JP3172355B2 - Optical pickup device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device using a reflection type hologram element.

[0002]

2. Description of the Related Art In recent years, research and development of an optical pickup device using a hologram element have been conducted in accordance with a demand for a small, lightweight and low-cost optical pickup device.

FIG . 7 is a Japanese Patent Application Laid-Open No. 3-76035 (G11B) .
FIG. 7/135) is a schematic configuration diagram of an optical pickup device having a hologram element that performs tracking servo using a three-beam method described in Japanese Unexamined Patent Application Publication No. 7-135).

In the figure, 101 is a disk as an optical recording medium, 102 is a semiconductor laser element for outputting a laser beam (laser light) upward, and 103 is a first hologram element for dividing the laser beam into three beams. (Transmission type three-division diffraction grating), 104 is a second hologram element that transmits the three beams and diffracts the return beam (reflected light) from the disk 101, and 105 is the second hologram element 104. The three transmitted beams are used for disc 101
An objective lens for forming three spots by condensing the light beam thereon is a servo detecting light detecting element 106 for detecting a return beam from the disk 101 diffracted by the second hologram element 104.

However, it has been difficult to reduce the thickness of this device. This is because the distance from the semiconductor laser element to the optical recording medium needs to be at least a certain amount in order to converge the laser beam on the optical recording medium.

To solve this problem, Japanese Patent Laid-Open No.
Japanese Patent Application Laid-Open No. 60931 (G11B 7/135) discloses an optical pickup device in which the direction of a laser beam output from a semiconductor laser element is changed to a right angle to reduce the thickness.

In the optical pickup device including the above example, the light output from the semiconductor laser device needs to be controlled to be constant. In the conventional device, the laser beam output from the rear end face of the semiconductor laser device is generally used for monitoring. The output is detected by a photodiode, and the output of the laser beam is controlled to be constant by operating an automatic output control circuit (hereinafter, referred to as an APC circuit) based on the output of the photodiode.

[0008]

However, in the above-described method for detecting a laser beam from the rear end face of the semiconductor laser device, it is necessary to extract a laser beam having a certain intensity or more from the rear end face, and the reflectivity of this rear end face is required. Can not be raised. Therefore, there is a problem that it is difficult to increase the output and the efficiency of the semiconductor laser device.

Further, according to this method, when the element is deteriorated due to long-time use or when the return beam from the optical recording medium is incident on the laser element, the light from the front end face for converging and irradiating the optical recording medium is emitted. Since the output change of the laser beam and the output change of the laser beam from the rear end face do not correspond to each other, the laser beam output from the front end face cannot be accurately and constantly controlled by detecting the laser beam output from the rear end face. In addition, there is also a problem that the S / N is reduced in the reproduction of the optical recording medium and the like.

In contrast to the method of monitoring the laser beam output from the rear end face, a method of monitoring the laser beam output from the front end face is also known. For example, a method is known in which a part of a laser beam is split using a beam splitter or the like, and the split beam is monitored. However, since such a method uses a beam splitter, the size of the apparatus cannot be reduced. There was a problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and directly detects a laser beam to be applied to an optical recording medium in order to control the output of the laser beam to be applied to the optical recording medium accurately and to a constant level. It is another object of the present invention to provide an optical pickup device using a reflective hologram element which can be reduced in size.

[0012]

An optical pickup device according to the present invention comprises: a semiconductor laser element for outputting a laser beam;
The face is disposed on the semiconductor laser element, an optical pickup device and a reflection type hologram element having a hologram surface for guiding the laser beam the reflected reflecting the laser beam to the optical recording medium, the reflection Type holog
The ram element is a laser beam from the semiconductor laser element.
Monitor the laser beam to keep the output of the laser constant
Having a monitor photodiode for monitoring
The ram surface is on the photodiode and the hollow
When part of the laser beam incident on the gram plane is
Reflects another part of the laser beam to the hologram
The surface of the surface is made of a conductive material,
It is also characterized by serving as an electrode for the gate .

