Optical measurement device

Abstract

[Problem] To provide an optical measurement device capable of improving deterioration of measurement accuracy caused by mode hop. [Solution] An optical measurement device according to an embodiment of the present disclosure comprises: a wavelength sweeping light source that emits light of a wavelength corresponding to a supply current; at least one delay interferometer that has a plurality of light-guiding waveguides that have different lengths; and an analyzer that, based on a phase difference between a plurality of beat signals obtained by photoelectrically converting the output light of the delay interferometer guided to the plurality of waveguides, identifies a mode hop interval where a mode hop in which the wavelength changes discontinuously is generated.

Description

Optical Measurement Device

[0001] The present disclosure relates to optical metrology devices.

[0002] Known examples of optical measurement devices equipped with a wavelength-swept light source that emits laser light whose wavelength changes continuously and linearly over time include frequency-modulated continuous wave (FMCW) light detection and ranging (LiDAR) and swept source-optical coherence tomography (SS-OCT).

[0003] Furthermore, one of the characteristics of laser light emitted from a wavelength-swept light source is the so-called mode hop, which is an operating point where the wavelength change becomes discontinuous between sections (continuous sweep sections) where the wavelength continuously increases with respect to the supplied current. When mode hopping occurs, the output of the photodetector becomes discontinuous, which can reduce measurement accuracy.

[0004] Special table 2017-526911 publication

[0005] The present disclosure provides an optical measurement device capable of improving the degradation of measurement accuracy caused by mode hopping.

[0006] An optical measurement device according to an embodiment of the present disclosure includes: a wavelength swept light source that emits light of a wavelength corresponding to a supply current; at least one delay interferometer having a plurality of waveguides with different lengths for guiding light; and an analyzer that identifies a mode hop section in which a mode hop, in which the wavelength changes discontinuously, has occurred, based on the phase difference between a plurality of beat signals obtained by photoelectrically converting the output light of the delay interferometer that has been guided to the plurality of waveguides.

[0007] The plurality of waveguides may be provided in the plurality of delay interferometers, respectively, and the optical path differences of the plurality of waveguides may be different for each delay interferometer.

[0008] The wavelength swept source may be a ring laser or a Distributed Bragg Reflector (DBR) laser.

[0009] The delay interferometer may be an asymmetric Mach-Zehnder interferometer.

[0010] The optical measurement device may further include a phase difference detector that detects a phase difference between the plurality of beat signals.

[0011] The phase difference detector may include a subtractor that performs subtraction processing on the plurality of beat signals.

[0012] The plurality of waveguides may be provided in one delay interferometer.

[0013] A plurality of distributed Bragg reflector mirrors may be provided at different positions in one of the plurality of waveguides.

[0014] The optical measurement device may further include: a first splitter disposed between the wavelength swept light source and the delay interferometer, the first splitter splitting the light into a plurality of laser beams; a second splitter splitting one of the plurality of laser beams into a first beam and a second beam; a mixer outputting a composite wave obtained by combining the first beam and a third beam formed by reflection of the second beam from an object to be measured; a first photodetector photoelectrically converting the composite wave to output a beat signal including depth information; and a second photodetector photoelectrically converting output light from the delay interferometer.

[0015] The analyzer may perform compensation processing on the beat signal of the first photodetector by removing signal data in the mode hopping section and connecting signal data in sections before and after the mode hopping section.

[0016] 1 is a block diagram showing the configuration of an optical measurement device according to a first embodiment; FIG. 2 is a block diagram showing an example of the circuit configuration of an AFE; FIG. 3 is a diagram showing the configuration of a delay interferometer and a second photodetector according to the first embodiment; FIG. 4 is a diagram showing a modified example of the configuration of a delay interferometer and a second photodetector according to the first embodiment; FIG. 5 is a diagram showing an example of the characteristics of light emitted from a wavelength swept light source; FIG. 6 is a diagram showing an example of the waveform of an output signal of a second photodetector; FIG. 7 is a diagram showing an example of a spectrum analysis result; FIG. 8 is a diagram showing an example of a change over time in the phase difference calculated by the first subtractor when no mode hop occurs; FIG. 9 is a diagram showing an example of a change over time in the phase difference calculated by the second subtractor when no mode hop occurs; FIG. 10 is a diagram showing an example of a change over time in the phase difference calculated by the third subtractor when no mode hop occurs; FIG. 11 is a diagram showing an example of a change over time in the phase difference calculated by the first subtractor when a mode hop occurs; FIG. 12 is a diagram showing an example of a change over time in the phase difference calculated by the second subtractor when a mode hop occurs; FIG. 13 is a diagram showing an example of a change over time in the phase difference calculated by the third subtractor when a mode hop occurs; 10B is a waveform diagram showing a compensation process performed on the phase difference signal shown in FIG. 10A. FIG. 10C is a waveform diagram showing a compensation process performed on the beat signal shown in FIG. 10B. FIG. 10D is a diagram showing the spectral intensity distribution of the beat signal of the first photodetector before and after compensation. FIG. 10C is a diagram showing a configuration of a delay interferometer according to a second embodiment. FIG. 10D is a diagram showing a simplified result of FFT processing by a phase detector. FIG. 10C is a diagram showing a configuration of a delay interferometer according to a third embodiment. FIG. 10D is a block diagram showing an example of a schematic configuration of a vehicle control system. FIG. 10E is an explanatory diagram showing an example of the installation positions of an outside-vehicle information detection unit and an imaging unit.

