Distance measuring device

Abstract

A distance measuring device (1, 11, 21) comprises: a modulated light output unit (2, 12) configured to output modulated light; a transmitting scanner (3, 13) configured to transmit input light as one of branch lights of the modulated light as transmitted light; a receiving scanner (4, 14) into which transmitted light reflected by a target object is incident as incident light, and the receiving scanner outputs the incident light as reflected light; and a measuring unit (5, 15) configured to measure the distance to the target object by combining the reflected light with a reference light as another branch light of the modulated light. The transmitting scanner has frequency dependence, wherein the emission angle of the transmitted light depends on the frequency of the input light. The modulated light output unit outputs the at least two modulated lights by chirping the modulation frequencies of at least two modulated lights having different modulation frequencies to make them close to each other.

Description

Technical Field

[0001] The present disclosure relates to a distance measuring device. Background Art

[0002] Laser imaging detection and ranging (LiDAR) is developed for applications in environmental recognition sensors used in automobiles and autonomous robots, and shape measurement at construction and civil engineering sites. IEEE PHOTONICS TECHNOLOGY LETTERS, Vol. 31, No. 22, November 15, 2019, published "a frequency modulated continuous wave (FMCW) ranging device using coherent detection". In the FMCW method, light reflected by a target object can be detected with high sensitivity. Not only can the distance to the target object be measured, but also the speed of the target object can be measured. Summary of the invention

[0003] However, in the FMCW method, the chirp band must be expanded to some extent to improve the distance resolution and the frame rate. However, in the case where the transmission scanner is used to transmit two or more transmission lights into space and has frequency dependence on the transmission angle, if the chirp band is excessively expanded, the spatial resolution becomes large. When the size of the target object is small, it is likely that all the transmitted lights will not hit the target object.

[0004] An object of the present disclosure is to provide a distance measuring device capable of appropriately measuring the distance to a target object by improving the distance resolution and the frame rate and suppressing the increase in the spatial resolution.

[0005] According to one aspect of the present disclosure, in a distance measuring device, a transmitting scanner emits input light, which is a branch light of modulated light, as emitted light into space. The modulated light is provided by modulating the oscillating light of a laser source. A receiving scanner into which emitted light reflected by a target object is incident as incident light outputs the incident light as reflected light. A measuring unit is configured to measure the distance to a target object by combining the reflected light with a reference light, which is another branch light of the modulated light. The transmitting scanner has frequency dependence, wherein an emission angle of the emitted light depends on the frequency of the input light. A modulated light output unit outputs the at least two modulated lights having different modulation frequencies by chirping the modulation frequencies of the at least two modulated lights to be close to each other so that the modulation frequencies become the same at the same time.

[0006] Using a frequency-dependent transmission scanner in which the emission angle of the emitted light depends on the frequency of the input light, the modulated light is output by chirping the modulation frequencies so that they are close to each other so that the modulation frequencies of the two modulated lights are the same at the same time. The chirp frequency band can be extended to twice the maximum RF center frequency band, and the distance resolution and frame rate can be improved. In addition, the emission angle emitted from the transmission scanner does not widen beyond the initial value, thereby suppressing the increase in spatial resolution. As a result, by improving the distance resolution and frame rate and suppressing the increase in spatial resolution, the distance to the target object to be measured can be appropriately measured.

[0007] According to another aspect of the present disclosure, in a distance measuring device, a transmitting scanner emits input light, which is one branch light of modulated light, into space as emitted light. The modulated light is provided by modulating the oscillating light of a laser source. A receiving scanner into which emitted light reflected by a target object is incident as incident light outputs the incident light as reflected light. The measuring unit is configured to measure the distance to the target object by combining the reflected light with a reference light, which is another branch light of the modulated light. The transmitting scanner has frequency dependence, wherein the emission angle of the emitted light depends on the frequency of the input light. The modulated light output unit outputs the at least two modulated lights by chirping the modulation frequencies of at least two modulated lights having different modulation frequencies from each other so that the modulation frequencies do not become the same at the same time.

