JP2020056658A - An optical heterodyne detector and a laser radar device using the optical heterodyne detector. - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a laser radar device using an optical heterodyne detector and an optical heterodyne detector capable of highly sensitive measurement and having high reliability. An imaging lens 20 in which a transmitted light 46 output by a laser light source 114 collects a received light 42 reflected by an object, a reference light 44 which is a part of the light output by the laser light source 114, and a reference light 44. A photodiode that receives light generated as a result of interference between the waveguide 102A, in which the received light 42 focused by the imaging lens 20 propagates, and the reference light 44 and the received light 42 in the waveguide 120A, and converts the light into an electric signal. 30 and. [Selection diagram] FIG. 9

Description

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

  In a laser radar device, for example, a distance to an object is measured based on a phase difference between transmitted light and received light reflected by the antenna and reflected by the antenna. Although a photodiode is used to detect the received light, since the received light may include various noises, a component derived from the received light and transmitted light is generated by multiplexing and interfering the received light with a reference light having a constant wavelength. Is performed by optical heterodyne detection.

  Patent Literature 1 discloses an invention of a laser radar device capable of performing highly sensitive measurement using optical heterodyne detection and having high reliability, and an optical receiving method of the laser radar device.

JP-A-2006-105082

  By the way, the laser radar device disclosed in Patent Document 1 has an advantage that a configuration capable of optical heterodyne detection can be easily constructed. However, depending on the wavelength to be received, it is necessary to use a thick heteroepitaxial substrate for the photodiode. However, the production cost of the product may increase.

  The present invention has been made in view of the above-described problems, and uses an optical heterodyne detector and an optical heterodyne detector that can perform high-sensitivity measurement with a simple configuration and perform highly reliable optical heterodyne detection. It is an object of the present invention to realize a laser radar device.

  In order to achieve the above object, an optical heterodyne detector according to claim 1, wherein a condensing unit that condenses received light, in which transmission light output from a laser light source is reflected by an object, is output by the laser light source. Reference light that is a part of the reflected light, and a waveguide through which the reception light collected by the light collection unit propagates, and light generated as a result of causing the reference light and the reception light to interfere with each other in the waveguide. And a light receiving unit that receives light and converts it into an electric signal.

  The optical heterodyne detector according to claim 2 is the optical heterodyne detector according to claim 1, wherein the waveguide is a thin-film waveguide, and the light receiving unit is the thin-film waveguide. Is provided with an absorption layer and an electrode laminated on one end side of the.

  In the optical heterodyne detector according to a third aspect, in the optical heterodyne detector according to the first or second aspect, the condensing unit is an optical lens.

  The optical heterodyne detector according to claim 4 is the optical heterodyne detector according to any one of claims 1 to 3, wherein the waveguide expands the reference light to the light receiving unit. An enlargement unit for receiving light is provided.

  In the optical heterodyne detector according to a fifth aspect, in the optical heterodyne detector according to the fourth aspect, the enlarged portion is formed in a reverse tapered shape with respect to the incident direction of the reference light.

  The optical heterodyne detector according to claim 6 is the optical heterodyne detector according to any one of claims 1 to 5, wherein a diffraction for reception is provided between the condensing unit and the waveguide. It has a grid.

  In the optical heterodyne detector according to claim 7, in the optical heterodyne detector according to claim 6, the pattern of the diffraction grating for reception is on an optical axis of the reception light emitted from the diffraction grating for reception. Concentric elliptical arc-shaped grooves centered at one point are arranged at predetermined intervals.

  The optical heterodyne detector according to claim 8 is the optical heterodyne detector according to claim 7, wherein the pattern is centered on one point on the optical axis of the reception light emitted from the reception diffraction grating. Concentric arc-shaped grooves are arranged at predetermined intervals.

  The optical heterodyne detector according to claim 9 is the optical heterodyne detector according to claim 6 or 7, wherein the reference light is transmitted through the receiving diffraction grating and is incident on the waveguide. .

  An optical heterodyne detector according to a tenth aspect is the optical heterodyne detector according to the sixth or seventh aspect, wherein a reflecting mirror is provided between the receiving diffraction grating and the waveguide. The mirror reflects the reference light incident from the side of the optical axis of the waveguide toward the waveguide.

  The optical heterodyne detector according to claim 11 is the optical heterodyne detector according to claim 6 or 7, wherein the receiving diffraction grating comprises: an optical axis of the reference light; and the receiving diffraction grating. Is arranged so that the optical axis of the received light emitted from the intersection, the optical axis of the reference light and the optical axis of the received light emitted from the receiving diffraction grating are arranged at a position where they intersect, Interfering the received light and the reference light, further comprising a coupling diffraction grating that emits light resulting from the interference in the optical axis direction of the received light and in the optical axis direction of the reference light, respectively. The waveguide is 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 is transmitted through the first waveguide. A second waveguide that propagates, wherein the light receiving unit is A first light receiving unit that receives the light propagated through the first waveguide and converts the light into an electric signal; and a second light receiving unit that receives the light propagated through the second waveguide and converts the light into an electric signal. ing.

