Distance and speed measuring device and distance and speed measuring method

Abstract

To provide a distance and speed measuring device and a distance and speed measuring method that shorten the measurement time in measuring the distance and speed of either a stationary target object or a moving target object.SOLUTION: A carrier light source which is a continuous wave is input to an electro-optical modulator operating in a carrier suppressed double sideband mode and reference light composed of an upper sideband and a lower sideband is generated. An interference signal of scattered light and reference light when a target body is irradiated with reference light is measured. The frequency of reference light is swept from νc to νc+ΔCW, The oscillation frequency of an RF oscillator is swept from fm to fm+Δm by control of the RF oscillator by a second control device. A distance τ from beat signals fbeat+, fbeat- calculated from the interference signal to the target object and a speed V of the target object are calculated.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a distance and speed measurement device and a distance and speed measurement method, and more particularly to a distance and speed measurement device and a distance and speed measurement method using an FMCW lidar. [Background technology]

[0002] "Light Detection and Ranging (LiDAR)" is a technology that irradiates a target with a laser, detects the scattered light, and measures the distance to the target. One of the techniques is frequency-modulated cw LiDAR (FMCW LiDAR). FMCW LiDAR is a method of detecting the distance and speed of a target by irradiating the target with a frequency-modulated CW laser and measuring the frequency of the beat signal generated by the interference between the reference light and the scattered light.

[0003] A method for detecting the distance to an object and the speed of the object by an FMCW LIDAR will be described with reference to Figs. 10, 11, and 12. Fig. 10 shows an example of the configuration of a distance measuring device 100 using a conventional FMCW LIDAR. A CW laser 1009 emitted from a CW laser source device 1001 is separated into a reference light 1010 and a reference light 1016 by an optical directional coupler 1002. The reference light 1010 enters an angle sweep mechanism 1004 via a circulator 1003, and is irradiated in the direction of an angle α by the angle sweep mechanism 1004. The irradiated reference light 1012 is scattered by an object 1005 located in the direction of the angle α, and the scattered light 1013 enters the angle sweep mechanism 1004. The scattered light 1013 entering the angle sweep mechanism 1004 is input to the circulator as scattered light 1014 as it is, and is output as scattered light 1015. The scattered light 1015 is merged with the reference light 1016 by the optical directional coupler 1006 and output as an output light 1017. An interference signal of the output light 1017 is detected by the photodetector 1007, and the detected interference signal 1018 is input to the calculation device 1008. While the angle sweep mechanism 1004 keeps irradiating the reference light 1012 in the direction of the angle α, the CW laser light source device 1001 sweeps the frequency of the CW laser 1009, thereby calculating the distance to the target object 1005.

[0004] As an example of frequency sweep of the CW laser 1009, the frequency of the CW laser 1009 is changed over time with a triangular waveform as shown in Figures 11(a) and 12(a). When the object 1005 is stationary, the scattered light 1015 propagates with a delay relative to the reference light 1016, so the amount of frequency change when the frequency of the output light 1017 is swept is expressed as shown in Figure 11(b). A beat signal is generated by interference between the scattered light 1015 and the reference light 1016, and the frequency f of the beat signal is detected by the photodetector 1007 as shown in Figure 11(c). beat The frequency of the beat signal is expressed by the following formula:

[0005]

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[0006] When the object 1005 is moving, the scattered light 1015 propagates with a delay relative to the reference light 1016, but the frequency also changes due to the Doppler shift. In the example shown in Fig. 12(b), the frequency shifts to the high frequency side. The frequency of the beat signal is expressed as shown in Fig. 12(c), and the distance L to the object 1005 and the speed V of the object can be calculated by the following equation.

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[0009] In such a method of detecting the distance and speed of a target object using FMCW LIDAR, it is necessary to sweep the frequency of the CW laser at all irradiation angles while sweeping the irradiation angle of the CW laser, which results in a long measurement time. In response to this, a method of shortening the measurement time when detecting the distance and speed of a target object using FMCW LIDAR is disclosed in, for example, Non-Patent Documents 1 and 2.

