JPH07212310A - Optical detector - Google Patents

Abstract

PURPOSE:To share a detection optical system with a discharge optical system and to make positioning easy by unnecessitating a deflection means separating a discharge system and a detection system, drastically reducing the influence of return light from a reflector to a semiconductor laser. CONSTITUTION:On the optical path between a semiconductor laser 21 and a reflector 24 reflecting laser light emitted from this semiconductor laser 21, an optical axis shift optical element 26 shifting optical axes 23 and 34 depending on a polarization direction and a polarization control optical element 27 controlling the polarization direction of light are arranged. Further, in the vicinity of the semiconductor laser 21, an optical detector 29 receiving light which is reflected from the reflector 24 and transmits a polarization control optical element 27 and an optical axis shift optical element 26 is arranged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodetector applicable to an optical transmission device, an optical measuring instrument and the like in optical communication including an optical disc pickup.

[0002]

2. Description of the Related Art Generally, when a laser beam emitted from a semiconductor laser is reflected by a reflector on the same optical axis (beam center) as the incident beam, the laser beam is reflected by the same optical system for the incident beam and the reflected beam. The light returns again to the position where the laser light was emitted to the semiconductor laser. This is what is generally called "return light to the semiconductor laser" in optical disk devices, optical communications, and the like. The presence of such returning light is not preferable because it changes the oscillation state of the semiconductor laser and causes a change in the laser power, wavelength, mode, or the like.

For example, description will be made with reference to FIG. 12 showing an example of an optical pickup optical system for detecting the reflectance of pits of an optical disk. First, the beam 3 of laser light emitted from the emission position 2 of the semiconductor laser 1 is converted into parallel light by the collimator lens 4 and then straightly transmitted through the non-polarizing beam splitter 5 (the amount of transmitted light is half). By being condensed by the objective lens 6, a spot is formed on the recording surface of the optical disk 7 and reflected. At this time, if the spot image forming position is the focus position of the objective lens 6, it can be considered that the irradiated laser light is reflected by the diffraction surface in the same direction.
This reflected light becomes parallel light by passing through the objective lens 6 again, and is reflected by the non-polarizing beam splitter 5 in different directions by 90 ° (the amount of reflected light is half), becomes a beam 8 for detection, and a condenser lens 9 A spot is connected to the detection position 11 of the photodetector 10 after the light is condensed by and is converted into an electric signal. That is, the optical axis 12 of the beam 3 going to the optical disk 7 and the optical axis 13 of the beam 8 returning to the photodetector 10 reflected by the optical disk 7 are deflected by 90 °. .

In the case of such a configuration, the semiconductor laser 1 also has a light amount substantially the same as the light amount incident on the photodetector 10 as return light (about half of the reflected light is the unpolarized beam splitter 5). Through the straight), the return light is large.

In such an optical pickup optical system, the beam splitter is used to deflect the laser beam because the photodetector 10 cannot be arranged at the laser beam emission position 2 of the semiconductor laser 1. Therefore, focus information, track information, pit information, and the like are obtained based on the incident light and the light that is separated and deflected by the beam splitter.

For this reason, conventionally, some measures have been taken to reduce the light returning to the semiconductor laser. For example, in optical communication, there is an example using an optical isolator in which a Faraday rotator and two polarizers are combined. In addition, some optical disk pickups have a combination of a polarization beam splitter and a quarter-wave plate so as to reduce the return light (for example, refer to "Disc System", Applied Physics Society of Japan Kai, edited by Asakura Shoten, 1989, pp. 37-39, “3. Optical System Design Theory”).

[0007]

However, as a measure to reduce such return light, an optical system from a semiconductor laser to a reflector such as an optical disk using a polarization beam splitter and the like, and optical detection from this reflector. It is necessary to configure the optical system up to the detector differently (the same applies to the configuration of FIG. 12), which is complicated and requires high-precision positioning of the photodetector. It is also necessary to use an expensive polarization beam splitter.

As described above, according to the present invention, the influence of the returning light from the reflector to the semiconductor laser can be greatly reduced, the position of the photodetector can be easily adjusted, and the entire detection optical system can be easily constructed. The purpose is to obtain a photodetector capable of

[0009]

According to another aspect of the present invention, there is provided a semiconductor laser, a reflector for reflecting laser light emitted from the semiconductor laser, and an optical path between the semiconductor laser and the reflector. And an optical axis shift optical element that shifts the optical axis depending on the polarization direction, and is disposed on the optical path between the optical axis shift optical element and the reflector to control the polarization direction of light. And a photodetector which is arranged near the semiconductor laser and receives light reflected by the reflector and transmitted through the polarization control optical element and the optical axis shift optical element.

According to a second aspect of the present invention, the photodetector according to the first aspect of the present invention is an optical integrated device in which light reflected from a reflector and transmitted through the polarization control optical element and the optical axis shift optical element is combined. The waveguide type photodetector is formed on the waveguide of the circuit.

