JP7180866B2 - An optical heterodyne detector and a laser radar system using an optical heterodyne detector. - Google Patents

Description

The present invention relates to an optical heterodyne detector and a laser radar apparatus using the optical heterodyne detector.

In a laser radar device, for example, the distance to an object is measured based on the phase difference between the transmitted light and the received light received by the antenna after the transmitted light is reflected. A photodiode is used for the detection of the received light, and since the received light may contain various noises, components originating from the transmitted light are extracted from the received light by combining and interfering with the received light with a reference light having a constant wavelength. Optical heterodyne detection is performed to extract .

Patent Literature 1 discloses an invention of a highly reliable laser radar device and an optical receiving method for the laser radar device, which enables highly sensitive measurement using optical heterodyne detection.

JP 2016-105082 A

By the way, the laser radar device disclosed in Patent Document 1 has the advantage that a configuration capable of optical heterodyne detection can be easily constructed. However, there is a risk that the manufacturing cost of the product will increase.

The present invention has been made in view of the above problems, and uses an optical heterodyne detector capable of highly sensitive measurement with a simple configuration and capable of highly reliable optical heterodyne detection, and an optical heterodyne detector. It is an object of the present invention to realize a laser radar device that meets the requirements of the present invention.

In order to achieve the above object, an optical heterodyne detector according to claim 1 comprises: a light collecting part for collecting light received by reflecting off an object from a transmission light output from a laser light source; The reference light, which is a part of the received light, and the received light condensed by the condensing section propagate, and the width of the reference light gradually expands in the incident direction of the reference light. and a light receiving portion receiving light generated as a result of interference between the reference light and the received light in the waveguide and converting the light into an electric signal.

The optical heterodyne detector according to claim 2 is the optical heterodyne detector according to claim 1, wherein the enlarged portion is formed in a reverse tapered shape with respect to the incident direction of the reference light. .

Further, the optical heterodyne detector according to claim 3 is the optical heterodyne detector according to claim 1 or claim 2 , wherein the waveguide is a thin-film waveguide, and the light-receiving part is the thin-film waveguide. It comprises an absorbing layer and an electrode laminated on one end side of a waveguide of the type.

Further, the optical heterodyne detector according to claim 4 is the optical heterodyne detector according to any one of claims 1 to 3, wherein the condensing part is an optical lens.

Further, the optical heterodyne detector according to claim 5 is the optical heterodyne detector according to any one of claims 1 to 4 , wherein a receiving diffraction light is provided between the light collecting part and the waveguide. Equipped with a grid.

Further, the optical heterodyne detector according to claim 6 is the optical heterodyne detector according to claim 5 , wherein the pattern of the reception diffraction grating is on the optical axis of the reception light emitted from the reception diffraction grating. Concentric elliptical arc-shaped grooves centered on one point are arranged at predetermined intervals.

The optical heterodyne detector according to claim 7 is the optical heterodyne detector according to claim 6 , wherein the pattern is centered on a point on the optical axis of the received light emitted from the reception diffraction grating. Concentric arcuate grooves are arranged at predetermined intervals.

Further, the optical heterodyne detector according to claim 8 is the optical heterodyne detector according to claim 5 or 6 , wherein the reference light is incident on the waveguide after passing through the reception diffraction grating. .

Further, the optical heterodyne detector according to claim 9 is the optical heterodyne detector according to claim 5 or 6 , wherein a reflecting mirror is provided between the reception diffraction grating and the waveguide, and the reflection The mirror reflects the reference light incident from the side of the optical axis of the waveguide toward the waveguide.

Further, the optical heterodyne detector according to claim 10 is the optical heterodyne detector according to claim 5 or 6 , wherein the reception diffraction grating has an optical axis of the reference light and a distance from the reception diffraction grating. arranged so that the optical axis of the emitted received light intersects, arranged at a position where the optical axis of the reference light intersects the optical axis of the received light emitted from the reception diffraction grating, a coupling diffraction grating that causes the received light and the reference light to interfere with each other, and emits light resulting from the interference in each of the optical axis direction of the received light and the reference light; Wave paths include a first waveguide in which light emitted from the coupling diffraction grating in the optical axis direction of the received light propagates, and a wave path in which light emitted from the coupling diffraction grating in the optical axis direction of the reference light propagates. and the light receiving section includes a first light receiving section for receiving light propagated through the first waveguide and converting the light into an electric signal, and receiving the light propagated through the second waveguide. and a second light receiving portion that converts the light into an electric signal.

Further, the optical heterodyne detector according to claim 11 is the optical heterodyne detector according to claim 5 or 6 , wherein the reception diffraction grating includes the optical axis of the reference light and the reception diffraction grating arranged so that the optical axis of the received light emitted from the optical axis of the reference light intersects with the optical axis of the received light emitted from the reception diffraction grating, a coupling diffraction grating that causes the received light and the reference light to interfere with each other and emits light resulting from the interference in each of the optical axis direction of the received light and the optical axis direction of the reference light; a first reflecting portion that reflects light emitted from the diffraction grating in the optical axis direction of the received light toward the waveguide; and a second reflector that reflects toward the waveguide.

The optical heterodyne detector according to claim 12 is the optical heterodyne detector according to claim 11 , wherein each of the first reflector and the second reflector has a grating pitch equal to the coupling diffraction grating. It is a finer diffraction grating than

The optical heterodyne detector according to claim 13 is the optical heterodyne detector according to claim 11 , wherein each of the first reflector and the second reflector is a reflector.

Further, the optical heterodyne detector according to claim 14 is the optical heterodyne detector according to any one of claims 11 to 13 , in which the reception diffraction grating, the coupling diffraction grating, the first An optical heterodyne light-receiving module is configured by mounting a plurality of configurations including the reflecting section, the second reflecting section, and the light-receiving section on the same chip.

Further, the optical heterodyne detector according to claim 15 is the optical heterodyne detector according to claim 14 , arranged for each of the plurality of mounted configurations, and directing the reference light to the coupling diffraction grating. It further comprises a diffraction grating for reference light emitted toward.

Further, the laser radar device according to claim 16 comprises the optical heterodyne detector according to any one of claims 1 to 15, and a light projecting unit for projecting transmission light output from the laser light source to the outside world. a feedback unit for returning part of the light output from the laser light source to the waveguide as the reference light; and a calculation unit for measuring the distance to an object based on the electrical signal output from the light receiving unit; Prepare.

