 47. For example, the shape of the aperture is similar to the diameter of the condenser lens 47. It is a square whose sides are approximately equal in length.

FIG. 10 is a front view of the photodetector of FIG. 9.

This photodetector 50 includes a two-split photodetector 51 that is a first photodetector and a two-split photodetector 52 that is a second photodetector.
and a two-split photodetector 53, which is a third photodetector, and are arranged so that the y-axis direction is substantially parallel to the track direction of the optical disc.

The two-split photodetector 51 has a dividing line 51c which is a first dividing line substantially parallel to the Z-axis direction, a light receiving surface 51a which is a first light receiving surface and a second light receiving surface which are divided by the dividing line 51C. It has a light receiving surface 51b. The dividing line 51c is
It is placed on the focal point S2, which is the first focal point of the divided light L28.

The two-split photodetector 52 has a dividing line 52c which is a second dividing line substantially parallel to the Z-axis direction, a light receiving surface 52a which is a third light receiving surface and a fourth light receiving surface which are divided by the dividing line 52C. It has a light receiving surface 52b. The dividing line 52c is
It is juxtaposed with the dividing line 51c along the y-axis direction, and is placed on the focal point S3, which is the second focal point of the divided light L29.

The two-split photodetector 53 has light-receiving surfaces 53a and 53b arranged close to both sides of the two-split detector 5L 52 with respect to the track direction.

FIG. 11 is a configuration block diagram of the signal detection circuit in FIG. 9.

This signal detection circuit includes light receiving surfaces 51a and 52b.

51b, 52a, 53a, and 53b, respectively,
Each light receiving surface 51a, 52b, 51b, 52a.

It has amplifiers 61, 62, 64, 65, 68, 69 which convert changes in current output from 53a and 53b into voltage changes. Amplifier 6 is connected to the output side of amplifier 61 and 62.
An amplifier 63 that takes the sum of the outputs of 1.62 is connected, and an amplifier 66 that takes the sum of the outputs of the amplifiers 64.65 is connected to the output side of the amplifiers 64.65. Amplifier 63.6
An amplifier 67 is connected to the output side of 6, which calculates the difference between the outputs of amplifiers 63 and 66 and outputs a focus error signal Ef. Amplifier 6 is connected to the output side of amplifier 68 and 69.
An amplifier 70 is connected which calculates the difference between the outputs of 8.69 and outputs a track error signal Et.

Next, the operation will be explained.

Similar to the first embodiment, the reflected light L23 that is totally reflected from the polarizing beam splitter 22 in a direction parallel to the X-axis direction is converted into a convergent light L26 and an annular light L
It is separated into 27 parts. At this time, as shown in FIG. 12, the annular light L27 includes the 0th-order light component L23-0 of the reflected light L23 and the ±1st-order photoacid L23-1. Condensing lens 47
The convergent light L26 converged by the lens action is divided by the ridgeline 48a of the wedge prism 48 into divided light L28 and divided light L29. Split light L28 is split line 5
The focal point S2 is connected on the dividing line 52c, and the divided light L29 is connected to the dividing line 52c.
Focus S3 on top.

A portion of the annular light L25 illuminates the same area of the light receiving surfaces 53a and 53b.

The two-split photodetectors 51 and 52 that receive the convergent light L26 are
The focus error signal Ef is detected as follows.

13(a), (b), and (c) are image formation diagrams of the divided beams in FIG.
) and (c) are out-of-focus images.

■ In the case of FIG. 13(a), the objective lens 24 is in focus on the track 25a, and at this time, the divided light L28.29 is at the dividing line 51c.
, 52c, there is no output from the light receiving surfaces 51a, 51b and the light receiving surfaces 52a, 52b, and no focus error signal Ef is output.

(2) In the case of FIG. 13(b), the track 25a has moved away from the focal point of the objective lens 24. At this time, the divided beams L28 and 29 are irradiated onto the light receiving surfaces 51a and 52b, respectively. At this time, the light receiving surface 51b,
52a split light L28. L29 is not irradiated. Therefore, the light receiving surface 51a.

Since current flows from each of the amplifiers 61 and 62 from 52b and no current flows from the light receiving surfaces 51b and 52a, the amplifier 67 outputs a focus error signal Ef.

■ In the case of FIG. 7(c), the track 25a is too close to the objective lens 24 than the focal point of the objective lens 24, and at this time, the divided light L28
．． L29 is a light receiving surface 51b.

52a. At this time, the divided light L28. L29 is not irradiated. Therefore, current flows from the light-receiving surfaces 51b and 52a to the amplifiers 64 and 65, and since no current flows from the light-receiving surfaces 51a and 52b, the amplifier 67 outputs a focus error signal Ef.

The two-split photodetector 53 that has received the annular light L27 detects the annular light L27 on the light receiving surfaces 53a and 53b by diffracting the reflected light L23 from the track 25a, as in the case of FIG.
27 intensity distribution changes.

As a result, the four-track error signal Et is detected in the same way as the two-split photodetector 32 of the first embodiment.

The second embodiment has almost the same advantages as the first embodiment (I
) to (III), and also has the following advantages.

(i) Since the wedge prism 48 is provided, the reflected light L2
3 is split light L28. The divided light L28
．． Focal point S2.L29 connects. The focus error signal Ef can be easily detected based on the shift in S3.

(ii) In the second embodiment, although it is necessary to provide the wedge prism 48, the light-receiving surfaces 51a, 51b, 5
There is no loss in the amount of light received by 2a and 52b, and the detection sensitivity of the focus error signal Ef can be improved accordingly.

Note that the present invention is not limited to the illustrated embodiment, and various modifications are possible. Examples of such modifications include the following.