According to the invention of claim 3, claim 1 or 2
With regard to the configuration of the invention described above, the emission position of the laser light of the semiconductor laser and the detection position of at least one or more photodetectors are arranged in a direction parallel to the substrate on which the semiconductor laser is mounted.

According to the invention of claim 4, claim 1 or 2
With regard to the configuration of the invention described above, the detection positions of at least two or more photodetectors are arranged at positions not including the emission position of the laser light of the semiconductor laser in a direction parallel to the substrate on which the semiconductor laser is mounted.

According to the invention of claim 5, claim 1 or 2
Regarding the configuration of the described invention, the semiconductor laser and the photodetector or the optical integrated circuit having the waveguide type photodetector are brought into close contact with each other and integrated.

According to the invention of claim 6, claim 1 or 2
Regarding the configuration of the described invention, a semiconductor laser and an optical integrated circuit having a photodetector or a waveguide type photodetector are manufactured on the same substrate.

According to the invention of claim 7, claim 1 or 2
In the structure of the invention described, the reflector is an optical disk,
A signal processing means for obtaining at least one of focus information, track information or pit information based on the detection output of the photodetector is provided.

According to an eighth aspect of the invention, in the configuration of the second aspect of the invention, a plurality of waveguide type photodetectors are provided,
A guided light separating / deflecting element is provided on the waveguide between the respective waveguide type photodetectors.

According to the invention of claim 9, claim 1 or 2
Regarding the configuration of the described invention, the polarization control optical element is a quarter wavelength plate.

According to a tenth aspect of the invention, in addition to the structure of the first or second aspect of the invention, a parallel plate is provided in front of the semiconductor laser or the photodetector.

The eleventh aspect of the present invention relates to the configuration of the first or second aspect of the invention, in which the optical axis shift optical element and the polarization control optical element are integrated.

[0020]

According to the invention of claim 1, an optical axis shift optical element for shifting the optical axis depending on the polarization direction and a polarization for controlling the polarization direction of the light are provided on the optical path between the semiconductor laser and the reflector. Since the control optical element is provided, it is possible to obtain the emitted light having different optical axes and the reflected light with almost no light amount loss by the shift in the common optical system, and dispose the photodetector near the semiconductor laser. In addition to having a simple optical system configuration, the return light to the semiconductor laser itself can be greatly reduced.

Particularly, in the invention described in claim 2, since the photodetector in the configuration of the invention described in claim 1 is a waveguide type photodetector formed on the waveguide of the optical integrated circuit, Light from the lateral direction with respect to the optical integrated circuit board having the waveguide type photodetector can be efficiently detected, and further, an optical integrated circuit using wavefront information in the direction parallel to the optical integrated circuit board is possible.

According to the third aspect of the present invention, the laser light emission position of the semiconductor laser and the detection position of the photodetector are arranged in a direction parallel to the substrate on which the semiconductor laser is mounted. It can be held in the same direction on the substrate for the semiconductor laser, and the alignment of the photodetector becomes easy.

In a fourth aspect of the present invention, the detection positions of the plurality of photodetectors are arranged in a position parallel to the substrate on which the semiconductor laser is mounted and at a position not including the laser light emission position of the semiconductor laser. Therefore, the photodetector can be held on the opposite surface of the substrate for the semiconductor laser, and the alignment of the photodetector becomes relatively easy.

In the fifth aspect of the invention, the semiconductor laser and the optical integrated circuit having the photodetector or the waveguide type photodetector are brought into close contact with each other so as to be integrated, so that the light emitting / receiving unit can be made compact. Can be configured.

According to the invention of claim 6, the semiconductor laser and the photodetector or the optical integrated circuit having the waveguide type photodetector are formed on the same substrate. Therefore, the semiconductor laser and the photodetector are provided. The photolithography method enables simple and highly accurate alignment.

According to the seventh aspect of the invention, since the reflector is an optical disk and the signal processing means for obtaining the focus information, the track information or the pit information based on the detection output of the photodetector is provided, the influence of the returning light is affected. Almost none, and
It is possible to provide an optical pickup having a high optical utilization efficiency and a simple optical system configuration.

In the eighth aspect of the present invention, since a plurality of waveguide type photodetectors are provided and a guided light separating / deflecting element is provided on the waveguide between the waveguide type photodetectors, a plurality of waveguide type photodetectors are provided. The waveguide-type photodetectors can be configured so that the effective spacing between them can be reduced, and the waveguide-type photodetectors can be easily manufactured.

In the invention described in claim 9, since the polarization control optical element is a quarter wavelength plate, it is simple and compact.
Since 90 ° rotation of the polarization direction can be realized at low cost, the size and cost of the entire detection optical system can be reduced.

According to the tenth aspect of the invention, since the parallel plate is provided in front of the semiconductor laser or the photodetector, the optical path lengths of the emitted light and the reflected light can be adjusted, and the detection of the photodetector can be performed. This makes it possible to easily change the characteristics of the laser light at the position.