According to a seventeenth aspect of the present invention, there is provided a laser radar apparatus according to the sixteenth aspect, wherein the light projecting section includes a transmission diffraction grating that refracts and emits the transmission light output from the laser light source.

The laser radar apparatus according to claim 18 is the laser radar apparatus according to claim 17, wherein the pattern of the transmission diffraction grating is a point on the optical axis of the transmission light incident on the transmission diffraction grating. Centered concentric elliptical arc-shaped grooves are arranged at predetermined intervals.

Further, the laser radar apparatus according to claim 19 is the laser radar apparatus according to claim 18, wherein the pattern is concentric arc-shaped around a point on the optical axis of the transmission light incident on the transmission diffraction grating. are arranged at predetermined intervals.

Further, the laser radar apparatus according to claim 20 is the laser radar apparatus according to any one of claims 17 to 19 , wherein the light projecting unit includes the transmission light emitted from the transmission diffraction grating. is projected to the outside world through the transmission lens.

Further, the laser radar device according to claim 21 is the laser radar device according to any one of claims 17 to 20 , wherein the light projecting unit modulates the intensity and waveform of the transmission light. Have equipment.

The laser radar apparatus according to claim 22 is the laser radar apparatus according to claim 21 , wherein the modulator is a Mach-Zehnder interferometer capable of modulating the waveform of the transmission light into a rectangular wave.

The laser radar device according to claim 23 is the laser radar device according to any one of claims 16 to 22 , wherein the waveguide is a thin-film waveguide covered with a silicon layer. It has a double clad structure.

The laser radar device according to claim 24 is the laser radar device according to any one of claims 16 to 23 , wherein the waveguide is a planar waveguide formed on the substrate plane.

Further, the laser radar device according to claim 25 is the laser radar device according to any one of claims 16 to 24 , wherein the waveguide includes a straight waveguide composed of straight lines. .

In addition, the laser radar device according to claim 26 is the laser radar device according to any one of claims 16 to 25 , wherein the laser light source is provided with a polarizing filter, and application of the polarizing filter enables orthogonal Either polarized waves or parallel polarized waves can be output.

Advantageous Effects of Invention According to the present invention, it is possible to realize an optical heterodyne detector capable of highly sensitive measurement and having high reliability.

1 is a schematic diagram showing an example of a minimum configuration of an optical heterodyne detector according to a first embodiment of the invention; FIG. FIG. 2 is a side view of the photodiode shown in FIG. 1 when viewed in the direction of arrow A; 1 is a schematic diagram illustrating the principle of optical heterodyne detection of an optical heterodyne detector according to an embodiment of the present invention; FIG. FIG. 4 is a side view of the photodiode shown in FIG. 3 when viewed in the direction of arrow B; (A) is an explanatory diagram showing an example of a silicon waveguide that widens the luminous flux of reference light, and (B) shows an example of a silicon waveguide that is widened to facilitate reception of received light. FIG. 2 is a schematic diagram showing the detailed structure of a photodiode; FIG. 7 is a cross-sectional view showing a state in which the photodiode of FIG. 6 is cut along line CC; FIG. 8 is a bird's-eye view of the photodiode shown in FIG. 7 as viewed in the direction of arrow D; 1 is a block diagram showing an example of a distance sensor using an optical heterodyne detector including photodiodes according to an embodiment of the present invention; FIG. FIG. 10 is a block diagram showing a modified example of an optical integrated circuit chip in which a plurality of photodiodes are arranged corresponding to an image plane formed by an imaging lens; FIG. 10 is a schematic diagram showing a modification of the optical integrated circuit chip in which a plurality of photodiodes are arranged so as to receive received light in the horizontal direction imaged by the imaging lens; 1 is a schematic diagram showing an example of a configuration in which a diffraction grating is combined with a photodiode and a silicon waveguide according to the first embodiment of the present invention; FIG. FIG. 5 is a schematic diagram showing another example of a configuration in which a photodiode and a silicon waveguide are combined with a diffraction grating according to the first embodiment of the present invention; 14 is a block diagram showing an example of a rangefinder chip including the configuration shown in FIG. 13; FIG. 15 is a schematic diagram showing an example of a configuration of a rangefinder using the rangefinder chip shown in FIG. 14; FIG. FIG. 15 is a schematic diagram of a rangefinder chip that is a modification of the rangefinder chip shown in FIG. 14; FIG. 17 is a schematic diagram showing an example of a configuration of a rangefinder using the rangefinder chip shown in FIG. 16; FIG. 14 is a schematic diagram of a configuration in which the incident direction of reference light is changed from the configuration shown in FIG. 12 or FIG. 13; This is one of the modifications of the configuration shown in FIG. FIG. 20 is a schematic diagram showing a modified example of the configuration shown in FIG. 19 and having a diffraction grating and mirrors instead of the diffraction gratings. It is the schematic which showed an example of the mirror. FIG. 21 is a schematic diagram showing an example when a plurality of configurations shown in FIG. 20 are provided; FIG. 23 is a schematic diagram showing an example of an optical heterodyne detection light-receiving module including the configuration shown in FIG. 22;

[First embodiment]
A first embodiment of the present invention will be described in detail below with reference to the drawings. First, the basic configuration of an optical heterodyne detector 10 according to the present invention will be described with reference to FIG.

FIG. 1 is a schematic diagram showing an example of the minimum configuration of an optical heterodyne detector 10 according to this embodiment. As shown in FIG. 1, the optical heterodyne detector 10 includes an imaging lens 20 and a waveguide photodiode (hereinafter abbreviated as "photodiode") 30 as a light receiving element.

The imaging lens 20 receives light generated by a laser beam output from a laser light source, which will be described later, being reflected by an object. In FIG. 1, the configuration is simple like a single convex lens, but in order to focus the received light on the photodiode 30, a plurality of lenses including a convex lens and a concave lens may be configured, and the shape of the lens surface is spherical. Alternatively, an aspherical surface may be employed as required.

The photodiode 30 is formed in a belt shape on a SiO ₂ substrate 38 so that the longitudinal direction of a silicon waveguide 36 made of Si (silicon) is parallel to the optical axis of the imaging lens 20 . A Ge (germanium) absorption layer 34 is laminated on one end side, and an electrode 32 is formed on the Ge absorption layer 34 . The silicon waveguide 36 and the Ge absorption layer 34 are each formed by heteroepitaxial, as an example. The photodiode 30 according to the present embodiment has a Ge absorption layer 34 instead of Si, so that it can detect light of wavelengths other than visible light to near-infrared light.