[0010] Non-Patent Document 1 discloses a method for shortening the angle sweep time by using a microcomb as a light source and using each comb mode of the microcomb as a CW laser light source. According to the method disclosed in Non-Patent Document 1, each comb mode of the microcomb is irradiated in an angular direction according to the comb mode frequency of each comb mode by a diffractive optical element or the like, and the frequency of the excitation CW laser light and the resonance frequency of the microcomb are swept simultaneously to perform frequency sweep of the microcomb, thereby shortening the angle sweep time.

[0011] According to the method described with reference to Fig. 12, in order to calculate the distance and speed of a moving object, when the frequency is swept in a triangular waveform as shown in Fig. 12(a), the frequency is increased from time 0 to T, and then decreased from time T to 2T in Fig. 12, so that the distance and speed can be calculated. According to the method disclosed in Non-Patent Document 2, the distance and speed can be measured at the same time by using carrier suppressed double sideband modulation as the light source, and therefore the sweep time can be shortened.

[0012] Fig. 13 shows an example of the configuration of a distance and speed measurement device 130 using the method disclosed in Non-Patent Document 2. The speed measurement device 130 shown in Fig. 13 has the same configuration as the distance measurement device 100 using FMCW LIDAR shown in Fig. 10, except that an electro-optic modulator 1301 is connected to a CW laser light source device 1001. The electro-optic modulator 1301 is adjusted to suppress the carrier, i.e., the CW laser 1009, and output only the sidebands on both sides, and the modulation frequency is f m Assume that the input is driven by an RF oscillator 1302 having a frequency of 100 kHz.

[0013] The frequency ν c The CW laser 1009 is modulated by the electro-optic modulator 1301, and the CW laser 1009 is suppressed and the frequency is changed to ν c +f m and ν c -f m The oscillation frequency of the RF oscillator 1302 is f m From f m +Δ, the frequency of the upper sideband (A) is shifted to ν c +f m From ν c +f m +Δ, the frequency of the lower sideband (B) is ν c -f m From ν c -(f m +Δ).

[0014] When the upper side band (A) and the lower side band (B) are irradiated onto a stationary object, the scattered light propagates with a delay relative to the upper side band (A) and the lower side band (B), as shown by the scattered light (C) and the scattered light (D) in FIG. 14(b). When the upper side band (A) and the lower side band (B) are irradiated onto a moving object, the scattered light is shifted in frequency by the Doppler shift, as shown by the scattered light (E) and the scattered light (F) in FIG. 14(b). By detecting the beat frequency (G) between the upper side band (A) and the scattered light (E) and the beat frequency (H) between the lower side band (B) and the scattered light (F) using the photodetector 907, as shown in FIG. 14(c), the distance and the speed can be calculated simultaneously. [Prior art documents] [Non-patent literature]

[0015] [Non-Patent Document 1] J.Riemensberger,et al.,Nature,581,164(2020) [Non-Patent Document 2] Z.Xu,et al.,IEEE Photonics Technology Letters,Vol.29,No.24,December 15,pp.2254-2257(2017) Summary of the Invention [Problem to be solved by the invention]

[0016] According to the method disclosed in Non-Patent Document 2, when an upper side band (A) and a lower side band (B) are irradiated onto a moving object, the beat frequency (G) and the beat frequency (H) are different from each other as shown in Fig. 13(c), so that the distance and the speed can be calculated. However, for a stationary object, the beat frequency between the upper side band (A) and the scattered light (C) and the beat frequency between the lower side band (B) and the scattered light (D) are the same value, and the scattered light by the upper side band (A) and the scattered light by the lower side band (B) interfere with each other and cancel each other out, so that a situation exists in which a signal cannot be detected by the photodetector and the distance cannot be calculated.