[0017] Hereinafter, specific embodiments to which the present technology is applied will be described in detail with reference to the drawings. The drawings are schematic or conceptual, and the proportions of each part are not necessarily the same as those in reality. In the specification and drawings, elements similar to those described above with reference to the previous drawings are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0018] First Embodiment Fig. 1 is a block diagram showing the configuration of an optical measurement device according to a first embodiment. The optical measurement device 1 shown in Fig. 1 can be applied to, for example, FMCW LiDAR and SS-OCT. The optical measurement device 1 according to this embodiment includes a wavelength swept light source 11, a first splitter 12, a second splitter 13, a routing unit 14, an optical scanner 15, a mixer 16, a first photodetector 17, an AFE (Analog Front End) 18, a spectrum analyzer 19, a delay interferometer group 21, a second photodetector group 22, a phase detector 23, and a phase difference detector 24.

[0019] The wavelength swept light source 11 emits laser light whose wavelength changes continuously and linearly over time. The wavelength swept light source 11 can be, for example, a verniering laser or a DBR (Distributed Bragg Reflector) laser. A verniering laser is a wavelength swept light source that uses a microring resonator formed with a silicon wire waveguide as an external resonator. On the other hand, a DBR laser is a wavelength swept light source that has a distributed Bragg reflector (DBR) diffraction grating structure instead of a ring resonator. The waveguide of the wavelength swept light source 11 can be manufactured from any material usable in silicon photonics, such as silicon (Si), silicon nitride (SiN), or aluminum nitride (AlN).

[0020] The first splitter 12 splits the emitted light from the wavelength swept light source 11 into three or more laser beams L0. In this embodiment, the first splitter 12 splits the emitted light into five laser beams L0, but the number of splits is not particularly limited as long as it is three or more. One of the multiple laser beams L0 is guided to the second splitter 13. The remaining laser beam L0 is guided to the delay interferometer group 21.

[0021] The second splitter 13 further splits the single laser light L0 split by the first splitter 12 into a first light L1 and a second light L2. The split ratio between the first light L1 and the second light L2 may be 1:1 or any other ratio. The first light L1, which is one of the split lights of the laser light L0, is guided to the routing unit 14. The second light L2, which is the other split light of the laser light L0, is guided to the mixer 16. For example, a 1x2 MMI (Multi Mode Interference) coupler, a 2x2 MMI coupler, a directional coupler, or a bent directional coupler can be used for the second splitter 13.

[0022] The routing unit 14 transfers the first light L1 split by the second splitter 13 to the optical scanner 15. The routing unit 14 also transfers the third light L3 input from the optical scanner 15 to the mixer 16. The routing unit 14 may be, for example, a 1×2 MMI (Multi Mode Interference) coupler, a 2×2 MMI coupler, a directional coupler, or an optical circulator.

[0023] The optical scanner 15 emits the first light L1 transferred from the routing unit 14 toward the object 10. The optical scanner 15 also outputs the third light L3 reflected by the object 10 to the routing unit 14 as received light.

[0024] The mixer 16 outputs a composite wave obtained by combining the second light L2 input from the second splitter 13 and the third light L3 input from the routing unit 14 to the first photodetector 17 .

[0025] The first photodetector 17 includes a photodiode that photoelectrically converts the composite wave combined by the mixer 16 into an analog electrical signal. The mixer 16 and the first photodetector 17 may be, for example, a heterodyne detector, a homodyne detector, or a balance photodiode (BPD).

[0026] 2 is a block diagram showing an example of the circuit configuration of the AFE 18. The AFE 18 according to this embodiment includes an amplifier circuit 181 and an analog-to-digital conversion circuit 182. The amplifier circuit 181 amplifies the analog electrical signal photoelectrically converted by the first photodetector 17. The amplifier circuit 181 may be, for example, a TIA (Trans Impedance Amplifier) ​​circuit having closed-loop feedback.

[0027] The analog-to-digital conversion circuit 182 converts the analog electrical signal amplified by the amplifier circuit 181 into a digital electrical signal. The analog-to-digital conversion circuit 182 can be, for example, a time-to-digital converter (TDC) having a frequency-to-time converter using an SAR system, a pipeline system, a σΔ system, or a hybrid system that combines these systems.

[0028] The result of the FFT processing, that is, the output of the analog-to-digital conversion circuit 182, is input to the spectrum analyzer 19.

[0029] The spectrum analyzer 19 is an analyzer that converts the time domain signal of the analog-to-digital conversion circuit 182 into a frequency domain signal and calculates the peak frequency of the difference frequency of the composite wave. The difference frequency (beat frequency) of the composite wave depends on the distance from the optical measurement device 1 to the object 10 to be measured. The distance from the optical measurement device 1 to the object 10 is proportional to the difference frequency between the transmitted light (second light L2) and the received light (third light L3). For example, when the distance from the optical measurement device 1 to the object 10 is relatively short, the difference frequency becomes small. When the distance from the optical measurement device 1 to the object 10 is relatively long, the difference frequency becomes large. The peak frequency of the difference frequency is output to the outside of the optical measurement device 1 as depth data indicating the distance from the optical measurement device 1 to the object 10 and speed data indicating the speed.

