JPH10302301A - Optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contrive simplification and miniaturization of the whole device and to stably obtain a tracking signal such as a tracking error signal, etc., and also facilitate the manufacture in a semiconductor process. SOLUTION: This device has a converging means 3 for converging and projecting reflected light LF reflected by a reflecting surface M1 to a part 2 to be irradiated with this light from a semiconductor laser LD, and moreover, converging return light LR reflected from the irradiated part 2. The reflected surfaces 4 (M1 and M2 ) are formed in the vicinity of a focusing plane of the converging means 3, and are composed of a prescribed crystalline surface by growing crystals in a semiconductor substrate 1, and a recessed part 1a having a required depth (d) retreated from the substrate surface 4s of the semiconductor substrate 1 in a part for forming the semiconductor laser LD, is formed on the semiconductor substrate 1. Then, a photodetecting element PD is formed in this recessed part 1a, and a part of the return light LR from the converging means 3 is projected to the photodetecting element PD by the reflecting surface M2 , and the tracking servo signal is obtained by this photodetecting element PD.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of irradiating light from a light emitting portion to an irradiated portion of an optical recording medium, such as an optical disk or a magneto-optical disk, and detecting and detecting return light due to reflection from the irradiated portion. The present invention relates to an optical device suitable for application to

[0002]

2. Description of the Related Art In a conventional optical device, that is, an optical pickup of a so-called compact disk (CD) player or an optical pickup of a magneto-optical disk drive, an optical device such as a grating and a beam splitter is individually assembled, so that the entire device is configured. Complex and large,
In addition, when assembling in a hybrid manner on a substrate, strict alignment accuracy is required in setting the optical arrangement.

FIG. 5 shows a conventional compact disk (CD).
FIG. 1 shows a configuration diagram of an example of a read-only optical pickup.
The optical pickup 81 includes a semiconductor laser 82, a diffraction grating 83, a beam splitter plate 84, an objective lens 85, and a light receiving element 86 including a photodiode. Laser light L from the semiconductor laser 82 is reflected by the beam splitter plate 84. The light is converged by the objective lens 85 and irradiated onto the optical disc 90.
The return light reflected by the beam splitter plate 84
And is detected by the light receiving element 86.

[0004]

However, such an optical pickup 81 not only has a large number of components and is very large, but also requires high precision in its arrangement and low productivity. Was.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and in an optical device such as an optical pickup, it is possible to reduce the number of optical components and to simplify alignment when setting an optical arrangement. It is intended to simplify the entire system and reduce the size thereof, to stably obtain a tracking signal such as a tracking error signal, and to facilitate manufacture by a semiconductor process.

[0006]

According to an optical device of the present invention, an illuminated portion, a semiconductor laser, a reflection surface for reflecting light emitted from the semiconductor laser, and a photodetector are formed on the same semiconductor substrate. And a convergence means for converging and irradiating the reflected light reflected by the reflecting surface from the semiconductor laser to the irradiated portion, and further converging the return light reflected from the irradiated portion. The reflection surface is constituted by a predetermined crystal surface formed by crystal growth on a semiconductor substrate formed near the focal plane of the converging means. In the semiconductor substrate, a concave portion is formed with a required depth from the substrate surface of the semiconductor substrate in the portion where the semiconductor laser is formed, and the light detecting element is formed in the concave portion. The light detecting element is configured to irradiate a part of the return light from the converging means by the reflection surface, and a tracking servo signal is obtained by the light detecting element.