In the eleventh aspect of the invention, since the optical axis shift optical element and the polarization control optical element are integrated, it is possible to facilitate position adjustment of these optical elements at the time of assembling, and at the same time, the detection optical element. The system can be further miniaturized.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIG. The present embodiment corresponds to the invention described in claim 1, and first of all, a reflector 24 is arranged oppositely on an optical axis 23 defined by a laser emission position 22 of a semiconductor laser 21. A collimator lens 25, a calcite 26, a Faraday rotator 27, and an objective lens 28 are provided in this order from the semiconductor laser 21 side on the optical path connecting the semiconductor laser 21 and the reflector 24. Further, in the vicinity of the semiconductor laser 21, a photodetector 29 for receiving and detecting the light reflected from the reflector 24 is arranged in parallel.

The collimator lens 25 converts the outgoing beam 30 emitted from the semiconductor laser 21 into parallel light, and the return beam 32 reflected from the reflection position 31 of the reflector 24 to the photodetector 29. The light is focused on the detection position 33. The calcite 26
Is an optical axis shift optical element, and the outgoing beam 30
The optical axis of the return beam 32 is shifted depending on the polarization direction of the light. The calcite 26 of this embodiment is
The crystal plane direction is set so as to be an ordinary ray with respect to the polarization direction of the outgoing beam 30. The Faraday rotator 27 serves as a polarization control optical element and rotates the polarization direction of transmitted light by 45 °. The objective lens 28 is for focusing the light spot emitted from the semiconductor laser 21 and passing through the collimator lens 25, the calcite 26 and the Faraday rotator 27, at the reflection position 31 of the reflector 24. The photodetector 29 is, for example, a photosensor such as a phototransistor.

In such a structure, the semiconductor laser 2
1. Beam 30 of laser light emitted from emission position 22
Is converted into parallel light by the collimator lens 25,
It is incident on the calcite 26. Since the calcite 26 is set to be an ordinary ray with respect to the beam 30 whose crystal direction is the going direction as described above, the beam 30 is the calcite 26.
Travels straight through and enters the Faraday rotator 27. The beam 30 has a polarization direction of 45 with the Faraday rotator 27.
The image is rotated by an angle of ° and is focused and imaged on the reflector 24 by the objective lens 28. The return beam 32 reflected at the reflection position 31 of the reflector 24 passes through the objective lens 28 and becomes a parallel beam again and enters the Faraday rotator 27.
By further rotating the Faraday rotator 27 by 45 ° in the same polarization direction, the Faraday rotator 27 is rotated.
The return beam 32 that passed through is 9
The polarization directions are different by 0 °. Therefore, the return beam 32 that enters the calcite 26 through the Faraday rotator 27 becomes an extraordinary ray, and the optical axis 34 of the return beam 32 after passing through the calcite 26 is the optical axis 23 of the going beam 30. It will be shifted in parallel. Thereafter, the beam 32 is focused by the collimating lens 25 and focused on the detection position 33 of the photodetector 29 disposed on the optical axis 34, and converted into an electric signal.

According to this embodiment, a calcite 26 having a different refractive index depending on the polarization direction of light is used on the optical path,
The polarization direction of the incoming beam 30 and the returning beam 32 is 9
Since the Faraday rotator 27 that rotates by 0 ° is provided, the same optical system that connects the semiconductor laser 21 side and the reflector 24 side is used, and two optical axes 2 that are deviated in parallel on the going and returning sides are provided.
Since the light beams 3 and 34 can be obtained, the return light from the reflector 24 does not enter the semiconductor laser 21, and the photodetectors 29 arranged in the vicinity of the semiconductor laser 21 are arranged.
All the returning beams 32 can be collected and used for detection, and detection with little optical loss becomes possible. That is, in the method using the conventional beam splitter, the return light component to the semiconductor laser side, which has been a loss for the detection system,
The light can be condensed on the photodetector 29, and the loss is small. In this case, the optical axis 23 of the beam 30 emitted from the semiconductor laser 21 and the detection position 33 of the photodetector 29.
Since the optical axis 34 of the return beam 32 focused on is parallel and the photodetector 29 is arranged in the vicinity of the semiconductor laser 21, the position adjustment and configuration of the optical system including the photodetector 29 can be performed. It will be easy.

In this embodiment, the calcite 26 is used as the optical axis shift optical element, but the invention is not limited to this, and an optical element having a birefringence index represented by rutile or the like may be used. Further, an optical element such as a diffraction grating or a hologram may be used. Further, regarding the calcite 26, by changing its crystal plane and thickness, the optical axes 23, 3
The positional relationship of 4 can be changed relatively freely.
Further, in this embodiment, the optical axis 34 of the returning beam 32 is shifted, but it is relative, and the optical axis 23 of the outgoing beam 30 is shifted, and the returning beam 32 is shifted.
May go straight.