  The optical heterodyne detector according to claim 12 is the optical heterodyne detector according to claim 6 or claim 7, wherein the receiving diffraction grating comprises: an optical axis of the reference light; and the receiving diffraction grating. Is arranged so that the optical axis of the received light emitted from the intersection, the optical axis of the reference light and the optical axis of the received light emitted from the receiving diffraction grating are arranged at a position where they intersect, 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 the optical axis direction of the received light and the optical axis direction of the reference light, respectively; A first reflection unit that reflects light emitted from the diffraction grating in the optical axis direction of the reception light toward the waveguide, and light emitted in the optical axis direction of the reference light from the coupling diffraction grating. A second reflector for reflecting light toward the waveguide; Further comprising.

  The optical heterodyne detector according to claim 13 is the optical heterodyne detector according to claim 12, wherein each of the first reflection section and the second reflection section has a grating pitch of the coupling diffraction grating. This is a finer diffraction grating.

  The optical heterodyne detector according to claim 14 is the optical heterodyne detector according to claim 12, wherein each of the first reflection section and the second reflection section is a reflection mirror.

  The optical heterodyne detector according to claim 15 is the optical heterodyne detector according to any one of claims 12 to 14, wherein the receiving diffraction grating, the coupling diffraction grating, and the first An optical heterodyne light receiving module in which a plurality of components including a reflecting portion, the second reflecting portion, and the light receiving portion are mounted on the same chip.

  The optical heterodyne detector according to claim 16 is the optical heterodyne detector according to claim 15, wherein the optical heterodyne detector is arranged for each of the plurality of components, and directs the reference light toward the coupling diffraction grating. It further comprises a reference light diffraction grating to be emitted.

  A laser radar device according to claim 17, an optical heterodyne detector according to any one of claims 1 to 16, and a light emitting unit that emits transmission light output from the laser light source to the outside world, A feedback unit that returns a part of the light output by the laser light source to the waveguide as the reference light, and a calculation unit that measures a distance to an object based on the electric signal output by the light receiving unit. ing.

  The laser radar device according to claim 18 is the laser radar device according to claim 17, wherein the light projecting unit includes a transmission diffraction grating that refracts and emits the transmission light output from the laser light source. Prepare.

  In the laser radar device according to the nineteenth aspect, in the laser radar device according to the eighteenth aspect, the pattern of the transmission diffraction grating is a point on the optical axis of transmission light incident on the transmission diffraction grating. Concentric elliptical arc-shaped grooves at the center are arranged at predetermined intervals.

  According to a twentieth aspect of the present invention, in the laser radar apparatus according to the nineteenth aspect, the pattern has a concentric arc shape centered on a point on an optical axis of transmission light incident on the transmission diffraction grating. Are arranged at predetermined intervals.

  The laser radar device according to claim 21 is the laser radar device according to any one of claims 18 to 20, wherein the light projecting unit is configured to transmit the transmission light emitted from the transmission diffraction grating. Is projected to the outside world via a transmission lens.

  The laser radar device according to claim 22 is the laser radar device according to any one of claims 18 to 21, wherein the light projecting unit modulates an intensity and a waveform of the transmission light. Equipped with a vessel.

  The laser radar device according to claim 23 is the laser radar device according to claim 22, wherein the modulator is a Mach-Zehnder interferometer capable of modulating a waveform of the transmission light into a rectangular wave.

  The laser radar device according to claim 24 is the laser radar device according to any one of claims 17 to 23, wherein the waveguide covers the thin film type waveguide with a silicon layer. It is a configured double clad structure.

  A laser radar device according to a twenty-fifth aspect is the laser radar device according to any one of the seventeenth to twenty-fourth aspects, wherein the waveguide is a planar waveguide formed on a plane of the substrate.

  A laser radar device according to a twenty-sixth aspect is the laser radar device according to any one of the seventeenth to twenty-fifth aspects, wherein the waveguide includes a linear waveguide configured by a straight line. .

  A laser radar device according to a twenty-seventh aspect is the laser radar device according to any one of the seventeenth to twenty-sixth aspects, wherein the laser light source includes a polarization filter, and the laser light source is orthogonalized by applying the polarization filter. Either polarized wave or parallel polarized wave can be output.

  ADVANTAGE OF THE INVENTION According to this invention, there exists an effect that highly sensitive measurement is possible and an optical heterodyne detector with high reliability can be implement | achieved.