(A) The condensing lens 26 is arranged so that the boundary line 27 is substantially parallel to the Z-axis direction, but the rotation angle position of the boundary line 27 can be freely changed approximately within the yz plane. In this case, depending on the change, the two-split photodetector 31 needs to be arranged so that its dividing line 31c is substantially parallel to the boundary line 27. Similarly, the direction of the ridgeline 48a of the wedge prism 48 can be changed.

(B) Light receiving surfaces 31a to 32b and light receiving surfaces 51a to 53b
The planar shape of is not limited to the illustrated example.

(C) The present invention can be widely applied other than optical disk devices.

(Effects of the Invention) As described in detail above, according to the first invention, the condenser lens provided in the optical head has a diameter smaller than the aperture of the light emitted from the optical path changing means, and has a transparent part and a light shielding part. The division was formed. Therefore, the emitted light can be separated into the annular light and the convergent light that focuses inside the annular light, and the first method for detecting a focus error signal based on the change in the imaging pattern of the convergent light can be used. The photodetector and a second photodetector for detecting a tracking error signal based on changes in the intensity distribution of the annular light can be placed in close proximity. Furthermore, the diameter of the condensing lens is made as small as possible so that only the 0th-order light component of the output light enters, so that the convergent light is ±1
It is possible to prevent a decrease in the detection accuracy of the focus error signal caused by the contamination of secondary light components and the like.

According to the second invention, the condensing lens provided in the optical head has a diameter smaller than the aperture of the emitted light from the optical path changing means, so that the emitted light is transformed into an annular light and travels inside the annular light. It can be separated into convergent light and convergent light.

The wedge prism can divide the convergent light into a first divided light and a second divided light, each having a first focal point and a second focal point inside the annular light.

Therefore, a third photodetector for detecting a tracking error signal based on a change in the intensity distribution of the annular light;
．． The first . The second photodetector can be placed in close proximity to the second photodetector. Furthermore, the diameters of the condenser lens and wedge prism are made as small as possible so as to mainly contain only the zero-order light component of the emitted light. ± to the second split light
It is possible to prevent a decrease in the detection accuracy of the focus error signal caused by the mixing of the primary light component and the like.

Therefore, it is possible to reduce the size and weight of the optical head and reduce the number of parts while maintaining improved detection accuracy of focus error signals and the like. Furthermore, the configuration of the circuit for detecting and controlling the focus error signal and the track error signal can be simplified. It becomes possible to shorten the A adjustment time.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an example of the configuration of an optical head showing a first embodiment of the present invention, FIG. 2 is a configuration diagram of a conventional optical head, and FIG. 3 is a front view of the photodetector shown in FIG. 1. 4 is a configuration block diagram of the signal detection circuit in FIG. 1, FIG. 5 is an explanatory diagram of ±1st-order light, FIG. 6 is a sectional view taken along line A-A in FIG. 1, and FIG.
a>, (b). (C) is an image diagram of the convergent light in FIG. 1, and FIG. 8(a). (b) and (c) are intensity distribution diagrams of the annular light shown in FIG. 1, FIG. 9 is a front view of the photodetector, FIG. 11 is a configuration block diagram of the signal detection circuit in FIG. 9, FIG. 12 is a sectional view taken along line B-B in FIG. 9, and FIG.
b) and (c) are images of the divided lights in FIG. 9. 22... Polarizing beam splitter, 25... Disc, 25a... Track, 26.47... Condensing lens, 26a... Transmissive part, 26b... Light shielding part, 27...
・Boundary line, 28.50...Photodetector, 31,32,5
1,52゜53・=2-split photodetector, 31a-32b
, 51a to 53b...light receiving surface, 31c, 51c,
52c...Parting line, L23...Reflected light, L24. L
26... Convergent light, L25. L27... annular light, L2
8. L29...Divided light, 48...Wedge prism, 48a...Ridge line, SL, 32. S3...Focus.

Claims (1)

[Claims] 1. An optical head that changes the optical path of light from a disk using an optical path changing means, receives the light with a photodetector, and then detects a focus error signal and a tracking error signal based on the output of the photodetector, Mainly receives only the zero-order light component included in the light emitted from the optical path changing means, has a diameter smaller than the aperture of the emitted light, and has the center of the diameter located on the optical axis of the optical path changing means. and a condenser lens having a transmitting part for converging the emitted light on one side and a light shielding part on the other side with a boundary line passing through the center as a boundary, and the photodetector is located approximately on the boundary line. a first photodetector for detecting a focus error signal, the first photodetector having first and second light-receiving surfaces parallel to each other and separated by a dividing line located at the focal point of the transparent section; An optical head comprising: a second photodetector for detecting a track error signal having third and fourth light receiving surfaces disposed close to both sides of the first photodetector. . 2. In an optical head that changes the optical path of light from the disk by an optical path changing means, receives the light with a photodetector, and then detects a focus error signal and a track error signal based on the output of the photodetector, comprising: A condenser lens that mainly enters only the zero-order light component included in the emitted light and converges the emitted light, and has a diameter smaller than the aperture of the emitted light; a wedge prism having a ridge line that divides the light into a first divided light that connects one focal point and a second divided light that connects a second focal point, and that has approximately the same aperture as the condensing lens; a first photodetector for detecting a focus error signal having first and second light-receiving surfaces divided by a first dividing line that is substantially parallel to the ridgeline and located at the first focal point; , a second photodetector for detecting a focus error signal, the second photodetector having third and fourth light-receiving surfaces divided by a second dividing line that is substantially parallel to the ridgeline and located at the second focal point; a third photodetector for detecting a track error signal having fifth and sixth light receiving surfaces disposed close to both sides of the first and second photodetectors with respect to the track direction of the disk; An optical head comprising: