JP2508485B2 - Optical pickup device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A Industrial field of use B Outline of the invention C Conventional technology D Problems to be solved by the invention E Means for solving the problem F Working G Example H Effect of the invention A Industrial field of use The present invention Emits a laser light beam to an optical recording medium, receives a reflected laser light beam from the optical recording medium, guides it to a photodetector, and obtains a read output of information recorded on the optical recording medium from the photodetector. The present invention relates to an optical pickup device.

B. Summary of the Invention The present invention makes a laser light beam incident on a recording medium such as an optical disk, receives a reflected laser light beam from the recording medium, detects it by a photodetector, and responds to the reflected laser light beam from the photodetector. In an optical pickup device for obtaining a detected output, a semiconductor substrate is provided with first and second photodetectors, and a semiconductor laser element and a prism having a semi-transmissive reflective surface are arranged on the semiconductor substrate. The light semi-transmissive reflecting surface of the prism reflects the laser light beam emitted from the semiconductor laser element to the recording medium side and transmits the laser light beam from the recording medium side. The protective film portion disposed between the portion where the first and second photodetectors are formed and the prism is incident on the prism from the light semi-transmissive reflection surface. The laser light beam transmitted through the prism Te,
Approximately 1/2 of the above is transmitted to the first photodetector, the other approximately 1/2 is reflected to the inside of the prism, and is further reflected on the surface of the prism and transmitted through the prism. By using a material and thickness selected so that most of the approximately 1/2 laser light beam reaches the second photodetector, the protective film portion provided on the semiconductor substrate is used. , The laser light beam from the recording medium side which is incident on the prism after passing through the light semi-transmissive reflecting surface is properly guided to each of the first and second photodetectors based on the simplified configuration. It was made possible.

C Conventional Technology An optical disc player is equipped with an optical pickup device which is adapted to make a laser light beam incident on an optical disc to read information recorded on the optical disc. Such an optical pickup device generates a laser light beam, makes it incident on an extremely narrow recording track formed on an optical disc with an appropriate focusing state, and accurately follows the recording track, and further records on the optical disc. It is required to accurately guide the reflected laser light beam from the track to the photodetector. Therefore, various optical elements such as a semiconductor laser device, various lenses, a light beam splitter, a mirror or prism, and a photodetector are precise. Arranged and configured. Therefore, a normal optical pickup device requires an optical element arrangement space having a relatively large volume, and also tends to require a troublesome adjustment work for each part.

In relation to such a situation, as an improved optical pickup device capable of eliminating the disadvantages associated with the optical pickup device as described above, a photodetector is formed on a semiconductor substrate, and a laser beam is formed on the semiconductor substrate. And a prism for guiding the laser light emitted by the semiconductor laser element to the optical recording medium side such as an optical disk and guiding the reflected laser light from the optical recording medium to the photodetector. An integrated optical pickup device has already been proposed by the present applicant (Japanese Patent Application No. 61-38576).

In such an integrated type optical pickup device, for example, a configuration as shown in FIG. 4 is adopted. In this configuration, the first and second photodetectors 12 and 13 are formed and formed inside the semiconductor substrate 11, and the semiconductor laser element 14 is soldered and arranged on the semiconductor substrate 11. Then, the surface of the semiconductor substrate 11 on which the semiconductor laser element 14 is arranged is covered with a protective film 15, and the prism is provided on the protective film 15 above the first and second photodetectors 12 and 13. 16 will be arranged. The prism 16 is such that the surface facing the semiconductor laser element 14 forms a light semi-transmissive reflection surface 16a that is inclined with respect to the surface of the semiconductor substrate 11 on which the semiconductor laser element 14 is arranged.

Under such a condition, the laser light beam Li emitted from the semiconductor laser device 14 is reflected by the semi-transmissive reflective surface 16 of the prism 16.
It is reflected by a, is focused by the objective lens 17, and is made incident on the recording track 18a of the optical disc 18. Then, the reflected laser light beam Lr from the recording track 18a of the optical disc 18 returns through the objective lens 17, and the prism 16
The light is transmitted through the light semi-transmissive reflective surface 16a and enters the prism 16. The reflected laser light beam Lr incident on the prism 16 is
It is assumed that a part thereof reaches the first photodetector 12 and another part thereof is reflected in the prism 16 and reaches the second photodetector 13. At that time, the reflected laser light beam Lr
Is set so as to have a focal point on the optical path formed in the prism 16 from the first photodetector 12 to the second photodetector 13.