Next, a second embodiment of the present invention will be described with reference to FIG. The same parts as those shown in the above-mentioned embodiments are designated by the same reference numerals (the same applies to the following embodiments).
This embodiment corresponds to the invention described in claim 2, and uses a waveguide type photodetector 35 instead of the photodetector 29 constituted by a single element such as a photosensor. The waveguide type photodetector 35 is formed as a part of an optical integrated circuit 37 having a waveguide 36. That is, the waveguide 36 is formed by the core region 39 surrounded by the cladding region 38, and the waveguide type photodetector 35 is formed at the boundary surface between these regions 38, 39. In such an optical integrated circuit 37, the end face of the core region 39 is set as the detection position 33 of the return beam 32 by the collimating lens 25, and the light can be guided by the end face coupling.

Here, the optical integrated circuits 37 are arranged side by side in the vicinity of the semiconductor laser 21 as in the case of the photodetector 29. In this embodiment, the substrate 40 for the semiconductor laser 21 is shared. It is mounted on the same surface.

In such a structure, the spot of the returning beam 32 condensed by the collimating lens 25 is adjusted in position on the end face of the core region 39, and this beam 32 is coupled into the waveguide 36 by the end face coupling to guide the guided light. Propagate as. This guided light is received by the waveguide photodetector 35 and converted into an electric signal.

Now, as a specific example, the collimator lens 25
Assuming that the numerical aperture NA = 0.3 is used and the wavelength of the laser light emitted from the semiconductor laser 21 is 0.78 μm, the diffraction-limited spot diameter is about 3 μm. When the thickness is about 2 μm, practically sufficient coupling efficiency is obtained (the coupling efficiency is further increased by further increasing the thickness of the core region 39).

Therefore, according to the present embodiment, in addition to the effects of the above-mentioned embodiment, the substrate 40 for the semiconductor laser 21 is used as the substrate of the optical integrated circuit 37 having the waveguide type photodetector 35 for position adjustment and the like. With a structure that facilitates, it is possible to detect efficiently.

In this embodiment, the waveguide structure is applied to the optical integrated circuit 37 having a three-dimensional structure, but the present invention is not limited to the three-dimensional structure, but can be similarly applied to the one having the slab type waveguide structure. In the case of this optical integrated circuit, the wavefront information of the laser light parallel to the substrate is used.

Next, a third embodiment of the present invention will be described with reference to FIG. This embodiment corresponds to the invention described in claim 3, and, for example, the optical integrated circuit 37 shown in the second embodiment.
3, the plurality of core regions 39a to 39d are provided, and the detection position defined by the end faces of the core regions 39a to 39d is the same as the emission position 22 of the semiconductor laser 21 on the substrate 40 for the semiconductor laser 21. It is arranged and formed in parallel with the substrate 40 so as to be aligned on a straight line. From another perspective, these core regions 39a-39
d is set to be aligned on the straight line in the shift direction of the optical axis 34. Here, a waveguide type photodetector (not shown) is individually provided for each of the core regions 39a to 39d.

According to such a configuration, in addition to the effect of the above-described embodiment, since the detection positions corresponding to the core regions 39a to 39d are on the same straight line as the emission position 22 of the semiconductor laser 21, the substrate 40 Since the height of
By designing the device manufactured on the substrate 40, the device can be easily set to a constant height (height of emission position and detection position), alignment can be easily performed, and the semiconductor laser 21 It is possible to hold a plurality of waveguide type photodetectors on the same substrate 40 in the same direction. Further, even when assembled, the substrate 4 common to the semiconductor laser 21 is used.
Since it can be held in the same direction on 0, the alignment can be easily performed by measuring the positional relationship with the semiconductor laser 21 by image recognition or the like. Also, these core regions 39a-39d (hence, in the direction perpendicular to the polarization direction of the return beam 32 reflected from the reflector 24 (hence,
Since the detection position or the waveguide type photodetector) is provided, the wavefront information of the light intensity in this direction can be detected by being divided by a plurality of waveguide type photodetectors.
As in the case of an optical pickup application example described later, it is possible to effectively use the received light information. Furthermore, since the shift direction of the optical axis 34 of the beam 32 with respect to the plurality of waveguide type photodetectors is also the same as the polarization direction of the semiconductor laser 21, it is possible to shift easily and with high precision.

Also in the case of this embodiment, the present invention is not limited to the one having a three-dimensional waveguide structure, but can be similarly applied to the one having a slab type waveguide structure, and is not limited to the one using a waveguide type photodetector. The same can be applied to the case of using a plurality of photodetectors having a single element structure such as the photodetector 29 of the first embodiment.

A fourth embodiment of the present invention will be described with reference to FIG. The present embodiment corresponds to the invention described in claim 4, and basically has the same configuration as that of the above-mentioned embodiment, but in the embodiment, the mounting array is arranged on the same surface of the substrate 40 for the semiconductor laser 21. In this embodiment, the optical integrated circuits 37 thus arranged are mounted and arranged on the opposite surface (lower surface) side of the substrate 40. That is,
The array direction of the plurality of core regions 39a to 39d (hence, the detection positions or the waveguide type photodetectors) arranged in a straight line is set to a position not including the emission position 22 of the semiconductor laser 21.