FIG. 2 is a schematic diagram illustrating an example of a minimum configuration of the optical heterodyne detector according to the first embodiment of the present invention. FIG. 2 is a side view of the photodiode illustrated in FIG. 1 when viewed from an arrow A direction. FIG. 3 is a schematic diagram illustrating the principle of optical heterodyne detection of the optical heterodyne detector according to the embodiment of the present invention. FIG. 4 is a side view of the photodiode illustrated in FIG. 3 when viewed from an arrow B direction. (A) is an explanatory view showing an example of a silicon waveguide for expanding the light flux of the reference light, and (B) is an explanatory diagram showing an example of a silicon waveguide widened to make it easier to receive the received light. It is the schematic which showed the detailed structure of the photodiode. FIG. 7 is a cross-sectional view showing a state where the photodiode of FIG. 6 is cut along the line CC. FIG. 8 is an overhead view of the photodiode illustrated in FIG. 7 when viewed from the direction of arrow D. FIG. 2 is a block diagram showing an example of a distance sensor using an optical heterodyne detector including a photodiode according to the embodiment of the present invention. FIG. 9 is a block diagram showing a modified example of an optical integrated circuit chip in which a plurality of photodiodes are provided corresponding to an image plane formed by an imaging lens. FIG. 9 is a schematic diagram showing a modified example of an optical integrated circuit chip in which a plurality of photodiodes are arranged so as to receive light received in the horizontal direction of the image formed by the imaging lens. FIG. 2 is a schematic diagram illustrating an example of a configuration in which a diffraction grating is combined with the photodiode and the silicon waveguide according to the first embodiment of the present invention. It is the schematic which showed the other example of the structure which combined the diffraction grating with the photodiode and silicon waveguide which concern on 1st Embodiment of this invention. FIG. 14 is a block diagram illustrating an example of a rangefinder chip including the configuration illustrated in FIG. 13. FIG. 15 is a schematic diagram illustrating an example of a configuration of a range finder using the range finder chip illustrated in FIG. 14. FIG. 15 is a schematic diagram of a rangefinder chip which is a modification of the rangefinder chip shown in FIG. 14. FIG. 17 is a schematic diagram illustrating an example of a configuration of a range finder using the range finder chip illustrated 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 13. This is one of modified examples of the configuration shown in FIG. FIG. 20 is a schematic diagram illustrating a modification of the configuration illustrated in FIG. 19 and including a mirror and a mirror instead of the diffraction grating. It is the schematic which showed an example of the mirror. FIG. 21 is a schematic diagram illustrating an example in which a plurality of configurations illustrated in FIG. 20 are provided. 23 is a schematic diagram illustrating an example of an optical heterodyne detection light receiving module including the configuration illustrated in FIG. 22.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings. First, a 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 illustrating an example of a minimum configuration of the optical heterodyne detector 10 according to the present embodiment. As shown in FIG. 1, the optical heterodyne detector 10 is configured to include 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 reflecting a laser beam output from a laser light source described later on an object. In FIG. 1, a simple configuration like a single convex lens is used. However, a plurality of lens configurations including a convex lens and a concave lens may be used in order to collect the received light on the photodiode 30. Alternatively, an aspherical surface may be employed if necessary.

The photodiode 30 is formed in a band shape on the SiO ₂ substrate 38 such that the longitudinal direction of the 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, for example, heteroepitaxial. The photodiode 30 according to the present embodiment is configured so that light having a wavelength other than the visible light to the near infrared region can be detected by mounting the Ge absorption layer 34 instead of Si.

  When light enters the junction surface between the silicon waveguide 36 and the Ge absorption layer 34, the photodiode 30 generates a current that changes according to the intensity of the incident light. The generated current is conducted outside through the electrode 32. The electrode 32 is formed by evaporating a metal having good conductivity, 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 when viewed from the direction of arrow A. As shown in FIG. 2, the photodiode 30 according to the present embodiment is disposed such that the bonding surface between the silicon waveguide 36 and the Ge absorption layer 34 coincides with the optical axis 22 of the imaging lens 20. You. Alternatively, the configuration may be such that the silicon waveguide 36 exists on the extension of the optical axis 22 of the imaging lens 20.

Further, the photodiode 30 is to protect the silicon waveguide 36, Ge absorbing layer 34 and the electrodes 32 formed on the SiO ₂ substrate 38 is covered with SiO ₂ constituting the SiO ₂ substrate 38. Even if the photodiode 30 is covered with SiO ₂ , the configuration of the photodiode 30 is a thin film, which is a simpler configuration than the light receiving element according to the laser radar device described in Patent Document 1.

  FIG. 3 is a schematic diagram illustrating the principle of optical heterodyne detection of the optical heterodyne detector 10 according to the present 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 the reception light 42. The reference light 44 is also incident on the silicon waveguide 36, and optical heterodyne detection for generating an intermediate frequency by causing the received light 42 and the reference light 44 to interfere with each other is performed. The signal of the intermediate frequency resulting from the interference between the received light 42 and the reference light 44 becomes a so-called beat signal, and a current that changes according to the strength of the beat signal is output as an electric signal.

  In the photodiode 30, the silicon waveguide 36 is formed integrally, the reference light 44 is guided to the silicon waveguide 36 with good reproducibility, and the reception light 42 is condensed by the imaging lens 20 so that the efficiency of the reference light 44 is reduced. Well multiplexed. By condensing the received light 42 by the imaging lens 20, the received light 42 is taken in beyond the frame of the silicon waveguide 36, the amount of the received light 42 increases, and the sensitivity of the photodiode 30 can be improved. it can.

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

  FIG. 5A shows an example of a silicon waveguide that expands the light flux of the reference light 44, and FIG. 5B shows an example of a silicon waveguide that is widened so that the reception light 42 can be easily received. FIG.

  As shown in FIG. 5A, the silicon waveguide 36A has an isosceles triangular shape having a vertex at the side where the reference light 44 is incident, and has a reverse tapered shape whose width gradually increases. The width is configured to be maximum and constant at the provided position. By gradually increasing the width of the silicon waveguide 36A with respect to the incident direction of the reference light 44, the luminous flux of the reference light 44 propagating through the silicon waveguide 36A is expanded, and interferes with the reception light 42 in optical heterodyne detection. Easier to do.

As shown in FIG. 5B, the silicon waveguide 36B is configured to be wide by the Si-rich SiO ₂ layer 36B2, and the received light 42 is captured by the widened silicon waveguide 36B. The silicon waveguide 36B has an isosceles triangular shape whose bottom is the side on which the received light 42 is incident and has a tapered shape whose width gradually decreases, and becomes a vertex near the position where the Ge absorption layer 34 is provided. The first Si layer 36B1 configured as described above is provided. The width of the first Si layer 36B1 gradually decreases in the incident direction of the received light 42, so that the light flux of the received light 42 propagating through the first Si layer 36B1 is converged. The light beam of the reception light 42 may be wider than the light beam of the reference light 44 in some cases. Therefore, by converging the light beam of the reception light 42, it becomes easy to interfere with the reference light 44 in optical heterodyne detection.