[0013]

According to the structure of the present invention, since the reflection type hologram element has the monitor photodiode and the hologram surface, it is possible to use an optical element such as a beam splitter or the like to adjust the intensity of the laser beam irradiated on the optical recording medium. And the optical path from the semiconductor laser device to the optical recording medium is refracted by the hologram surface. Therefore, the output of the laser beam can be accurately and constantly controlled, and the size and thickness can be reduced.

In the case where the hologram surface is on a photodiode and transmits part of a laser beam incident on the hologram surface and reflects another part of the laser beam, a laser having a high light intensity is used. Since the light intensity at the center of the beam diameter can be detected, the detection output of the photodiode does not vary even if there is a difference in the beam intensity distribution based on the individual difference of each semiconductor laser element. Furthermore,
When the surface of the hologram surface is made of a conductive material and also serves as an electrode of a photodiode, the distance from the position where a photon is incident on the photodiode and electron-hole pairs are generated inside the photodiode to the electrode is reduced. Because they are short, the electrons and holes are less scattered (impedance is lower). Therefore, such a photodiode has a faster response than a photodiode in which an electrode is provided at the end of the light receiving surface. In addition, the area of ohmic contact between the photodiode and the electrode increases,
Low resistance reduces power consumption.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical pickup device according to a reference example serving as a basis of the present invention will be described in detail with reference to the drawings. Figure 1 is a book
Schematic diagram of an optical pickup device which performs tracking servo by using the three-beam method of Reference Example, 2 is a fragmentary schematic perspective view of the present reference example instrumentation <br/> location, FIG. 3 (a) present reference example FIG. 3B is a schematic cross-sectional view taken along a broken line AA in FIG. 3A, showing a reflection type hologram element (reflection type three-division diffraction grating) of the apparatus. Note that electrodes and bonding wires are not shown in FIGS.

1 and 2, reference numeral 1 denotes an optical recording medium composed of an optical disk such as a compact disk. 2 is n ⁺
A conductive semiconductor material such as silicon (Si) or a conductive metal such as copper, which is a good heat conductive base, which is formed by an upper plane 2a and an angle of 45 degrees with respect to the upper plane 2a. And an inclined portion 2b.

Reference numeral 3 denotes an n ⁺ as a conductive heat sink for mounting a semiconductor laser device (laser diode) die-bonded on the upper plane portion 2a and electrically connected to the substrate 2.
Type Si semiconductor substrate.

Reference numeral 4 denotes a semiconductor laser device having another electrode (not shown) on the upper surface which is die-bonded to an electrode (not shown) on one end surface of the semiconductor substrate 3 and is electrically connected to the substrate 3; The front end face is arranged so as to face the inclined portion 2b. The element 4 generates a laser beam in an active area (not shown) extending in parallel with the surface portion, and outputs a laser beam (laser light) for detecting an optical recording medium signal from the front end face side of the element 4.

Reference numeral 5 denotes a signal detecting light detecting element (such as a PIN type photodiode) for detecting a return beam (reflected light) returned from the optical recording medium 1 and performing tracking servo, focusing servo and reproduction. A signal detecting light detecting unit), which is die-bonded to an electrode side (not shown) on the upper flat surface 2a of the base 2 where a beam other than the return beam does not enter the detecting element 5 and is electrically connected to the substrate 2. I have.

As shown in FIG. 3, reference numeral 6 denotes the inclined portion 2b.
Is a reflection type hologram element (reflection type diffraction grating for three divisions). The element 6 includes a semiconductor substrate 7a made of n ⁺ -type Si and an n ^-- type Si formed on the substrate 7a.
Semiconductor layer 7b composed of:
Consists of On the central surface of the semiconductor layer 7b, equally spaced gratings (irregularities) provided on the surface, and a reflection film (not shown) made of gold or aluminum provided on the grating, preferably a total reflection film (Hologram surface for reflection-type three-division grating) 8 is provided. A semiconductor layer 9 made of p-type Si is selectively formed on the surface of the semiconductor layer 7b around the hologram surface 8 by diffusion, and the n ⁺ -type semiconductor substrate 7a and the n ⁻ -type semiconductor layer 7 are formed.
The PIN photodiode 10 for monitoring is constituted by the b and p-type semiconductor layers 9. 11a is a front electrode made of gold or the like of 0.3~2μm thick for the photodiode 10, the insulating made of 0.2 [mu] m SiO ₂ having a thickness formed on the periphery of the semiconductor layer 7b of the photodiode 10 It is formed over the film 12. Reference numeral 11b denotes a back-side electrode made of gold or the like having a thickness of 0.3 to 2 μm for the photodiode 10 formed on the back surface of the substrate 7a,
It is fixed to the inclined portion 2b via a conductive adhesive such as silver paste.