The photodiode 30 generates a current that changes according to the intensity of the incident light when light is incident on the junction surface between the silicon waveguide 36 and the Ge absorption layer 34 . The generated current is conducted outside through the electrode 32 . The electrode 32 is formed by vapor-depositing a highly conductive metal such as copper, aluminum, gold, or silver on the Ge absorption layer 34 or the like by CVD (chemical vapor deposition) or the like.

FIG. 2 is a side view of the photodiode 30 shown in FIG. 1 as viewed in the direction of arrow A. FIG. As shown in FIG. 2, the photodiode 30 according to the present embodiment is arranged such that the joint surface between the silicon waveguide 36 and the Ge absorption layer 34 coincides with the optical axis 22 of the imaging lens 20. be. Alternatively, the configuration may be such that the silicon waveguide 36 exists on an extension of the optical axis 22 of the imaging lens 20 .

The photodiode 30 is also covered with SiO 2 forming a SiO ₂ substrate 38 in order to protect the silicon waveguide 36, the Ge absorption layer 34 and the electrode ₃₂ formed on the SiO ₂ substrate 38. FIG. Even if covered with SiO ₂ , the structure of the photodiode 30 is a thin film, which is simpler than the light receiving element according to the laser radar device described in Patent Document 1.

FIG. 3 is a schematic diagram for explaining the principle of optical heterodyne detection by the optical heterodyne detector 10 according to this embodiment. As shown in FIG. 3, the incident light 40 of the imaging lens 20 is condensed by the imaging lens 20 and guided to the silicon waveguide 36 of the photodiode 30 as received light 42 . The reference light 44 is also incident on the silicon waveguide 36, and optical heterodyne detection is performed in which the received light 42 and the reference light 44 interfere with each other to generate an intermediate frequency. An intermediate frequency signal resulting from interference between the received light 42 and the reference light 44 is a so-called beat signal, and a current that varies according to the strength of the beat signal is output as an electrical signal.

The photodiode 30 is integrally formed with a silicon waveguide 36, and the reference light 44 is guided to the silicon waveguide 36 with good reproducibility. well combined. By condensing the received light 42 with the imaging lens 20 , the received light 42 is captured beyond the frame of the silicon waveguide 36 , the light amount of the received light 42 increases, and the sensitivity of the photodiode 30 can be improved. can.

FIG. 4 is a side view of the photodiode 30 shown in FIG. 3 as viewed in the direction of arrow B. FIG. By setting the length L of the photodiode 30 parallel to the optical axis 22 of the imaging lens 20 to be the Rayleigh length of the intermediate frequency signal, the signal can be efficiently converted into an electrical signal.

FIG. 5A shows an example of a silicon waveguide that widens the luminous flux of the reference light 44, and FIG. 5B shows an example of a silicon waveguide that is widened to facilitate reception of the received light 42. It is an explanatory diagram.

As shown in FIG. 5A, the silicon waveguide 36A has an isosceles triangle shape with the vertex on the side on which the reference light 44 is incident, and exhibits an inverse tapered shape in which the width gradually increases. It is constructed such that the width is maximum and constant at the position provided. As the width of the silicon waveguide 36A gradually expands with respect to the incident direction of the reference light 44, the luminous flux of the reference light 44 propagating in the silicon waveguide 36A is expanded and interferes with the received light 42 in optical heterodyne detection. easier to do.

As shown in FIG. 5(B), the silicon waveguide 36B is composed of a widened Si-rich SiO ₂ layer 36B2, and the widened silicon waveguide 36B traps the received light 42 . In addition, the silicon waveguide 36B has an isosceles triangle shape whose base is the side on which the received light 42 is incident and whose width is gradually reduced, and the peak is formed near the position where the Ge absorption layer 34 is provided. A first Si layer 36B1 configured as above is provided. The width of the first Si layer 36B1 is gradually reduced in the incident direction of the received light 42, so that the luminous flux of the received light 42 propagating through the first Si layer 36B1 is converged. Since the luminous flux of the received light 42 may be wider than the luminous flux of the reference light 44, converging the luminous flux of the received light 42 facilitates interference with the reference light 44 in optical heterodyne detection.

A second Si layer 36 B 3 is provided around the Ge absorption layer 34 . By configuring the second Si layer 36B3 to be wider than the width of the Ge absorption layer 34, even when the light beam of the received light 42 is not sufficiently converged by the first Si layer 36B1, the wide second Si layer 36B3 can be used for optical heterodyne detection. It facilitates interference between the received light 42 and the reference light 44 .

FIG. 6 is a schematic diagram showing the detailed structure of the photodiode 30. As shown in FIG. The photodiode 30 has a strip-shaped silicon waveguide 36 made of Si formed on a SiO ₂ substrate 38 , a Ge absorption layer 34 formed on the silicon waveguide 36 , and a Ge absorption layer 34 on the Ge absorption layer 34 . An N-electrode 32N is formed on the silicon waveguide 36, and a P-electrode 32P is formed on the silicon waveguide 36, respectively. The silicon waveguide 36 and the Ge absorption layer 34 are each formed by heteroepitaxial, as an example.

FIG. 7 is a cross-sectional view of the photodiode 30 of FIG. 6 taken along line CC. A silicon waveguide 36 formed on a SiO ₂ substrate 38 is composed of a P-type semiconductor obtained by doping Si with an impurity such as boron. The silicon waveguide 36 has a P+Si layer 36C rich in impurities and a P-Si layer 36D lean in impurities, and a P electrode 32P is electrically connected to the surface of the P+Si layer 36C.

The Ge absorption layer 34 formed on the silicon waveguide 36 is composed of an N-type semiconductor obtained by doping Ge with an impurity such as arsenic or phosphorus. An N electrode 32N is electrically connected to the surface of the Ge absorption layer 34 .

As shown in FIG. 7, the photodiode 30 includes a SiO ₂ substrate 38 in order to protect the silicon waveguide 36, the Ge absorption layer 34, the P-electrode 32P and the N-electrode 32N formed on the SiO ₂ substrate 38. It is covered with constituent SiO ₂ .

