Distance measuring device

Abstract

To increase a distance resolution and a frame rate and suppress an increase in spatial resolution, so as to appropriately measure a distance from a local device to a distance measurement object.SOLUTION: A distance measuring device 1 comprises: a modulated light output unit 2 for outputting modulated light; a scanner 3 for transmission for emitting input light which is one of branched light beams of the modulated light to a space as emitted light; a scanner 4 for reception for receiving, as incident light, the emitted light having been reflected by a distance measurement object, and outputting the received incident light as reflected light; and a measurement unit 5 for multiplexing reference light, which is the other of the branched light beams of the modulated light, and the reflected light, and measuring the distance from the local device to the distance measurement object. In the scanner for transmission, an emission angle of the emitted light has a frequency dependent characteristic on the input light. The modulated light output unit includes at least two modulated light beams having mutually different modulation frequencies, and chirps the modulation frequencies in a direction in which they become closer to each other so that the modulation frequencies of the two modulated light beams simultaneously become the same modulation frequency, and outputs the modulated light beams.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a distance measuring device. [Background technology]

[0002] Development of LiDAR (Laser Imaging Detection and Ranging) is progressing for the purpose of application to surrounding environment recognition sensors of automobiles and autonomous robots, shape measurement at construction sites, etc. For example, Non-Patent Document 1 discloses a distance measuring device of the FMCW (Frequency Modulated Continuous Wave) method using coherent detection. The FMCW method can detect light reflected from an object to be measured with high sensitivity, and can measure the distance from the device to the object to be measured, as well as the speed of the object to be measured. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 31, NO. 22, NOVEMBER 15, 2019 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the FMCW system, the distance resolution and frame rate cannot be improved unless the chirp band is widened to a certain extent. On the other hand, when a scanner that emits two or more emitted beams into space and has a frequency-dependent emission angle is used as a transmitting scanner, if the chirp band is widened too much, the spatial resolution increases, and there is a high possibility that not all of the emitted beams will hit the object to be measured when the object is small.

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and its object is to provide a ranging device that can appropriately measure the distance from the device to an object to be measured by increasing distance resolution and frame rate while suppressing an increase in spatial resolution. [Means for solving the problem]

[0006] According to the invention described in claim 1, in the distance measuring device (1, 11, 21), the transmitting scanner (4, 14) emits, into space as output light, input light, which is one of the lights branched from modulated light obtained by modulating the oscillation light of the laser light source (2, 3, 12). The receiving scanner (5, 15) receives, as incident light, light reflected by an object to be measured from the output light, and outputs the received incident light as reflected light. The measurement unit (6, 16) combines the reflected light with reference light, which is the other light branched from the modulated light, to measure the distance from the device to the object to be measured. The transmitting scanner has an emission angle that is frequency-dependent with respect to the input light. The modulated light output unit includes at least two modulated lights having different modulation frequencies, and chirps the modulation frequencies in directions approaching each other so that the modulation frequencies of the two modulated lights simultaneously become the same modulation frequency. When the modulation frequencies of the two modulated lights become the same, the chirp direction is switched so that the modulation frequencies are chirped in directions away from each other. The modulated light is output.

[0007] A transmitting scanner is used in which the angle of emission light has frequency dependence with respect to the input light, and the modulation frequencies of the two modulated lights are chirped in a direction approaching each other so that the modulation frequencies of the two modulated lights simultaneously become the same modulation frequency. When the modulation frequencies of the two modulated lights become the same, the chirp direction is switched so that the modulation frequencies are chirped in directions away from each other. The chirp band can be expanded to twice the maximum RF center frequency band, improving distance resolution and frame rate. In addition, the emission angle from the transmitting scanner does not expand beyond the initial value, making it possible to suppress an increase in spatial resolution. This increases distance resolution and frame rate while suppressing an increase in spatial resolution, making it possible to properly measure the distance from the device to an object to be measured.

