JPH01237939A - Optical pickup device - Google Patents

Abstract

PURPOSE:To reduce the manufacturing cost by guiding in turn a laser beam emitted from a laser element on a semiconductor substrate to one pair of detectors formed in the substrate via a prism provided on the substrate. CONSTITUTION:The 1st and 2nd photo detectors 32 and 33 are disposed in the semiconductor substrate 31, and the semiconductor laser element 34 is soldered with pewter 35 on an upper surface 31a of the substrate 31. The upper surface except the section where the pewter 35 is disposed is covered with a protective film 41, and a semitransparent film 42 is provided to cover a corresponding section to the photo detector 32. A prism 36 is provided via an adhesive layer 43 of an epoxy resin. The laser light beam Li' emitted from the laser 34 is reflected by a semitransparent film reflecting surface 36a of the prism 36 and incident upon an optical disk, while a reflected laser beam Lr' from the disk is transmitted through the surface 36a. The beam Lr' is transmitted through the layer 43 and the films 42 and 41 to be incident upon the photo detector 32, and then reflected by an interface between the films 42 and 41 and also the upper surface 36c of the prism to be incident upon the photo detector 33.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A. Industrial field of application B. Outline of the invention C. Prior art D. Problem to be solved by the invention E. Means for solving the problem F. Effect G. Example H. Effect of the invention A. Field of industrial application. An optical pickup device that makes a light beam incident on an optical recording medium, receives a reflected laser beam from the optical recording medium, guides it to a photodetector, and obtains a reading output of information recorded on the optical recording medium from the photodetector. .

B. Summary of the Invention The present invention allows a laser beam to be incident on a recording medium such as an optical disk, receives the reflected laser beam from the recording medium and detects it with a photodetector, and detects the reflected laser beam from the photodetector in response to the reflected laser beam. In an optical pickup device that obtains a detection output, first and second photodetectors are formed on a semiconductor substrate, and a semiconductor laser element and a prism having a semi-transparent reflective surface are arranged on the semiconductor substrate. The semi-transparent reflective surface of the prism reflects the laser beam emitted from the semiconductor laser element toward the recording medium and transmits the laser beam from the recording medium. A protective film part and a light semi-transmissive film part are arranged between the part where the first photodetector is formed and the prism, and the laser beam enters the prism from the light semi-transmissive reflective surface and passes through the prism. The material and thickness of the beam are selected so that approximately 1/2 of the beam reaches the first photodetector and the other 1/2 is reflected inside the prism, and the semiconductor substrate The protective film part disposed between the prism and the part where the second photodetector is formed is reflected to the inside of the prism by the protective film part and the semi-transparent film part, and the light of the prism is Most of the other approximately 1/2 of the laser beam that was further reflected on the surface and transmitted through the prism is transferred to the second laser beam.
By selecting the material and thickness so as to reach the photodetector of the semiconductor substrate, the protective film part and the light semi-transparent film part provided on the semiconductor substrate can be used to simplify the cylindrical structure.
In addition, based on a configuration that is easy to manufacture, a laser beam from the recording medium side that is incident on the prism after passing through its semi-transparent reflective surface is applied to each of the first and second photodetectors. This allows for proper guidance.

C. Prior Art An optical disc player is equipped with an optical pickup device that makes a laser beam enter the optical disc and reads information recorded on the optical disc. Such an optical pickup device generates a laser beam, makes it incident on an extremely narrow recording track formed on an optical disk with an appropriate focusing state, and accurately follows the recording track, and furthermore, the laser beam is made to accurately track the recording track. It is necessary to accurately guide the reflected laser beam from the truck to the photodetector, and therefore various optical elements such as semiconductor laser elements, various lenses, optical beam splitters, mirrors or prisms, and photodetectors are required. are precisely arranged and constructed. Therefore, a typical optical pickup device requires a relatively large space for arranging the optical elements, and also tends to require troublesome adjustment work for each part.