[0008] Using a frequency-dependent transmission scanner in which the emission angle of the emitted light depends on the frequency of the input light, the modulated light is output by chirping the modulation frequency so that it is close to each other so that the modulation frequencies of the two modulated lights are not the same at the same time. The chirp frequency band can be extended to twice the maximum RF center frequency band, and the distance resolution and frame rate can be improved. In addition, the emission angle emitted from the transmission scanner does not widen to exceed the initial value, thereby suppressing the improvement of spatial resolution. As a result, by improving the distance resolution and frame rate and suppressing the improvement of spatial resolution, the distance to the target object to be measured can be appropriately measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a functional block diagram showing the distance measurement device according to the first embodiment.

[0010] Figure 2 It is a graph showing the frequency change of modulated light.

[0011] Figure 3 is a functional block diagram showing a distance measurement device according to the second embodiment.

[0012] Figure 4It is a graph showing the frequency change of modulated light.

[0013] Figure 5 It is a graph showing the frequency change of modulated light.

[0014] Figure 6 It is a graph showing the frequency change of modulated light.

[0015] Figure 7 It is a graph showing the frequency change of modulated light.

[0016] Figure 8 It is a graph showing the frequency change of modulated light.

[0017] Fig. 9 It is a graph showing the frequency change of modulated light.

[0018] Fig.10 It is a graph showing the frequency change of modulated light and reflected light.

[0019] Fig.11 This is a graph showing the FFT period.

[0020] Fig.12 It is a graph showing the relationship between the frequency of the beat signal and the FFT intensity.

[0021] Fig.13 is a functional block diagram showing a distance measurement device according to the third embodiment.

[0022] Fig.14 is a graph showing the relationship between the frequency of the beat signal and the FFT intensity.

[0023] Fig.15 is a functional block diagram showing a distance measurement device according to a fourth embodiment.

[0024] Fig.16 is a graph showing the relationship between the frequency of the beat signal and the FFT intensity.

[0025] Fig.17 is a functional block diagram showing a distance measuring device according to a modification of the first embodiment.

[0026] Fig.18 is a functional block diagram showing a distance measuring device according to a modification of the second embodiment. DETAILED DESCRIPTION

[0027] Hereinafter, embodiments will be described with reference to the accompanying drawings. In these embodiments, elements corresponding to elements already described in the previous embodiments are denoted by the same reference numerals, and repeated descriptions may be omitted.

[0028] (First embodiment)

[0029] Will refer to Figure 1 to Figure 2 A first embodiment is described. A distance measuring device 1 is installed in, for example, a car, and is used to detect other vehicles or pedestrians around the car as target objects so as to ensure safe and reliable driving by avoiding collisions. Figure 1 As shown, 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 receiver 8 and a digital signal processor (DSP) 9. The first tunable laser 6 and the second tunable laser 7 correspond to laser sources and have variable wavelengths.

[0030] Each of the first tunable laser 6 and the second tunable laser 7 is, for example, a distributed feedback (DFB) laser, a distributed Bragg reflector (DBR) laser, or an external resonant laser. The first tunable laser 6 outputs a modulated light whose modulation frequency is up-chirped or down-chirped on the high-frequency band side of the carrier frequency. The second tunable laser 7 outputs a modulated light whose modulation frequency is up-chirped or down-chirped on the low-frequency band side of the carrier frequency. That is, when the carrier frequency is fc, the RF center frequency is fo, the RF chirp frequency 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, and the modulation frequency f2 of the modulated light output by the second tunable laser 7 is f2=fc-fo±kt.

[0031] As will be described later, the first tunable laser 6 and the second tunable laser 7 output modulated light that is modulated so that the modulation frequencies of the modulated light are close to each other. Therefore, the chirp rate of f1 and the chirp rate of f2 are opposite when modulated by kt. The "±" in the formula f1 = fc + fo ± kt means "plus or minus", and the "±" in the formula f2 = fc - fo ± kt means "minus or plus".