As shown in FIG. 7, a P+Si layer 36C, a P-Si layer 36D, and a Ge absorption layer 34, which is an N-type semiconductor, are interposed between the P electrode 32P and the N electrode 32N. Holes are more likely to occur in the P+Si layer 36C than in the P-Si layer 36D, and electrons are more likely to move to the holes. In addition, the Ge absorption layer 34, which is an N-type semiconductor, is rich in free electrons that easily move to a P-type semiconductor or the like. The photodiode 30 shown in FIG. 7 converts an intermediate frequency signal between the received light 42 and the reference light 44 into an electric signal by movement of free electrons from the Ge absorption layer 34 to the P+Si layer 36C. In the photodiode 30 shown in FIG. 7, a P--Si layer 36D in which hole generation is less pronounced than the P+Si layer 36C is provided between the Ge absorption layer 34 and the P+Si layer 36C. The abrupt movement of free electrons from the absorption layer 34 to the P+Si layer 36C is moderately suppressed, and the electrical signal output based on the received light 42 is stabilized.

FIG. 8 is a bird's-eye view of the photodiode 30 shown in FIG. 7 as viewed in the direction of arrow D. FIG. FIG. 8 shows the state in which the SiO ₂ substrate 38 has been removed so that the connections between the Ge absorption layer 34, the P+Si layer 36C, the P-Si layer 36D, the P electrode 32P and the N electrode 32N are clear. As shown in FIG. 8, the photodiode 30 is composed of a pn junction. By providing the P-Si layer 36D in which the generation of holes is less significant than that of the P+Si layer 36C, rapid movement of free electrons from the Ge absorption layer 34 to the P+Si layer 36C is suppressed. By suppressing the movement of free electrons, it is possible to suppress the occurrence of noise that suddenly occurs immediately after the received light 42 enters the photodiode 30, and to stably output an electrical signal based on the received light 42. become.

FIG. 9 is a block diagram showing an example of a distance sensor using the optical heterodyne detector 10 including the photodiode 30 according to this embodiment. A distance sensor 100 shown in FIG. 9 is used in a laser radar device or the like, and mainly includes an optical integrated circuit chip 110 including a photodiode 30 and a control/arithmetic processor 126 as a control device.

In the optical integrated circuit chip 110, laser light propagates through the waveguide 102 from a laser light source 114 driven by a drive circuit 112, and a portion of the propagated laser light (for example, incident laser light 10%) is looped back into waveguide 102 A and enters photodiode 30 as reference light 44 . Directional coupler 116 is an example of a feedback section. As shown in FIG. 9, the optical integrated circuit chip 110 has a laser light transmitting/receiving mechanism mounted on the same chip. Therefore, when the chip is used in a laser radar device, the alignment adjustment of the laser radar device is basically necessary. practically unnecessary.

The waveguide 102, together with the waveguide 102A and 102B described later, has a double-clad structure in which the core is double-coated. The core is made of a Si-based material such as SiO ₂ with a high refractive index, and the clad surrounding the core is made of fluorine-doped SiO ₂ or the like with a lower refractive index than the core. The laser light output from the laser light source 114 basically propagates straight through the cores of the waveguides 102, 102A, and 102B, but the bent portions of the waveguides 102, 102A, and 102B propagate through the high-refractive-index cores. propagates by repeated reflections between the cladding and the low-refractive-index cladding.

The waveguides 102, 102A, 102B shown in FIG. 9 are planar waveguides mounted on a plane on the optical integrated circuit chip 110, and in particular, the waveguides 102, 102B pass light from the laser light source 114 to the transmission lens 24. It is a straight waveguide in which the propagating laser light is less attenuated by being arranged in a straight line up to the axis. Although the waveguide 102A through which the reference light 44 propagates is also partially bent, it is made to be a straight waveguide as much as possible to suppress attenuation of the propagating reference light 44. FIG.

The laser beam separated from the reference beam 44 by the directional coupler 116 is phase-modulated by the phase modulator 118 . The phase modulator 118 heats the waveguide 102B through which the laser light incident from the laser light source 114 propagates to change the refractive index of the waveguide 102B, thereby converting the laser beam emitted from the transmission lens 24 into the transmission light 46. Change the phase of light. As an example, the waveguide 102B is made of SiO ₂ or the like whose refractive index changes according to the temperature, and a heater or the like that generates heat when the waveguide 102B is energized is mounted as the phase modulator 118. The phase of laser light propagating through waveguide 102B is changed.

The laser light whose phase has been changed by the phase modulator 118 is emitted as the transmission light 46 through the transmission lens 24 . At this time, the phase of the laser light is changed by the phase modulator 118, so that the direction of the laser light emitted as the transmission light 46 is changed. This makes it possible to scan the laser light projected as the transmission light. Phase modulator 118 is driven by drive circuit 120 , which is controlled by control and arithmetic processor 126 . As an example, the control/arithmetic processor 126 controls the drive circuit 120 so that the heater, which is the phase modulator 118, becomes significantly heated when the phase of the transmission light 46 needs to be modulated significantly.

The optical integrated circuit chip 110 receives the reflected light of the transmitted light 46 from the object as the received light 42 with the imaging lens 20 . The received light 42 received is focused on the photodiode 30 by the imaging lens 20 . The photodiode 30 performs optical heterodyne detection that generates an intermediate frequency by causing the collected received light 42 to interfere with the reference light 44 . As a result of optical heterodyne detection, a beat signal corresponding to the intermediate frequency between the received light 42 and the reference light 44 is output as an electrical signal.

An electrical signal output from the photodiode 30 is input to the AD converter 124 via the preamplifier 122 . The AD converter 124 converts the analog signal output from the preamplifier 122 into a digital signal and outputs the digital signal to the control/arithmetic processor 126 .

The control/arithmetic processor 126 performs predetermined arithmetic processing on the digital signal based on the beat signal, and detects at least one of the amplitude and phase of the received light 42 corresponding to the object. The distance to the object is calculated from information on at least one of the amplitude and phase of the detected received light 42 . The control/arithmetic processor 126 performs the above arithmetic processing for each direction of the laser beam, and calculates the distance to the object for each direction.

The laser light source 114 has a polarizing filter, and by applying the polarizing filter, the transmission light 46 is limited to only TE waves (orthogonal polarized waves: transverse electric waves) or TM waves (parallel polarized waves: transverse magnetic waves). may be configured as possible. The TE wave is polarized with an electric field component oriented transversely to the plane of incidence, and the TM wave is polarized with a magnetic field component oriented transversely with respect to the plane of incidence.

By limiting the transmission light 46 to the TE wave or the TM wave, when the light generated by the reflection of the transmission light 46 from the object is received as the reception light 42, optical heterodyne detection can be performed with the light based on the same kind of polarization. It can be carried out. As a result, intermediate frequency signal generation between the reference light 44 and the received light 42 becomes more pronounced, and the sensitivity of the photodiode 30 can be improved.