  Further, a second Si layer 36B3 is provided around the Ge absorption layer 34. By configuring the second Si layer 36B3 wider than the width of the Ge absorption layer 34, even when the light flux of the received light 42 is not sufficiently converged by the first Si layer 36B1, the second Si layer 36B3 is wide in the optical heterodyne detection. The interference between the reception light 42 and the reference light 44 is facilitated.

FIG. 6 is a schematic diagram showing the detailed structure of the photodiode 30. In the photodiode 30, a silicon waveguide 36 made of Si is formed in a band shape on an SiO ₂ substrate 38, a Ge absorption layer 34 is formed on the silicon waveguide 36, and a Ge absorption layer 34 is formed on the Ge absorption layer 34. Are formed with an N electrode 32N and a P electrode 32P on the silicon waveguide 36, respectively. The silicon waveguide 36 and the Ge absorption layer 34 are each formed by, for example, heteroepitaxial.

FIG. 7 is a cross-sectional view showing a state where the photodiode 30 of FIG. 6 is cut along the line CC. The silicon waveguide 36 formed on the SiO ₂ substrate 38 is made of a P-type semiconductor in which Si is doped with an impurity such as boron. The silicon waveguide 36 has a P + Si layer 36C rich in the impurity and a P-Si layer 36D lean in the impurity, 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 made of an N-type semiconductor in which Ge is doped 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 an SiO ₂ substrate 38 for protecting 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 the constituent SiO ₂ .

  As shown in FIG. 7, a P + Si layer 36C, a P-Si layer 36D, and a Ge absorption layer 34 that is an N-type semiconductor are interposed between the P electrode 32P and the N electrode 32N. In the P + Si layer 36C, holes are more easily generated than in the P-Si layer 36D, and electrons are easily transferred to the holes. In addition, the Ge absorption layer 34, which is an N-type semiconductor, has abundant free electrons that can easily move to a P-type semiconductor or the like. The photodiode 30 shown in FIG. 7 converts a signal of an intermediate frequency between the reception light 42 and the reference light 44 into an electric signal by moving free electrons from the Ge absorption layer 34 to the P + Si layer 36C. In the photodiode 30 shown in FIG. 7, the Ge generation layer is provided between the Ge absorption layer 34 and the P + Si layer 36C by providing a P-Si layer 36D in which the generation of holes is less remarkable than that of the P + Si layer 36C. Abrupt movement of free electrons from the absorption layer 34 to the P + Si layer 36C is appropriately suppressed, and the output of an electric signal based on the received light 42 is stabilized.

FIG. 8 is an overhead view of the photodiode 30 shown in FIG. 7 when viewed from the direction of arrow D. FIG. 8 shows a state in which the SiO ₂ substrate 38 is removed so that the connection 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 is clear. As shown in FIG. 8, the photodiode 30 is configured by a pn junction, but does not directly join the Ge absorption layer 34 and the P + Si layer 36C, and between the Ge absorption layer 34 and the P + Si layer 36C. By providing the P-Si layer 36D in which the generation of holes is not remarkable as compared with the P + Si layer 36C, the rapid movement of free electrons from the Ge absorption layer 34 to the P + Si layer 36C is suppressed. By suppressing the movement of the free electrons, it is possible to suppress the generation of sudden noise immediately after the reception light 42 enters the photodiode 30, and to stably output an electric signal based on the reception 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 the present embodiment. The distance sensor 100 shown in FIG. 9 is used for a laser radar device or the like, and mainly includes an optical integrated circuit chip 110 including the photodiode 30 and a control / operation processor 126 as a control device.

  The laser light propagates through the waveguide 102 from the laser light source 114 driven by the drive circuit 112 to the optical integrated circuit chip 110, and the propagated laser light is partially (for example, incident laser light) in the directional coupler 116. 10%) is looped back to the waveguide 102A and enters the photodiode 30 as the reference light 44. The directional coupler 116 is an example of a feedback unit. 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, alignment adjustment of the laser radar device is basically performed. Is unnecessary.

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

  The waveguides 102, 102A, and 102B shown in FIG. 9 are planar waveguides mounted on a plane on the optical integrated circuit chip 110. In particular, the waveguides 102 and 102B The linear waveguide is arranged so as to make a straight line to the axis, so that the propagating laser light is hardly attenuated. The waveguide 102A through which the reference light 44 propagates also partially bends. However, the waveguide 102A is formed as a straight waveguide as much as possible to suppress the attenuation of the propagating reference light 44.

The phase of the laser light from which the reference light 44 has been separated by the directional coupler 116 is 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, and changes the refractive index of the waveguide 102B, so that the laser emitted from the transmission lens 24 as the transmission light 46. Changes 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 by energizing the waveguide 102B is mounted as the phase modulator 118, and the heat generated by the heater causes The phase of the laser light propagating through the waveguide 102B is changed.

  The laser light whose phase has been changed by the phase modulator 118 is emitted as transmission light 46 via the transmission lens 24. At this time, when the phase of the laser light changes by the phase modulator 118, the direction of the laser light irradiated as the transmission light 46 changes. This makes it possible to scan with laser light projected as transmission light. The phase modulator 118 is driven by a drive circuit 120, which is controlled by a control / arithmetic processor 126. As an example, when it is necessary to greatly modulate the phase of the transmission light 46, the control / arithmetic processor 126 controls the drive circuit 120 so that the heater of the phase modulator 118 generates remarkable heat.