[0017] In consideration of the above problems, the present invention aims to provide an FMCW LIDAR distance and speed measurement device and method that shortens the measurement time for both distance and speed measurement of stationary and moving objects. [Means for solving the problem]

[0018] A first aspect of the present invention is a distance and speed measuring device, comprising: a laser light source device for irradiating excitation light which is a continuous wave; a current controller for controlling the oscillation frequency of the excitation light; a first control device for controlling the current controller; an RF oscillator for oscillating a modulated signal at a modulation frequency; an electro-optic modulator which receives a carrier light source obtained from the excitation light, is driven by a modulation signal from the RF oscillator, suppresses the carrier light source, generates an upper side band shifted to the high frequency side of the carrier light source by the modulation frequency and a lower side band shifted to the low frequency side of the carrier light source by the modulation frequency, and outputs a mixed light of the upper side band and the lower side band as a reference light; a second control device for controlling the modulation frequency of the RF oscillator; a photodetector for measuring an interference signal between the scattered light and the reference light when the reference light is irradiated to an object; and a calculation device for calculating a distance to the object and a speed of the object from the interference signal detected by the photodetector. The first control device controls the frequency of the reference light to ν c From ν c +Δ CWand sweeping the oscillation frequency of the RF oscillator to f by controlling the RF oscillator with the second control device. m From f m +Δ m The control of the current controller by the first control device and the control of the RF oscillator by the second control device are performed in synchronization with each other, and the computing device derives a beat signal f from the interference signal. beat+ , f beat- Calculate and then

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[0021] In the first aspect of the present invention, an angle sweeping mechanism that sweeps the angle of the reference light irradiated onto the object may be further provided.

[0022] In the first aspect of the present invention, the excitation light and the carrier light source may be the same.

[0023] In the first aspect of the present invention, the sweep amount of the frequency of the reference light and the sweep amount of the oscillation frequency of the RF oscillator may be measured using an unbalanced Mach-Zehnder interferometer.

[0024] In the first aspect of the present invention, the sweep amount of the frequency of the reference light and the sweep amount of the oscillation frequency of the RF oscillator may be measured using an interference CW laser.

[0025] In a first aspect of the present invention, the device may further include an optical frequency comb generator that generates an optical frequency comb from excitation light as a carrier light source, a frequency change measurement unit that measures a sweep amount of the comb mode frequency of the optical frequency comb under the control of a current controller by a first control device, and a first wavelength division multiplexing transmission device that inputs the optical frequency comb to an electro-optical modulator, separates mixed light of upper sidebands and lower sidebands generated for each comb mode of the optical frequency comb for each mode of each comb mode, and irradiates each of the mixed light separated for each mode at an angle corresponding to the mode frequency of each comb mode.

[0026] In a first aspect of the invention, the optical frequency comb generator may consist of an electro-optic modulator.

[0027] In a first embodiment of the invention, the optical frequency comb generator may be comprised of a microresonator.

[0028] In the first aspect of the present invention, the frequency change measuring section may be composed of an unbalanced Mach-Zehnder interferometer.

[0029] In the first aspect of the present invention, the frequency change measuring section may be composed of an interferometer between an optical frequency comb and an interfering CW laser.

[0030] In a first aspect of the invention, the modulator is an intensity modulator, which may be tuned to provide carrier suppressed double sideband modulation by adjusting the DC bias voltage.

[0031] A second aspect of the present invention is a distance and speed measurement method, comprising the steps of irradiating excitation light which is a continuous wave, obtaining a carrier light source from the excitation light, inputting the excitation light to an electro-optic modulator driven by an RF oscillator which oscillates a modulation signal at a modulation frequency, suppressing the carrier light source, generating an upper side band shifted to the high frequency side of the carrier light source by the modulation frequency and a lower side band shifted to the low frequency side of the carrier light source by the modulation frequency, and outputting a mixed light of the upper side band and the lower side band as a reference light, measuring an interference signal between the scattered light and the reference light when the reference light is irradiated to an object, and changing the frequency of the reference light to ν c From ν c +Δ CW The RF oscillator frequency is swept to f m From f m +Δ m and sweeping from the interference signal to the beat signal f beat+ , f beat- and calculating

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[0034] The second aspect of the present invention may further include a step of sweeping the angle of the reference light irradiated onto the object.