[0030] The delay interferometer group 21 includes a plurality of delay interferometers 211 to 214. In the plurality of delay interferometers 211 to 214, the delay amount of the laser light L0 is set to a value different from each other.

[0031] The second photodetector group 22 includes a plurality of second photodetectors 221 to 224. The plurality of second photodetectors 221 to 224 are optically connected to the output sides of the plurality of delay interferometers 211 to 214, respectively. Here, the configurations of the delay interferometer 211 and the second photodetector 221 will be described with reference to FIG.

[0032] FIG. 3 is a diagram showing the configuration of the delay interferometer and the second photodetector according to the first embodiment.

[0033] First, a description will be given of the configuration of the delay interferometer 211. The delay interferometer 211 is an asymmetric Mach-Zehnder interferometer, and includes a first coupler 2111, a second coupler 2112, a first waveguide 2113, and a second waveguide 2114.

[0034] In the first coupler 2111, the laser light L0 branches into a first waveguide 2113 and a second waveguide 2114. In the second coupler 2112, the branched light from the first waveguide 2113 and the branched light from the second waveguide 2114 join together and branch again. The second waveguide 2114 is longer than the second waveguide 2113.

[0035] In this embodiment, the optical path difference ΔL between the first waveguide 2113 and the second waveguide 2114 is set to 7.5000 mm. The circular portion of the second waveguide 2114 may be a coiled waveguide. In this case, a long delay length can be ensured in a limited area.

[0036] The remaining configurations of the delay interferometers 212 to 214 are the same as the configuration of the above-described delay interferometer 211, and therefore description thereof will be omitted. However, in this embodiment, the optical path differences ΔL of the delay interferometers 212, 213, and 214 are set to 7.5075 mm, 7.5750 mm, and 8.2500 mm, respectively.

[0037] Next, a description will be given of the configuration of the second photodetector 221. The second photodetector 221 includes a first photodiode 2211, a second photodiode 2212, and a differential amplifier 2213.

[0038] The first photodiode 2211 and the second photodiode 2212 are connected in series. The non-inverting input terminal (+) of the differential amplifier 2213 is connected to the cathode of the first photodiode 2211. The inverting input terminal (-) of the differential amplifier 2213 is connected to the cathode of the second photodiode 2212. The output terminal of the differential amplifier 2213 is connected to the phase detector 23. The configuration of the remaining second photodetectors 221 to 224 is the same as the configuration of the second photodetector 221 described above, so a description thereof will be omitted.

[0039] In this embodiment, the first photodiode 2211 and the second photodiode 2212 each receive the two output light beams output from the second coupler 2112 and photoelectrically convert them into electrical signals. The differential amplifier 2213 amplifies the difference between the electrical signals photoelectrically converted by the diode 2211 and the second photodiode 2212. The amplified electrical signal is input to the phase detector 23 as a beat signal, which is the output signal of the second photodetector 221. The beat frequencies of the beat signals differ among the second photodetectors 221 to 224 depending on the optical path difference ΔL of the corresponding delay interferometer. For example, the beat frequency of the second photodetector 221 is 1000 kHz. The beat frequency of the second photodetector 222 is 1001 kHz. The beat frequency of the second photodetector 223 is 1010 kHz. The beat frequency of the second photodetector 224 is 1100 kHz.

[0040] The configuration in this embodiment in which the output light of the second coupler 2112 is received individually by two photodiodes is preferable because it can reduce the influence of noise and the like from the DC power supply supplied to each photodiode. However, the second photodetector 221 may also be configured as a single configuration in which one of the output lights of the second coupler 2112 is received by one photodiode. With a single configuration, the number of photodiodes is reduced, thereby making it possible to save the area of ​​the second photodetector 221.

[0041] The configurations of the delay interferometer 211 and the second photodetector 221 are not limited to the configuration shown in Fig. 3. Here, modified examples of the configurations of the delay interferometer 211 and the second photodetector 221 will be described.

[0042] Fig. 4 is a diagram showing a modified example of the configuration of the delay interferometer and second photodetector according to the first embodiment. In the delay interferometer 211 shown in Fig. 4, the second coupler 2112 is a 90° hybrid coupler that further splits each of the branched light from the first waveguide 2113 and the branched light from the second waveguide 2114 into two lights with the same intensity and shifts the phase by 90°.

[0043] The second photodetector 221 further includes a third photodiode 2214 and a fourth photodiode 2215 connected in series, in addition to the first photodiode 2211 and the second photodiode 2212 connected in series. The second photodetector 221 has an IQ light-receiving configuration in which these four photodiodes receive the output light of the delay interferometer 211. With this configuration, the phase can be determined directly and instantaneously from the two voltage outputs of the I phase and the Q phase.

[0044] The phase detector 23 detects the phase of each output signal from the second photodetectors 221 to 224. The phase detector 23 detects the phase by, for example, performing Hilbert transform processing on the output signal from each second photodetector 221. Note that when each delay interferometer and each second photodetector have the configuration shown in Fig. 4, Hilbert transform processing is not required, and therefore the calculation load on the phase detector 23 is reduced.