The laser beam output from the front end face of the semiconductor laser element 4 is incident on the reflection type hologram element 6 arranged opposite to the semiconductor laser element 4. Since the laser beam output from the semiconductor laser element has a distribution (in general, a Gaussian distribution intensity) in which the intensity of the divergence angle and the center of the diameter is high and the intensity is weaker toward the periphery,
A central portion of the laser beam having a large intensity is incident on at least the hologram surface 8 of the reflection hologram element 6, and a peripheral portion of the laser beam having a small intensity is incident on the photodiode 10.

The hologram surface 8 converts the incident laser beam at the center of the diameter into a 0th-order, ± 1st-order diffraction beam (hereinafter, the 0th-order beam is a main beam, the + 1st-order beam is a sub-beam X,
(A primary beam is referred to as a sub-beam Y) and is reflected upward.

On the other hand, the photodiode 10 photoelectrically converts the incident laser beam at the peripheral portion thereof, and the photoelectrically converted signal is sent to an APC driving circuit (not shown). The laser beam output from the surface is controlled to be constant.

Reference numeral 13 denotes a transmission type (light transmission type) hologram element provided above the reflection type hologram element 6. In this embodiment, a light transmission substrate made of glass or the like and a top surface formed on the substrate are formed. And a curve group in which the pitch of the grating is gradually changed. This element 13 is
Next, ± 1 order beams (main beam and sub beams X and Y) are transmitted (zero order diffraction), and these 0 order and ± 1 order return beams (primary and primary beams) reflected and returned from the optical recording medium 1 are returned. The beam and the sub-beams X and Y) are diffracted in the first order (or −1 order) and converged (condensed) on the light detecting portion of the light detecting element 5 located on the side of the reflective hologram element 6.

In the transmission type hologram element 13, the feedback beam diffracted by +1 order (or -1 order) by the element 13 converts its optical axis obliquely with respect to the optical axis of the incident beam. Light is condensed (astigmatism) so that the focal length is different between one direction orthogonal to the beam traveling direction and a direction orthogonal to the one direction. That is, the transmission hologram element 13 has the functions of a beam splitter, a converging lens, and a cylindrical lens.

A numeral 14 is provided above the transmission type hologram element 13 and transmits through the hologram element 13 (zero-order diffraction).
The 0-order and ± 1st-order beams (main beam and sub-beams X and Y) converge on the surface of the optical recording medium 1, and the main beam spot and the sub-beam spots X and Y on both sides of the main beam spot, respectively. This is an objective lens as a converging optical system for forming a beam spot Y. Here, the optical system of the optical pickup device is arranged so that the main spot scans the track to be reproduced, and the sub-spots X and Y scan both sides of the main spot slightly over the track. .

As shown in FIG. 2, the light detecting element 5 of the present embodiment has a light detecting section 5a divided into four parts at the center for performing a focusing servo using the astigmatism method, and both sides thereof. And a photodetector 5b for performing tracking servo using the three-beam method provided at the center of the hologram element 1 at the center of the four divided photodetectors 5a.
The primary beam diffracted by the first (or −1) order at 3 enters,
Similarly, the primary (or -1) light detectors 5b and 5b are respectively provided.
Next, a conventionally well-known configuration in which diffracted sub beams X and Y are incident. The detection signals of these detection units are sent to an arithmetic circuit (not shown), and a focus error (FE) signal, a tracking error (TE) signal, and a reproduction signal are calculated.

The reproduction, tracking servo, focusing servo, and the like in such an optical pickup device are performed as follows.