In connection with this situation, as an improved optical pickup device that can eliminate the inconveniences associated with the above-mentioned optical pickup device, a photodetector is formed on a semiconductor substrate, and a laser beam is formed on the semiconductor substrate. A semiconductor laser device that emits a beam and a prism that guides the laser beam emitted by the semiconductor laser device toward an optical recording medium such as an optical disk and guides the reflected laser beam from the optical recording medium to a photodetector are arranged. The applicant of the present application has already proposed an integrated type optical pickup device constructed using the following methods (Japanese Patent Application No. 38576/1983).

Such an integrated optical pickup device has a configuration as shown in FIG. 4, for example. In this configuration, first and second photodetectors 12 and 13 are arranged and formed inside a semiconductor substrate 11, and a semiconductor laser element 14 is soldered and arranged on the semiconductor substrate 11. The surface of the semiconductor substrate 11 on which the semiconductor laser element 14 is disposed is covered with a protective film 15, and a prism is placed on the protective film 15 at a position above the first and second photodetectors 12 and 13. 16 are placed.

The surface of the prism 16 facing the semiconductor laser element 14 forms a semi-transmissive and reflective surface 16a that is inclined with respect to the surface of the semiconductor substrate 11 on which the semiconductor laser element 14 is disposed.

In such a situation, the laser beam Li emitted from the semiconductor laser element 14 is reflected by the semi-transparent reflection surface 16a of the prism 16, focused by the objective lens 17, and made to enter the recording track 18a of the optical disc 18. . Then, the reflected laser beam Lr from the recording track 18a of the optical disk 18 returns through the objective lens 17, passes through the semi-transparent reflective surface 16a of the prism 16, and enters the prism 16. A part of the reflected laser beam Lr that has entered the prism 16 reaches the first photodetector 12, and the other part reaches the prism 1.
6 and reaches the second photodetector 13. At that time, the reflected laser beam Lr is transmitted through the prism 1
It is set to have a convergence point on the optical path formed in the photodetector 6 from the first photodetector 12 to the second photodetector 13.

Therefore, detection output signals of the reflected laser beam Lr from the recording track 18a of the optical disk 18 are obtained from each of the first and second photodetectors 12 and 13, and based on these, an information read signal, a tracking signal, and a tracking signal are obtained. An error signal, focus error signal, etc. are formed.

FIG. 5 shows, for example, a configuration in which a focus error signal is generated. In such a configuration, the first photodetector 12 is formed by disposing a central photosensitive element 12a and both side photosensitive elements 12b and 12c sandwiching it in the same plane, and the second photodetector 13 is formed such that a central photosensitive element 13a and both side photosensitive elements 13b and 13c sandwiching the central photosensitive element 13a are arranged in the same plane. And the first and second
The photosensitive element 1 corresponds to the spot formed on each of the photodetectors 12 and 13 by the reflected laser beam Lr.
Detection outputs are obtained from each of photosensitive elements 2a-12c and 13a-13c, but the detection outputs from each of photosensitive elements 12b and 12c are added in an adder 20, and the added output from the adder 20 and the detection from the photosensitive element 12a are The output is subtracted by the subtracter 21, and the subtracted output Sa
is derived, and the detection outputs from each of the photosensitive elements 13b and 13c are added in the adder 22.
The addition output from 2 and the detection output from the photosensitive element 13a are subtracted in a subtracter 23, and a subtracted output sb is derived from the subtracter 23. Then, the subtraction output Sa and the subtraction output sb are further subtracted in the subtracter 24, and the subtraction output Sc is obtained from the subtracter 24.

The reflected laser beam Lr forming a spot on each of the first and second photodetectors 12 and 13 is a laser beam Lr that is incident on the recording track 18a of the optical disc 18.
When i is in just focus, prism 1
The laser beam Li has a convergence point at an intermediate position on the optical path from the first photodetector 12 to the second photodetector 13 formed in the laser beam 6, and the laser beam Li is in an over-focus state. When the prism 16 has a convergence point at a position closer to the first photodetector 12 than an intermediate position on the optical path from the first photodetector 12 to the second photodetector 13, and , when the laser beam Li is in an under-focus state, a second photodetector is detected from an intermediate position on the optical path formed in the prism 16 from the first photodetector 12 to the second photodetector 13. The focusing point is assumed to be at the position on the 13 side. Therefore, the spots on each of the first and second photodetectors 12 and 13 have the same dimensions when the laser beam Li is in the just focus state, and when the laser beam Li is in the over-focus state, In the focus state, the spot on the first photodetector 12 is smaller than in the just focus state, and the spot on the second photodetector 13 is larger than in the just focus state, and further, When the laser beam Li is under focus, the spot on the first photodetector 12 is larger than when it is in just focus, and the spot on second photodetector 13 is larger than when it is in just focus. becomes small.