[0008] According to the invention described in claim 4, in the distance measuring device (1, 11, 21), the transmitting scanner (4, 14) emits, into space as output light, input light, which is one of the lights branched from modulated light obtained by modulating the oscillation light of the laser light source (2, 3, 12). The receiving scanner (5, 15) receives, as incident light, light reflected by an object to be measured from the output light, and outputs the received incident light as reflected light. The measurement unit (6, 16) combines the reflected light with reference light, which is the other light branched from the modulated light, to measure the distance from the device to the object to be measured. The transmitting scanner has an emission angle that is frequency-dependent with respect to the input light. The modulated light output unit includes at least two modulated lights having different modulation frequencies, and chirps the modulation frequencies in directions approaching each other so that the modulation frequencies of the two modulated lights do not simultaneously become the same modulation frequency. In response to the modulation frequencies of the two modulated lights becoming different predetermined modulation frequencies, the chirp direction is switched so that the slope of the chirp of the modulation frequency of one modulated light coincides with the extension line of the slope of the chirp of the modulation frequency of the other modulated light, and the modulation frequencies are chirped in directions away from each other. The modulated light is output.

[0009] A transmitting scanner is used in which the angle of emission light has frequency dependence with respect to the input light, and the modulation frequencies of the two modulated lights are chirped in a direction approaching each other so that they do not simultaneously have the same modulation frequency. In response to the modulation frequencies of the two modulated lights becoming different predetermined modulation frequencies, the chirp direction is switched so that the slope of the chirp of the modulation frequency of one modulated light coincides with the extension line of the slope of the chirp of the modulation frequency of the other modulated light, and the modulation frequencies are chirped in directions away from each other. The chirp band can be expanded to twice the maximum RF center frequency band, improving distance resolution and frame rate. In addition, the emission angle from the transmitting scanner does not expand beyond the initial value, making it possible to suppress an increase in spatial resolution. This increases distance resolution and frame rate while suppressing an increase in spatial resolution, making it possible to properly measure the distance from the device to an object to be measured. [Brief description of the drawings]

[0010] [Figure 1] Functional block diagram showing the first embodiment [Diagram 2] Diagram showing frequency change of modulated light [Diagram 3] Functional block diagram showing a second embodiment [Figure 4] Diagram showing frequency change of modulated light [Diagram 5] Diagram showing frequency change of modulated light [Figure 6] Diagram showing frequency change of modulated light [Figure 7] Diagram showing frequency change of modulated light [Figure 8] Diagram showing frequency change of modulated light [Figure 9] Diagram showing frequency change of modulated light [Figure 10] A diagram showing frequency changes of modulated light and reflected light. [Figure 11] Diagram showing FFT interval [Figure 12] A graph showing the relationship between beat signal frequency and FFT intensity. [Figure 13] Functional block diagram showing a third embodiment. [Figure 14] A graph showing the relationship between beat signal frequency and FFT intensity. [Figure 15] Functional block diagram showing a fourth embodiment. [Figure 16] A graph showing the relationship between beat signal frequency and FFT intensity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, a number of embodiments will be described with reference to the drawings. In each of the following embodiments, parts corresponding to those described in the preceding embodiment will be designated by the same reference numerals, and duplicated descriptions may be omitted.

[0012] (First embodiment) A first embodiment will be described with reference to Fig. 1 and Fig. 2. A distance measuring device is mounted on, for example, an automobile and is used for the purpose of detecting other vehicles, pedestrians, etc. around the vehicle as distance measuring objects and ensuring safe and secure driving by avoiding collisions. As shown in Fig. 1, the distance measuring device 1 includes a modulated light output unit 2, a transmitting scanner 3, a receiving scanner 4, and a measuring unit 5. The modulated light output unit 2 includes a first tunable laser 6 and a second tunable laser 7. The measuring unit 5 includes a coherent detector 8 and a DSP (Digital Signal Processor) 9. The first tunable laser 6 and the second tunable laser 7 correspond to laser light sources.

[0013] The first tunable laser 6 and the second tunable laser 7 are each composed of a distributed feedback (DFB) laser, a distributed Bragg reflector (DBR) laser, an external resonator laser, or the like. The first tunable laser 6 outputs modulated light with a modulation frequency that is up-chirped or down-chirped on the higher frequency band side than the carrier frequency. The second tunable laser 7 outputs modulated light with a modulation frequency that is up-chirped or down-chirped on the lower frequency band side than the carrier frequency. In other words, assuming that the carrier frequency is fc, the RF center frequency is fo, the RF chirp band is k, and the time is t, the modulation frequency f1 of the modulated light output by the first tunable laser 6 is f1=fc+fo±kt The modulation frequency f2 of the modulated light output by the second wavelength tunable laser 7 is given by f2=fc-fo±kt It becomes. As described later, the first tunable laser 6 and the second tunable laser 7 modulate and output the modulated light so that the modulation frequencies of the modulated light are close to each other, so that the inclination of the chirp of f1 and the inclination of the chirp of f2 when modulated with kt are in opposite directions. f1=fc+fo±k In the formula, "±" means "plus or minus," f2=fc-fo±kt In this formula, "±" means "minus plus."