[0032] 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 receiver 8. When the input light is input from the first tunable laser 6 and the second tunable laser 7, the transmitting scanner 3 uses the input light as the transmitted light to illuminate the space. The transmitting scanner 3 has frequency dependence, and the emission angle of the transmitted light depends on the frequency of the input light. When the transmitted light emitted from the transmitting scanner 3 hits the target object and is reflected, the reflected light is incident on the receiving scanner 4 as incident light. When the incident light is incident on the receiving scanner 4, the receiving scanner 4 outputs the incident light as reflected light to the coherent receiver 8. Each of the transmitting scanner 3 and the receiving scanner 4 is, for example, an optical phased array (OPA for short).

[0033] When the reflected light is input from the receiving scanner 4 to the coherent receiver 8, the coherent receiver 8 combines the reflected light with the reference light input from the first tunable laser 6 and the second tunable laser 7 to obtain and output a beat signal. In this case, a frequency difference is generated between the reflected light and the reference light due to a time difference depending on the distance from the distance measuring device 1 (own device) to the target object, and the frequency difference is included in the beat signal.

[0034] The in-phase component I and the quadrature signal Q of the beat signal are input to the DSP 9 from the coherent receiver 8. The DSP converts the in-phase component I and the 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 target object. In addition, the DSP 9 removes the Doppler shift component from the phase and calculates the average value of the absolute value of the phase. The DSP 9 calculates the distance from the own device to the target object based on the relationship between the average value of the absolute value of the phase and the pre-stored distance.

[0035] In the distance measuring device 1, the first tunable laser 6 and the second tunable laser 7 are modulated and output modulated light as follows. The first modulated light output by the first tunable laser 6 has an initial value "fc+fo" as the +1st order frequency. The second modulated light output by the second tunable laser 7 has an initial value "fc-fo" as the -1st order frequency. Figure 2As shown, the first tunable laser 6 outputs a first modulated light by linearly chirping the modulation frequency from "fc+fo" to "fc" in the time period from T0 to T1. The second tunable laser 7 outputs a second modulated light by linearly chirping the modulation frequency from "fc-fo" to "fc" in the time period from T0 to T1. Thereafter, the first tunable laser 6 outputs a first modulated light by linearly chirping the modulation frequency from "fc" to "fc+fo" in the time period from T1 to T2. The second tunable laser 7 outputs a second modulated light by linearly chirping the modulation frequency from "fc" to "fc-fo" in the time period from T1 to T2. That is, the first tunable laser 6 and the second tunable laser 7 output modulated light that is modulated so that the modulation frequency of the first modulated light and the modulation frequency of the second modulated light are close to each other, and the chirp direction is switched at the time (or moment) when the modulation frequency of the first modulated light and the modulation frequency of the second modulated light become the same.

[0036] By controlling the modulation output of the first modulated light and the second modulated light, the chirp frequency band, which is a frequency band from the +1 order frequency to the -1 order frequency, can be extended to twice the maximum RF center frequency band, wherein the maximum RF center frequency band is a frequency band from the 0th order frequency to the +1st order frequency or the -1st order frequency. Therefore, the distance resolution and the frame rate can be improved. In addition, the chirp frequency band is suppressed within the frequency band from the +1st order frequency to the -1st order frequency. Therefore, the emission angle of the emission light emitted from the transmitting scanner 3 will not be widened to exceed the initial value, and the improvement of the spatial resolution can be suppressed.

[0037] According to the first embodiment, the following effects can be obtained.

[0038] In the distance measuring device 1, a transmitting scanner 3 in which the emission angle of the emitted light has a frequency dependency on the input light is used to chirp the modulation frequency in directions approaching each other so that the modulation frequency of the first modulated light and the modulation frequency of the second modulated light are the same at the same time. The chirp frequency band can be extended to twice the maximum RF center frequency band, and the distance resolution and frame rate can be improved. In addition, the emission angle emitted from the transmitting scanner 3 does not widen beyond the initial value, and the improvement of the spatial resolution can be suppressed. As a result, by using the first tunable laser 6 and the second tunable laser 7 without using an external modulator, by improving the distance resolution and frame rate and suppressing the improvement of the spatial resolution, the distance from the own device to the target object and the speed of the target object can be appropriately measured.