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

  The electric 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 by 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 the phase of the reception light 42 corresponding to the target. The distance to the target is calculated from at least one of the detected amplitude and phase of the 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 includes a polarization filter, and the transmission light 46 is limited to only a TE wave (Transverse Electric Wave) or only a TM wave (Transverse Magnetic Wave) by applying the polarization filter. You may comprise so that it is possible. The TE wave is polarized light having an electric field component transverse to the incident surface, and the TM wave is polarized light having a magnetic field component transverse to the incident surface.

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

  FIG. 10 is a block diagram showing a modified example of the optical integrated circuit chip 110A in which a plurality of photodiodes 30 are provided corresponding to the image plane of the imaging lens 20. The image plane of the imaging lens 20 is not necessarily flat, and may be curved as shown in FIG. 10, but the plurality of photodiodes 30 are directed in the incident direction of the reception light 42 from the imaging lens 20. By aligning and arranging according to the image plane, each photodiode 30 can capture the received light 42 at the focal position where the received light 42 sharply forms an image, thereby improving the sensitivity of the optical integrated circuit chip 110A. At the same time, it is possible to stably output an electric signal corresponding to the intensity of the reception light 42.

FIG. 11 is a schematic diagram showing a modified example of the optical integrated circuit chip 110A in which a plurality of photodiodes 30 are arranged so as to receive the horizontal reception light 42 of the image formed by the imaging lens 20. Each of the plurality of photodiodes 30 is mounted on a SiO ₂ substrate 38A, SiO ₂ substrate 38A is across the center of the imaging lens 20 is combined with the imaging lens 20. In a state where the SiO ₂ substrate 38A and the imaging lens 20 are coupled, each of the silicon waveguides 36 of the plurality of photodiodes 30 is placed on the SiO ₂ substrate 38A so as to coincide with the incident direction of the reception light 42. Each of the diodes 30 is mounted. By optimizing the direction of each photodiode 30 according to the incident direction of the received light 42, the received light 42 can be efficiently captured, the sensitivity of the optical integrated circuit chip 110A is improved, and the intensity of the received light 42 is reduced. The corresponding electric signal can be output stably.

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

  Further, in the optical heterodyne detector 10 according to the present embodiment, the light quantity of the reception light 42 increases because the reception light 42 is condensed by the imaging lens 20 and guided to the silicon waveguide 36 of the photodiode 30. The sensitivity of the photodiode 30 can be improved.

  Therefore, the optical heterodyne detector 10 according to the present embodiment has a simple thin-film structure, but can perform high-sensitivity measurement by condensing the received light 42 by the imaging lens 20 and has a simple structure. Has high reliability.

  Since the photodiode 30 having the above-described simple thin film structure is easy to manufacture and low in cost, the manufacturing cost of the optical heterodyne detector 10 including the photodiode 30 can be reduced.

  In the photodiode 30, the silicon waveguide 36 is formed integrally, the reference light 44 is guided to the silicon waveguide 36 with good reproducibility, and the reception light 42 is condensed by the imaging lens 20. The light is efficiently multiplexed with the reference light 44, and the optical heterodyne detection is effectively performed by the interference between the received light 42 and the reference light 44.

  Further, in the laser radar device using the optical heterodyne detector 10 according to the present embodiment, the laser light transmitting / receiving mechanism is mounted on the same chip, so that alignment adjustment of the laser radar device is basically unnecessary. This has the effect.

[Second embodiment]
Next, a second embodiment of the present invention will be described. FIG. 12 is a schematic diagram illustrating an example of a configuration in which the 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 made incident on the silicon waveguide 36 which is a planar waveguide by the diffraction grating 50, and the reference light 44 is made incident on the silicon waveguide 36 by transmitting the grating of the diffraction grating 50. Then, 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 the configuration in which the photodiode 30 and the silicon waveguide 36 according to the first embodiment are combined with the diffraction grating 50. The configuration illustrated in FIG. 13 is different from the configuration illustrated in FIG. 12 in that a mirror 28 that reflects a reference light 44 that is substantially perpendicularly incident on the reception light 42 from the side is provided.

  In the configuration shown in FIG. 13, unlike the configuration shown in FIG. 12, it is not necessary to dispose the waveguide of the reference light 44 so as to pass through the grating of the diffraction grating 50, so that the function of the diffraction grating 50 is Since the waveguide of the reference light 44 can be made shorter than the configuration shown in FIG. 12 without hindrance, attenuation of the reference light 44 propagating through the waveguide can be suppressed. The patterns of the diffraction grating 50 shown in FIGS. 12 and 13 are configured such that concentric arc-shaped or concentric elliptical-shaped grooves centered on one point on the optical axis of the reception 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 the rangefinder chip 60 including the configuration shown in FIG. In the range finder chip 60, the laser light propagates from the laser light source 114 through the waveguide 102, and a part (for example, 10% of the incident laser light) of the propagated 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 reference light 44. The directional coupler 116 is an example of a feedback unit.