According to the configuration of the present invention described above, a concave portion is formed in the semiconductor substrate where the semiconductor laser is formed to recede from the substrate surface of the semiconductor substrate with a required depth, and a light detecting element is formed in the concave portion. Therefore, the distance from the reflection surface, that is, the convergence position of the return light to the photodetector can be made longer, and the diffraction pattern formed by the 0th-order diffracted light and the 1st-order diffracted light is sufficiently separated and introduced into the photodetector. be able to. As described above, since the photodetector can receive the return light having the separated diffraction pattern, a tracking error signal can be reliably obtained, and tracking servo can be performed with high sensitivity. Also,
Since the semiconductor laser, the reflection surface, and the photodetector are formed on the same semiconductor substrate, the optical device can be configured simply and compactly with a reduced number of components.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In an optical device according to the present invention, a portion to be irradiated, a semiconductor laser, a reflection surface for reflecting light emitted from the semiconductor laser, and a photodetector are formed on the same semiconductor substrate. The semiconductor portion and the reflected light reflected by the reflecting surface from the semiconductor laser are convergently irradiated on the irradiated portion,
Further, there is provided converging means for converging the return light reflected from the irradiated portion. The reflection surface is constituted by a predetermined crystal surface formed by crystal growth on a semiconductor substrate formed near the focal plane of the converging means. In the semiconductor substrate, there is formed a concave portion which recedes from the substrate surface of the semiconductor substrate in a portion where the semiconductor laser is formed with a required depth, and a light detecting element is formed therein. The reflecting surface irradiates a part of the return light from the converging means to the light detecting element, and a tracking servo signal is obtained by the light detecting element.

According to the present invention, in the above optical device, the surface of the concave portion on which the photodetector is formed is 20 μm to 100 μm from the substrate surface of the semiconductor substrate in the semiconductor laser forming portion.
It is configured to be formed at a position receded to the extent.

Further, according to the present invention, in the above optical device, a tracking servo signal is obtained by heterodyne detection.

Hereinafter, an example of the optical device of the present invention will be described with reference to the drawings. As shown in a perspective view of the optical apparatus in FIG. 1, in this example, an irradiated portion is, for example, an optical disk 2 having recording pits, and an optical pickup in which recording is read out by irradiating the optical disk 2 with a laser beam. This is the case when applied to. 2A is a side view of the optical device, and FIG. 2B is a plan view.

This optical device 10 has the same semiconductor substrate 1
A semiconductor laser LD having a cavity length direction parallel to, for example, a tangential direction T of the optical disk 2 as a portion to be irradiated, which extends along the substrate surface;
A triangular prism-shaped semiconductor structure 4 having a reflecting surface M ₁ for reflecting the emitted light L _F from the provided facing one firing end face of the semiconductor laser LD, 4 division photodiode PD (PD _1, PD as a light receiving portion _2, PD _3, PD ₄₎ constituted by an optical semiconductor element 7 and the light detecting element is formed consisting of. This optical semiconductor element 7 can be manufactured in a series of semiconductor manufacturing steps by a so-called wafer batch process in which a plurality of optical semiconductor elements 7 are simultaneously formed on a wafer.

The emitted light L _F reflected by the reflecting surface M ₁ is converged and irradiated on the optical disk 2 by the objective lens 3 as a converging means, and the return light L _R reflected from the optical disk 2 is converted into a common objective lens. 3 and return to the optical semiconductor element 7.

The return light L _R is intended to be focused by the objective lens 3 to the vicinity (the diffraction limit of the or lens) light diffraction limit, the light diffraction limit, i.e., the wavelength of the emitted light L _F from the semiconductor laser LD λ, the numerical aperture of the objective lens 3 is N.
A. When a, the diameter of the emission light L _F 1.22λ / N.
A. The emission light L _{F of the} triangular prism-shaped semiconductor structure 4 is made smaller.
To be irradiated on the reflecting surface M ₁ for reflecting. Here, the use of semiconductor laser LD as a light source of the light emitting section 4, the diameter of the emission light L _F, may be about 1 to 2 [mu] m. On the other hand, the numerical aperture N. A. But for example 0.09 to 0.1, the wavelength of the emitted light L _F lambda 780
nm, the diffraction limit is 1.22λ / N. A. $ 1
It is about 0 μm.