FIG. 10 is a block diagram showing a modification of the optical integrated circuit chip 110A in which a plurality of photodiodes 30 are arranged corresponding to the image plane formed by the imaging lens 20. As shown in FIG. The image plane of the imaging lens 20 is not necessarily flat and may be curved as shown in FIG. By aligning them and arranging them according to the image plane, each photodiode 30 can capture the received light 42 at the focal position where the received light 42 forms a sharp image, improving the sensitivity of the optical integrated circuit chip 110A. At the same time, an electrical signal corresponding to the intensity of the received light 42 can be stably output.

FIG. 11 is a schematic diagram showing a modified example of an optical integrated circuit chip 110A in which a plurality of photodiodes 30 are arranged so as to receive horizontally received light 42 imaged by the imaging lens 20. As shown in FIG. Each of the plurality of photodiodes 30 is mounted on a SiO ₂ substrate 38A, and the SiO ₂ substrate 38A is coupled with the imaging lens 20 so as to cross the center of the imaging lens 20. FIG. In a state in which the SiO ₂ substrate 38 A and the imaging lens 20 are coupled, the silicon waveguide 36 of each of the plurality of photodiodes 30 emits photons on the SiO ₂ substrate 38 A so as to match the incident direction of the received light 42 . Each of the diodes 30 is implemented. By optimizing the orientation of each photodiode 30 according to the incident direction of the received light 42, the received light 42 can be captured efficiently, the sensitivity of the optical integrated circuit chip 110A can be improved, and the intensity of the received light 42 can be controlled. A corresponding electric signal can be stably output.

As described above, in the optical heterodyne detector 10 according to the present embodiment, the photodiode 30 as a light receiving element is formed from the silicon waveguide 36 formed on the SiO ₂ substrate 38, the Ge absorption layer 34 and the electrode 32. It has a simple thin film structure.

Further, in the optical heterodyne detector 10 according to the present embodiment, the received light 42 is condensed by the imaging lens 20 and guided to the silicon waveguide 36 of the photodiode 30, thereby increasing the light amount of the received light 42. , the sensitivity of the photodiode 30 can be improved.

Therefore, although the optical heterodyne detector 10 according to the present embodiment has a simple thin-film structure, it is possible to perform highly sensitive measurement by condensing the received light 42 by the imaging lens 20, and is based on a simple structure. It has high reliability.

Since the photodiode 30 having the simple thin film structure described above can be manufactured easily and at low cost, the manufacturing cost of the optical heterodyne detector 10 including the photodiode 30 can be reduced.

In addition, the photodiode 30 is integrally formed with a silicon waveguide 36, and the reference light 44 is guided to the silicon waveguide 36 with good reproducibility. The light is efficiently multiplexed with the reference light 44, and optical heterodyne detection is effectively performed by interference between the received light 42 and the reference light 44. FIG.

Furthermore, since the laser radar device using the optical heterodyne detector 10 according to the present embodiment has a laser light transmitting/receiving mechanism mounted on the same chip, alignment adjustment of the laser radar device is basically unnecessary. It has the effect of

[Second embodiment]
Next, a second embodiment of the present invention will be described. FIG. 12 is a schematic diagram showing an example of a configuration in which a diffraction grating 50 is combined with the photodiode 30 and the silicon waveguide 36 according to the first embodiment.

In the configuration shown in FIG. 12, the received light 42 is incident on the silicon waveguide 36, which is a planar waveguide, through the diffraction grating 50, and the reference light 44 is transmitted through the grating of the diffraction grating 50 and is incident on the silicon waveguide 36. , the signal light 42 and the reference light 44 are interference-multiplexed and made incident on the photodiode 30 .

FIG. 13 is a schematic diagram showing another example of a configuration in which a diffraction grating 50 is combined with the photodiode 30 and silicon waveguide 36 according to the first embodiment. The configuration shown in FIG. 13 is different from the configuration shown in FIG. 12 in that it includes a mirror 28 that reflects the reference light 44 incident substantially perpendicularly to the received light 42 from the side.

Unlike the configuration shown in FIG. 12, the configuration shown in FIG. 13 does not require the waveguide of the reference light 44 to pass through the grating of the diffraction grating 50. Therefore, the function of the diffraction grating 50 is eliminated. Since there is no obstruction and the waveguide of the reference light 44 can be made shorter than the configuration shown in FIG. 12, attenuation of the reference light 44 propagating through the waveguide can be suppressed. In the pattern of the diffraction grating 50 shown in FIGS. 12 and 13, concentric arc-shaped or concentric elliptical arc-shaped grooves centered on a point on the optical axis of the received light 42 emitted from the diffraction grating 50 are arranged at predetermined intervals. It is a thing.

FIG. 14 is a block diagram showing an example of rangefinder chip 60 including the configuration shown in FIG. In the rangefinder chip 60, laser light propagates through the waveguide 102 from the laser light source 114, and part of the propagated laser light (for example, 10% of the incident laser light) passes through the waveguide 102D in the directional coupler 116. is looped back to The laser light looped back to the waveguide 102D is reflected by the mirror 28 and enters the photodiode 30 as the reference light 44. FIG. Directional coupler 116 is an example of a feedback section.

The waveguide 102, together with a waveguide 102D and 102C described later, has a double-clad structure in which the core is double-coated. The core is made of a Si-based material such as SiO ₂ with a high refractive index, and the clad surrounding the core is made of fluorine-doped SiO ₂ or the like with a lower refractive index than the core. The laser light output from the laser light source 114 basically propagates straight through the cores of the waveguides 102, 102C, and 102D, but the bent portions of the waveguides 102, 102C, and 102D propagate through the high-refractive-index cores. propagates by repeated reflections between the cladding and the low-refractive-index cladding. Waveguides 102 , 102 C, 102 D shown in FIG. 14 are planar waveguides mounted on a plane on rangefinder chip 60 .

The laser light separated from the reference light 44 by the directional coupler 116 propagates through the waveguide 102C, is incident on the diffraction grating 52 as the transmission light 46, and is emitted from the diffraction grating 52 to the outside world. The pattern of the diffraction grating 52 shown in FIG. 14 is such that concentric arc-shaped or concentric elliptical arc-shaped grooves centered on a point on the optical axis of the incident transmission light 46 are arranged at predetermined intervals.