[0045] The phase difference detector 24 includes a first subtractor 241, a second subtractor 242, and a third subtractor 243. However, the number of subtractors is not limited to three. The phase difference detector 24 may be included in the configuration of the AFE 18 together with the phase detector 23.

[0046] The first subtractor 241 calculates the phase difference between the first beat signal having the lowest beat frequency detected by the second photodetector 221 and the second beat signal having the second lowest beat frequency detected by the second photodetector 222. The second subtractor 242 calculates the phase difference between the first beat signal and the third beat signal having the third lowest beat frequency detected by the third photodetector 223. The third subtractor 243 calculates the phase difference between the first beat signal and the beat signal having the highest beat frequency detected by the second photodetector 224. Each subtractor outputs the calculated phase difference to the spectrum analyzer 19.

[0047] The spectrum analyzer 19 determines whether or not mode hopping has occurred based on the phase difference detected by the phase difference detector 24. Here, mode hopping and the degradation of measurement accuracy caused by mode hopping will be described.

[0048] 5 is a diagram showing an example of the characteristics of light emitted from the wavelength swept light source 11. In FIG. 5, the horizontal axis represents time t, and the vertical axis represents the wavelength λ of the light. When the current supplied to the wavelength swept light source 11 is increased over time, the wavelength λ also increases linearly. However, there exists an operating point at which the wavelength λ changes nonlinearly at a certain timing. This operating point corresponds to a mode hop.

[0049] Fig. 6 is a diagram showing an example of the waveform of the output signal of the second photodetector. In Fig. 6, the horizontal axis represents time t and the vertical axis represents voltage V. As shown in Fig. 6, in a section where mode hopping occurs, the waveform of the output signal is discontinuous compared to a section where mode hopping does not occur.

[0050] FIG. 7 shows an example of the results of FFT processing by the spectrum analyzer 19. In FIG. 7, the horizontal axis represents frequency, and the vertical axis represents spectral intensity. As shown in FIG. 7, when mode hopping occurs, the spectrum has smaller peaks and a broader shape than the spectrum without mode hopping, shown by the dotted line. This reduces the signal-to-noise ratio (SNR) after spectrum analysis and degrades measurement accuracy.

[0051] A method for determining whether or not a mode hop occurs using the spectrum analyzer 19 will be described below.

[0052] Fig. 8A is a diagram showing an example of a change over time in the phase difference calculated by the first subtractor 241 when no mode hopping occurs. Fig. 8B is a diagram showing an example of a change over time in the phase difference calculated by the second subtractor 242 when no mode hopping occurs. Fig. 8C is a diagram showing an example of a change over time in the phase difference calculated by the third subtractor 243 when no mode hopping occurs.

[0053] Fig. 9A is a diagram showing an example of a change over time in the phase difference calculated by the first subtractor 241 when a mode hop occurs. Fig. 9B is a diagram showing an example of a change over time in the phase difference calculated by the second subtractor 242 when a mode hop occurs. Fig. 9C is a diagram showing an example of a change over time in the phase difference calculated by the third subtractor 243 when a mode hop occurs.

[0054] As shown in Figures 8A, 8B, and 8C, when no mode hopping occurs, the phase difference varies continuously and linearly within the range of -π to +π, whereas as shown in Figures 9A, 9B, and 9C, when mode hopping occurs, the phase difference varies discontinuously within the range of -π to +π.

[0055] In this embodiment, the spectrum analyzer 19 compares the phase difference characteristics shown in Figures 9A, 9B, and 9C with the phase difference characteristics shown in Figures 8A, 8B, and 8C, and determines whether or not mode hopping has occurred based on the comparison results. For example, if the characteristic difference is within a predetermined range, the spectrum analyzer 19 determines that mode hopping has not occurred. Conversely, if the characteristic difference is outside the predetermined range, the spectrum analyzer 19 determines that mode hopping has occurred.

[0056] 10A is an enlarged view of the waveform of the phase difference signal output from the phase difference detector 24. Fig. 10A shows the waveforms of the first phase difference signal Sω1 from the first subtractor 241, which indicates the phase difference between the second beat signal and the first beat signal, and the second phase difference signal Sω2 from the second subtractor 242, which indicates the phase difference between the third beat signal and the first beat signal. As shown in Fig. 10A, in the mode hopping section, the first phase difference signal Sω1 and the second phase difference signal Sω2 change discontinuously or abruptly.

[0057] Fig. 10B is an enlarged view of the waveforms of the beat signals, showing the first beat signal Sb1, the second beat signal Sb2, and the third beat signal Sb3 output from the second photodetector 221. As shown in Fig. 10B, in the mode hopping section, each beat signal oscillates sharply or gently.

[0058] Therefore, for example, if compensation processing is performed to remove the phase difference signal data in the mode hopping section and connect the phase difference signal data before and after the mode hopping section, the phases of the beat signals are smoothly connected, as shown in Fig. 11A. Fig. 11A is a waveform diagram showing the phase difference signal shown in Fig. 10A after compensation processing.

[0059] Furthermore, when compensation processing is performed to remove the beat signal data in the mode hopping section and connect the signal data of the beat signals before and after the mode hopping section, the phases of the beat signals are smoothly connected, as shown in Fig. 11B. Fig. 11B is a waveform diagram showing the beat signal shown in Fig. 10B after compensation processing.