Therefore, the above-mentioned subtraction outputs Sa and sb have level changes depending on the focus state of the laser beam Li on the recording track 18a of the optical disk 18, as shown by the dashed line and dashed line in FIG. 6, respectively. becomes. Thereby, as shown by the solid line in FIG. 6, the subtraction output Sc takes the level to zero when the laser beam Li is in the just-focus state on the recording track 18a of the first day of the optical disk, and reduces the level to over
In the focused state and in the under-focused state, levels with different polarities are taken symmetrically and are used as a focus error signal.

The optical pickup device shown in FIG. 4 described above has a detailed configuration as shown in FIG. 7, which is a partially enlarged view. That is, the protective film 15 provided on the semiconductor substrate Fill includes, for example, a first layer 15a formed of 5i02 (silicon oxide) and a layer of 5iJa formed thereon.
Second layer 15b formed of (silicon nitride)
The prism 1 is placed on the second layer 15b forming the protective film 15.
6 is fixed by an adhesive layer 25. For example, in the portion corresponding to the first photodetector 12 on the lower surface 16b of the prism 16 facing the protection IIU 15,
A multilayer light semi-transmissive film 26 having approximately 10 layers is formed by vacuum deposition.

Then, the reflected laser light beam Lr that has passed through the light semi-transmissive reflective surface 16a of the prism 16 and entered the prism 16 travels through the prism 16 and enters the multilayer light semi-transmissive film 26. As a result, a part of the light passes through the multilayer light semi-transparent film 26, and further passes through the adhesive layer 25 and the protective film 1.
5 and reaches the first photodetector 12, and another part is reflected to the inside of the prism 16 at the multilayer light semi-transparent film 26, and is reflected again at the upper surface 16c of the prism 16. The light is reflected inside the prism 16 and then passes through the adhesive layer 25 and the protective film 15 to reach the second photodetector 13. That is, in this case, the reflected laser beam L incident on the prism 16
Distribution of r to each of the first and second photodetectors 12 and 13 is performed by a multilayer light semi-transmissive film 26 provided on the lower surface 16b of the prism 16.

D Problems to be Solved by the Invention However, as described above, in the integrated optical pickup device in which the prism 16 whose lower surface 16b is provided with the multilayer light transmissive film 26 is used, the prism incorporated therein is 16, a step is involved in forming the multilayer light semi-transmissive film 26 by stacking the light semi-transparent film 26 on the prism 16 many times using, for example, a vacuum evaporation method. Prism 1 with
In addition, the protective film 15 is supposed to have a two-layer structure in which, for example, a layer of SiO2 and a layer of Sj3N are laminated;
It is difficult to make the film thickness uniform during the formation of layer No. 4, resulting in an inconvenience that the apparatus becomes expensive.

In view of the above, the present invention provides a semiconductor substrate with first and second
A photodetector is formed, and a semiconductor laser element and a prism having a semi-transmissive and reflective surface are arranged on the semiconductor substrate, and the semi-transmissive and reflective surface of the prism detects the light emitted from the semiconductor laser element. The laser beam is reflected toward a recording medium such as an optical disk so as to be incident on the recording medium, and the laser beam from the recording medium is transmitted to each of the first and second photodetectors. The laser beam is guided from the first and second photodetectors to obtain a detection output corresponding to the laser beam from the recording medium side. In addition to using a prism that can be obtained at a relatively low cost and having a structure that is easy to manufacture, the first laser beam from the recording medium side that has passed through the light semi-transmissive reflective surface and entered the prism. It is an object of the present invention to provide an optical pickup device that can properly distribute light to a second photodetector and a second photodetector.