[0014] The modulated light output from the first tunable laser 6 and the second tunable laser 7 is branched into input light and reference light, the input light is input to the transmitting scanner 3, and the reference light is input to the coherent detector 8. When the transmitting scanner 3 receives input light from the first tunable laser 6 and the second tunable laser 7, it irradiates the input light into space as output light. The transmitting scanner 3 has frequency dependency, and the output angle of the output light depends on the frequency of the input light. When the output light irradiated into space from the transmitting scanner 3 hits an object to be measured and is reflected, the reflected light is incident on the receiving scanner 4 as incident light. When the receiving scanner 4 receives incident light, it outputs the incident light to the coherent detector 8 as reflected light. The transmitting scanner 3 and the receiving scanner 4 are composed of, for example, an optical phased array (OPA).

[0015] When the coherent detector 8 receives the reflected light from the receiving scanner 4, it combines the received reflected light with the reference light received from the first tunable laser 6 and the second tunable laser 7 to generate and output a beat signal. In this case, a frequency difference occurs between the reflected light and the reference light due to a time difference according to the distance from the distance measuring device 1 (the device itself) to the object to be measured, and this frequency difference is included in the beat signal.

[0016] The DSP 9 receives the in-phase component I and quadrature signal Q of the beat signal output from the coherent detector 8, converts the received in-phase component I and quadrature signal Q into digital signals, and calculates the phase and frequency of the beat signal. The DSP 9 calculates the average value of the frequency, calculates the Doppler shift, and calculates the speed of the object to be measured. The DSP 9 also removes the Doppler shift component from the phase, calculates the average value of the absolute values ​​of the phase, and calculates the distance from the device to the object to be measured based on the relationship between the calculated average value of the absolute values ​​of the phase and a distance stored in advance.

[0017] In the distance measuring device 1 described above, the first tunable laser 6 and the second tunable laser 7 modulate and output modulated light as shown below. The modulated light output by the first tunable laser 6 with an initial value of +1st order "fc+fo" is called the first modulated light, and the modulated light output by the second tunable laser 7 with an initial value of -1st order "fc-fo" is called the second modulated light. As shown in Fig. 2, the first tunable laser 6 linearly down-chirps the modulation frequency of the first modulated light from "fc+fo" to "fc" over the time period from "T0" to "T1" and outputs the first modulated light, and the second tunable laser 7 linearly up-chirps the modulation frequency of the second modulated light from "fc-fo" to "fc" over the time period from "T0" to "T1" and outputs the second modulated light. Thereafter, the first tunable laser 6 linearly up-chirps the modulation frequency of the first modulated light from "fc" to "fc+fo" over the time from "T1" to "T2", and outputs the first modulated light, and the second tunable laser 7 linearly down-chirps the modulation frequency of the second modulated light from "fc" to "fc-fo" over the time from "T1" to "T2". That is, the first tunable laser 6 and the second tunable laser 7 modulate and output the first modulated light and the second modulated light so that their modulation frequencies approach each other, and switch the chirp direction at the timing when the first modulated light and the second modulated light become the same.

[0018] By controlling the modulation output of the first modulated light and the second modulated light as described above, the chirp band, which is the band from +1st frequency to -1st frequency, can be expanded to twice the maximum RF center frequency band, which is the band from 0th frequency to +1st frequency or -1st frequency, and distance resolution and frame rate can be improved. Also, by restricting the chirp band to the frequency band from +1st frequency to -1st frequency, the emission angle of the emission light emitted from the transmission scanner 3 does not widen beyond the initial value, and an increase in spatial resolution can be suppressed.