The semiconductor structure 4 having a triangular prism shape has a predetermined crystal plane, for example, {111} B
It is composed of reflective surfaces M ₁ and M ₂ formed by crystal planes, and is arranged at a position near the confocal point of the objective lens 3 with respect to the return light L _R described above. A so-called CLC (Confocal Laser) for forming a light receiving portion near a confocal position where the light emitting portion is located.
Coupler). In this case, under normal growth conditions, crystal growth is automatically stopped after the semiconductor structure 4 is grown in a triangular prism shape, and thus the reproducibility of the manufacturing process is excellent.

Even under other specific growth conditions, the crystal growth is automatically stopped, so that the triangular prism-shaped semiconductor structure 4 can be formed with good reproducibility as designed. For example, in the case of high-temperature growth and a crystal growth condition in which the ratio of group III element / group V element is low, the reflection surface is set to {11}.
In this case, the triangular prism-shaped semiconductor structure 4 can be similarly formed with good reproducibility as designed.

[0017] Then, by this another reflective surface M ₂ is a reflective surface M ₁ one which reflects the emitted light L _F of the triangular-shaped semiconductor structure 4, part of the return light L _R is reflected, 4 splitting photodiode _{PD (PD 1, PD 2,} PD 3, P
D ₄ ).

[0018] The quadrant photodiode PD, the semiconductor laser and the formation of the LD is arranged on the opposite side, it is formed set back from the surface of the semiconductor substrate 1 formed of the semiconductor laser LD across the reflecting mirror M ₁ It is formed in the concave portion 1a.

At this time, in the confocal optical system having the CLC configuration, all the rays diffracted near the focal position, that is, 0
The two-dimensional diffraction pattern formed by the first and second order light (FIG. 1
0) has the characteristic of having a distribution but all overlapping in the same plane on the confocal point. Therefore, even in the case of this example in which a part of the returned light is cut off, all the diffraction components are The light propagates in a certain direction of the four-division photodiode PD.

In this case, in order to spatially separate the overlapping interference components again, it is necessary to propagate a distance of preferably about 100 μm. However, as shown in FIG.
A four-division photodiode PD is formed in the concave portion 1a of the semiconductor substrate 1 formed at the surface of the optical semiconductor element 7 in the formation portion of the semiconductor laser LD, that is, at a position where the distance d from the upper surface of the semiconductor laser LD is at least 20 μm or more, for example, 100 μm. Is formed, the return light L from the triangular prism-shaped semiconductor structure 4 to the four-division photodiode PD is obtained.
_By increasing the propagation distance D of _R , the diffraction pattern of the return light L _R can be sufficiently separated.

When the return light L _R from the optical disk 2 is irradiated on the four-division photodiode PD,
An arithmetic operation is performed on a signal obtained from each of the photodiodes PD _{1 to} PD ₄ as described later to detect a tracking error signal and the like. Further, it is possible to perform the four-division across the photodiode PD ₁ -PD _4, the detection of the read namely RF (radio frequency) signal recorded on the optical disc 2.

Next, prior to the description of signal detection in the configuration of the optical device 10, a conventional tracking correction method (tracking servo) detection method will be described.

As a tracking servo method in an optical device such as an optical pickup, a push-pull method, a three-beam method, a heterodyne method, or the like is generally used.

In the conventional push-pull method, when the light spot of the incident light on the disk is displaced from the track or pit, an intensity difference occurs in ± first-order diffracted light generated by the disk. Since the far-field image is asymmetric, a signal corresponding to the asymmetry is extracted by, for example, two detectors, and these signals are calculated by a calculator to detect a shift of the light spot (FIG. 6). reference).

FIG. 6 is a schematic configuration diagram of a tracking servo using the push-pull method. As shown in FIG. 6B, when light is applied to the unevenness due to the pits on the surface of the disk 52, the light is diffracted by the unevenness and converted into 0th-order diffracted light (main beam B) and ± 1st-order diffracted light (sub-beam B '). Divided.
In FIG. 6, S ₀ and S ₁ are 0-order diffracted light, respectively.
Indicates the irradiation spot of ± 1st-order diffracted light. The circle of S ₀ is due to the aperture of the objective lens.