The laser beam output from the front end face side of the semiconductor laser element 4 is received by the photodiode 10 at the peripheral portion where the beam intensity is weak, and an APC (not shown) is performed based on a signal corresponding to the amount of received light. The laser beam is controlled to be constant by the circuit. On the other hand, a central portion having a high light intensity is divided into 0th-order and ± 1st-order diffracted beams (main beam and sub-beams X and Y) on the reflection hologram surface 8.
Reflected upward at right angles. The main beam and the sub beams X and Y reflected upward are incident from one of the transmission hologram elements 13. After that, the main beam and the sub-beams X and Y diffracted (transmitted) by the 0th order by the element 13 are converged (condensed) on the optical recording medium 1 by the objective lens 14 as the main beam spot and the sub-beam spots X and Y described above. ) Is done. Return beams (main beam and sub-beams X and Y) containing information signals from these main spots and sub-spots X and Y
After passing through the objective lens 14, is diffracted in the first order (or -1st order) by the transmission hologram element 13, the main beam is incident on the light detecting portion 5a of the light detecting element 5, and the sub beams X and Y are respectively The light is incident on the light detectors 5b and 5b. Then, the signal obtained by the photodetector 5 is subjected to arithmetic processing by the above-mentioned arithmetic circuit (not shown) to obtain a reproduced signal, an FE signal, and a TE signal. Based on the FE signal and the TE signal, the objective lens 14 is driven by a driving mechanism (not shown) to perform tracking servo and focusing servo.

In such an optical pickup device, the reflection type hologram element 6 is provided on the surface of the semiconductor substrate 7 for monitoring the laser beam in order to control the output of the laser beam from the semiconductor laser element 4 at a constant level. Since the diode 10 and the hologram surface 8 are formed, the laser beam on the side converging and irradiating the optical recording medium 1 can be directly detected without using an optical element such as a beam splitter. Thereby, the optical path from the semiconductor laser element 4 to the optical recording medium 1 is refracted. Therefore, the output of the laser beam can be accurately and constantly controlled, and the size and thickness can be reduced.

In particular, since the photodiode 10 is formed around the hologram surface 8, the peripheral portion where the laser beam intensity is weak can be detected by the photodiode 10, and the radial center of the laser beam having high light intensity can be detected. The portion is reflected by the hologram surface 8, and this strong reflected light can be converged on the optical recording medium 1. Therefore, the intensity of the laser beam on the side that converges and irradiates the optical recording medium 1 can be directly detected in a state where the reduction of the intensity of the laser beam to the optical recording medium 1 is suppressed (in a state where the S / N is good).

Further, since the return light from the optical recording medium 1 to the reflection type hologram element 6 does not enter the photodiode 10 even if it enters the hologram surface 8, the sensitivity of the photodiode 10 does not decrease due to the return light.

Further, since the semiconductor laser element 4 and the signal detecting light detecting element 5 are provided on the same upper plane portion 2a, wire bonding to these elements is easy.

Next, an optical pickup device according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a schematic configuration diagram of an optical pickup device capable of performing tracking servo by the three-beam method of the present embodiment, and FIG. 5 is a schematic cross-sectional view of a reflection type hologram element (reflection type three-division diffraction grating) of the device of the present embodiment. is there. The difference from the reference example is that the reflection hologram element has a hologram surface on the photodiode, and this hologram surface is a semi-reflective film (semi-transmissive film: a so-called half mirror film), and a part of the incident light. (A film that transmits light and partially reflects light), the same reference numerals are given to the same or corresponding parts as in the reference example, and description thereof will be omitted.

In FIG. 4, reference numeral 26 denotes a reflection type hologram element (reflection type diffraction grating for three divisions) fixed to the inclined portion 2b. As shown in FIG. 5, the element 26 includes a semiconductor substrate 27a made of n ⁺ -type Si and a semiconductor substrate 27 made of a semiconductor layer 27b made of n ^-- type Si formed on the substrate 27a. P-type S on the central surface
A semiconductor layer 29 made of i is selectively formed by diffusion, and a PIN photodiode 30 for monitoring is constituted by the n ⁺ type semiconductor substrate 27a, the n ⁻ type semiconductor layer 27b and the p type semiconductor layer 29. Numeral 28 denotes equally spaced gratings (apertures) 28a formed on the surface of the p-type semiconductor layer 29 constituting the photodiode 30 and a conductive material made of gold or the like having a thickness of 300 mm or less formed on the grating 28a. Semi-reflective film (conductive half mirror film) 2
8b (reflection type diffraction grating surface for three-division). The conductive semi-reflective film 28b also functions as a front electrode of the photodiode 30. Reference numeral 31 denotes a back electrode of the photodiode 30 made of gold or the like formed on the back surface of the substrate 27a.