According to such a configuration, the above-mentioned first,
In addition to the effect of the second embodiment, since the detection positions corresponding to the core regions 39a to 39d are on the same straight line not including the emission position 22 of the semiconductor laser 21, the height from the lower surface of the substrate 40 is the same. By designing the device manufactured on the substrate 40, the height can be easily made constant (the height of the detection position), and the alignment can be easily performed. In particular, since the optical integrated circuit 37 can be held on the surface opposite to the semiconductor laser 21, the design latitude is large. However, the optical integrated circuit 37 may be held on the semiconductor laser 21 via another support. Further, even in this embodiment, the reflector 24
Since these core regions 39a to 39d (therefore, detection positions or waveguide type photodetectors) are arranged in the direction perpendicular to the polarization direction of the return beam 32 reflected from
Regarding the light intensity in this direction, the wavefront information can be detected by dividing it with a plurality of waveguide type photodetectors, and it is possible to effectively use the received light information as in the case of the optical pickup application described later. Become. Furthermore, since the shift direction of the optical axis 34 of the beam 32 with respect to the plurality of waveguide type photodetectors is also the same as the polarization direction of the semiconductor laser 21, it is possible to shift easily and with high precision.

The present embodiment is not limited to the one having a three-dimensional waveguide structure, but can be similarly applied to the one having a slab type waveguide structure, and is not limited to the one using a waveguide type photodetector. The same can be applied to the case of using a plurality of photodetectors having a single element structure such as the photodetector 29 of the first embodiment.

A fifth embodiment of the present invention will be described with reference to FIG. This embodiment corresponds to the invention described in claim 5, and the semiconductor laser 21 and the optical integrated circuit 37 having the waveguide type photodetector 35 are provided in close contact with each other via the bonding surface 41 and provided on the substrate 40. It is a thing. The integration by the bonding surface 41 may be performed by simply aligning the optical integrated circuit 37 on the semiconductor laser 21 and then adhering it, or by forming concavo-convex shape on at least one side and self-aligning and adhering. Alternatively, an intermediate layer may be interposed.

In any case, according to the configuration of this embodiment, in addition to the effects of the first and second embodiments described above, the semiconductor laser 2
Since the integrated circuit 1 and the optical integrated circuit 37 are integrated, the light emitting / receiving portion around the semiconductor laser 21 can be made compact.

Also in the case of this embodiment, the photodetector 29 as shown in the first embodiment is used instead of the optical integrated circuit 37 having the waveguide type photodetector 35. Applicable.

A sixth embodiment of the present invention will be described with reference to FIG. This embodiment corresponds to the invention described in claim 6 and is one in which an optical integrated circuit 37 including a waveguide type photodetector 35 is manufactured on a substrate 40 for the semiconductor laser 21. That is, since the photodetector can be made of the same material as the semiconductor laser 21 and there are many common parts in the manufacturing process, the optical integrated circuit 37 is manufactured adjacent to the semiconductor laser 21 on the same substrate 40. can do. According to such a manufacturing method, the optical integrated circuit 3 for the semiconductor laser 21
Since the alignment of 7 (waveguide type photodetector 35) is performed by the photolithography method, the alignment can be performed with extremely high precision, and the light emitting / receiving unit can be configured in a small size. Also in the case of the present embodiment, the applicable photodetector is not limited to the waveguide type photodetector. Further, in the case of the manufacturing method of epitaxially growing a different material, the photodetector can be arranged in the direction perpendicular to the substrate 40 as in the structure of FIG.

The seventh embodiment of the present invention will be described with reference to FIG. This embodiment is applied to an optical pickup,
This corresponds to the invention described in claim 7. Therefore, the reflector 24
For this, an optical disk is used. An optical integrated circuit 43 having a slab type waveguide (waveguide) 42 is adjacent to the substrate 40 on which the semiconductor laser 21 is mounted. In the slab type waveguide 42, a plurality of waveguide type photodetectors 44a to 44d are formed linearly on the same plane. These waveguide type photodetectors 44a to 44d are reflected from the reflector 24 (optical disk) and collimate lens 25.
The return beam 32 focused by the slab type waveguide 4
The waveguide type photodetectors 44a and 44b are coupled to each other at the end face (detection position) of 2 to receive the guided light 45.
Is located at one of the boundary portions of the waveguide type photodetector 44c,
44d is located at the other boundary portion of the guided light 45.

Further, these waveguide type photodetectors 44a
Signal processing means 46 such as an adder for obtaining the focus information ΔF, the track information ΔT, and the pit information S by appropriately adding / subtracting the output signal photoelectrically converted by ˜44d is provided.