[0019] As described above, according to the first embodiment, the following advantageous effects can be obtained. In the distance measuring device 1, a transmitting scanner 3 is used in which the emission angle of the emitted light has frequency dependency with respect to the input light, and the modulation frequencies of the first modulated light and the second modulated light are chirped in a direction approaching each other so that the modulation frequency of the first modulated light and the modulation frequency of the second modulated light are simultaneously the same modulation frequency. The chirp band can be expanded to twice the maximum RF center frequency band, and distance resolution and frame rate can be improved. In addition, the emission angle of the light emitted from the transmitting scanner 3 does not expand beyond the initial value, and an increase in spatial resolution can be suppressed. This increases the distance resolution and frame rate while suppressing an increase in spatial resolution, and allows the distance from the device to the object to be measured and the speed of the object to be measured to be properly measured. By using the first wavelength tunable laser 6 and the second wavelength tunable laser 7, this can be achieved without using an external modulator.

[0020] Second embodiment The second embodiment will be described with reference to Figs. 3 to 9. The first embodiment is configured to use two tunable lasers, a first tunable laser 6 and a second tunable laser 7, while the second embodiment is configured to use one laser and an external modulator. As shown in Fig. 3, the distance measuring device 11 includes a modulated light output unit 12, a transmitting scanner 13, a receiving scanner 14, and a measuring unit 15. The modulated light output unit 12 includes a laser 16 and an external modulator 17. The measuring unit 15 includes a coherent detector 18 and a DSP 19. The laser 16 corresponds to a laser light source. The transmitting scanner 14, the receiving scanner 15, the coherent detector 18, and the DSP 19 are equivalent to the transmitting scanner 3, the receiving scanner 4, the coherent detector 8, and the DSP 9 described in the first embodiment, respectively.

[0021] The laser 16 outputs oscillating light of a predetermined frequency to the external modulator 17. The external modulator 17 is, for example, a Mach-Zehnder modulator, and when oscillating light is input from the laser 16, the external modulator 17 externally modulates the input oscillating light based on an RF signal (AC signal) and DC bias input from outside, and outputs modulated light of a modulation frequency that is up-chirped or down-chirped on the high-frequency band side and low-frequency band side of the predetermined frequency. In other words, if the carrier frequency corresponding to the predetermined frequency is fc, the RF center frequency is fo, the RF chirp band is k, and the time is t, the modulated light f1 and f2 output by the external modulator 17 are, as in the first embodiment, f1=fc+fo±kt f2=fc-fo±kt It becomes.

[0022] The modulated light output from the external modulator 1 is split into input light and reference light in the same manner as in the first embodiment, the input light is input to the transmitting scanner 14, and the reference light is input to the coherent detector 18. The transmitting scanner 14, the receiving scanner 15, the coherent detector 18, and the DSP 19 perform the same processes as in the first embodiment.

[0023] In the distance measuring device 11 described above, the external modulator 17 modulates and outputs modulated light as shown below. Among the modulated light output by the external modulator 17, the modulated light having +1st order "fc+fo" as an initial value is called the first modulated light, and the modulated light having -1st order "fc-fo" as an initial value is called the second modulated light. As shown in Fig. 4, the external modulator 17 linearly down-chirps the modulation frequency of the first modulated light from "fc+fo" to "fc" over the time from "T0" to "T1" and outputs it, and linearly up-chirps the modulation frequency of the second modulated light from "fc-fo" to "fc" over the time from "T0" to "T1" and outputs it. Thereafter, the external modulator 17 linearly up-chirps the modulation frequency of the first modulated light from "fc" to "fc+fo" over the time from "T1" to "T2" and outputs the first modulated light, and linearly down-chirps the modulation frequency of the second modulated light from "fc" to "fc-fo" over the time from "T1" to "T2". That is, the external modulator 17 modulates and outputs the first modulated light and the second modulated light in the same way that the first wavelength tunable laser 6 and the second wavelength tunable laser 7 described in the first embodiment modulate and output the first modulated light and the second modulated light, respectively.