E. Means for Solving the Problems In order to achieve the above-mentioned object, an optical pickup device according to the present invention includes a semiconductor laser element disposed on a semiconductor substrate, and first and second laser elements formed on the semiconductor substrate. a photodetector; a protective film portion disposed to cover a portion of the semiconductor substrate where at least the first and second photodetectors are formed;
a light semi-transparent film part disposed to cover a portion of the protective film part corresponding to the first photodetector; an adhesive layer part formed at least on the protective film part; and a light semi-transparent film part and the adhesive layer part formed on the protective film part. and a prism whose surface facing the semiconductor laser element is an optical transmissive reflective surface inclined at a predetermined angle with respect to the surface of the semiconductor substrate on which the semiconductor laser element is arranged. The transmissive/reflective surface reflects the laser beam emitted from the semiconductor laser element toward the recording medium side, and transmits the laser beam from the recording medium side. The film portion enters the prism through the light transmissive reflective surface, and allows approximately 1/2 of the laser beam that has passed through the prism to reach the first photodetector, and transmits approximately the other 1/2. The material and thickness of the material are determined so that most of the above-mentioned approximately 1/2 that passes through the prism is reflected to the inside of the prism, further reflected on the surface of the prism, and reaches the second photodetector. are selected and configured.

F effect In the optical pickup device according to the present invention having such a configuration, the laser beam emitted from the semiconductor laser element is reflected toward the recording medium at the semi-transparent reflecting surface of the prism, and is incident on the recording medium. I am forced to do it. Then, the reflected laser beam from the recording medium passes through the semi-transparent reflective surface of the prism and enters the prism. The reflected laser beam that has entered the prism passes through the prism and enters the protective film from the semi-transmissive film, and approximately half of the beam is reflected by the semi-transmissive film and the protective film. It is assumed that the light passes through the semi-transparent film part and the protective film part and reaches the first photodetector formed on the semiconductor substrate, and approximately the other half of the light passes through the semi-transparent film part and the protective film part. The light is reflected to the inside of the prism, further reflected within the prism, transmitted through the adhesive layer section and the protective film section, and reaches the second photodetector formed on the semiconductor substrate. and,
Detection outputs corresponding to the reflected laser light beams are obtained from the first and second photodetectors.

Therefore, the distribution of the reflected L/-the light beam incident into the prism to the first photodetector and the second photodetector is as follows:
A protective film section provided on the semiconductor substrate is utilized, and further,
This is carried out by using a light semi-transmissive film section disposed on the protective film section in correspondence with the first photodetector, and as a result,
It is not necessary to use an expensive prism or the like provided with a multilayer light transmissive film, or to form a two-layer protective film portion covering the semiconductor substrate, resulting in a significant reduction in manufacturing costs.

G. Embodiment FIG. 1 schematically shows an example of an optical pickup device according to the present invention. In this example, the recording medium is also an optical disc, and the relationship with the optical disc is as follows:
This is similar to the case of the optical pickup device shown in FIG. 4 described above.

In the example shown in FIG. 1, first and second photodetectors 32 and 33 are arranged inside a semiconductor substrate 31, and a semiconductor laser element 34 is soldered on the upper surface 31a of the semiconductor substrate 31. 35 is soldered and arranged. The upper surface 31a of the semiconductor substrate 31 is covered with a protective film 41 except for the portion where the tin solder 35 is disposed.

The protective film 41 has a substantially uniform thickness and a flat surface, and has a refractive index, for example, in order to protect the upper surface 31a of the semiconductor substrate 31 from erosion by other members. It is formed of SiO□ with a thickness of about 1.46, and its thickness is selected to be, for example, about 4,500. Further, on the upper surface of the protective film 41, a light semi-transmissive film 42 is disposed to cover a portion of the protective film 41 corresponding to the first photodetector 32. This light semi-transparent film 42
is formed of, for example, Si3N having a refractive index of approximately 2.10, and its thickness is selected to be, for example, approximately 4900 mm.