In such a structure, the semiconductor laser 2
The outgoing beam 30 emitted from the beam No. 1 passes through the collimator lens 25, the calcite 26, the Faraday rotator 27 and the objective lens 28 and is focused on the reflector 24 (optical disk). An image is formed on the end surface of the slab type waveguide 42 by shifting from the optical axis 23 to the optical axis 34. As a result, the beam 32 is end-face-coupled to the slab-type waveguide 42 and becomes the guided light 45, which is the slab-type waveguide 4
Waveguide in 2 and, according to the state, a waveguide type photodetector 44
The received light is detected by a to 44d, photoelectrically converted, and output to the signal processing unit 46.

More specifically, the focus information ΔF is detected by the beam size method (photodetectors 44a and 44b).
Of the difference between the output of the photodetector 44c and the output of the photodetector 44d) and the track information Δ by the push-pull method.
T is detected (due to the positive or negative difference between the sum of the outputs of the photodetectors 44a and 44b and the sum of the outputs of the photodetectors 44c and 44d).
And the pit information S is detected by the sum of the outputs of the photodetectors 44a to 44d.

As described above, according to this embodiment, since the optical pickup optical system is constructed by utilizing the construction of the embodiment described above, the influence of the returning light is small, and the construction and alignment of the optical system are small. Can be made easy.

Also in the case of being applied to the optical pickup as in this embodiment, the detection system is the waveguide type photodetectors 44a to 44.
Not limited to d (or the waveguide type photodetector 35), a plurality of photodetectors 29 having a single element configuration may be used. Further, even in the case of the waveguide structure, the focus signal may be detected by the knife edge method by deflecting again with a lens (a waveguide lens may be used) in the waveguide.

An eighth embodiment of the present invention will be described with reference to FIG. The present embodiment corresponds to the invention described in claim 8, and, for example, a guided light separating / deflecting element is provided between a plurality of waveguide type photodetectors 44a to 44d formed in the slab type waveguide 42 as in the above embodiment. 47a to 47c are provided. These guided light separating / deflecting elements 47a to 47c may be formed as a waveguide mirror which forms an air layer by vertically etching the slab type waveguide 42 and utilizes total reflection at the boundary surface thereof. As described above, the shape is not limited to the triangular shape, and the shape having an appropriate curvature may be provided so as to have the light converging property.

In FIG. 8, each of the waveguide type photodetectors 44a to 44a is used.
The traveling direction of the guided light 45 toward 4d is indicated by an arrow for the sake of convenience.
By providing 47c to widen the traveling direction of each guided light 45, it is possible to widen the arrangement interval of each of the waveguide type photodetectors 44a to 44d and increase the degree of freedom of arrangement. Easy to make.

In the case of this embodiment, not only the slab type waveguide 42 but also the one using a three-dimensional waveguide can be similarly applied.

The ninth embodiment of the present invention will be described with reference to FIG. This embodiment corresponds to the invention described in claim 9, and is one in which, for example, a quarter wavelength plate 48 is provided as a polarization control optical element instead of the Faraday rotator 27 shown in the first embodiment. . As a result, in this embodiment, the optical system up to the quarter wavelength plate 48 is configured as the linear polarization portion 49a, and the optical system after the quarter wavelength plate 48 is the rotation polarization portion 49b.
Is configured as.

In such a structure, the semiconductor laser 2
Assuming that the substrate of the laser beam emitted from No. 1 is horizontal to the paper surface, the polarization plane of the outgoing beam 30 is also vertical to the paper surface, and the vibrating surface is horizontal to the paper surface as indicated by the arrow. This is maintained up to the quarter-wave plate 48, and is converted into right-handed polarized light by passing through the quarter-wave plate 48. Then, the light reflected by the reflector 24 rotates counterclockwise,
As it passes through the quarter-wave plate 48 again, the vibrating surface of the returning beam 32 becomes perpendicular to the paper surface as indicated by the arrow in the figure. Since this becomes an extraordinary ray with respect to the calcite 26, it goes toward the photodetector 29 along the optical axis 34 shifted from the going optical axis 23, as described above.

According to this embodiment, since the quarter-wave plate 48 is used as the polarization control optical element, it is possible to achieve the initial purpose by performing 90 ° conversion of the polarization direction with a small size and at a low cost. .

Also in the case of the present embodiment, an optical integrated circuit having a waveguide type photodetector may be used instead of the photodetector 29.

The tenth embodiment of the present invention will be described with reference to FIG. This embodiment corresponds to the invention described in claim 10, and, for example, in the configuration of the seventh embodiment shown in FIG. 7, a parallel plate 50 having a high transmittance is provided in front of the coupling end face of the slab type waveguide 42. It is arranged so that the light passing through the parallel plate 50 is coupled and guided.