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

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

  The reflected light generated by the reflection of the transmitted light 46 emitted from the diffraction grating 52 to the outside by the object enters the diffraction grating 50 and becomes the received light 42. The reception light 42 is incident on the silicon waveguide 36 together with the reference light 44, and the photodiode 30 performs heterodyne detection in which the signal light 42 and the reference light 44 are interference-multiplexed.

  FIG. 15 is a schematic diagram showing an example of the configuration of a range finder using the range finder 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 via the transmission lens 24.

  The rangefinder shown in FIG. 15 receives the reflected light of the transmission light 46 from the object as the reception light 42 by the imaging lens 20. The received light 42 received is focused on 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 focused received light 42 to interfere with the reference light 44. Done. As a result of the optical heterodyne detection, a beat signal corresponding to an intermediate frequency between the reception light 42 and the reference light 44 is output as an electric signal.

  The beat signal generated by the optical heterodyne detection includes information on the frequency difference between the transmission light 46 and the reception light 42. In the range finder shown in FIG. 15, information on the frequency difference between the transmission light 46 and the reception light 42 is extracted from the electrical signal related to the beat signal, and the distance to the target is measured by FMCW (frequency modulated continuous wave). I do.

  In the range finder 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 is measured by the FMCW. Can be changed to the optimal frequency.

  FIG. 16 is a schematic diagram of a range finder chip which is a modification of the range finder chip 60 shown in FIG. 14. The range finder chip 62 further includes a modulator 130 for intensity-modulating the transmission light 46. This is different from the rangefinder chip 60 of FIG. However, since other configurations are the same as those of the distance measuring chip 60, the same configurations as those in FIG. 14 are denoted by the same reference numerals, and detailed description is omitted.

  As an example, the modulator 130 uses a Mach-Zehnder interferometer. The Mach-Zehnder interferometer in the modulator 130 has, for example, an optical path made of a semiconductor such as InP, and adjusts the intensity and waveform of the transmission light 46 according to the intensity and waveform of a 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 range finder using the range finder chip 62 shown in FIG. The range finder shown in FIG. 17 differs from the range finder of FIG. 15 in further including a modulator 130, an external power supply 140, and a phase comparator 142. However, since the other configuration is the same as that of the range finder of FIG. 15, the same components as those of FIG. 15 are denoted by the same reference numerals, and detailed description is omitted.

  The range finder shown in FIG. 17 changes the wavelength of the laser light output from the laser light source 114 by changing the waveform of the current supplied to the laser light source 114 to a triangular wave and 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 the waveform of the transmission light 46 according to the intensity and the waveform of the current supplied from the external power supply 140. Since the modulator 130 modulates the transmission light 46 in accordance with the phase of the current supplied from the external power supply 140, when a current that changes in a rectangular wave shape is supplied from the external power supply 140 to the modulator 130, the modulator 130 The transmission light 46 is modulated from a triangular wave to a rectangular wave.

  The rangefinder shown in FIG. 17 receives the reflected light of the transmission light 46 from the object as the reception light 42 by the imaging lens 20. The received light 42 received is focused on 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 focused received light 42 to interfere with the reference light 44. Done. As a result of the optical heterodyne detection, a beat signal corresponding to an intermediate frequency between the reception light 42 and the reference light 44 is output as an electric signal.

  The phase comparator 142 compares the phase of the electric signal output from the photodiode 30 with the phase of the current of the external power supply 140, and compares the phase of the electric signal output from the photodiode 30 with the phase of the current of the external power supply 140. (Phase shift) is detected. Since the phase shift changes according to the distance to the object, the distance to the object can be measured based on the phase shift.

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

  However, a rectangular wave makes it easier to detect a phase shift than a triangular wave. The range finder shown in FIG. 17 compares the phase of the electric signal output from the photodiode 30 based on the received light 42 with the phase of the current output from the external power supply 140, so that the Perform distance measurement.

  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. When the optical axis of the received light 42 and the optical axis of the reference light 44 are made to coincide with each other as in the configuration shown in FIG. In the configuration shown in FIG. 12, the diffraction grating 50 has a portion through which the reference light 44 passes, and in the configuration shown in FIG. 13, the mirror 28 that reflects the reference light 44 exists.

  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 from each other by an arbitrary angle without making the optical axis of the received light 42 coincide with the optical axis of the reference light 44. Cross. A diffraction grating 54 is provided at a position where the optical axis of the reception light 42 and the optical axis of the reference light 44 intersect, and the diffraction grating 54 couples (interferences) the reception light 42 and the reference light 44.

  The diffraction grating 54 emits light generated as a result of causing the received light 42 and the reference light 44 to interfere with each other 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 the photodiode 30A formed integrally with the silicon waveguide 36A and the photodiode 30B formed integrally with the silicon waveguide 36B, and is converted into an electric signal.

  If the optical axis of the received light 42 and the optical axis of the reference light 44 coincide with each other, the reception of a part of the received light 42 is hindered as described above. Such a problem is solved by shifting the optical axis at a predetermined angle without being coincident with the optical axis.

  FIG. 19 is a modification of the configuration shown in FIG. The configuration shown in FIG. 18 requires two photodetectors, the photodiode 30A and the photodiode 30B, but the configuration shown in FIG. 19 includes the diffraction grating 56 and the diffraction grating 58, and the diffraction grating 56 and the diffraction grating The light emitted from the diffraction grating 54 is turned (reflected) by 58 and collected on the photodiode 30. The diffraction grating 56 and the diffraction grating 58 are arranged so that the reflected lights intersect each other, and the photodiode 30 is provided at the intersection position.