[0060] Furthermore, when the spectrum analyzer 19 performs compensation processing on the beat signal containing the depth information of the first photodetector 17 by similarly removing the signal data of the beat signal in the mode hopping section and connecting the signal data of the beat signal before and after the mode hopping section, the SNR is improved as shown in FIG. 12 .

[0061] FIG. 12 is a diagram showing the spectral intensity distribution of the beat signal of the first photodetector 17 before and after compensation processing. In FIG. 12, the horizontal axis represents depth corresponding to the distance to the object 100, and the vertical axis represents power spectral density (PSD). FIG. 12 shows a spectral signal SD1 before compensation processing and a spectral signal SD2 after compensation processing. As shown in FIG. 12, the signal-to-noise ratio SNR2 of the spectral signal SD2 is significantly improved compared to the spectral signal SD1.

[0062] Therefore, it is possible to improve the degradation of measurement accuracy caused by mode hopping.

[0063] Generally, if a delay interferometer does not have a certain delay amount, the beat frequency may become lower than necessary. In this case, it may be unsuitable for identifying mode hops due to the influence of low-frequency noise caused by the laser light or electrical circuits.

[0064] Therefore, in this embodiment, as an example, the optical path difference of the delay interferometers 211 to 214 is set to a minimum of 7.5 mm, and a beat frequency of 1000 kHz or more is ensured when the sweep speed of the wavelength swept light source 11 is 100 nm / msec.

[0065] In this embodiment, the optical path differences are increased by a factor of 10 to 1:10:100, thereby widening the detection range so that the spectrum analyzer 19 can accurately detect both large and small mode hops. Therefore, the ratio of the delay amounts in the delay interferometer group 21 is set to 1000:1001:1010:1100. However, the ratio of the delay amounts is not limited to this.

[0066] For example, the delay ratio may be set to be pairwise coprime, such as 1000:1011:1013:1017, resulting in a delay difference of 11:13:17. This lengthens the period during which the phase difference signal repeats the same pattern. As a result, as shown in FIG. 11A, the accuracy of identifying the appropriate seam by overlapping the phase difference signal data can be improved.

[0067] Second Embodiment A second embodiment of the present disclosure will be described. In this embodiment, the configuration of the delay interferometer is different from that of the first embodiment. Here, the delay interferometer according to the second embodiment will be described with reference to FIG. 13 .

[0068] 13 is a diagram showing the configuration of a delay interferometer according to the second embodiment. In a delay interferometer 211A according to this embodiment, in addition to a first waveguide 2113 and a second waveguide 2114, a third waveguide 2115 and a fourth waveguide 2116 are also provided between a first coupler 2111 and a second coupler 2112. The third waveguide 2115 is shorter than the first waveguide 2113. Furthermore, the fourth waveguide 2116 is shorter than the third waveguide 2115.

[0069] In the first embodiment described above, the delay interferometer group 21 includes a plurality of delay interferometers, and the second photodetector group 22 includes a plurality of second photodetectors.

[0070] In contrast to this, in this embodiment, one delay interferometer 211A includes multiple waveguides, as shown in Fig. 13. Furthermore, in this embodiment, one second photodetector 221 is shared by the multiple waveguides. That is, in the optical measurement device according to this embodiment, multiple waveguides with different lengths are provided in one delay interferometer, instead of multiple delay interferometers, and one second photodetector is provided, instead of multiple second photodetectors.

[0071] The second photodetector outputs a beat signal based on the optical path difference between the first waveguide 2113 and the second waveguide 2114, a beat signal based on the optical path difference between the first waveguide 2113 and the third waveguide 2115, and a beat signal based on the optical path difference between the first waveguide 2113 and the fourth waveguide 2116. Subsequently, the phase detector 23 performs FFT processing on these three beat signals.

[0072] 14 is a simplified diagram showing the results of FFT processing by phase detector 23. As shown in FIG. 14, three different peak frequencies P1, P2, and P3 appear. The three peak frequencies P1, P2, and P3 correspond to either second waveguide 2114, third waveguide 2113, or fourth waveguide 2114. Phase detector 23 determines the instantaneous phase of each peak frequency P1, P2, and P3 based on the peak frequencies P1, P2, and P3. Subsequently, phase difference detector 24 calculates the phase difference based on the phase determined by phase detector 23.

[0073] Thereafter, similarly to the first embodiment, the spectrum analyzer 19 identifies the mode hop section and performs compensation processing on the beat signal of the first photodetector 17 .

[0074] Therefore, in this embodiment as well, it is possible to improve the degradation of measurement accuracy due to mode hopping. In particular, according to this embodiment, the number of delay interferometers and second photodetectors is reduced, which makes it possible to reduce the circuit area and reduce product costs.

[0075] In this embodiment, as in the modified example of the first embodiment, the second coupler 2112 may be a hybrid coupler. In this case, the second photodetector 221 further includes a third photodiode 2214 and a fourth photodiode 2215 connected in series, in addition to the first photodiode 2211 and the second photodiode 2212 connected in series.