In this case, as shown in FIG. 6A, two divided photodiodes PD _R and PD _L are arranged and formed as light receiving portions. The signals received by the photodiodes PD _R and PD _L are processed by a differential amplifier or the like (not shown), for example, as (PD _L -PD _R ) to obtain a tracking error signal TE as a tracking signal. it can.

When the track and the beam are displaced, the center of the spot is displaced from the dividing line of the two-division photodiode, so that TE = (PD _L -PD _R ) does not become 0, and the position of the spot depends on the displaced direction. Indicates a positive or negative value. As a result, the direction and amount of deviation from the track can be detected.

The tracking servo using the push-pull method can be realized by using a two-part photodiode, and can be constructed at low cost. However, when the lens is shifted, the return light from the disk is received on the light receiving surface. There is a problem that the signal is shifted vertically with respect to the element dividing line, and a large offset occurs in the signal.

Here, as shown in FIG.
There Shifting laterally accordingly shifted as shown photodiode PD _L, even light spot PD _R is received by the dashed line, it will not become even match tracking is the tracking error signal TE = 0. FIG. 7B
As shown in (2), even when the lens 51 is tilted with respect to the disk 52, the spot of the received light shifts as shown by a broken line, and the tracking error signal TE does not become 0 even if the tracking is correct.

FIG. 4 shows the influence of the lens shift on the tracking error signal as described above in the case of the conventional push-pull signal. The vertical axis is represented by a relative value.
The disc has a groove pitch of 1.60 μm, a groove depth (depth) of / 8, and a duty (dut).
The calculation was performed assuming that the disc (y: groove ratio) was 65%. The wavelength was 0.78 μm.

As shown in FIG. 4, in the conventional push-pull signal, the entire tracking error signal is shifted by the shift of the lens.

In the push-pull method, when the wavelength of the reproducing laser is λ and the refractive index of the transparent substrate of the disk 52 is n, the pit depth of the disk 52 is λ / 4n.
In the case of, the signal becomes 0 due to the interference between the 0th-order diffracted light and the ± 1st-order diffracted light, so that a tracking error signal cannot be detected in principle. Therefore, the pit depth is λ /
4n cannot be used for the disc 52 of the standard.

As the tracking servo, there is another three-beam method as described above. In the three-beam method, light is split by a diffraction grating to form a main beam and two sub-beams on both sides thereof. As shown in FIG. 8, the spot position on the disk surface in the three-beam method is used. The spot S ₀ and the spots S ₁ and S _{2 formed} by the sub-beams on both sides of the spot S ₀ are irradiated onto the grooves or pits of the disk 52, the reflected light of the two sub-beams is detected, and the difference signal is obtained to perform the tracking servo. Is what you do.

Here, when the spot S ₀ of the main beam deviates from the center of the track, the light reflected by the spots S ₁ and S ₂ of the sub beam is not symmetrical, and the tracking error signal due to the difference signal fluctuates from zero. Since the amount of fluctuation of the tracking error signal changes in accordance with the amount of deviation of the spot S ₀ of the main beam from the track center, tracking servo can be performed. The reflected light of the main beam is used for detecting a disk recording signal.

In this case, it is possible to cope with the above-described lens shift, but since it is necessary to pass through a diffraction grating such as a grating, the number of parts increases, and the amount of light of the main beam decreases. It has disadvantages such as an increase in power, complicated adjustment, and a high manufacturing cost.