[0039] (Second embodiment)

[0040] Will refer to Figures 3 to 9The second embodiment is described. The first embodiment uses two tunable lasers, for example, a first tunable laser 6 and a second tunable laser 7. In the second embodiment, one laser and an external modulator are used. Figure 3 As shown, 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 receiver 18 and a DSP 19. The laser 16 corresponds to a laser source. The transmitting scanner 13, the receiving scanner 14, the coherent receiver 18, and the DSP 19 are respectively equivalent to the transmitting scanner 3, the receiving scanner 4, the coherent receiver 8, and the DSP 9 described in the first embodiment.

[0041] The laser 16 outputs an oscillating light having a predetermined frequency to an external modulator 17. The external modulator 17 is, for example, a Mach-Zender modulator. When the oscillating light is input from the laser 16 to the external modulator 17, the oscillating light is externally modulated based on a radio frequency signal (AC signal) and a DC bias voltage (DC bias) input from the outside. The external modulator 17 outputs a modulated light having a modulation frequency that is chirped up or down relative to a predetermined frequency on the high-band side and the low-band side. That is, when the carrier frequency corresponding to the predetermined frequency is fc, the radio frequency center frequency is fo, the radio frequency chirp frequency band is k, and the time is t, as in the first embodiment, the modulation frequencies f1 and f2 of the modulated light output by the external modulator 17 are as follows:

[0042] f1=fc+fo±kt; and

[0043] f2=fc-fo±kt.

[0044] The modulated light output from the external modulator 17 is branched into input light and reference light as in the first embodiment. The input light is input to the transmission scanner 13, and the reference light is input to the coherent receiver 18. The transmission scanner 13, the reception scanner 14, the coherent receiver 18, and the DSP 19 perform the same processing as in the first embodiment.

[0045] In the distance measuring device 11, the external modulator 17 modulates and outputs the modulated light as follows. The first modulated light has "fc+fo" as the initial value as the +1st order frequency, and the second modulated light has "fc-fo" as the initial value as the -1st order frequency. Figure 4As shown, the external modulator 17 linearly chirps down the modulation frequency of the first modulated light from "fc+fo" to "fc" in the time period from T0 to T1 and outputs it. The external modulator 17 linearly chirps up the modulation frequency of the second modulated light from "fc-fo" to "fc" in the time period from T0 to T1 and outputs it. Thereafter, the external modulator 17 linearly chirps up the modulation frequency of the first modulated light from "fc" to "fc+fo" in the time period from T1 to T2 and outputs it, and linearly chirps down the modulation frequency of the second modulated light from "fc" to "fc-fo" in the time period from T1 to T2 and outputs it. That is, in the external modulator 17, the first modulated light and the second modulated light are modulated and output similarly to the first embodiment in which the first tunable laser 6 and the second tunable laser 7 modulate and output the first modulated light and the second modulated light, respectively.

[0046] In this case, the external modulator 17 can control the chirp rate of the modulation frequency by changing the frequency of the radio frequency signal, and can suppress the output of the carrier frequency by adjusting the DC bias, thereby maintaining the balance of the modulation frequency. In the first embodiment, since the first tunable laser 6 outputting the first modulated light and the second tunable laser 7 outputting the second modulated light are separated, it is not easy to match the downward chirp rate of the modulation frequency of the first modulated light and the downward chirp rate of the modulation frequency of the second modulated light with the upward chirp rate of the modulation frequency of the second modulated light and the upward chirp rate of the modulation frequency of the first modulated light. In contrast, by flexibly controlling the chirp rate using the external modulator 17, the linearity of the chirp rate can be ensured. In addition, by suppressing the output of the carrier frequency that becomes noise when measuring the distance from the self device to the target object and the speed of the target object, the measurement accuracy can be improved.

[0047] The external modulator 17 can modulate and output Figure 4 Modulated light with different waveforms shown.