[0024] In this case, the external modulator 17 controls the chirp slope of the modulation frequency by changing the frequency of the RF signal, and the output of the carrier frequency can be suppressed by adjusting the DC bias, so that the balance of the modulation frequency can be maintained. That is, in the first embodiment in which the first wavelength-tunable laser 6 that outputs the first modulated light and the second wavelength-tunable laser 7 that outputs the second modulated light are separate, it is not easy to match the slope of the down-chirp of the modulation frequency of the first modulated light with the slope of the down-chirp of the modulation frequency of the second modulated light, and the slope of the up-chirp of the modulation frequency of the second modulated light with the slope of the up-chirp of the modulation frequency of the first modulated light. In contrast, the linearity of the chirp slope can be ensured by freely controlling the chirp slope using the external modulator 17. In addition, the measurement accuracy can be improved by suppressing the output of the carrier frequency that becomes noise when measuring the distance from the device to the object to be measured and the speed of the object to be measured.

[0025] The external modulator 17 may output modulated light with a waveform different from the waveform shown in FIG. 5, the external modulator 17 linearly down-chirps the modulation frequency of the first modulated light from "fc+fo" to a frequency below "fc" over the time period from "T0" to "T2", and linearly up-chirps the modulation frequency of the second modulated light from "fc-fo" to a frequency above "fc" over the time period from "T0" to "T2". After that, the external modulator 17 linearly up-chirps the modulation frequency of the first modulated light from a frequency below "fc" to "fc+fo" over the time period from "T2" to "T4", and linearly down-chirps the modulation frequency of the second modulated light from a frequency above "fc" to "fc-fo" over the time period from "T2" to "T4". In other words, the first wavelength tunable laser 6 and the second wavelength tunable laser 7 modulate and output the first modulated light and the second modulated light so that their modulation frequencies approach each other, and do not switch the chirp direction when the modulation frequencies of the first modulated light and the second modulated light become identical, but switch the chirp direction when a certain time has elapsed since the modulation frequencies of the first modulated light and the second modulated light become identical.

[0026] In this case, the external modulator 17 can ensure a long time from the start of the modulation output to switching the chirp directions of the first modulated light and the second modulated light ("T0" to "T1" in FIG. 4, and "T0" to "T2" in FIG. 5) for the modulated output described in FIG. 4, and can reduce the number of times the chirp direction is switched when compared with the same measurement time. Since the frame rate decrease can be suppressed more as the number of times the chirp direction is switched is reduced when compared with the same measurement time, the frame rate decrease can be suppressed for the modulated output described in FIG. 4.

[0027] As shown in Fig. 6, the external modulator 17 linearly down-chirps the modulation frequency of the first modulated light from "fc+fo" to "fc-fo" over the time from "T0" to "T2", and outputs the modulation frequency of the second modulated light from "fc-fo" to "fc+fo" over the time from "T0" to "T2". After that, the external modulator 17 linearly up-chirps the modulation frequency of the first modulated light from "fc-fo" to "fc+fo" over the time from "T2" to "T4", and outputs the modulation frequency of the second modulated light from "fc+fo" to "fc-fo" over the time from "T2" to "T4". The occupied frequency band of the first modulated light and the occupied frequency band of the second modulated light are the same.

[0028] In this case, the external modulator 17 can ensure a longer time ("T0" to "T2" in FIG. 6) from the start of the modulation output to switching the chirp directions of the first modulated light and the second modulated light, compared to the modulation output described in FIG. 5, and can further reduce the number of times the chirp direction is switched when compared with the same measurement time. The decrease in frame rate can be further suppressed compared to the modulation output described in FIG. 4 and FIG. 5.

[0029] As shown in Fig. 7, the external modulator 17 linearly down-chirps the modulation frequency of the first modulated light from "fc+fo" to "fc" over the time from "T0" to "T1", and outputs the modulation frequency of the second modulated light from "fc-fo" to "fc" over the time from "T0" to "T1". After that, the external modulator 17 linearly up-chirps the modulation frequency of the first modulated light from "fc" to "fc+fo" over the time from "T1" to "T2", and outputs the modulation frequency of the second modulated light from "fc" to "fc-fo" over the time from "T1" to "T2". In this case, the external modulator 17 monitors the slope of the down-chirp of the first modulated light, and adjusts the slope of the down-chirp of the second modulated light so that it matches the slope of the down-chirp of the monitored first modulated light, thereby ensuring linearity. In addition, the external modulator 17 monitors the slope of the up-chirp of the second modulated light, and adjusts the slope of the up-chirp of the first modulated light so that it matches the slope of the up-chirp of the monitored second modulated light, thereby ensuring linearity.