Other tracking servo methods include:
There is a heterodyne method. For example, as shown in FIG.
Photodiodes PD ₁ , PD ₂ , PD ₃ , PD divided into four parts in the tangential direction T, which is, for example, the pit row direction, of the optical disk as the irradiated portion and in the direction perpendicular to this direction T about the optical axis. Form ₄ . Then, return light from the optical disk is detected by the four-division photodiodes PD _{1 to} PD ₄ . In FIG. 10, the center circle corresponds to the pupil of the lens and corresponds to the spot of the 0th-order diffracted light.
The other eight circles correspond to spots of the first-order diffracted light. The dotted line in the center is an image corresponding to the pit P of the disk.

The four-division photodiodes PD _{1 to} PD
Signal processing is performed on the configuration of ₄ as follows. An RF signal (PD ₁₎ which is a sum of detection signals of the respective photodiodes
+ PD ₂ + PD ₃ + PD ₄ ) and a signal obtained by calculating a detection signal of each photodiode (for example, PD ₁ + PD ₃ −PD ₂₎
-PD ₄ ) is heterodyne detected in consideration of the phase. Equation 1 shows the contents of the operation signal at this time.

[0038]

Calculated signal = (PD ₁ + PD ₃ ) − (PD ₂ + PD ₄ ) = C sin (2πv _t / v _p ) sin (2πaωt / v _p ) where v _t : detrack amount v _p : pit train A: radius of reading position ω: angular velocity of optical disk C: constant (amplitude)

Here, C sin (2πv _t / v _p ) of Expression 1 is obtained.
Is the RF signal (PD ₁ + PD ₂ + PD ₃ + P
D ₄ ) is a signal obtained when the operation signal is subjected to heterodyne detection with reference to D ₄ ). Thus it is possible to obtain the de-track amount v _t from the signal obtained by heterodyne detection.

In this case, there is an advantage that the offset of the tracking error signal hardly occurs due to the lens shift, but on the other hand, there is a disadvantage that the signal processing becomes complicated.

On the other hand, in order to improve the above-mentioned drawbacks of the conventional optical device, it is possible to reduce the number of optical components and to simplify the alignment when setting the optical arrangement, and to simplify and reduce the size of the entire device. For the purpose, the above-mentioned CLC (Confocal Laser Coupler) configuration in which a light emitting unit is arranged at a confocal position of a converging means such as a lens and a light receiving unit is formed near a confocal position where the light emitting unit is located. I have.

In order to eliminate the offset of the tracking error signal due to the lens shift and the tilt of the disk, the present applicant has arranged the divided photodiodes forming the light receiving section at the confocal position, and An optical device for performing tracking servo using a push-pull method or the like by a split photodiode has been proposed (see Japanese Patent Application No. 7-35528, “Optical Device”).

According to such an optical device, since the tracking error signal is detected by the push-pull method (CPP method) using the light receiving portion near the confocal position, it is stable against lens offset and disk warpage. The detected tracking error signal can be detected, and alignment at the time of assembly is greatly simplified. Further, since the light emitting unit and the light receiving unit are formed on the same substrate, the number of components can be reduced, and the manufacturing cost can be reduced and the reliability can be improved.

However, the above-mentioned CPP method has a defect peculiar to a confocal optical system. In particular, when a defocus occurs instead of a just focus, it appears clearly.

FIG. 9 shows an example. FIG. 9 is an example of numerical calculation results showing the relationship between the tracking error signal and the detrack amount by the CPP method when defocus occurs. The disk was a model having the same shape as that used in the calculation of FIG.

From FIG. 9, it can be seen that an error occurs in the tracking error detection by the CPP method even when the focus direction does not change within the focus depth of ± 1 μm or less, or even when the focus direction shifts within the focus depth. In FIG. 9, a signal having a frequency different from the original tracking error signal (in the case of defocus = 0.00 μm indicated by the curve E), such as the case where the defocus indicated by the curve G = −0.50 μm, In addition, for example, a tracking error signal having a double frequency may be generated. In addition, the positive and negative of the signal may be reversed as shown by the curves H and I.