[0048] like Figure 5As shown, the external modulator 17 linearly chirps the modulation frequency of the first modulated light from "fc+fo" to a frequency lower than "fc" in the time period from T0 to T2, and linearly chirps the modulation frequency of the second modulated light from "fc-fo" to a frequency higher than "fc" in the time period from T0 to T2. Thereafter, the external modulator 17 linearly chirps the modulation frequency of the first modulated light from a frequency lower than "fc" to "fc+fo" in the time period from T2 to T4, and linearly chirps the modulation frequency of the second modulated light from a frequency higher than "fc" to "fc-fo" in the time period from T2 to T4. That is, the modulation frequency of the first modulated light and the modulation frequency of the second modulated light are modulated to be close to each other, but the chirping direction is not switched at the time / moment when the modulation frequency of the first modulated light and the modulation frequency of the second modulated light become the same. The chirp direction is switched when a certain period of time has passed from the time when the modulation frequency of the first modulated light and the modulation frequency of the second modulated light become the same.

[0049] In this case, relative to Figure 4 The modulated output depicted in Figure 4 The external modulator 17 can ensure a longer time (in Figure 5 Therefore, the number of switching times of the chirp direction can be reduced compared with the same measurement time. Since the number of switching times of the chirp direction becomes smaller than that in the same measurement time, the decrease in the frame rate is suppressed. Figure 4 The modulated output depicted can suppress the decrease in frame rate.

[0050] like Figure 6 As shown, the external modulator 17 linearly chirps the modulation frequency of the first modulated light from "fc+fo" to "fc-fo" in the time period from T0 to T2. The external modulator 17 linearly chirps the modulation frequency of the second modulated light from "fc-fo" to "fc+fo" in the time period from T0 to T2. Thereafter, the external modulator 17 linearly chirps the modulation frequency of the first modulated light from "fc-fo" to "fc+fo" in the time period from T2 to T4, and linearly chirps the modulation frequency of the second modulated light from "fc+fo" to "fc-fo" in the time period 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 (see Figure 6 ).

[0051] In this case, relative to Figure 5The external modulator 17 can further ensure a further longer time ( Figure 6 Thus, the number of chirp direction switching times can be further reduced compared to the same measurement time. Figure 4 and 5 The modulation output described can further suppress the reduction of the frame rate.

[0052] like Figure 7 As shown, the external modulator 17 linearly chirps the modulation frequency of the first modulated light from "fc+fo" to "fc" in the time period from T0 to T1, and linearly chirps the modulation frequency of the second modulated light from "fc-fo" to "fc" in the time period from T0 to T1. Thereafter, the external modulator 17 linearly chirps the modulation frequency of the first modulated light from "fc" to "fc+fo" in the time period from T1 to T2, and linearly chirps the modulation frequency of the second modulated light from "fc" to "fc-fo" in the time period from T1 to T2. In this case, the external modulator 17 monitors the downward chirp rate of the first modulated light (T0 to T1), and controls the downward chirp rate of the second modulated light (T1 to T2) to match the monitored downward chirp rate of the first modulated light (see Figure 7 ) to ensure linearity. In addition, the external modulator 17 monitors the upward chirp rate (T0 to T1) of the second modulated light, and controls the upward chirp rate (T1 to T2) of the first modulated light to match the monitored upward chirp rate of the second modulated light (see Figure 7 ) to ensure linearity.

[0053] like Figure 8As shown, the external modulator 17 linearly chirps the modulation frequency of the first modulated light from "fc+fo" to "fc+fo'" in the time period from T0 to T1, and linearly chirps the modulation frequency of the second modulated light from "fc-fo" to "fc-fo'" in the time period from T0 to T1. After that, the external modulator 17 linearly chirps the modulation frequency of the first modulated light from "fc+fo'" to "fc+fo" in the time period from T2 to T3, so that the upward chirp rate of the first modulation frequency of the first modulated light approaches and matches the extended line of the upward chirp rate of the modulation frequency of the second modulated light. In this case, the upward chirp rate of the modulation frequency of the first modulated light does not have to completely match the extended line of the upward chirp rate of the modulation frequency of the second modulated light, but can be close to it to a certain extent. In addition, the external modulator 17 linearly chirps the modulation frequency of the second modulated light from "fc-fo'" to "fc-fo", so that the downward chirp rate of the modulation frequency of the second modulated light approaches and matches the extended line of the downward chirp rate of the modulation frequency of the first modulated light. In this case, the downward chirp rate of the modulation frequency of the second modulated light does not have to completely match the extended line of the downward chirp rate of the modulation frequency of the first modulated light, but can be close to it to a certain extent.