In such an optical pickup device, at least the central portion of the laser beam output from the front end face side of the semiconductor laser element 4 where the light intensity is strong is partially transmitted through the reflection type hologram surface 28 and the photodiode 30 is transmitted. APC (not shown) based on a signal corresponding to the amount of received light.
The laser beam is controlled to be constant by the circuit, and another part is divided into a plurality of beams including the 0th-order and ± 1st-order diffracted beams (main beam and sub-beams X and Y) on the reflection type hologram surface 28. And is reflected upward at right angles. 0-order reflected in the upward, ± 1-order diffracted beam (main beam and sub-beams X, Y) so that functions similarly to the device of the reference example, the same tracking servo and reference examples, the focusing servo, and playback Is performed.

In this apparatus, since the hologram surface 28 is on the photodiode 30 and transmits a part of the laser beam incident on the hologram surface 28, the center of the diameter of the laser beam having high light intensity can be detected. Therefore, the semiconductor laser element has a difference in beam intensity distribution based on individual differences, and in the reference example using a weak peripheral portion, the detection signal intensity of the photodiode may vary depending on the semiconductor laser element. However, such a problem does not occur in the present embodiment.

The surface of the hologram surface 28 is made of a conductive material and also serves as an electrode of the photodiode 30. Accordingly, since the distance from the position where electron-hole pairs are generated inside the photodiode 30 by the incidence of photons to the photodiode 30 to the semi-reflective film 28b as the front electrode is short, the electrons and holes scatter. (Less impedance). Therefore,
Such a photodiode 30 has a faster response than a photodiode in which an electrode is provided at the end of the light receiving surface. In addition, the photodiode 30 and the semi-reflective film 28 as an electrode
Since the area of the ohmic contact with b is large, the resistance is low.

However, in the case of the present embodiment, since the return light from the optical recording medium 1 to the reflection type hologram element 26 is incident on the photodiode 30, the sensitivity of the photodiode is lower than in the case of the reference example .

Therefore, in the case of this embodiment, the response speed (frequency characteristic) of the APC drive circuit needs to be lower by about one digit than the response speed of the information detection circuit of the optical recording medium.
As described above, even if the response speed of the APC circuit is reduced as described above, the S / N and the like do not decrease so much.

Alternatively, since the returning light is obliquely incident on the photodiode 30, Au or the like is further applied on the semi-reflective film 28b on the unevenness except for the bottom surface of the unevenness, and this portion is entirely covered. It is necessary to prevent light from returning to the photodiode 30 by reflecting the light, that is, by forming a semi-reflective film on the bottom surface of the concave portion of the concave and convex portions and a total reflective film on the other concave and convex portions. is there.

Next, an optical pickup device according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 6 is a schematic configuration diagram of an optical pickup device capable of performing tracking servo by the three-beam method according to the present embodiment. Reference example and first
The same reference numerals are given to the same portions as those of the embodiment or corresponding portions, and the description is omitted.

In FIG. 6, reference numeral 33 denotes a transmission type hologram element (transmission type three-division diffraction grating) provided opposite to the front end face of the semiconductor laser element 4, and converts the laser beam output from the laser element 4 into a zero-order laser beam. , ± 1st-order diffracted beams (main beam and sub-beams X and Y).

Numeral 36 reflects the 0th-order and ± 1st-order diffracted beams, which are substantially perpendicular to the 0th-order, and the reflected 0th-order and ± 1st-order diffraction beams.
The next diffracted beam is condensed on the optical recording medium 1 via the objective lens 14 as a main beam spot and sub beam spots X and Y through the objective lens 14 as in the reference example and the first embodiment, and is returned from the optical recording medium 1. This is a reflection hologram element for diffracting the 0-order and ± 1st-order diffracted beams in the first order (or the -1st order) to enter the detection element 5.