[0030] As shown in FIG. 8, the external modulator 17 linearly down-chirps the modulation frequency of the first modulated light from "fc+fo" to "fc+fo'" over the time from "T0" to "T1", and outputs the modulation frequency of the second modulated light, linearly up-chirps the modulation frequency of the second modulated light from "fc-fo" to "fc-fo'" over the time from "T0" to "T1". After that, the external modulator 17 linearly up-chirps the modulation frequency of the first modulated light from "fc+fo'" to "fc+fo" over the time from "T2" to "T3" so that the gradient of the up-chirp of the modulation frequency of the first modulated light approaches and matches the extension line of the gradient of the up-chirp of the modulation frequency of the second modulated light. In this case, the gradient of the up-chirp of the modulation frequency of the first modulated light does not need to completely match the extension line of the gradient of the up-chirp of the modulation frequency of the second modulated light, as long as it approaches to a certain extent. Moreover, the external modulator 17 linearly down-chirps the modulation frequency of the second modulated light from "fc-fo'" to "fc-fo" so that the slope of the down-chirp of the modulation frequency of the second modulated light approaches and matches the extension line of the slope of the down-chirp of the modulation frequency of the first modulated light. In this case, the slope of the down-chirp of the modulation frequency of the second modulated light does not need to perfectly match the extension line of the slope of the down-chirp of the modulation frequency of the first modulated light, as long as it approaches to a certain extent.

[0031] 9, the external modulator 17 linearly down-chirps the modulation frequency of the first modulated light from "fc+fo" to "fc+fo'" and outputs the modulation frequency of the second modulated light, and linearly up-chirps the modulation frequency of the second modulated light from "fc-fo" to "fc-fo'". The external modulator 17 specifies the starting point for starting the up-chirp of the modulation frequency of the first modulated light and the down-chirp of the modulation frequency of the second modulated light, based on the timing at which the down-chirp of the modulation frequency of the first modulated light and the up-chirp of the modulation frequency of the second modulated light end and the slope of the down-chirp of the modulation frequency of the first modulated light or the slope of the down-chirp of the modulation frequency of the second modulated light.

[0032] That is, if the timing when the external modulator 17 ends the down-chirp of the modulation frequency of the first modulated light and the up-chirp of the modulation frequency of the second modulated light is “T1”, and the timing when the external modulator 17 starts the up-chirp of the modulation frequency of the first modulated light and the down-chirp of the modulation frequency of the second modulated light is “T2”, then T2=T1+2fo´ / k Calculate "T2" using the formula below.

[0033] Thereafter, the external modulator 17 linearly up-chirps the modulation frequency of the first modulated light from "fc+fo'" to "fc+fo" over the time period from "T2" to "T3" so that the modulation frequency of the second modulated light matches an extension line of the up-chirp slope, and also linearly down-chirps the modulation frequency of the second modulated light from "fc-fo'" to "fc-fo" over the time period from "T2" to "T3" so that the modulation frequency of the first modulated light matches an extension line of the down-chirp slope.

[0034] As described above, according to the second embodiment, the following advantageous effects can be obtained. In the distance measuring device 11, a transmitting scanner 14 is used in which the emission angle of the emitted light has frequency dependency with respect to the input light, and the modulation frequencies of the first modulated light and the second modulated light are chirped in a direction approaching each other so that the modulation frequencies of the first modulated light and the second modulated light are the same modulation frequency at the same time. Also, the modulation frequencies of the first modulated light and the second modulated light are chirped in a direction approaching each other so that the modulation frequencies of the first modulated light and the second modulated light are not the same modulation frequency at the same time. As in the first embodiment, the distance resolution and frame rate are increased while suppressing an increase in spatial resolution, so that the distance from the device to the object to be measured and the speed of the object to be measured can be measured appropriately. The chirp slope can be freely controlled using the external modulator 17, so that the linearity of the chirp slope can be ensured. Also, the measurement accuracy can be improved by suppressing the output of the carrier frequency that becomes noise when measuring the distance from the device to the object to be measured and the speed of the object to be measured.

[0035] Moreover, by ensuring a long time from the start of modulation output to switching the chirp direction of each of the first modulated light and the second modulated light, it is possible to suppress a decrease in frame rate. Moreover, by monitoring the chirp slope to further ensure linearity, it is possible to further improve measurement accuracy.