  The diffraction gratings 56 and 58 have a larger number of grooves per unit area and a finer pitch of the grating than the diffraction grating 54. By making the pitch finer, the diffraction gratings 56 and 58 can efficiently reflect the light emitted by the diffraction grating 54.

  FIG. 20 is a modification of the configuration shown in FIG. 19, which differs from the configuration shown in FIG. 19 in that a mirror 64 and a mirror 66 are provided instead of the diffraction grating 56 and the diffraction grating 58, but other configurations are the same. Since the configuration is the same as that shown in FIG. 19, the same configuration is denoted by the same reference numeral and detailed description is omitted.

FIG. 21 is a schematic diagram showing an example of the mirrors 64 and 66. The light emitted from the diffraction grating 54 travels inside the block-shaped medium as shown by the arrow in FIG. 21 and is reflected. The blocks constituting the mirrors 64 and 66 are made of a material having a higher refractive index than SiO ₂ . The material is, for example, Si alone or Ge alone.

  FIG. 22 is a schematic diagram illustrating an example in which a plurality of the configurations illustrated in FIG. 20 are provided. The configuration shown in FIG. 22 includes a unit including the diffraction gratings 50A and 54A, the mirrors 64A and 66A, and the photodiode 30C integrally formed with the silicon waveguide 36C, the diffraction gratings 50B and 54B, the mirrors 64B and 66B, and the silicon waveguide. It includes a unit including the photodiode 30D integrally formed with the wave path 36D, and a unit including the photodiode 30E integrally formed with the diffraction gratings 50C and 54C, the mirrors 64C and 66C, and the silicon waveguide 36E. In FIG. 22 and FIG. 23 described later, three units each including the diffraction gratings 50A, 50B, and 50C are shown for convenience of description using the drawings. However, the configuration may be such that more units are included. Good.

  The configuration shown in FIG. 22 is such that 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 and emitted by the diffraction grating 54A. The light emitted from 54A is reflected by mirrors 64A and 66A and is focused on photodiode 30C.

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

  The light transmitted through the diffraction grating 58B is diffracted by the diffraction grating 58C, and is emitted to the diffraction grating 54C as reference light 44C. Since the received light 42C emitted by the diffraction grating 50C is incident on the diffraction grating 54C, the diffraction grating 54C combines the received light 42C and the reference light 44C and emits the light, and furthermore, mirrors the light emitted by the diffraction grating 54C. The light is reflected by 64C and 66C and condensed on the photodiode 30E. Each of the mirrors 64A, 64B, 64C, 66A, 66B, 66C may be a reflecting member other than a mirror, such as a diffraction grating having a fine grating pitch, such as the diffraction gratings 56, 58 shown in FIG.

  By mounting the configuration shown in FIG. 22 on one chip, an optical heterodyne light receiving module that performs heterodyne detection by efficiently coupling the received light 42 and the reference light 44 can be configured. FIG. 23 is a schematic diagram showing an example of the optical heterodyne detection and reception module 160 including the configuration shown in FIG.

  The optical heterodyne detection and reception module 160 shown in FIG. 23 causes the reception light 42 to be incident on the diffraction gratings 50A, 50B and 50C by the imaging lens 220, and receives the reception lights 42A, 42B and 42C in the same manner as 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 includes a plurality of imaging lenses corresponding to each of the diffraction gratings 50A, 50B, and 50C, and the plurality of imaging lenses are provided. A lens array may be configured.

  The configurations shown in FIGS. 12 to 23 are provided with the diffraction grating 52 and the like, so that the transmission light 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. In addition, the configurations shown in FIGS. 12 to 23 include the diffraction grating 50 and the like, and are provided at an 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. The received light can be received and guided to the thin film waveguide 36 and the like.

  In the laser radar device, an optical lens is required for the projection of the transmission light 46 and the convergence of the reception light 32. However, when the diffraction gratings 50, 52, etc. are not provided, the waveguides 36, 102, etc. Are arranged in series along the optical axis, the volume of the device in the front-rear direction increases, and it may be difficult to make the device compact.

  In the present embodiment, the optical paths of the transmission light 46 and the reception light 42 are bent by the diffraction gratings 50, 52, etc., so that the laser radar apparatus having the optical lens has a front end with the optical lens. The dimension up to the rear end is set to about the focal length of the optical lens.

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

Reference Signs List 10 optical heterodyne detector 20 imaging lens 22 optical axis 24 transmitting 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 layer 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 grating 60, 62 Distance measuring chip 64, 64A, 64B, 64C, 66 Mirror 100 Distance sensor 102, 102A, 102B, 102C, 102D Waveguide 110, 110A Optical integrated circuit chip 112 Drive circuit 114 Laser light source 116 directional coupler 118 phase modulator 1 Reference Signs List 20 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 (27)