On the other hand, in the optical system of the optical disk, when recording and reproducing signals, it is necessary to control not only tracking but also focus. Normally, in focus control,
The defocus amount is suppressed to a level equal to or less than the focal depth of the objective lens by a method such as a spot size method, an astigmatism method, and a knife edge method. However, the defocus amount is
It is not always 0 μm. Therefore, when detecting a tracking error by the CPP method, it is necessary to use a correction method or a detection method in consideration of the influence of defocus.

The detection of a signal in the optical device 10 of this embodiment is performed, for example, as follows. The tracking error signal is a difference signal (aPD ₁ + bPD ₃ ) − (bPD ₂ +
aPD ₄ ) (where a and b are constants), and
F signal, that is, the sum signal (P
D ₁ + PD ₂ + PD ₃ + PD ₄ ) can be obtained by performing the above-described heterodyne detection using the reference as a reference.

[0049] The focus error signal by comparison of the side and far side closer to the triangular prism shape of the semiconductor structure 4, i.e. for example _{c (PD 2 + PD 3)} -d (PD 1 + PD 4)
(C and d are constants).

By performing signal detection in this manner,
Even if there is a slight defocus corresponding to the actual focus servo, it is possible to accurately detect the tracking error signal.

According to the above-described optical device, the following advantages are obtained by having characteristics in the detection of the CLC device and the tracking servo signal. (1) As in the case of the conventional ordinary heterodyne detection method, the tracking error signal becomes strong against lens shift. (2) Since there is no additional optical component for detecting the tracking error signal and the focus error signal, a simple optical system with a reduced number of components can be configured. Therefore, the assembly process and the adjustment process can be simplified. (3) Manufacturing cost can be reduced by reducing the number of parts and simplifying the process. (4) Since there is no additional optical component, optical loss is reduced and power consumption can be reduced. (5) a semiconductor laser, a photodetector,
Also, since the semiconductor structure has a triangular prism shape, there is little change with time after completion. (6) It is possible to reduce the size and weight, thereby improving the response speed. (7) Recording / reproducing of an optical recording medium having a higher linear velocity can be performed with substantially the same power consumption as the conventional one. (8) Since the device can be manufactured by a semiconductor batch process, it can be manufactured at low cost. (9) In the crystal growth of the semiconductor structure formed near the end face of the semiconductor laser LD, the growth is automatically stopped after growing a predetermined shape, so that the semiconductor structure can be formed as designed and the yield can be increased. Since it can be manufactured well, it can be manufactured inexpensively and with good reproducibility.

The optical device shown in FIG. 1 is manufactured, for example, as follows. First, as shown in FIG. 3A, a laminated semiconductor layer 11 constituting a semiconductor laser LD including a cladding layer, an active layer, and the like is formed on a semiconductor substrate 1.

Next, as shown in FIG. 3B, the laminated semiconductor layer 11 and a part of the semiconductor substrate 1 thereunder are etched off except for the portion where the semiconductor laser LD is formed.

Subsequently, as shown in FIG. 3C, the reflection surfaces M ₁ and M ₁ are formed near the emission end face of the semiconductor laser LD on the etched-off portion of the semiconductor substrate 1 by crystal growth of the semiconductor layer.
_A triangular prism-shaped semiconductor structure 4 made of 2 is formed.

Subsequently, as shown in FIG. 3D, a portion other than the portion where the triangular prism-shaped semiconductor structure 4 is formed on the surface of the semiconductor substrate 1 formed by etching off earlier is further dug down by etching to form the concave portion 1a. I do. Preferably,
As described above, the recess 1a is formed by digging down d = 20 to 30 μm from the bottom surface 4s of the triangular prism-shaped semiconductor structure 4. After that, although not shown, the four-divided photodiode PD (PD ₁
To PD ₄ ).

Thus, the optical device 10 shown in FIGS. 1 and 2 can be manufactured. Note that all of the above manufacturing steps are performed by a series of semiconductor wafer batch processes.

By manufacturing as described above, the return light L
It is possible to configure the optical device 10 in which the propagation distance D of _R is set so that the diffraction pattern is sufficiently separated.