[0036] Third embodiment The third embodiment will be described with reference to Figs. 10 to 14. In the vicinity of a frequency where modulated signals overlap, a beat signal may be generated due to factors other than distance, resulting in noise. That is, as shown in Fig. 10, a beat signal "f R ” and the beat signal between the reference beams “f △ ” and the beat signal between the reflected lights “f △´ ”, the beat signal between the reference light and other reflected light “f △+R In the FFT (Fast Fourier Transform) section shown in FIG. 11, the FFT intensity is a beat signal "f R ” does not reach its maximum, and the beat signal between the reference beams “f △ Therefore, the DSP 19 selects the beat signal "f △ " needs to be removed.

[0037] As shown in Fig. 13, the DSP 19 inputs an RF signal that is the same as the RF signal input from the outside to the external modulator 17. The DSP 19 calculates the difference between the +1st order modulation frequency and the -1st order modulation frequency from a linear signal of a linear frequency modulator (LFM: linear-frequency-modulated) for generating an RF signal. That is, the DSP 19 calculates the modulation frequency at which the first modulated light down-chirps as follows: f1=fc+fo-kt The modulation frequency at which the second modulated light is up-chirped is calculated as follows: f2=fc-fo+kt The difference is calculated as f1-f2=2(f0-kt) It is calculated as follows.

[0038] The DSP 19 ignores the calculated frequency band in the FFT result after coherent detection or multiplies it by "0", so that the beat signal "f R The peak of the beat signal "f" caused by the object to be measured is set as the maximum. R By maximizing the peak of "", the distance from the device to the object to be measured and the speed of the object to be measured can be measured appropriately.

[0039] As described above, according to the third embodiment, the beat signal “f △ The beat signal "f" caused by the object being measured is eliminated. R By maximizing the peak of "", the distance from the device to the object to be measured and the speed of the object to be measured can be measured appropriately.

[0040] (Fourth embodiment) The fourth embodiment will be described with reference to FIGS. As shown in FIG. 15, the distance measuring device 21 includes a photodetector 22 that monitors the reference light in addition to the configuration described in the second embodiment. The modulated light output from the external modulator 17 is split into input light and reference light, and the reference light is input to the coherent detector 18 and the photodetector 22. The DSP 19 detects a beat signal "f" between the +1st order and -1st order reference lights from the signal input from the photodetector 22. △ ” is detected, and the detected beat signal is subtracted from the measurement result after coherent detection, and FFT processing is performed to obtain the beat signal between the reference lights, “f △ By removing the beat signal "f R In this case, the peak of the beat signal "f R By maximizing the peak of "", the distance from the device to the object to be measured and the speed of the object to be measured can be measured appropriately.

[0041] As described above, according to the fourth embodiment, similarly to the third embodiment, the beat signal “f R By maximizing the peak of "", the distance from the device to the object to be measured and the speed of the object to be measured can be measured appropriately.

[0042] (Other embodiments) Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and concept of the present disclosure.

[0043] Although an OPA has been given as an example of a scanner having frequency dependence, a SAW (Surface Acoustic Wave) device, a prism, liquid crystal, etc. may also be applied. Although a configuration in which the transmitting scanner and the receiving scanner are separate has been exemplified, a single scanner may be used as both the transmitting scanner and the receiving scanner, and a circulator may be provided between the modulated light output unit and the scanner to separate the input light and the reflected light. [Explanation of symbols]

[0044] In the drawing, 1, 11, and 21 are distance measuring devices, 2 and 12 are modulated light output units, 6 is a first wavelength tunable laser (laser light source), 7 is a second wavelength tunable laser (laser light source), 16 is a laser (laser light source), 17 is an external modulator, 3 and 13 are transmitting scanners, 4 and 14 are receiving scanners, 5 and 15 are measuring units, and 22 is a photodetector.

Claims

1. A modulated light output unit (2, 12) for outputting modulated light; a transmission scanner (3, 13) for emitting an input light, which is one of the lights branched from the modulated light, into space as an output light; a receiving scanner (4, 14) that receives the emitted light reflected by an object to be measured as incident light and outputs the incident light as reflected light; a measuring unit (5, 15) that combines the reflected light with a reference light, which is the other light branched from the modulated light, to measure a distance from the device to the object to be measured, the transmitting scanner has an emission angle of the emission light having frequency dependence with respect to the input light, The modulated light output unit includes at least two modulated lights having different modulation frequencies, chirps the modulation frequencies of the two modulated lights in directions approaching each other so that the modulation frequencies of the two modulated lights simultaneously become the same modulation frequency, and when the modulation frequencies of the two modulated lights become the same modulation frequency, switches the chirp direction to chirp the modulation frequencies in directions moving away from each other, and outputs the modulated light.