[0035] In the second aspect of the present invention, the excitation light and the carrier light source may be the same as each other.

[0036] The method may further comprise the step of measuring the sweep amount of the frequency of the reference light and the sweep amount of the oscillation frequency of the RF oscillator using an unbalanced Mach-Zehnder interferometer.

[0037] The method may further comprise the step of measuring the sweep amount of the frequency of the reference light and the sweep amount of the oscillation frequency of the RF oscillator by using an interference CW laser.

[0038] In a second aspect of the present invention, a step of generating an optical frequency comb from an excitation light as the carrier light source, and setting the frequency of a reference light to v c From ν c +Δ CW The RF oscillator frequency is swept to f m From f m +Δ m The step of sweeping to may further include a step of measuring a sweep amount of the comb mode frequency of the optical frequency comb, and a step of separating the mixed light of the upper sideband and the lower sideband generated for each comb mode of the optical frequency comb for each mode of each comb mode, and irradiating each of the mixed light separated for each mode at an angle corresponding to the mode frequency of each comb mode. Effect of the Invention

[0039] According to the present invention, it is possible to provide a distance and speed measurement device and a distance and speed measurement method using FMCW LIDAR that enables measurement in a short period of time for both the distance and speed of a stationary or moving object. [Brief description of the drawings]

[0040] [Figure 1] 1 is a block diagram showing an example of the configuration of a distance and speed measuring device according to a first embodiment. [Diagram 2] 1 is a graph showing the time changes of the upper sideband frequency, the lower sideband frequency and the beat frequency of the reference light and the scattered light by the distance and speed measuring device of the first embodiment, where (a) and (b) are graphs for the upper sideband frequency and the lower sideband frequency, and (c) is graphs for the beat frequency. [Diagram 3] FIG. 11 is a block diagram showing an example of the configuration of a distance and speed measuring device according to a second embodiment. [Figure 4]FIG. 11 is a block diagram showing an example of the configuration of a LIDAR section of a distance and speed measuring device according to a second embodiment. [Diagram 5] 11 is a block diagram showing an example of the configuration of a frequency change measuring unit when an electro-optic modulator is used as an optical frequency comb generator. FIG. [Figure 6] 11 is a block diagram showing an example of the configuration of a frequency change measuring unit when a microresonator is used as an optical frequency comb generator. FIG. [Figure 7] FIG. 2 is a block diagram showing the configuration of a distance and speed measuring device used in the experiment. [Figure 8] 1 is a graph showing the change over time in the observed frequencies of the upper sideband and the lower sideband. [Figure 9] 1 is a graph showing an observed beat signal. [Figure 10] FIG. 1 is a block diagram showing an example of the configuration of a distance measurement device using a conventional FMCW LIDAR. [Figure 11] 1 is a graph showing the change in reference light, scattered light, and beat frequency by a conventional FMCW lidar when the target object is stationary, where (a) is a graph of the reference light, (b) is a graph of the reference light and scattered light, and (c) is a graph of the beat frequency. [Figure 12] 1A and 1B are graphs showing the changes in reference light, scattered light, and beat frequency when a target object is moving, using a conventional FMCW lidar; (a) is a graph of the reference light, (b) is a graph of the reference light and scattered light, and (c) is a graph of the beat frequency. [Figure 13] FIG. 11 is a block diagram showing an example of the configuration of a distance and speed measuring device using the method disclosed in Non-Patent Document 2. [Figure 14] 13 is a graph showing the time changes of the upper sideband frequency, the lower sideband frequency and the beat frequency of the reference light and the scattered light of the distance and speed measuring device according to the method disclosed in Non-Patent Document 2, where (a) and (b) are graphs for the upper sideband frequency and the lower sideband frequency, and (c) is graphs for the beat frequency. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] Next, an embodiment of the present invention will be described with reference to the drawings. In the description of the drawings relating to the embodiment, the same or similar parts are given the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between thickness and planar dimensions, the thickness ratio of each member, etc. are different from the actual ones. Therefore, the specific thickness and dimensions should be determined with reference to the following description. In addition, it goes without saying that the drawings include parts with different dimensional relationships and ratios.