[0054] like Fig. 9 As shown, the external modulator 17 linearly chirps the modulation frequency of the first modulated light from "fc+fo" down to "fc+fo'", and linearly chirps the modulation frequency of the second modulated light from "fc-fo" up to "fc-fo'". The external modulator 17 specifies the starting point for starting the up-chirp in the modulation frequency of the first modulated light and the down-chirp in the modulation frequency of the second modulated light based on the moment when the down-chirp in the modulation frequency of the first modulated light and the up-chirp in the modulation frequency of the second modulated light are completed and the down-chirp rate of the modulation frequency of the first modulated light or the down-chirp rate of the modulation frequency of the second modulated light.

[0055] That is, the external modulator 17 calculates T2 by the following calculation formula:

[0056] T2=T1+2fo' / k

[0057] Wherein, T1 represents the time when the downward chirping of the modulation frequency of the first modulated light and the upward chirping of the modulation frequency of the second modulated light are completed, and

[0058] T2 represents the time when the upward chirp of the modulation frequency of the first modulated light and the downward chirp of the modulation frequency in the second modulated light are started.

[0059] Specifically, the starting point for starting the chirping of the one modulation frequency in the second direction and the chirping of the other modulation frequency in the first direction can be specified based on the frequency difference (2fo') when the chirping of the one modulation frequency in the first direction and the chirping of the other modulation frequency in the second direction are completed and the chirping rate (k) of the one modulation frequency in the first direction or the chirping rate (k) of the other modulation frequency in the second direction.

[0060] Afterwards, the external modulator 17 linearly chirps the modulation frequency of the first modulated light from "fc+fo'" to "fc+fo" in the time period from T2 to T3 to match the extended line of the upward chirp rate of the modulation frequency of the second modulated light, and linearly chirps the modulation frequency of the second modulated light from "fc-fo'" to "fc-fo" in the time period from T2 to T3 to match the extended line of the downward chirp rate of the modulation frequency of the first modulated light.

[0061] According to the second embodiment, the following effects can be obtained.

[0062] In the distance measuring device 11, using a transmitting scanner 13 in which the emission angle of the emitted light has a frequency dependence relative to the input light, the modulation frequencies are chirped to be close to each other so that the modulation frequency of the first modulated light and the modulation frequency of the second modulated light become the same at the same time. In addition, the modulation frequencies are chirped to be close to each other so that the modulation frequency of the first modulated light and the modulation frequency of the second modulated light do not become the same at the same time. Similar to the first embodiment, by improving the distance resolution and the frame rate and suppressing the improvement of the spatial resolution, the distance from the own device to the target object and the speed of the target object can be appropriately measured. By flexibly controlling the chirp rate using the external modulator 17, the linearity of the chirp rate can be ensured. In addition, by suppressing the output of the carrier frequency that becomes noise when measuring the distance from the own device to the target object and the speed of the target object, the measurement accuracy can be improved.

[0063] Furthermore, by ensuring a long time from the start of modulation output to the switching of the chirp directions of the first modulated light and the second modulated light, a decrease in the frame rate can be suppressed. Furthermore, by monitoring the chirp rate to further ensure linearity, the measurement accuracy can be further improved.

[0064] (Third Embodiment)

[0065] Will refer to Figures 10 to 14 The third embodiment is described. In the vicinity of the frequency at which the modulation signals overlap, noise may be generated due to reasons other than the beat signal generated by the distance. That is, Fig.10 As shown, the beat signal f caused by the target object is generated R , the beat signal f between the reference light Δ, the beat signal f between the reflected light Δ' , and the beat signal f between the reference light and other reflected light Δ+R .exist Fig.11 The FFT (Fast Fourier Transform) cycle is shown in FIG. In the FFT cycle, Fig.12 As shown, the FFT intensity is the beat signal f caused by the target object. R is not the maximum value because the beat signal f between the reference lights Δ Therefore, DSP 19 needs to remove the beat signal f between the reference lights with the maximum FFT intensity. Δ . Fig.12 Part f Δ Depends on the FFT period and / or the chirp rate.