A condensing unit that condenses the transmission light output by the laser light source and the reception light reflected by the object,
Reference light, which is a part of the light output by the laser light source, and a waveguide through which the received light collected by the light collecting unit propagates.
A light receiving unit that receives light resulting from the interference between the reference light and the received light in the waveguide and converts the light into an electric signal,
Optical heterodyne detector equipped with. The waveguide is a thin-film waveguide,
The optical heterodyne detector according to claim 1, wherein the light receiving unit includes an absorption layer and an electrode stacked on one end side of the thin-film waveguide.   The optical heterodyne detector according to claim 1, wherein the light collecting unit is an optical lens.   The optical heterodyne detector according to any one of claims 1 to 3, wherein the waveguide includes an expansion unit for expanding the reference light and causing the light receiving unit to receive the reference light.   The optical heterodyne detector according to claim 4, wherein the enlargement portion is formed in a reverse taper shape with respect to the incident direction of the reference light.   The optical heterodyne detector according to any one of claims 1 to 5, further comprising a receiving diffraction grating between the condensing unit and the waveguide.   7. The pattern of the diffraction grating for reception according to claim 6, wherein concentric elliptical arc-shaped grooves centered at one point on the optical axis of the reception light emitted from the diffraction grating for reception are arranged at predetermined intervals. Optical heterodyne detector.   8. The optical heterodyne detector according to claim 7, wherein the pattern includes concentric arc-shaped grooves centered on one point on the optical axis of the reception light emitted from the reception diffraction grating and arranged at predetermined intervals. 9.   8. The optical heterodyne detector according to claim 6, wherein the reference light is transmitted through the receiving diffraction grating and is incident on the waveguide.   7. A reflecting mirror is provided between the receiving 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. Alternatively, the optical heterodyne detector according to claim 7. The receiving diffraction grating is arranged so that an optical axis of the reference light and an optical axis of the received light emitted from the receiving diffraction grating intersect with each other,
The optical axis of the reference light and the optical axis of the received light emitted from the receiving diffraction grating are arranged at positions where they intersect with each other, causing the received light and the reference light to interfere with each other, and resulting from the interference. Further provided is a coupling diffraction grating that emits light in each of the optical axis direction of the reception light and the optical axis direction of the reference light,
The waveguide is a first waveguide through which light emitted from the coupling diffraction grating in the optical axis direction of the reception light propagates, and light emitted from the coupling diffraction grating in the optical axis direction of the reference light. Comprises a second waveguide through which
A light receiving unit configured to receive the light propagated through the first waveguide and convert the light into an electric signal; and a light receiving unit configured to receive the light propagated through the second waveguide and convert the light into an electric signal. The optical heterodyne detector according to claim 6 or 7, further comprising two light receiving units. The receiving diffraction grating is arranged so that an optical axis of the reference light and an optical axis of the received light emitted from the receiving diffraction grating intersect with each other,
The optical axis of the reference light and the optical axis of the received light emitted from the receiving diffraction grating are arranged at positions where they intersect with each other, causing the received light and the reference light to interfere with each other, and resulting from the interference. A coupling diffraction grating that emits light in each of the optical axis direction of the reception light and the optical axis direction of the reference light,
A first reflector that reflects light emitted from the coupling diffraction grating in the optical axis direction of the reception light toward the waveguide;
A second reflector that reflects light emitted from the coupling diffraction grating in the optical axis direction of the reference light toward the waveguide;
The optical heterodyne detector according to claim 6, further comprising:   13. The optical heterodyne detector according to claim 12, wherein each of the first reflection unit and the second reflection unit is a diffraction grating having a grating pitch smaller than the coupling diffraction grating.   The optical heterodyne detector according to claim 12, wherein each of the first reflection unit and the second reflection unit is a reflection mirror.   13. An optical heterodyne light receiving module comprising a plurality of components including the receiving diffraction grating, the coupling diffraction grating, the first reflecting portion, the second reflecting portion, and the light receiving portion mounted on the same chip. Item 15. An optical heterodyne detector according to any one of items 14.   The optical heterodyne detector according to claim 15, further comprising a reference light diffraction grating arranged for each of the plurality of components and emitting the reference light toward the coupling diffraction grating. An optical heterodyne detector according to any one of claims 1 to 16,
A light emitting unit that emits the transmission light output by the laser light source to the outside world,
A feedback unit that returns a part of the light output by the laser light source to the waveguide as the reference light,
An arithmetic unit that measures a distance to an object based on the electric signal output by the light receiving unit,
Laser radar device provided with.   The laser radar device according to claim 17, wherein the light projecting unit includes a transmission diffraction grating that refracts and emits the transmission light output from the laser light source.   19. The pattern of the transmission diffraction grating according to claim 18, wherein concentric elliptical arc-shaped grooves centered at one point on the optical axis of transmission light incident on the transmission diffraction grating are arranged at predetermined intervals. Laser radar equipment.   20. The laser radar device according to claim 19, wherein the pattern is such that concentric arc-shaped grooves centered on one point on the optical axis of transmission light incident on the transmission diffraction grating are arranged at predetermined intervals.   21. The laser radar device according to claim 18, wherein the light projecting unit projects the transmission light emitted from the transmission diffraction grating to the outside via a transmission lens.   The laser radar device according to any one of claims 18 to 21, wherein the light projecting unit includes a modulator that modulates an intensity and a waveform of the transmission light.   23. The laser radar device according to claim 22, wherein the modulator is a Mach-Zehnder interferometer capable of modulating a waveform of the transmission light into a rectangular wave.   The laser radar device according to any one of claims 17 to 23, wherein the waveguide has a double clad structure in which a thin-film waveguide is covered with a silicon layer.   25. The laser radar device according to claim 17, wherein the waveguide is a planar waveguide formed on a substrate plane.   The laser radar device according to any one of claims 17 to 25, wherein the waveguide includes a straight waveguide formed of a straight line.   The laser radar device according to any one of claims 17 to 26, wherein the laser light source includes a polarization filter, and is capable of outputting one of orthogonal polarization and parallel polarization by applying the polarization filter.