Furthermore, the first and second photodetectors 3 in the protective film 41
At a position above 2 and 33, the prism 36 has an adhesive layer formed of an epoxy resin adhesive having a refractive index of approximately 1.56 and covering the lubricant film 41 and the light semi-transparent film 42. 43. The surface of the prism 36 facing the semiconductor laser element 34 is inclined with respect to the upper surface 31a of the semiconductor substrate 31, and is provided with a first transmission reflection film to form a light semi-transmission reflection surface 36a. has been done.

In this way, the laser beam Li" emitted from the semiconductor laser element 34 is reflected by the semi-transparent reflective surface 36a of the prism 36, and the optical disc 1 shown in FIG.
The laser light beam Lr' reflected from the recording track of the optical disc is incident on the recording track of the optical disc arranged in the same manner as in 8, and the reflected laser light beam Lr' from the recording track of the optical disc passes through the light transmissive reflective surface 36a of the prism 36 and enters the prism 36. is assumed to be incident. The semiconductor laser element 34 then adjusts the wavelength of the generated laser beam LX° to, for example, 780°.
r+++++, and the reflected laser light beam Lr' that passes through the light transmissive reflection surface 36a of the prism 36 and enters the prism 36 is set to be, for example, S-polarized light.

The reflected laser beam Lr'' that entered the prism 36 passes through the prism 36 and exits from its lower surface 36b,
After passing through the adhesive layer 43, the light enters an optical path forming portion formed by the light semi-transmissive film 42 and the f/JM 41 above the first photodetector 32.

At this time, the incident angle θ1 of the reflected laser beam Lr' with respect to this optical path forming portion is set to approximately 17 to 27 degrees.

As mentioned above, it is formed by 5iOz and approximately 4500
A protective film 41 having a human thickness and a Si3N
4 and has a thickness of approximately 4,900 nm, the optical path forming portion is configured to form a light path forming portion with a light semi-transmissive film 42 formed by 4 and having a thickness of approximately 4,900 nm. , provides the relationship between the incident angle θ1 and the transmittance T as shown by the curve XI in FIG. Based on this relationship, with the incident angle θ1 set to approximately 17 to 27 degrees, the reflected laser beam 1 at the optical path forming portion described above,
r.

The transmittance T is approximately 50%.

Therefore, the reflected laser light beam Lr' incident on the optical path forming portion formed by the protective film 41 and the light semi-transparent film 42 is
Approximately 1/2 of the light passes through the optical path forming portion and reaches the first photodetector 32, and approximately 1/2 of the light is reflected at the optical path forming portion, passes through the adhesive layer 43, and forms the prism. 3
The light enters the inside of the cell again through the lower surface 36b of the cell. A portion of the reflected laser beam Lr', which is reduced to approximately 1/2 and enters the prism 36 from its lower surface 36b, travels through the prism 36 by being reflected at its upper surface 36c, and then exits from its lower surface 36b again. , passes through the adhesive layer 43 above the second photodetector 33 and enters the protective film 41 . At that time, the reflected laser light beam Lr to this protective film 41
The incident angle θ2 of a portion of ' is approximately 17 to 27 degrees.

As mentioned above, it is formed by 5i02 and approximately 4500
The protective film 41, which has a human thickness, has a wavelength of 7
Reflected laser beam Lr with S polarization of 80 nm
', the relationship between the incident angle θ2 and the transmittance T is provided as shown by the curve X2 in FIG. Based on this relationship, the incident angle θ2 is approximately 1.
In the case where the angle is set to 7 to 27 degrees, the reflected laser light beam Lr, which is approximately 1/2 of the angle at the protective film 41,
The transmittance T of a portion of " is approximately 80%.

Therefore, on the -L side of the second photodetector 33, the protection M4
Reflected laser beam L incident on x and reduced to approximately 1/2
Most of the part of r" passes through the protective film 41 and enters the second
The light reaches the photodetector 33 of .

In this way, in the example shown in FIG.
approximately 1/2 is distributed to each of the first and second photodetectors 32 and 33.
Detection outputs corresponding to the reflected laser beam Lr'' are obtained from each of the detection outputs 3 and 3, and an information read signal, a tracking error signal, a focus error signal, etc. are formed based on the detection outputs.