[0066] like Fig.13 As shown, the RF signal is input to the DSP 19, which is the same as the RF signal input to the external modulator 17 from the outside. The DSP 19 calculates the difference between the +1-order modulation frequency and the -1-order modulation frequency from the linear signal of the linear frequency modulator (LFM) for generating the RF signal. That is, the DSP 19 calculates the modulation frequency of the first modulated light chirping downward as f1=fc+fo-kt, and calculates the modulation frequency of the second modulated light chirping upward as f2=fc-fo+kt. The DSP 19 calculates the difference as f1-f2=2(fo-kt).

[0067] The DSP 19 ignores the frequency bands calculated in the FFT result after coherent detection, for example, by multiplying them by zero. Fig.14 The part f corresponding to 2(fo-kt) Δ is ignored. Fig.14 As shown, the beat signal f caused by the target object R The peak value of can be the maximum value. By maximizing the beat signal f caused by the target object R The peak value of the target object can appropriately measure the distance from the own device to the target object and the speed of the target object.

[0068] According to the third embodiment, the beat signal f between the reference lights having the maximum FFT intensity is removed. Δ By maximizing the beat signal f caused by the target object R The peak value of the target object can appropriately measure the distance from the own device to the target object and the speed of the target object.

[0069] (Fourth embodiment)

[0070] Will refer to Figure 15 to Figure 16 A fourth embodiment is described.

[0071] like Fig.15 As shown, the distance measuring device 21 includes a photodetector 22 for monitoring reference light in addition to the configuration described in the second embodiment. The modulated light output from the external modulator 17 is branched into input light and reference light. The reference light is input to the coherent receiver 18 and the photodetector 22. The DSP 19 detects a beat signal f between the reference light with respect to the +1st order frequency and the -1st order frequency from the signal input from the photodetector 22. Δ The DSP 19 subtracts the detected beat signal from the measurement result after coherent detection, and performs FFT processing to remove the beat signal f between the reference lights. Δ Therefore, if Fig.16 As shown, the beat signal f caused by the target object R The peak value of is maximized. Also in this case, it is possible to maximize the beat signal f caused by the target object. R The distance from the own device to the target object and the speed of the target object are appropriately measured by the peak value.

[0072] According to the fourth embodiment, as in the third embodiment, by maximizing the beat signal f caused by the target object R The peak value of the target object can appropriately measure the distance from the own device to the target object and the speed of the target object.

[0073] (Other embodiments)

[0074] Although the present disclosure has been described according to the embodiments, it should be understood that the present disclosure is not limited to such examples or structures. The present disclosure includes various modifications and variations within the scope of equivalents. In addition, various combinations and forms and other combinations and forms including one, more than one or less than one element may be included in the scope and spirit of the present disclosure.

[0075] Although the OPA is illustrated as a scanner having frequency dependence, the scanner may be a surface acoustic wave (SAW) device, a prism, or a liquid crystal display. The transmitting scanner and the receiving scanner are shown as having different configurations. Alternatively, the transmitting scanner 3 and the receiving scanner 4 may be composed of one scanner 10 (see Fig.17 ) and the sending scanner 13 and the receiving scanner 14 can be made of a scanner 20 (see Fig.18 For example, a circulator is provided between the modulated light output unit and the scanner, and the circulator separates the input light and the reflected light from each other.