The transmitted light 46 emitted from the diffraction grating 52 to the outside world is reflected by the object, and the reflected light is incident on the diffraction grating 50 and becomes the received light 42 . The received light 42 enters the silicon waveguide 36 together with the reference light 44 , and the photodiode 30 performs heterodyne detection for interference-multiplexing the signal light 42 and the reference light 44 .

FIG. 15 is a schematic diagram showing an example of the configuration of a rangefinder using the rangefinder chip 60 shown in FIG. As shown in FIG. 15, the transmission light 46 emitted from the diffraction grating 52 is emitted to the outside through the transmission lens 24 .

In the rangefinder shown in FIG. 15, the imaging lens 20 receives the reflected light of the transmitted light 46 from the object as the received light 42 . The received light 42 is condensed onto the diffraction grating 50 by the imaging lens 20, and the photodiode 30 performs optical heterodyne detection to generate an intermediate frequency by causing the condensed received light 42 to interfere with the reference light 44. done. As a result of optical heterodyne detection, a beat signal corresponding to the intermediate frequency between the received light 42 and the reference light 44 is output as an electrical signal.

The beat signal generated by optical heterodyne detection contains information about the frequency difference between the transmitted light 46 and the received light 42 . The rangefinder shown in FIG. 15 extracts information on the frequency difference between the transmitted light 46 and the received light 42 from the electrical signal related to the beat signal, and measures the distance to the object by FMCW (frequency modulated continuous wave). I do.

Further, in the rangefinder shown in FIG. 15, the waveform of the current supplied to the laser light source 114 is a triangular wave, and by modulating the triangular wave, the wavelength of the transmission light 46 output from the laser light source 114 can be measured by FMCW. can be changed to the optimum frequency.

FIG. 16 is a schematic diagram of a rangefinder chip that is a modification of rangefinder chip 60 shown in FIG. This is different from the rangefinder chip 60 in FIG. However, since other configurations are the same as the rangefinder chip 60, the same configurations as in FIG.

Modulator 130 uses, as an example, a Mach-Zehnder interferometer. As an example, the Mach-Zehnder interferometer in the modulator 130 has an optical path composed of a semiconductor such as InP, and changes the intensity and waveform of the transmitted light 46 according to the intensity and waveform of the voltage applied to the semiconductor from an external power supply. modulate. In the rangefinder chip 62, for example, the modulator 130 modulates the transmission light 46 from a triangular wave to a rectangular wave.

FIG. 17 is a schematic diagram showing an example of the configuration of a rangefinder using the rangefinder chip 62 shown in FIG. 17 differs from the rangefinder in FIG. 15 in that it further includes a modulator 130, an external power source 140, and a phase comparator 142. The rangefinder shown in FIG. However, since other configurations are the same as those of the rangefinder in FIG. 15, the same reference numerals are assigned to the same configurations as in FIG. 15, and detailed description thereof will be omitted.

In the rangefinder shown in FIG. 17, the waveform of the current supplied to the laser light source 114 is a triangular wave, and the wavelength of the laser light output from the laser light source 114 is changed by modulating the triangular wave.

The intensity and waveform of the transmission light 46 output from the laser light source 114 are modulated by the modulator 130 . The modulator 130 modulates the intensity and waveform of the transmitted light 46 according to the intensity and waveform of the current supplied from the external power supply 140 . Since the modulator 130 modulates the transmission light 46 according to the phase of the current supplied from the external power supply 140, when the current changing in a rectangular wave form is supplied from the external power supply 140 to the modulator 130, the modulator 130 , modulates the transmitted light 46 from a triangular wave to a rectangular wave.

In the rangefinder shown in FIG. 17, the imaging lens 20 receives the reflected light of the transmitted light 46 from the object as the received light 42 . The received light 42 is condensed onto the diffraction grating 50 by the imaging lens 20, and the photodiode 30 performs optical heterodyne detection to generate an intermediate frequency by causing the condensed received light 42 to interfere with the reference light 44. done. As a result of optical heterodyne detection, a beat signal corresponding to the intermediate frequency between the received light 42 and the reference light 44 is output as an electrical signal.

The phase comparator 142 compares the phase of the electrical signal output by the photodiode 30 and the phase of the current of the external power supply 140 to determine the phase of the electrical signal output by the photodiode 30 and the phase of the current of the external power supply 140. Detects the shift (phase shift) from the Since the phase shift changes according to the distance to the object, it is possible to measure the distance to the object based on the phase shift.

In the rangefinder shown in FIG. 15, both the received light 42 and the reference light 44 are triangular waves. Therefore, since it is difficult to detect the phase shift between the received light 42 and the reference light 44, the distance to the object is measured based on the frequency difference between the received light 42 and the reference light 44. FIG.

However, with a square wave, it is easier to detect a phase shift than with a triangular wave. 17 compares the phase of the electrical signal output by the photodiode 30 based on the received light 42 with the phase of the current output by the external power supply 140, thereby determining the distance to the object by FMCW. Measure the distance.

FIG. 18 is a schematic diagram of a configuration in which the incident direction of the reference light 44 is changed from the configuration shown in FIG. 12 or 13. FIG. If the optical axis of the received light 42 and the optical axis of the reference light 44 are aligned as in the configuration shown in FIG. 12 or 13, the reception of part of the received light 42 is blocked. This is because the structure shown in FIG. 12 has a portion through which the reference light 44 is transmitted, and the structure shown in FIG. 13 has the mirror 28 that reflects the reference light 44 .

In the configuration shown in FIG. 18, the optical axis of the received light 42 and the optical axis of the reference light 44 are shifted by an arbitrary angle instead of being aligned, so that the optical axis of the received light 42 and that of the reference light 44 are aligned. cross. A diffraction grating 54 is provided at the position where the optical axis of the received light 42 and the optical axis of the reference light 44 intersect, and the received light 42 and the reference light 44 are coupled (interfered) by the diffraction grating 54 .

The diffraction grating 54 emits light resulting from interference between the received light 42 and the reference light 44 in the optical axis direction of the received light 42 and the optical axis direction of the reference light 44 . The light emitted from the diffraction grating 54 is received by a photodiode 30A integrated with the silicon waveguide 36A and a photodiode 30B integrated with the silicon waveguide 36B, and converted into an electric signal.

If the optical axis of the received light 42 and the optical axis of the reference light 44 are coincident, the reception of part of the received light 42 is blocked as described above. This problem is solved by shifting the optical axis by a predetermined angle instead of aligning it with the optical axis.