[0076] Third Embodiment A third embodiment of the present disclosure will be described. In this embodiment, the configuration of the delay interferometer is different from that of the first embodiment. Here, the delay interferometer according to the third embodiment will be described with reference to FIG. 15 .

[0077] 15 is a diagram showing the configuration of a delay interferometer according to the third embodiment. In a delay interferometer 211B according to this embodiment, a first distributed Bragg reflector mirror 2117, a second distributed Bragg reflector mirror 2118, and a third distributed Bragg reflector mirror 2119 are provided at different positions in a second waveguide 2114. The branched light traveling through the second waveguide 2114 is reflected back and forth by each distributed Bragg reflector mirror, thereby generating an optical path difference with the first waveguide 2113. A beat signal corresponding to the optical path difference is then output from a differential amplifier 2213. The subsequent processing is the same as in the second embodiment, and therefore description thereof will be omitted.

[0078] According to the present embodiment described above, it is possible to improve the degradation of measurement accuracy caused by mode hopping, as in the second embodiment. In particular, in this embodiment, delayed interference is performed in the optical path due to round-trip reflection in the distributed Bragg reflector mirror. Therefore, it is possible to reduce the physical length of the delay line (including the spiral delay line) required to obtain the same beat frequency to half that of the second embodiment.

[0079] <Application to a Mobile Body> The technology according to the present disclosure (the present technology) can be applied to various products. For example, the technology according to the present disclosure may be realized as a device mounted on any type of mobile body, such as an automobile, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, personal mobility, an airplane, a drone, a ship, or a robot.

[0080] FIG. 16 is a block diagram showing a schematic configuration example of a vehicle control system, which is an example of a mobile object control system to which the technology according to the present disclosure can be applied.

[0081] The vehicle control system 12000 includes a plurality of electronic control units connected via a communication network 12001. In the example shown in Fig. 16, the vehicle control system 12000 includes a drive system control unit 12010, a body system control unit 12020, an outside-vehicle information detection unit 12030, an inside-vehicle information detection unit 12040, and an integrated control unit 12050. Also shown as functional components of the integrated control unit 12050 are a microcomputer 12051, an audio / video output unit 12052, and an in-vehicle network I / F (interface) 12053.

[0082] The drivetrain control unit 12010 controls the operation of devices related to the drivetrain of the vehicle in accordance with various programs. For example, the drivetrain control unit 12010 functions as a control device for a drive force generating device for generating a drive force of the vehicle, such as an internal combustion engine or a drive motor, a drive force transmission mechanism for transmitting the drive force to the wheels, a steering mechanism for adjusting the steering angle of the vehicle, and a braking device for generating a braking force of the vehicle.

[0083] The body system control unit 12020 controls the operation of various devices equipped in the vehicle body according to various programs. For example, the body system control unit 12020 functions as a control device for a keyless entry system, a smart key system, a power window device, or various lamps such as headlamps, backup lamps, brake lamps, turn signals, and fog lamps. In this case, radio waves transmitted from a portable device that serves as a key or signals from various switches can be input to the body system control unit 12020. The body system control unit 12020 receives these radio waves or signals and controls the vehicle's door lock device, power window device, lamps, etc.

[0084] The outside-vehicle information detection unit 12030 detects information outside the vehicle equipped with the vehicle control system 12000. For example, an imaging unit 12031 is connected to the outside-vehicle information detection unit 12030. The outside-vehicle information detection unit 12030 causes the imaging unit 12031 to capture images outside the vehicle and receives the captured images. The outside-vehicle information detection unit 12030 may perform object detection processing or distance detection processing for people, cars, obstacles, signs, characters on the road surface, etc. based on the received images.

[0085] The imaging unit 12031 is an optical sensor that receives light and outputs an electrical signal corresponding to the amount of light received. The imaging unit 12031 can output the electrical signal as an image or as distance measurement information. The light received by the imaging unit 12031 may be visible light or invisible light such as infrared light.

[0086] The in-vehicle information detection unit 12040 detects information inside the vehicle. For example, a driver state detection unit 12041 that detects the state of the driver is connected to the in-vehicle information detection unit 12040. The driver state detection unit 12041 includes, for example, a camera that captures an image of the driver, and the in-vehicle information detection unit 12040 may calculate the degree of fatigue or concentration of the driver based on the detection information input from the driver state detection unit 12041, or may determine whether the driver is dozing off.

[0087] The microcomputer 12051 can calculate control target values ​​for the driving force generating device, steering mechanism, or braking device based on the information inside and outside the vehicle acquired by the outside-vehicle information detection unit 12030 or the inside-vehicle information detection unit 12040, and output control commands to the drive system control unit 12010. For example, the microcomputer 12051 can perform cooperative control aimed at realizing the functions of an ADAS (Advanced Driver Assistance System), including vehicle collision avoidance or impact mitigation, following driving based on the inter-vehicle distance, vehicle speed maintenance driving, vehicle collision warning, vehicle lane departure warning, etc.

[0088] In addition, the microcomputer 12051 can perform cooperative control for the purpose of autonomous driving, which allows the vehicle to travel autonomously without relying on driver operation, by controlling the driving force generating device, steering mechanism, braking device, etc. based on information about the surroundings of the vehicle obtained by the outside vehicle information detection unit 12030 or the inside vehicle information detection unit 12040.