The optical device of the present invention is not limited to the above-described example, and may take various other configurations without departing from the gist of the present invention.

[0059]

According to the above-described optical device according to the present invention,
Since the photodetector is formed in the concave portion of the semiconductor substrate formed at a required depth from the substrate surface of the semiconductor substrate in the portion where the semiconductor laser is formed, the convergence is applied to the photodetector by the reflection surface. The diffraction pattern of the return light from the means can be well separated and received by the photodetector. Thus, it is possible to eliminate the fluctuation of the tracking error signal caused by the defocus and perform the tracking servo more accurately. Further, the offset of the tracking error signal due to the lens shift can be greatly reduced as compared with the related art.

Since there is no additional optical component for detecting a tracking error signal, a simple optical system with a reduced number of components can be constructed. Therefore, the adjustment process can be simplified. As a result, the manufacturing cost of the optical device can be reduced, and the power loss can be reduced by reducing the loss of the light amount.

Further, according to the present invention, the optical device can be reduced in size and weight, and the response speed can be further improved. Therefore, according to the present invention, it is possible to record / reproduce an optical recording medium having a higher linear velocity with conventional power consumption.

Further, according to the present invention, a change with time after assembling the optical device can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram (perspective view) of an example of an optical device according to the present invention.

FIG. 2A is a side view of the optical device of FIG. 1; B FIG.
3 is a plan view of the optical device of FIG.

3A to 3D are manufacturing process diagrams of the optical device of FIG. 1;

FIG. 4 is a tracking error signal obtained by a conventional push-pull method.

FIG. 5 is a schematic configuration diagram of a conventional optical device.

6A and 6B are diagrams for explaining tracking servo by the push-pull method.

FIG. 7 is a diagram illustrating a problem in the push-pull method. FIG. 9 is a diagram illustrating an offset when the A lens shifts. It is a figure which shows the offset when B lens inclines.

FIG. 8 is a diagram illustrating tracking servo by the three-spot method.

FIG. 9 is a diagram showing a relationship between a tracking error signal by a CPP method and a defocus amount.

FIG. 10 is a diagram illustrating tracking servo by a heterodyne method.

[Explanation of symbols]

1 semiconductor substrate, 1a recess, 2 optical disc, 3 objective lens, a triangular prism-shaped semiconductor structure 4, 7 an optical semiconductor element, 10 an optical device, 11 laminated semiconductor layer, 51 a lens, 52 disk, L _F emitted light, L _R returning light , M
_1, M ₂ reflecting surfaces, LD laser, Tan T disc tangential direction, of the P disk pits, P
_{D, PD R, PD L,} PD 1, PD 2, PD 3, PD 4
Photodiode

Claims (3)

[Claims] A semiconductor section formed on a same semiconductor substrate, wherein the section to be irradiated, a semiconductor laser, a reflection surface for reflecting emitted light from the semiconductor laser, and a semiconductor laser; Converging means for converging and irradiating the reflected light reflected by the reflecting surface to the illuminated portion and further converging return light reflected from the illuminated portion; Formed near the focal plane,
The semiconductor substrate is formed by a predetermined crystal plane grown on the semiconductor substrate, and the semiconductor substrate is formed with a concave portion that recedes at a required depth from a substrate surface of the semiconductor substrate in a portion where the semiconductor laser is formed. The light detecting element is formed in the concave portion, and the reflecting surface is configured to irradiate a part of the return light from the converging means to the light detecting element, and the tracking servo signal is obtained by the light detecting element. An optical device, characterized in that: 2. The surface of the concave portion where the photodetector is formed,
The optical device according to claim 1, wherein the optical device is formed at a position recessed by about 20 μm to 100 μm from a substrate surface of the semiconductor substrate in a formation portion of the semiconductor laser. 3. The optical device according to claim 1, wherein the tracking servo signal is obtained by heterodyne detection.