[0045] The reflection hologram element 36 has the same configuration as the reflection type holographic optical element 6 or 26 shown in Reference Example or the first embodiment described above has the same effect as in Reference Example or the first embodiment. As described above, the reflection hologram element including the photodiode is not limited to the three-division diffraction grating.

In the above-mentioned reference examples and the respective embodiments, the reflection type hologram element comprising a semiconductor laser element for outputting a laser beam and a semiconductor substrate provided opposite to the semiconductor laser element and having a hologram surface for reflecting the laser beam is provided. A converging optical system that converges the laser beam from the hologram surface onto the optical recording medium, and a laser beam is applied to the surface of the semiconductor substrate in order to control the output of the laser beam from the semiconductor laser element to be constant. Since the monitoring photodiode and the hologram surface to be monitored are formed, the number of components of the optical pickup device having the reflection type hologram element is small, and the photodiode and the hologram surface are arranged with high precision by a conventionally known semiconductor technology or the like. it can.

[0047]

According to the present invention, since the reflection type hologram element has the monitoring photodiode and the hologram surface, the laser beam on the side of irradiating the optical recording medium is directly used without using an optical element such as a beam splitter. The optical path from the semiconductor laser element to the optical recording medium is refracted by the hologram surface while being detected. Therefore, the output of the laser beam that irradiates the optical recording medium can be accurately and constantly controlled, and the size and thickness can be reduced.

In the case where the hologram surface is on a photodiode and transmits a part of the laser beam incident on the hologram surface and reflects another part of the laser beam, a laser having a high light intensity is used. Since the light intensity at the center of the beam diameter can be detected, the detection output of the photodiode does not vary even if there is a difference in the beam intensity distribution based on the individual difference of each semiconductor laser element. Furthermore,
When the surface of the hologram surface is made of a conductive material and also serves as an electrode of a photodiode, the distance from the position where a photon is incident on the photodiode and electron-hole pairs are generated inside the photodiode to the electrode is reduced. Because they are short, the electrons and holes are less scattered (impedance is lower). Therefore, such a photodiode has a faster response than a photodiode in which an electrode is provided at the end of the light receiving surface. In addition, the area of ohmic contact between the photodiode and the electrode increases,
Low resistance reduces power consumption.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical pickup device according to a reference example of the present invention.

FIG. 2 is a schematic perspective view of a principal part of the reference example device.

FIG. 3 is a view showing a reflection type hologram element of the reference example device.

FIG. 4 is a schematic configuration diagram of an optical pickup device according to a first embodiment of the present invention.

FIG. 5 is a schematic sectional view showing a reflection type hologram element of the apparatus of the embodiment.

FIG. 6 is a schematic configuration diagram of an optical pickup device according to a second embodiment of the present invention.

FIG. 7 is a schematic configuration diagram of a conventional optical pickup device.
You.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 optical recording medium 4 semiconductor laser element 6 reflection hologram element 8 reflection hologram surface 10 monitoring photodiode 26 reflection hologram element 28 reflection hologram surface 36 reflection hologram element

Continuation of front page (72) Inventor Takao Yamaguchi 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-5-304313 (JP, A) JP-A-1- 253983 (JP, A) JP-A-4-89638 (JP, A) JP-A-5-342617 (JP, A) JP-A-5-243682 (JP, A) JP-A-1-175280 (JP, A) JP-A-1-270382 (JP, A) JP-A-5-327131 (JP, A) JP-A-3-124674 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 7/12-7/22 H01L 31/00-31/02 H01L 31 / 08,31 / 10 G02B 5 / 18,5 / 30,5 / 32

Claims (1)

(57) [Claims] 1. A reflection type hologram, comprising: a semiconductor laser device for outputting a laser beam; and a hologram surface arranged opposite to the semiconductor laser device, for reflecting the laser beam and guiding the reflected laser beam to an optical recording medium. An optical pickup device comprising:
The hologram element is a laser from the semiconductor laser element.
The laser beam is controlled to keep the beam output constant.
Having a monitoring photodiode for monitoring,
A hologram surface is on the photodiode, and
Part of the laser beam incident on the hologram surface is transmitted.
And reflects another part of the laser beam,
The surface of the gram surface is made of a conductive material,
An optical pickup device characterized by also serving as an electrode for an electrode .