[0089] Furthermore, the microcomputer 12051 can output a control command to the body system control unit 12020 based on the information outside the vehicle acquired by the outside information detection unit 12030. For example, the microcomputer 12051 can control the headlamps according to the position of a preceding vehicle or an oncoming vehicle detected by the outside information detection unit 12030, and perform cooperative control aimed at preventing glare, such as switching from high beams to low beams.

[0090] The audio / video output unit 12052 transmits at least one of audio and video output signals to an output device capable of visually or audibly notifying the passengers of the vehicle or the outside of the vehicle of information. In the example of Fig. 16, the output devices are exemplified by an audio speaker 12061, a display unit 12062, and an instrument panel 12063. The display unit 12062 may include, for example, at least one of an on-board display and a head-up display.

[0091] FIG. 17 is a diagram showing an example of the installation position of the imaging unit 12031.

[0092] In FIG. 17, a vehicle 12100 has imaging units 12101, 12102, 12103, 12104, and 12105 as the imaging unit 12031.

[0093] The imaging units 12101, 12102, 12103, 12104, and 12105 are provided, for example, at positions such as the front nose, side mirrors, rear bumper, back door, and the top of the windshield inside the vehicle cabin of the vehicle 12100. The imaging unit 12101 provided on the front nose and the imaging unit 12105 provided on the top of the windshield inside the vehicle cabin mainly acquire images of the front of the vehicle 12100. The imaging units 12102 and 12103 provided on the side mirrors mainly acquire images of the sides of the vehicle 12100. The imaging unit 12104 provided on the rear bumper or back door mainly acquires images of the rear of the vehicle 12100. The forward images acquired by the imaging units 12101 and 12105 are mainly used to detect preceding vehicles, pedestrians, obstacles, traffic lights, traffic signs, lanes, etc.

[0094] 17 shows an example of the imaging ranges of the imaging units 12101 to 12104. Imaging range 12111 indicates the imaging range of the imaging unit 12101 provided on the front nose, imaging ranges 12112 and 12113 indicate the imaging ranges of the imaging units 12102 and 12103 provided on the side mirrors, respectively, and imaging range 12114 indicates the imaging range of the imaging unit 12104 provided on the rear bumper or back door. For example, by overlaying the image data captured by the imaging units 12101 to 12104, an overhead image of the vehicle 12100 viewed from above can be obtained.

[0095] At least one of the image capturing units 12101 to 12104 may have a function of acquiring distance information. For example, at least one of the image capturing units 12101 to 12104 may be a stereo camera made up of multiple image capturing elements, or may be an image capturing element having pixels for phase difference detection.

[0096] For example, based on the distance information obtained from the imaging units 12101 to 12104, the microcomputer 12051 can calculate the distance to each three-dimensional object within the imaging ranges 12111 to 12114 and the change in this distance over time (relative speed with respect to the vehicle 12100), thereby extracting as a preceding vehicle, in particular, the three-dimensional object that is the closest three-dimensional object on the path of the vehicle 12100 and traveling in approximately the same direction as the vehicle 12100 at a predetermined speed (e.g., 0 km / h or higher). Furthermore, the microcomputer 12051 can set a vehicle-to-vehicle distance to be maintained in advance in front of the preceding vehicle, and perform automatic braking control (including follow-up stop control), automatic acceleration control (including follow-up start control), etc. In this way, cooperative control can be performed for the purpose of autonomous driving, which runs autonomously without relying on driver operation.

[0097] For example, the microcomputer 12051 classifies and extracts three-dimensional object data regarding three-dimensional objects into two-wheeled vehicles, ordinary vehicles, large vehicles, pedestrians, utility poles, and other three-dimensional objects based on distance information obtained from the imaging units 12101 to 12104, and can use the data for automatic obstacle avoidance. For example, the microcomputer 12051 distinguishes obstacles around the vehicle 12100 into obstacles that are visible to the driver of the vehicle 12100 and obstacles that are difficult to see. The microcomputer 12051 determines a collision risk that indicates the risk of collision with each obstacle, and when the collision risk is equal to or greater than a set value and a collision is possible, the microcomputer 12051 can provide driving assistance for collision avoidance by outputting an alarm to the driver via the audio speaker 12061 or the display unit 12062, or by performing forced deceleration or avoidance steering via the drive system control unit 12010.

[0098] At least one of the image capturing units 12101 to 12104 may be an infrared camera that detects infrared rays. For example, the microcomputer 12051 can recognize a pedestrian by determining whether a pedestrian is present in the images captured by the image capturing units 12101 to 12104. Such pedestrian recognition is performed, for example, by extracting feature points from the images captured by the image capturing units 12101 to 12104 as infrared cameras and performing pattern matching on a series of feature points that indicate the outline of an object to determine whether the object is a pedestrian. When the microcomputer 12051 determines that a pedestrian is present in the images captured by the image capturing units 12101 to 12104 and recognizes the pedestrian, the audio / image output unit 12052 controls the display unit 12062 to superimpose a rectangular outline on the recognized pedestrian for emphasis. The audio / image output unit 12052 may also control the display unit 12062 to display an icon or the like indicating the pedestrian at a desired position.