2. 2. The distance measuring device according to claim 1, wherein the modulated light output section outputs modulated light such that the two modulated lights have the same occupied frequency band.

3. 3. A distance measuring device as described in claim 1 or 2, wherein, when switching the chirp direction of the modulation frequencies of the two modulated lights, the modulated light output unit outputs modulated light so that the chirp slope of one modulation frequency in a first direction matches the chirp slope of the other modulation frequency in a first direction, and so that the chirp slope of one modulation frequency in a second direction matches the chirp slope of the other modulation frequency in a second direction.

4. A modulated light output unit (2, 12) for outputting modulated light; a transmission scanner (3, 13) for emitting an input light, which is one of the lights branched from the modulated light, into space as an output light; a receiving scanner (4, 14) that receives the emitted light reflected by an object to be measured as incident light and outputs the incident light as reflected light; a measuring unit (5, 15) that combines the reflected light with a reference light, which is the other light branched from the modulated light, to measure a distance from the device to the object to be measured, the transmitting scanner has an emission angle of the emission light having frequency dependence with respect to the input light, The modulated light output unit includes at least two modulated lights having different modulation frequencies, and chirps the modulation frequencies of the two modulated lights in directions approaching each other so that they do not simultaneously become the same modulation frequency, and in response to the modulation frequencies of the two modulated lights becoming different predetermined modulation frequencies, the chirp direction is switched so that the slope of the chirp of the modulation frequency of one modulated light matches an extension line of the slope of the chirp of the modulation frequency of the other modulated light, thereby chirping the modulation frequencies in directions moving away from each other and outputting modulated light.

5. 5. A distance measuring device as described in claim 4, wherein, when switching the chirp direction of the modulation frequencies of the two modulated lights, the modulated light output unit outputs modulated light such that the slope of the chirp of one modulation frequency in the first direction approaches the extension line of the slope of the chirp of the other modulation frequency in the first direction, and the slope of the chirp of one modulation frequency in the second direction approaches the extension line of the slope of the chirp of the other modulation frequency in the second direction.

6. The distance measuring device according to claim 5, wherein the modulated light output unit outputs modulated light so that the slope of the chirp of one modulation frequency in the first direction approaches and matches the extension line of the slope of the chirp of the other modulation frequency in the first direction, and so that the slope of the chirp of one modulation frequency in the second direction approaches and matches the extension line of the slope of the chirp of the other modulation frequency in the second direction.

7. 7. A distance measuring device as described in claim 5 or 6, wherein the modulated light output unit identifies a starting point for starting a chirp in the second direction at one modulation frequency and a chirp in the first direction at the other modulation frequency based on a frequency difference when a chirp in a first direction at one modulation frequency and a chirp in the second direction at the other modulation frequency are completed, and a slope of the chirp in the first direction at one modulation frequency or a slope of the chirp in the second direction at the other modulation frequency.

8. 8. The distance measuring device according to claim 1, wherein the modulated light output unit (2) comprises at least two tunable lasers (6, 7) and outputs modulated light output from the at least two tunable lasers.

9. The modulated light output unit (12) includes a laser light source (16) that outputs oscillating light, an external modulator (17) that externally modulates the oscillating light output from the laser light source, and a distance measuring device described in any one of claims 1 to 7 that outputs modulated light output from the external modulator.

10. 10. The distance measuring device according to claim 1, wherein the measurement unit calculates a beat signal generated by interference between the reference beams, removes the calculated beat signal, and then measures the distance from the device to the object to be measured.

11. A photodetector (22) is provided for monitoring the reference light, The distance measuring device according to claim 10 , wherein the measurement unit calculates a beat signal generated by interference between the reference beams by the photodetector monitoring the reference beams.

12. 12. The distance measuring device according to claim 1, wherein a single scanner is used as both the transmitting scanner and the receiving scanner.

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