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

FIG. 5 shows a structure in which, for example, a focus error signal is formed. In such a configuration, the first photodetector 12 includes the central photosensitive element 12a and the photosensitive elements 12b on both sides sandwiching the central photosensitive element 12a.
And 12c are formed in the same plane.
The photodetector 13 is formed by disposing the central photosensitive element 13a and the photosensitive elements 13b and 13c sandwiching the central photosensitive element 13a in the same plane. Then, the first and second photodetectors 12 and 13
According to the spot by the reflected laser light beam Lr formed on each of the, the detection output is obtained from each of the photosensitive elements 12a ~ 12c and 13a ~ 13c, the detection output from each of the photosensitive elements 12b and 12c. It is added in the adder 20, and the adder 20
The subtracted output Sa is derived from the subtractor 21 by subtracting the added output from the photosensitive element 12a and the detected output from the photosensitive element 12a, and the detected output from each of the photosensitive elements 13b and 13c is added by the adder 22. In the subtractor 23, the addition output from the adder 22 and the detection output from the photosensitive element 13a are subtracted, and the subtraction output Sb is derived from the subtractor 23. Then, the subtraction output Sa and the subtraction output Sb are further subtracted in the subtractor 24, and the subtraction output Sc is obtained from the subtractor 24.

The reflected laser light beam Lr that forms a spot on each of the first and second photodetectors 12 and 13 is a laser light beam Li that is incident on the recording track 18a of the optical disc 18 when it is in a just focus state. A focusing point is provided at an intermediate position on the optical path from the first photodetector 12 to the second photodetector 13 formed in the prism 16, and the laser light beam Li is in an over-focus state. At some point, a focusing point is provided 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 formed in the prism 16, Further, when the laser light beam Li is in the under-focus state, the second position from the intermediate position on the optical path formed in the prism 16 from the first photodetector 12 to the second photodetector 13 is reached.
It has a focusing point at the position on the photodetector 13 side.
Therefore, when the spot and the laser light beam Li in each of the first and second photodetectors 12 and 13 are in the just focus state, they have the same size and the laser light beam Li is over-focused. In this state, the spot on the first photodetector 12 becomes smaller than in the just focus state, and the second photodetector
The spot at 13 is larger than that in the just-focused state, and when the laser light beam Li is in the under-focused state, the spot at the first photodetector 12 is larger than that in the just-focused state, and The spot on the second photodetector 13 is smaller than that in the just focus state.

Therefore, the subtraction outputs Sa and Sb described above each have a level change according to the focus state of the laser light beam Li on the recording track 18a of the optical disc 18, as indicated by the alternate long and short dash line and the broken line in FIG. Becomes
As a result, the subtraction output Sc has its level set to zero when the laser light beam Li is in the just focus state on the recording track 18a of the optical disc 18, as shown by the solid line in FIG. The level at which the polarities are different is symmetrical between a certain state and an under-focus state,
It is 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 thereof. That is, the protective film 15 provided on the semiconductor substrate 11 is, for example, the first layer 15 formed of SiO _2.
It has a two-layer structure consisting of a and a second layer 15b formed of Si ₃ N ₄ on the second layer 15b. The prism 16 is formed on the second layer 15b forming the protective film 15. Are fixed by the adhesive layer 25. Then, the protective film 15 of the prism 16
In the portion corresponding to the first photodetector 12 on the lower surface 16b facing the, for example, a multilayer light semi-transmissive film having about 10 layers is provided.
26 is formed by a vacuum evaporation method.