FIG. 19 is one of modifications of the configuration shown in FIG. While the configuration shown in FIG. 18 required two photodetectors, photodiode 30A and photodiode 30B, the configuration shown in FIG. The light emitted from the diffraction grating 54 is folded back (reflected) by 58 and focused on the photodiode 30 . The diffraction gratings 56 and 58 are arranged so that the reflected light from each of them intersects, and the photodiode 30 is provided at the intersecting position.

The diffraction gratings 56 and 58 have a larger number of grooves per unit area than the diffraction grating 54 and have a finer grating pitch. Such fine pitch enables the diffraction gratings 56 and 58 to efficiently reflect the light emitted from the diffraction grating 54 .

FIG. 20 is a modification of the configuration shown in FIG. 19, and differs from the configuration shown in FIG. 19 in that mirrors 64 and 66 are provided instead of the diffraction gratings 56 and 58. Since the configuration is the same as that shown in FIG. 19, the same reference numerals are assigned to the same configurations, and detailed description thereof will be omitted.

FIG. 21 is a schematic diagram showing an example of the mirrors 64,66. Light emitted from the diffraction grating 54 travels in the block-shaped medium as indicated by arrows in FIG. 21 and is reflected. Blocks forming the mirrors 64 and 66 are made of a material having a higher refractive index than _SiO2 . The material is, for example, Si simple substance, Ge simple substance, or the like.

FIG. 22 is a schematic diagram showing an example in which a plurality of configurations shown in FIG. 20 are provided. The configuration shown in FIG. 22 includes a unit including diffraction gratings 50A, 54A, mirrors 64A, 66A, and photodiode 30C integrated with silicon waveguide 36C; A unit including a photodiode 30D integrated with a waveguide 36D, and a unit including a photodiode 30E integrated with diffraction gratings 50C, 54C, mirrors 64C, 66C and a silicon waveguide 36E. In FIG. 22 and FIG. 23, which will be described later, three units each including the diffraction gratings 50A, 50B, and 50C are shown for convenience of explanation using the drawings. good.

In the configuration shown in FIG. 22, the received light 42A emitted from the diffraction grating 50A and the reference light 44A generated by diffracting the reference light 44 by the diffraction grating 58A are combined by the diffraction grating 54A and emitted. Light emitted by 54A is reflected by mirrors 64A and 66A and condensed on photodiode 30C.

Since part of the reference light 44 is transmitted through the diffraction grating 58A, the transmitted light is diffracted by the diffraction grating 58B and emitted as the reference light 44B to the diffraction grating 54B. Since the received light 42B emitted from the diffraction grating 50B is incident on the diffraction grating 54B, the diffraction grating 54B couples the received light 42B and the reference light 44B and emits the light, and mirrors the light emitted from the diffraction grating 54B. The light is reflected by 64B and 66B and focused on the photodiode 30D.

The light transmitted through the diffraction grating 58B is diffracted by the diffraction grating 58C and emitted to the diffraction grating 54C as the reference light 44C. Since the received light 42C emitted from the diffraction grating 50C is incident on the diffraction grating 54C, the diffraction grating 54C couples the received light 42C and the reference light 44C and emits the light, and mirrors the light emitted from the diffraction grating 54C. The light is reflected by 64C and 66C and focused on the photodiode 30E. The mirrors 64A, 64B, 64C, 66A, 66B, and 66C may be reflecting members other than mirrors, such as diffraction gratings with a fine grating pitch, such as the diffraction gratings 56 and 58 shown in FIG.

If the configuration shown in FIG. 22 is mounted on one chip, an optical heterodyne photodetector module can be constructed that efficiently couples the received light 42 and the reference light 44 to perform heterodyne detection. FIG. 23 is a schematic diagram showing an example of an optical heterodyne detection light-receiving module 160 including the configuration shown in FIG.

The optical heterodyne detection light-receiving module 160 shown in FIG. 23 causes the received light 42 to enter the diffraction gratings 50A, 50B, and 50C through the imaging lens 220, and the received lights 42A, 42B, and 42C, similarly to the configuration shown in FIG. , and the reference beams 44A, 44B, and 44C can be efficiently coupled to perform heterodyne detection. In FIG. 23, the imaging lens 220 is represented by a single large lens, but has a plurality of imaging lenses corresponding to each of the diffraction gratings 50A, 50B, and 50C, and the plurality of imaging lenses are arranged. A lens array may be constructed.

The configurations shown in FIGS. 12 to 23 are provided with the diffraction grating 52 and the like, so that the transmission light is transmitted at an angle (for example, approximately 90 degrees) corresponding to the effective refractive index of the diffraction grating 52 with respect to the thin-film waveguide 102 and the like. 46 can be emitted. 12 to 23 is provided with the diffraction grating 50 and the like, the angle (for example, approximately 90 degrees) corresponding to the effective refractive index of the diffraction grating 50 with respect to the thin-film waveguide 36 and the like is provided. Incoming light can be received and guided to a thin-film waveguide 36 or the like.

In the laser radar device, optical lenses are required for projecting the transmission light 46 and for converging the reception light 32. If the diffraction gratings 50, 52, etc. are not provided, the waveguides 36, 102, etc. and the optical lenses are respectively required. This increases the volume of the device in the front-rear direction, making it difficult to make the device compact.

In this embodiment, by bending the optical paths of the transmission light 46 and the reception light 42 by means of diffraction gratings 50 and 52, etc., a laser radar device having an optical lens at its front end can be improved. The dimension to the rear end should be about the focal length of the optical lens.

As a result, the volume of the entire laser radar device including the optical lens is suppressed compared to the case where the diffraction gratings 50, 52 and the like are not provided, and the laser radar device can be made compact.