[0042] Furthermore, the embodiments are merely examples of devices and methods for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention does not specify the configuration, arrangement, layout, etc. of each component to those described below. The technical idea of ​​the present invention can be modified in various ways within the technical scope defined by the claims.

[0043] (First embodiment) A distance and speed measuring device and a distance and speed measuring method according to a first embodiment of the present invention will be described with reference to Fig. 1. As shown in Fig. 1, the distance and speed measuring device 10 according to this embodiment is composed of a CW laser light source device 101, an electro-optic modulator 102, an RF oscillator 103, a current controller 104, a first control device 105, a second control device 106, a first optical directional coupler 107, a circulator 108, an angle sweep mechanism 109, a second optical directional coupler 110, a photodetector 111, and a calculation device 112.

[0044] The CW laser source device 101 emits a laser beam with a frequency of ν c The CW laser 113 having a frequency of f is incident on an electro-optic modulator 102 configured for carrier suppressed double sideband modulation. The electro-optic modulator 102 has a modulation frequency of f mThe electro-optic modulator 102 is driven by an RF oscillator 103, which is a carrier suppression modulator. Carrier suppressed double sideband modulation is a type of modulation in which, when a carrier light source is input, the carrier light source is suppressed, and two sidebands having frequencies shifted from the frequency of the carrier light source to the higher and lower frequencies by the modulation frequency are generated and output. An intensity modulator is particularly suitable as the electro-optic modulator 102, and in this case, the DC bias voltage is adjusted to perform carrier suppressed double sideband modulation. The CW laser 113, which is the carrier light source, is suppressed by the electro-optic modulator 102, and the frequency ν c f on the high-frequency side and low-frequency side m Two sidebands are produced that have frequencies shifted by

[0045] The mixed light 114 of the two sidebands generated by the electro-optical modulator 102 is split into two reference light beams 115 and 116, the reference light 115 is irradiated onto an object 124, and the interference between the scattered light and the reference light is detected by a photodetector to calculate the distance to the object, similar to conventional FMCW lidar, as described below.

[0046] The mixed light 114 of the two sidebands is separated into reference light 115 and reference light 116 in the first optical directional coupler 107. The reference light 115 is input to the circulator 108 and output as reference light 117. The reference light 117 input to the angle sweep mechanism 109 is irradiated in the direction of angle α as viewed from the output hole of the angle sweep mechanism 109, the irradiated reference light 118 is scattered by an object 124 located in the direction of angle α, and the scattered light 119 is incident on the angle sweep mechanism 109. The incident scattered light 120 is merged with the reference light 116 by the circulator 108 and the second optical directional coupler 110, and is output as output light 122. An interference signal of the output light 122 is detected by the photodetector 111, and the interference signal 123 is input to the calculation device 112.

[0047] In the method disclosed in Non-Patent Document 2, the oscillation frequency of the RF oscillator 1202 is set to f m From f m+Δ, and as shown in Figure 13(c), the beat frequency (G) between the upper side band (A) and the scattered light (E) and the beat frequency (H) between the lower side band (B) and the scattered light (F) are detected to simultaneously calculate the distance and speed. With this method, for a stationary object, there are situations in which the beat frequency between the upper side band (A) and the scattered light (C) and the beat frequency between the lower side band (B) and the scattered light (D) are the same value, making it impossible to calculate the distance.

[0048] In this embodiment, the oscillation frequency of the RF oscillator 103 is f m From f m +Δ m At the same time, the frequency of the CW laser 113 irradiated from the CW laser light source device 101 is swept to ν c From ν c +Δ CW As shown in FIG. 2(a), the frequency of the upper sideband (I) generated by the electro-optic modulator 102 is ν c +f m From ν c +f m +Δ+Δ CW The frequency of the lower sideband (J) is ν c -f m From ν c -(f m +Δ)+Δ CW When the upper side band (I) and the lower side band (J) are irradiated onto a stationary object, the scattered light becomes the scattered light (K) and the scattered light (L) in Figure 2(b), and when they are irradiated onto a moving object, the scattered light becomes the scattered light (M) and the scattered light (N) in Figure 2(b).