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 in the prism 16 and enters the multilayer light semi-transmissive film 26, and the multilayer light semi-transmissive film 26. Thus, a part thereof is transmitted through the multilayer light semi-transmissive film 26, further is transmitted through the adhesive layer 25 and the protective film 15 to reach the first photodetector 12, and the other part is multilayered. The light semi-transmissive film 26 is reflected to the inner side of the prism 16, and is further reflected to the inner side of the prism 16 again on the upper surface 16c of the prism 16, and then is transmitted through the adhesive layer 25 and the protective film 15 to form a second film. It is supposed to reach the photodetector 13. That is, in this case, the distribution of the reflected laser light beam Lr entering the prism 16 to each of the first and second photodetectors 12 and 13 is such that the multi-layered semi-transmissive film provided on the lower surface 16b of the prism 16 is provided. It is done by 26.

D. Problems to be Solved by the Invention However, as described above, in the integrated optical pickup device in which the prism 16 having the lower surface 16b provided with the multilayer light semi-transmissive film 26 is used, the prism 16 incorporated therein is In the production, with respect to the prism 16, for example, a step of forming a multi-layered light transmissive film 26 by stacking a plurality of light semi-transmissive films by a vacuum vapor deposition method is involved, and therefore,
The manufacturing cost of the prism 16 having the multilayer light semi-transmissive film 26 is significantly increased, and there is a disadvantage that the device becomes expensive.

In view of such a point, the present invention is configured such that first and second photodetectors are formed on a semiconductor substrate, and a semiconductor laser element and a prism having a light semi-transmissive reflection surface are arranged on the semiconductor substrate. The semi-transmissive reflective surface of the prism reflects the laser light beam emitted from the semiconductor laser element toward the recording medium side such as an optical disk and makes it enter the recording medium. The light beam is transmitted and guided to each of the first and second photodetectors, and the detection output corresponding to the laser light beam from the recording medium side is obtained from the photodetector. Of a laser light beam from the side of the recording medium that is transmitted through the light semi-transmissive reflective surface and enters the prism by using a prism that is relatively inexpensive and does not require the provision of a multi-layer light semi-transmissive film. First To perform beauty the distribution of the second to the respective optical detectors properly and to provide an optical pickup device capable.

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 arranged on a semiconductor substrate, and first and second semiconductor laser elements formed on the semiconductor substrate. Of the photodetector, a protective film portion arranged to cover at least a portion of the semiconductor substrate on which the first and second photodetectors are formed, and a surface disposed on the protective film portion and facing the semiconductor laser element. Is provided with a prism which is a light semi-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, and the light semi-transmissive reflective surface is
It is supposed that the laser light beam emitted from the semiconductor laser element is reflected to the recording medium side and at the same time transmits the laser light beam from the recording medium side. Incident through
Approximately 1/2 of the laser light beam that has passed through the prism is made to reach the first photodetector, and the other approximately 1/2 is reflected to the inside of the prism and further reflected on the surface of the prism. The material and the thickness thereof are selected so that most of the other half of the above laser light beam passing through the prism can reach the second photodetector.

In the optical pickup device according to the present invention having such a configuration, the laser light beam emitted from the semiconductor laser element is reflected toward the recording medium side by the light semi-transmissive reflection surface of the prism, and is reflected on the recording medium. It is made incident.
Then, the reflected laser light beam from the recording medium passes through the light semi-transmissive reflecting surface of the prism and enters the prism.
The reflected laser light beam that has entered the prism passes through the prism and then enters the protective film portion.
Half of the light is transmitted through the protective film, and the first is formed on the semiconductor substrate.
Of the second film formed on the semiconductor substrate by being reflected to the inside of the prism in the protective film portion and further reflected in the prism. It is supposed to reach the photodetector. Then, the detection output corresponding to the reflected laser light beam is obtained from each of the first and second photodetectors.

Therefore, the distribution of the reflected laser light beam incident into the prism to each of the first photodetector and the second photodetector is:
Since the protection film portion provided on the semiconductor substrate is used for this purpose, an expensive prism or the like provided with the multilayer light semi-transmissive film is not required, and the manufacturing cost is significantly reduced.