When an optical system having an optical element having a birefringence, such as the calcite 26 described above, is configured to transmit and receive light in a reciprocating manner, the optical path lengths of the going and returning may change slightly, so this optical path length is adjusted. A parallel plate 50 is provided for this purpose. This parallel plate 50 is inserted in the direction where the optical path length is desired to be increased in the going and returning, and in the present embodiment, it is provided in front of the slab type waveguide 42 in order to increase the returning optical path. In the case of an optical system configuration in which it is desired to increase the length of the outgoing optical path, it may be arranged in front of the semiconductor laser 21. According to the optical system in which the reciprocal optical path length is adjusted in this way, the coupling end face which is the detection position of the slab type waveguide 42 can be set to the optimum beam waist position. That is, the characteristics of the laser light at the detection position can be easily adjusted. However, since the parallel plate 50 is inserted,
The configuration of the going optical system and the configuration of the returning optical system are slightly different, but there is no particular problem in assembling / positioning.

Also in this embodiment, the waveguide type photodetector 44 is used.
Not limited to a to 44d (or the waveguide type photodetector 35), a plurality of photodetectors 29 having a single element configuration may be used.

An eleventh embodiment of the present invention will be described with reference to FIG. This embodiment corresponds to the invention of claim 11,
For example, as shown in FIG. 8A, in the configuration of the ninth embodiment described above, the calcite 26 and the quarter-wave plate 48 are closely adhered and integrated by a photocurable resin or the like.
According to this, the position adjustment of the two optical components of the calcite 26 and the quarter-wave plate 48 at the time of assembling the optical system can be simplified, and at the same time, the size can be further reduced.

Alternatively, it is not limited to such a close contact, but as shown in FIG. 7B, by appropriately setting the crystal axis of calcite, the quarter-wave plate function and the birefringence function can be realized at the same time. By using the parallel plate 51 thus formed as an optical axis shift optical element and a polarization control optical element, both optical elements may be integrated. In particular, in the case of the configuration shown in FIG. 7B, it is more effective if a biaxial crystal is used for the parallel plate 51.

[0070]

According to the present invention, the semiconductor laser, the reflector for reflecting the laser light emitted from the semiconductor laser, and the optical path between the semiconductor laser and the reflector are arranged. An optical axis shift optical element that is provided to shift the optical axis depending on the polarization direction, and a polarization that is disposed on the optical path between the optical axis shift optical element and the reflector and that controls the polarization direction of light. Since it is constituted by a control optical element and a photodetector which is arranged in the vicinity of the semiconductor laser and receives the light reflected by the reflector and transmitted through the polarization control optical element and the optical axis shift optical element, common optical The emitted light having different optical axes and the reflected light with almost no light quantity loss can be obtained in the system by shifting, and the photodetector can be arranged near the semiconductor laser to form a simple optical system configuration. , Semiconductor laser The return light to the can be reduced significantly.

According to a second aspect of the present invention, the light reflected by the reflector and transmitted through the polarization control optical element and the optical axis shift optical element is coupled to the photodetector in the configuration of the first aspect. Since the waveguide type photodetector is formed on the waveguide of the optical integrated circuit, it is possible to efficiently detect light from the lateral direction with respect to the optical integrated circuit substrate having the waveguide type photodetector. It is also possible to use the wavefront information in the direction parallel to the circuit board for the optical integrated circuit.

According to a third aspect of the present invention, in the configuration of the first or second aspect of the invention, the emission position of the laser light of the semiconductor laser and the detection position of the photodetector are parallel to the substrate on which the semiconductor laser is mounted. Since the photodetectors can be held in the same direction on the substrate for the semiconductor laser, the photodetectors can be easily aligned.

According to a fourth aspect of the present invention, there is provided the structure of the first or second aspect of the invention, in which the detection positions of the plurality of photodetectors are set in a direction parallel to the substrate on which the semiconductor laser is mounted. Since the light detectors are arranged at the positions not including the light emission positions, the photodetectors can be held on the opposite surface of the substrate for the semiconductor laser, and the alignment of the photodetectors can be relatively easy.

According to a fifth aspect of the present invention, in the configuration of the first or second aspect of the invention, the semiconductor laser and the optical integrated circuit having the photodetector or the waveguide type photodetector are brought into close contact with each other and integrated. Therefore, the light emitting / receiving unit can be made compact.

According to a sixth aspect of the present invention, with respect to the structure of the first or second aspect of the invention, the semiconductor laser and the photodetector or the optical integrated circuit having the waveguide type photodetector are formed on the same substrate. Therefore, the semiconductor laser and the photodetector can be easily and highly accurately aligned by the photolithography method.

According to the invention of claim 7, in the structure of the invention of claim 1 or 2, the reflector is an optical disk, and a signal for obtaining focus information, track information or pit information based on the detection output of the photodetector. Since the processing means is provided, it is possible to provide an optical pickup having a simple optical system configuration, which is hardly affected by the returning light, has high light utilization efficiency.