In this example as well, the anti-1 laser light beam Lr' is the first laser light beam formed in the prism 36 when the laser light beam Li' incident on the recording track of the optical disk is in the just focus state. It has a convergence point at an intermediate position on the optical path from the photodetector 32 to the second photodetector 33, and when the laser beam Li'' is in an over-focus state, it is formed in the prism 36. The laser light beam Li
is under focus, the prism 36
The convergence point is located at a position closer to the second photodetector 33 than an intermediate position on the optical path from the first photodetector 32 to the second photodetector 33 formed inside. Further, the first and second photodetectors 32 and 33 are formed similarly to the first and second photodetectors 12 and 13 shown in FIG. 5, respectively. Therefore, in this example as well,
A focus error signal is formed in the same manner as in the case of the optical pickup device shown in FIGS. 4 and 7 described above.

Effects of the Invention H As is clear from the above explanation, according to the optical pickup device of the present invention, the first and second photodetectors are formed on the semiconductor substrate, and the semiconductor L is formed on the semiconductor substrate.
Based on the configuration in which a nose element and a prism having a light semi-transmissive reflective surface are arranged, the light semi-transmissive reflective surface of the prism
The laser beam emitted from the semiconductor laser element is reflected toward the recording medium such as an optical disk so that it is incident on the recording medium, and the laser beam from the recording medium is transmitted to the first and second In order to obtain a detection output corresponding to the laser beam from the recording medium side from the first and second photodetectors, the reflected laser beam that has entered the prism is Appropriate distribution of the first photodetector and the second photodetector to each of the first photodetector and the second photodetector is achieved by utilizing a protective film portion formed on the semiconductor substrate, and further distributing the first photodetector to the first photodetector on the protective film portion. This can be done by using the light semi-transparent film part placed only in the corresponding position.
Therefore, it is possible to eliminate the need for an expensive prism or the like provided with a multilayer light transmissive film, and the formation of the film portion disposed on the semiconductor substrate is facilitated, resulting in a significant reduction in manufacturing costs. can.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of an optical pickup device according to the present invention, FIGS. 2 and 3 are characteristic diagrams for explaining the operation of the example shown in FIG. 1, and FIG. 4 is an integrated type A schematic configuration diagram showing the optical pickup device, FIG. 5 and FIG.
FIG. 7 is a partially enlarged view of the integrated optical pickup device shown in FIG. 4, which is used to explain focus error signal formation in the integrated optical pickup device shown in FIG. In the figure, 31 is a semiconductor substrate, 32 is a first photodetector, 33
34 is a second photodetector, 34 is a semiconductor laser element, 36 is a prism, 36a is a light transmissive reflective surface, 41 is a protective film, 42
4 is a light semi-transparent film, and 43 is an adhesive layer. Figure 4 Figure 5 Under/□ Just° □ Focus Focus Focus Focus Error Signal Figure 6 1゛1 Partially enlarged view of integrated optical pickup device Figure 7

Claims (1)

[Scope of Claims] A semiconductor laser element disposed on a semiconductor substrate, first and second photodetectors formed on the semiconductor substrate, and at least the first and second photodetectors on the semiconductor substrate. a protective film portion disposed to cover a portion where the container is formed; a light semi-transparent film portion disposed to cover a portion of the protective film portion corresponding to the first photodetector; and at least the protective film. an adhesive layer portion formed on the semiconductor substrate; and a surface disposed on the adhesive layer portion and the light semi-transmissive film portion and facing the semiconductor laser device is a surface of the semiconductor substrate on which the semiconductor laser device is disposed. The light semi-transmissive reflective surface is tilted at a predetermined angle with respect to the prism, and the semi-transparent reflective surface directs the laser beam emitted from the semiconductor laser element toward the recording medium side. The laser light beam from the recording medium side is transmitted through the prism, and the semi-transmissive film portion and the protective film portion transmit the semi-transmissive reflective surface to the prism. Approximately 1/2 of the laser beam that entered and passed through the prism
reaches the first photodetector, and the other approximately half of the laser beam is reflected to the inside of the prism, further reflected on the surface of the prism, and passed through the prism. The optical pickup device is characterized in that the material and thickness of the optical pickup device are selected so that most of the other approximately 1/2 of the laser beam obtained by the laser beam reaches the second photodetector.