G Example FIG. 1 schematically shows an example of an optical pickup device according to the present invention. Also in this example, the recording medium is selected, for example, an optical disc, and the relationship with the optical disc is similar to that 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 formed in an array inside a semiconductor substrate 31, and a semiconductor laser element 34 is tin-soldered on a top surface 31a of the semiconductor substrate 31. Are soldered and arranged by. And
The upper surface 31a of the semiconductor substrate 31 is covered with the first protective film 41 except for the portion where the tin solder 35 is arranged and the portion where the second photodetector 33 is formed, and further, the first protective film. A portion of the upper surface 31a of the semiconductor substrate 31 on which the second photodetector 33 is formed is covered with a second protective film 42. The first protective film 41 and the second protective film 42 are both
It has a substantially uniform thickness and forms a flat surface, and the protective film portion 44 is formed on both surfaces. Then, the first protective film 41 is formed of, for example, SiO ₂ having a refractive index of about 1.46, and the thickness thereof is selected to be, for example, about 1000Å, and the second protective film 42 is, for example, Abbreviated refractive index
It is formed of Si ₃ N ₄ having a thickness of 2.0, and its thickness is selected to be, for example, approximately 3500Å.

Further, a prism 36 is fixed via an adhesive layer 43 at a position above the first and second photodetectors 32 and 33 in the second protective film 42. The surface of the prism 36 facing the semiconductor laser element 34 is the upper surface 31a of the semiconductor substrate 31.
The light semi-transmissive reflective film is provided to form a light semi-transmissive reflective surface 36a.

Under such a condition, the laser light beam Li ′ emitted from the semiconductor laser device 34 is reflected by the semi-transmissive reflective surface of the prism 36.
The reflected laser light beam Lr ′ reflected by 36a is incident on a recording track of an optical disk arranged similarly to the optical disk 18 shown in FIG. Transmission / reflection surface
It is assumed that the light passes through 36a and enters the prism 36.
The semiconductor laser element 34 is configured such that the wavelength of the generated laser light beam Li ′ is set to, for example, 780 nm, and is transmitted through the light semi-transmissive reflective surface 36a of the prism 36 to enter the prism 36. The laser light beam Lr ′ is, for example,
It is set to be S-polarized.

The reflected laser light beam Lr ′ incident on the prism 36 is
After passing through the prism 36, exiting from the lower surface 36b thereof, passing through the adhesive layer 43, protection formed by the first protective film 41 and the second protective film 42 above the first photodetector 32. Membrane
It is incident on 44. At that time, the incident angle θ ₁ of the reflected laser light beam Lr ′ with respect to the protective film portion 44 is set to be, for example, approximately 40 degrees.

As described above, the first protective film 41 formed of SiO ₂ and having a thickness of about 1000Å and the second protective film 41 formed of Si ₃ N ₄ and having a thickness of about 3500Å. The protective film portion 44 including the protective film 42 has a wavelength of 780n.
For the reflected laser light beam Lr 'which is S-polarized to be m, it provides the relationship between the incident angle θ ₁ and the transmittance T as shown by the curve X _{1 in} FIG. From this relationship, the transmittance T of the reflected laser light beam Lr ′ at the protective film portion 44 is about 50% when the incident angle θ ₁ is set to about 40 degrees.

Therefore, the reflected laser light beam L incident on the protective film portion 44
About r ', about 1/2 of the light passes through the protective film portion 44 and reaches the first photodetector 32, and the other about 1/2 is reflected by the protective film portion 44, and the adhesive layer 43. Through the lower surface 36 of the prism 36
It re-enters the inside from b. The lower surface 3 of the prism 36
Reflected laser light beam L that is halved from 6b
A part of r ′ travels inside the prism 36 by being reflected on the upper surface 36c thereof, then again exits from the lower surface 36b thereof, passes through the adhesive layer 43, and then goes above the second photodetector 33. It is incident on the second protective film 42. At this time, the incident angle θ ₂ of a part of the reflected laser light beam Lr ′ with respect to the second protective film 42 is approximately
It will be 40 degrees.

As described above, the second protective film 42 formed of Si ₃ N ₄ and having a thickness of approximately 3500Å has a wavelength of 78
For the S-polarized reflected laser light beam Lr ′ of 0 nm, the relationship between the incident angle θ ₂ and the transmittance T as shown by the curve X _{2 in} FIG. 3 is provided. From such a relationship, under the condition that the incident angle θ ₂ is set to about 40 degrees, a part of the reflected laser light beam Lr ′ which is about halved in the second protective film 42 is partially emitted. The transmittance T is about 95%.