According to an eighth aspect of the present invention, in the configuration of the second aspect of the invention, a plurality of waveguide type photodetectors are provided, and guided light separation is performed on the waveguide between the respective waveguide type photodetectors. Since the deflecting element is provided, the plurality of waveguide type photodetectors can be effectively spaced and configured, and the waveguide type photodetector can be easily manufactured.

According to a ninth aspect of the present invention, with respect to the configuration of the first or second aspect of the invention, the polarization control optical element is
Since it is a four-wave plate, it is possible to realize a 90 ° rotation of the polarization direction in a simple, compact and inexpensive manner, and to reduce the size and cost of the entire detection optical system.

According to the invention of claim 10, claim 1
Alternatively, in addition to the configuration of the invention described in 2, since the parallel plate is provided in front of the semiconductor laser or the photodetector, the optical path lengths of the emitted light and the reflected light can be adjusted, and the laser light at the detection position of the photodetector can be adjusted. The characteristics can be changed easily.

According to the invention of claim 11, claim 1
Alternatively, regarding the configuration of the invention described in 2, since the optical axis shift optical element and the polarization control optical element are integrated, position adjustment and the like at the time of assembling these optical elements can be facilitated, and a further improvement of the detection optical system can be achieved. Can be miniaturized.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an optical system showing a first embodiment of the present invention.

2A and 2B show a second embodiment of the present invention, in which FIG. 2A is a front view and FIG. 2B is a schematic sectional view of a part thereof.

FIG. 3 is a front view showing a third embodiment of the present invention.

FIG. 4 is a front view showing a fourth embodiment of the present invention.

FIG. 5 is a front view showing a fifth embodiment of the present invention.

FIG. 6 is a front view showing a sixth embodiment of the present invention.

FIG. 7 is a schematic plan view including signal processing means showing a seventh embodiment of the present invention.

FIG. 8 is a schematic plan view showing an eighth embodiment of the present invention.

FIG. 9 is a schematic configuration diagram of an optical system showing a ninth embodiment of the present invention.

FIG. 10 is a schematic plan view showing a tenth embodiment of the present invention.

FIG. 11 is a schematic side view of an optical element showing an eleventh embodiment of the present invention.

FIG. 12 is a schematic configuration diagram of an optical system showing a conventional example.

[Explanation of symbols]

 21 semiconductor laser 22 emission position 23 optical axis 24 reflector 26 optical axis shift optical element 27 polarization control optical element 29 photodetector 33 detection position 34 optical axis 35 waveguide type photodetector 36 waveguide 37 optical integrated circuit 40 semiconductor laser Substrate 42 Waveguide 43 Optical integrated circuit 44a-44d Waveguide type photodetector 46 Signal processing means 47a-47c Waveguide light separating / deflecting element 48 1/4 wavelength plate, polarization control optical element 50 Parallel plate 51 Optical axis shift optics Element and polarization control optical element

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Claims (11)

[Claims] 1. A semiconductor laser, a reflector for reflecting laser light emitted from the semiconductor laser, and an optical path disposed between the semiconductor laser and the reflector, the light depending on the polarization direction. An optical axis shift optical element for shifting the axis, a polarization control optical element arranged on the optical path between the optical axis shift optical element and the reflector for controlling the polarization direction of light, and near the semiconductor laser. A photodetector, comprising: a photodetector that is arranged and reflected from the reflector and receives light that has passed through the polarization control optical element and the optical axis shift optical element. 2. A photodetector formed on a waveguide of an optical integrated circuit to which light reflected from a reflector and transmitted through a polarization control optical element and an optical axis shift optical element is coupled. The photodetector according to claim 1, wherein 3. A laser beam emitting position of a semiconductor laser,
3. The photodetector according to claim 1, wherein at least one or more photodetector detection positions are arranged in a direction parallel to the substrate on which the semiconductor laser is mounted. 4. A detection position of at least two or more photodetectors is arranged in a position parallel to a substrate on which a semiconductor laser is mounted and at a position not including a laser light emission position of the semiconductor laser. The photodetector according to claim 1 or 2. 5. The photodetector according to claim 1, wherein the semiconductor laser and an optical integrated circuit having a photodetector or a waveguide type photodetector are brought into close contact with each other and integrated. 6. The photodetector according to claim 1, wherein the semiconductor laser and the photodetector or an optical integrated circuit having a waveguide photodetector are formed on the same substrate. 7. The optical disk as the reflector, and signal processing means for obtaining at least one of focus information, track information or pit information based on the detection output of the photodetector is provided. The photodetector described. 8. The photodetector according to claim 2, wherein a plurality of waveguide type photodetectors are provided, and a guided light separating / deflecting element is provided on a waveguide between the waveguide type photodetectors. . 9. The photodetector according to claim 1, wherein the polarization control optical element is a quarter wavelength plate. 10. The photodetector according to claim 1, wherein a parallel plate is provided in front of the semiconductor laser or the photodetector. 11. The optical axis shift optical element and the polarization control optical element are integrated with each other.
The photodetector described.