Claims

1. A distance measuring device, comprising: a modulated light output unit configured to output modulated light; a transmission scanner configured to transmit input light, which is a branch light of the modulated light, as transmission light; a receiving scanner, wherein the emission light reflected by the target object is incident on the receiving scanner as incident light, and the receiving scanner outputs the incident light as reflected light; and a measuring unit configured to measure a distance to the target object by combining the reflected light with a reference light which is another branch light of the modulated light, wherein The transmitting scanner has frequency dependence, wherein the emission angle of the emitted light depends on the frequency of the input light, and The modulated light output unit outputs the at least two modulated lights by chirping the modulation frequencies of at least two modulated lights having different modulation frequencies to make them close to each other so that the modulation frequencies become the same at the same time, and by switching the chirping direction of the modulation frequencies at the moment when the modulation frequencies become the same to chirp the modulation frequencies to separate them from each other.

2. The distance measuring device according to claim 1, wherein: The modulated light output unit outputs the at least two modulated lights such that occupied frequency bands of the at least two modulated lights are the same.

3. The distance measuring device according to claim 1, wherein: When the chirp directions of the modulation frequencies of the at least two modulated lights are switched so that the chirp rate of one modulation frequency in a first direction matches the chirp rate of another modulation frequency in the first direction and the chirp rate of the other modulation frequency in a second direction matches the chirp rate of the one modulation frequency in the second direction, the modulated light output unit outputs the at least two modulated lights.

4. A distance measuring device, comprising: a modulated light output unit configured to output modulated light; a transmission scanner configured to transmit input light, which is a branch light of the modulated light, as transmission light; a receiving scanner, wherein the emission light reflected by the target object is incident on the receiving scanner as incident light, and the receiving scanner outputs the incident light as reflected light; and a measuring unit configured to measure a distance to the target object by combining the reflected light with a reference light which is another branch light of the modulated light, wherein The transmitting scanner has frequency dependence, wherein the emission angle of the emitted light depends on the frequency of the input light, and The modulated light output unit outputs the at least two modulated lights by chirping the modulation frequencies of at least two modulated lights having different modulation frequencies to make them close to each other so that the modulation frequencies do not become the same at the same time, and by switching the chirping direction of the modulation frequencies so that the chirping rate of one of the modulation frequencies matches the extended line of the chirping rate of the other modulation frequency to chirp the modulation frequencies to separate them from each other.

5. The distance measuring device according to claim 4, wherein: When the chirping direction of the modulation frequencies of the at least two modulated lights is switched so that a modulation frequency chirped in a first direction is close to an extension line of another modulation frequency chirped in the first direction and the other modulation frequency chirped in a second direction is close to an extension line of the modulation frequency chirped in the second direction, the modulated light output unit outputs the at least two modulated lights.

6. The distance measuring device according to claim 5, wherein: The modulated light output unit outputs the at least two modulated lights so that the chirp rate of the one modulation frequency in the first direction matches the chirp rate of the other modulation frequency in the first direction and the chirp rate of the other modulation frequency in the second direction matches the chirp rate of the one modulation frequency in the second direction.

7. The distance measuring device according to claim 5, wherein: The modulated light output unit specifies a starting point for starting the chirp of the one modulation frequency in the second direction and the chirp of the other modulation frequency in the first direction based on the frequency difference when the chirp of the one modulation frequency in the first direction and the chirp of the other modulation frequency in the second direction are completed and the chirp rate of the one modulation frequency in the first direction or the chirp rate of the other modulation frequency in the second direction.

8. The distance measuring device according to any one of claims 1 to 7, wherein: The modulated light output unit includes at least two tunable lasers, and outputs modulated light from the at least two tunable lasers.

9. The distance measuring device according to any one of claims 1 to 7, wherein: The modulated light output unit includes a laser source for outputting oscillation light, and an external modulator that externally modulates the oscillation light output from the laser source, and The modulated light output unit outputs the modulated light from the external modulator.

10. The distance measuring device according to any one of claims 1 to 7, wherein: The measuring unit calculates a beat signal generated by interference between the reference lights and removes the beat signal to measure a distance to the target object.

11. The distance measuring device according to claim 10, further comprising: a light detector configured to monitor the reference light, wherein The measuring unit calculates a beat signal generated by interference between the reference lights by monitoring the reference lights through the photodetector.

12. The distance measuring device according to any one of claims 1 to 7, wherein: The transmitting scanner and the receiving scanner are formed by one scanner.

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