10 Optical heterodyne detector 20 Imaging lens 22 Optical axis 24 Transmission lens 30 Photodiode 32 Electrode 32N N electrode 32P P electrode 34 Ge absorption layers 36, 36A, 36B Silicon waveguide 36B1 First Si layer 36B2 SiO ₂ layer 36B3 Second Si Layer 36C P+Si layer 36D P-Si layers 38, 38A SiO ₂ substrate 40 Incident light 42 Received light 44 Reference light 46 Transmitted light 50, 50A, 50B, 50C, 52, 54, 54A, 54B, 54C, 56, 58, 58A , 58B, 58C diffraction gratings 60, 62 rangefinder chips 64, 64A, 64B, 64C, 66 mirror 100 distance sensors 102, 102A, 102B, 102C, 102D waveguides 110, 110A optical integrated circuit chip 112 drive circuit 114 laser light source 116 directional coupler 118 phase modulator 120 drive circuit 122 preamplifier 124 AD converter 126 control/arithmetic processor 130 modulator 140 external power supply 142 phase comparator 160 optical heterodyne detection light receiving module 220 imaging lens

Claims (26)

a condensing unit condensing received light that is reflected by an object from the transmitted light output by the laser light source;
As the reference light, which is a part of the light output from the laser light source, and the received light condensed by the condensing section propagate , the width of the reference light gradually expands in the direction of incidence of the reference light. , a waveguide comprising an enlarging portion for enlarging the light flux of the reference light ;
a light receiving unit that receives light generated as a result of interference between the reference light and the received light in the waveguide and converts the light into an electrical signal;
An optical heterodyne detector with 2. The optical heterodyne detector according to claim 1 , wherein said enlarged portion is formed in a reverse tapered shape with respect to the direction of incidence of said reference light. The waveguide is a thin-film waveguide,
3. An optical heterodyne detector according to claim 1, wherein said light receiving section comprises an absorption layer and an electrode laminated on one end side of said thin-film waveguide . The optical heterodyne detector according to any one of claims 1 to 3, wherein the condensing part is an optical lens. The optical heterodyne detector according to any one of claims 1 to 4 , further comprising a receiving diffraction grating between the light condensing section and the waveguide. 6. The pattern of the reception diffraction grating according to claim 5 , wherein concentric elliptical arc-shaped grooves centered at a point on the optical axis of the reception light emitted from the reception diffraction grating are arranged at predetermined intervals. optical heterodyne detector. 7. The optical heterodyne detector according to claim 6 , wherein said pattern comprises concentric arc-shaped grooves centered at a point on the optical axis of the received light emitted from said reception diffraction grating and arranged at predetermined intervals. 7. The optical heterodyne detector according to claim 5 , wherein the reference light is incident on the waveguide through the reception diffraction grating. 6. A reflecting mirror is provided between the reception diffraction grating and the waveguide, and the reflecting mirror reflects the reference light incident from the side of the optical axis of the waveguide toward the waveguide. Or the optical heterodyne detector according to claim 6 . the reception diffraction grating is arranged such that the optical axis of the reference light and the optical axis of the reception light emitted from the reception diffraction grating intersect;
is arranged at a position where the optical axis of the reference light and the optical axis of the received light emitted from the reception diffraction grating intersect, interferes the received light and the reference light, and is produced as a result of the interference further comprising a coupling diffraction grating for emitting light in each of the optical axis direction of the received light and the optical axis direction of the reference light;
The waveguides include a first waveguide through which light emitted from the coupling diffraction grating in the optical axis direction of the received light propagates, and light emitted from the coupling diffraction grating in the optical axis direction of the reference light. comprising a second waveguide through which propagates
The light-receiving unit includes a first light-receiving unit that receives light propagated through the first waveguide and converts it into an electric signal, and a second light-receiving unit that receives light propagated through the second waveguide and converts it into an electric signal. 7. The optical heterodyne detector according to claim 5 , comprising two light receiving sections. the reception diffraction grating is arranged such that an optical axis of the reference light and an optical axis of the reception light emitted from the reception diffraction grating intersect;
is arranged at a position where the optical axis of the reference light and the optical axis of the received light emitted from the reception diffraction grating intersect, interferes the received light and the reference light, and is produced as a result of the interference a coupling diffraction grating for emitting light in each of the optical axis direction of the received light and the optical axis direction of the reference light;
a first reflector that reflects the light emitted from the coupling diffraction grating in the optical axis direction of the received light toward the waveguide;
a second reflector that reflects the light emitted from the coupling diffraction grating in the optical axis direction of the reference light toward the waveguide;
7. An optical heterodyne detector according to claim 5 or claim 6 , further comprising: 12. The optical heterodyne detector according to claim 11 , wherein each of said first reflector and said second reflector is a diffraction grating having a finer grating pitch than said coupling diffraction grating. 12. The optical heterodyne detector according to claim 11 , wherein each of said first reflector and said second reflector is a reflector. 11. An optical heterodyne light-receiving module in which a plurality of structures including the reception diffraction grating, the coupling diffraction grating, the first reflector, the second reflector and the light-receiving part are mounted on the same chip. Item 14. The optical heterodyne detector according to any one of Item 13 . 15. The optical heterodyne detector according to claim 14 , further comprising a reference beam diffraction grating arranged for each of said plurality of mounted structures and emitting said reference beam toward said coupling diffraction grating. an optical heterodyne detector according to any one of claims 1 to 15 ;
a light projecting unit that projects the transmission light output from the laser light source to the outside world;
a feedback unit that feeds back part of the light output from the laser light source to the waveguide as the reference light;
a computing unit that measures the distance to an object based on the electrical signal output by the light receiving unit;
A laser radar device with 17. The laser radar device according to claim 16 , wherein the light projecting section includes a transmission diffraction grating that refracts and emits the transmission light output from the laser light source. 18. The pattern of the transmission diffraction grating according to claim 17 , wherein concentric elliptical arc-shaped grooves centered at a point on the optical axis of transmission light incident on the transmission diffraction grating are arranged at predetermined intervals. of laser radar equipment. 19. The laser radar device according to claim 18 , wherein said pattern is formed by concentric arcuate grooves centered at a point on the optical axis of the transmission light incident on said transmission diffraction grating, arranged at predetermined intervals. 20. The laser radar device according to any one of claims 17 to 19 , wherein the light projecting section projects the transmission light emitted from the transmission diffraction grating to the outside world through a transmission lens. 21. The laser radar device according to any one of claims 17 to 20 , wherein said light projecting section comprises a modulator that modulates the intensity and waveform of said transmission light. 22. The laser radar apparatus according to claim 21 , wherein said modulator is a Mach-Zehnder interferometer capable of modulating the waveform of said transmitted light into a rectangular wave. 23. The laser radar device according to any one of claims 16 to 22 , wherein the waveguide has a double clad structure in which a thin-film waveguide is covered with a silicon layer. 24. The laser radar device according to any one of claims 16 to 23 , wherein said waveguide is a planar waveguide formed on a substrate plane. 25. The laser radar device according to any one of claims 16 to 24 , wherein the waveguide includes a straight waveguide composed of straight lines. 26. The laser radar device according to any one of claims 16 to 25 , wherein the laser light source has a polarizing filter, and can output either orthogonally polarized waves or parallel polarized waves by applying the polarizing filter.

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