[0099] An example of a vehicle control system to which the technology according to the present disclosure can be applied has been described above. The technology according to the present disclosure can be applied to, for example, the image capturing unit 12031 among the components described above. Applying the technology according to the present disclosure to the image capturing unit 12031 can improve distance measurement accuracy. As a result, the performance of the vehicle 12100 can be improved.

[0100] The present technology can be configured as follows:

[0101] (1) An optical measurement device comprising: a wavelength swept light source that emits light of a wavelength corresponding to a supplied current; at least one delay interferometer having a plurality of waveguides with different lengths that guide the light; and an analyzer that identifies a mode hop section in which a mode hop in which the wavelength changes discontinuously occurs, based on a phase difference between a plurality of beat signals obtained by photoelectrically converting output light of the delay interferometer that is guided to the plurality of waveguides.

[0102] (2) The optical measurement device according to (1), wherein the plurality of waveguides are provided in the plurality of delay interferometers, respectively, and the optical path differences of the plurality of waveguides are different for each of the delay interferometers.

[0103] (3) The optical measurement device according to (1) or (2), wherein the wavelength swept light source is a ring laser or a DBR (Distributed Bragg Reflector) laser.

[0104] (4) The optical measurement device according to any one of (1) to (3), wherein the delay interferometer is an asymmetric Mach-Zehnder interferometer.

[0105] (5) The optical measurement device according to any one of (1) to (4), further comprising a phase difference detector that detects a phase difference between the plurality of beat signals.

[0106] (6) The optical measurement device according to (5), wherein the phase difference detector has a subtractor that performs subtraction processing of the plurality of beat signals.

[0107] (7) The optical measurement device according to any one of (1) to (6), wherein the plurality of waveguides are provided in one delay interferometer.

[0108] (8) The optical measurement device according to any one of (1) to (6), wherein a plurality of distributed Bragg reflector mirrors are provided at different positions in one of the plurality of waveguides.

[0109] (9) The optical measurement device according to any one of (1) to (8), further comprising: a first splitter disposed between the wavelength swept light source and the delay interferometer, the first splitter splitting the light into a plurality of laser beams; a second splitter splitting one of the plurality of laser beams into a first beam and a second beam; a mixer outputting a composite wave obtained by combining the first beam and a third beam resulting from reflection of the second beam from an object to be measured; a first photodetector photoelectrically converting the composite wave to output a beat signal including depth information; and a second photodetector photoelectrically converting the output light of the delay interferometer.

[0110] (10) The optical measurement device according to (9), wherein the analyzer performs compensation processing on the beat signal of the first photodetector by removing signal data in the mode hopping section and connecting signal data in sections before and after the mode hopping section.

[0111] 1, 2: Optical measurement device 11: Wavelength swept light source 12: First splitter 13: Second splitter 16: Mixer 17: First photodetector 19: Spectrum analyzer (analyzer) 24: Phase difference detector 211-214: Delay interferometers 221-224: Second photodetector 241: First subtractor 242: Second subtractor 243: Third subtractor 2113: First waveguide 2114: Second waveguide 2115: Third waveguide 2116: Fourth waveguide 2117: First distributed Bragg reflector mirror 2118: Second distributed Bragg reflector mirror 2119: Third distributed Bragg reflector mirror

Claims

1. An optical measurement device comprising: a wavelength swept light source that emits light of a wavelength corresponding to a supplied current; at least one delay interferometer having a plurality of waveguides of different lengths that guide the light; and an analyzer that identifies a mode hop section in which a mode hop in which the wavelength changes discontinuously has occurred, based on the phase difference of a plurality of beat signals obtained by photoelectric conversion of the output light of the delay interferometer that has been guided to the plurality of waveguides.

2. The optical measurement device according to claim 1, wherein the plurality of waveguides are provided in the plurality of delay interferometers, respectively, and the optical path differences of the plurality of waveguides are different for each of the delay interferometers.

3. The optical measurement device according to claim 1, wherein the wavelength swept light source is a ring laser or a DBR (Distributed Bragg Reflector) laser.

4. The optical metrology device of claim 1, wherein the delay interferometer is an asymmetric Mach-Zehnder interferometer.

5. The optical measurement device according to claim 1, further comprising a phase difference detector that detects a phase difference between the plurality of beat signals.

6. The optical measurement device according to claim 5, wherein said phase difference detector has a subtractor that performs subtraction processing of said plurality of beat signals.

7. The optical measurement device according to claim 1, wherein the plurality of waveguides are provided in one delay interferometer.

8. The optical metrology device of claim 1, wherein a plurality of distributed Bragg reflector mirrors are provided at different locations in one of said plurality of waveguides.

9. The optical measurement device according to claim 1, further comprising: a first splitter arranged between the wavelength swept light source and the delay interferometer, which splits the light into a plurality of laser beams; a second splitter which splits one of the plurality of laser beams into a first light and a second light; a mixer which outputs a composite wave obtained by combining the first light and a third light formed when the second light is reflected from an object to be measured; a first photodetector which photoelectrically converts the composite wave and outputs a beat signal containing depth information; and a second photodetector which photoelectrically converts the output light of the delay interferometer.

10. The optical measurement device according to claim 9, wherein the analyzer performs compensation processing on the beat signal of the first photodetector by removing signal data in the mode hopping section and connecting signal data in sections before and after the mode hopping section.

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