Therefore, a large part of the reflected laser light beam Lr ′ that has been incident on the second protective film 42 and has been halved is transmitted through the second protective film 42 and the second photodetector 33. Will be reached. Thus, in the example shown in FIG.
The reflected laser light beam Lr ′ that has entered the prism 36 is applied to the first photodetector 32 and the second photodetector 33 by the first protective film 41 and the second protective film 42, respectively. / 2, so that the detection output corresponding to the reflected laser light beam Lr 'is obtained from each of the first and second photodetectors 32 and 33, and the information read signal, A tracking error signal, a focus error signal, etc. are formed.

Note that, also in such an example, the reflected laser light beam Lr ′
On the optical path from the first photodetector 32 to the second photodetector 33 formed in the prism 36 when the laser light beam Li ′ incident on the recording track of the optical disc is in the just focus state. The first point is formed in the prism 36 when the laser light beam Li ′ is in the over-focus state and has a focal point at the intermediate position.
Has a focusing point at a position closer to the first photodetector 32 than the intermediate position on the optical path from the photodetector 32 to the second photodetector 33, and the laser light beam Li 'is in an under-focus state. In which the focal point is located at a position closer to the second photodetector 33 than the intermediate position on the optical path from the first photodetector 32 to the second photodetector 33 formed in the prism 36. It is said that In addition, the first and second photodetectors 32 and 33
Are the first and second photodetectors 12 shown in FIG. 5, respectively.
And 13 are formed. Therefore, also in this example, 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.

H Effects of the Invention As is apparent from the above description, according to the optical pickup device of the present invention, the first and second photodetectors are formed on the semiconductor substrate, and the semiconductor laser element and the optical detector are formed on the semiconductor substrate. Based on a configuration in which a prism having a semi-transmissive reflection surface and a light-transmissive reflection surface of the prism are arranged,
The laser light beam emitted from the semiconductor laser device is reflected to the recording medium side such as an optical disk so as to be incident on the recording medium, and the laser light beam from the recording medium side is transmitted to the first and second sides. Of the reflected laser light beam incident on the prism in obtaining the detection output according to the laser light beam from the recording medium side from the first and second photodetectors. Appropriate distribution to each of the first photodetector and the second photodetector can be performed by using the protective film portion provided on the semiconductor substrate. Therefore, the multilayer light semi-transmissive film is provided. It is possible to dispense with an expensive prism and the like, and it is possible to significantly reduce the manufacturing cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of an optical pickup device according to the present invention, FIGS. 2 and 3 are characteristic diagrams used to explain the operation of the example shown in FIG. 1, and FIG. FIG. 5 and FIG. 6 are schematic structural views showing an optical pickup device.
FIG. 7 is a diagram for explaining formation of a focus error signal in the integrated optical pickup device shown in FIG. 7, and FIG. 7 is a partially enlarged view of the integrated optical pickup device shown in FIG. In the figure, 31 is a semiconductor substrate, 32 is a first photodetector, and 33 is a second photodetector.
Photodetector, 34 is a semiconductor laser device, 36 is a prism, 36
a is a light semi-transmissive reflective surface, 41 is a first protective film, 42 is a second protective film, and 44 is a protective film portion.

Claims (1)

(57) [Claims] 1. A semiconductor laser device arranged 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 arranged to cover the portion where the is formed, and a surface that is arranged on the protective film portion and that opposes the semiconductor laser element, with respect to the surface of the semiconductor substrate on which the semiconductor laser element is arranged. And a prism formed as a light semi-transmissive reflective surface tilted at a predetermined angle, the light semi-transmissive reflective surface directs the laser light beam emitted from the semiconductor laser element to the recording medium side. It is assumed that the laser light beam from the recording medium side is transmitted while being reflected, and the protective film portion is incident on the prism through the light semi-transmissive reflection surface and then passes through the prism. About 1/2 of the laser light beam is made to reach the first photodetector, and at the other about 1 /
2 is reflected to the inside of the prism, and is reflected by the surface portion of the prism further, and the other approximately 1/2 of most of the laser light beam that has passed through the prism is detected by the second light detection. An optical pickup device characterized in that its material and thickness are selected so as to reach the container.