[0049] In the method disclosed in Non-Patent Document 2, the beat frequency between the upper side band (A) and the scattered light (C) and the beat frequency between the lower side band (B) and the scattered light (D) are the same value, and it may not be possible to calculate the distance. In contrast, in this embodiment, the beat frequencies of the upper side band (I) and the lower side band (J) are different from each other, so that the distance can be calculated even when the target object is stationary.

[0050] As shown in Figure 2(c), whether the target is stationary or moving, the beat frequency of the upper sideband (O) and the beat frequency of the lower sideband (P) are different from each other and can be expressed as follows:

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[0055] The distance and velocity obtained by the above formula are the distance from the angle sweep mechanism 109 to an object located in a predetermined angular direction and the velocity of the object when the reference light 115 is irradiated in the direction of the predetermined angle by the angle sweep mechanism 109. In the series of distance and velocity measurements in this embodiment, the angle sweep mechanism 109 sweeps the irradiation angle of the reference light 115, and the distance and velocity measurements are performed at each angle according to the above formula.

[0056] In this embodiment, an intensity modulator is particularly used as the electro-optical modulator 102, and a DC bias voltage is adjusted so that carrier suppression double sideband modulation is possible. A voltage controlled oscillator, for example, is used as the RF oscillator 103. The second control device 106 controls the RF oscillator 103 to change its oscillation frequency to f m From f m +Δm The CW laser light source device 101 is connected to a current controller 104, which is further connected to a first control device 105. The first control device 105 controls the current controller 104, and the frequency of the CW laser 113 irradiated from the CW laser light source device 101 is controlled to v c From ν c +Δ CW Sweep until

[0057] Methods for measuring the frequency sweep amount of the CW laser and the frequency sweep amount of the RF oscillator include, for example, a method using an unbalanced Mach-Zehnder interferometer, and a method in which an interfering CW laser is prepared for interference with the CW laser and the upper sideband, and the interference between the interfering CW laser and the CW laser and the interference between the interfering CW laser and the upper sideband are detected by a photodetector, and the frequency difference is measured.

[0058] When the frequency sweep amount of the CW laser and the frequency sweep amount of the RF oscillator are measured using an unbalanced Mach-Zehnder interferometer, in this embodiment, the CW laser 113 is split into two using an unbalanced Mach-Zehnder interferometer for measuring the frequency sweep amount (not shown), and the two light beams are propagated through two optical paths with different optical path lengths, and then superimposed. An interference signal due to interference is detected by a photodetector, and the frequency sweep amount of the CW laser is measured by measuring the change in phase of the interference signal due to the frequency change of the CW laser 113. Similarly, the frequency sweep amount of the RF oscillator is measured by detecting an interference signal of interference generated by an unbalanced Mach-Zehnder interferometer (not shown) of one of the mixed lights 114 of two sidebands by a photodetector. Note that the unbalanced Mach-Zehnder interferometer (not shown) for measuring the frequency sweep amount of the CW laser and the unbalanced Mach-Zehnder interferometer (not shown) for measuring the frequency sweep amount of the RF oscillator may be different interferometers from each other, or may be the same interferometer. When the interferometers are identical to each other, a CW laser 113 and one of the mixed light 114 of two sidebands are inputted from opposing input terminals of the unbalanced Mach-Zehnder interferometer for measuring the frequency sweep amount.

[0059] When the frequency sweep amount of the CW laser and the frequency sweep amount of the RF oscillator are measured using an interfering CW laser, in this embodiment, an interfering CW laser (not shown) is prepared to interfere with the CW laser 113, and an interference signal caused by the interference between the CW laser 113 and the interfering CW laser is detected by a photodetector, and the frequency sweep amount of the CW laser is measured by measuring the phase change of the interference signal caused by the frequency change of the CW laser 113. Similarly, the frequency sweep amount of the RF oscillator is measured by detecting an interference signal caused by the interference between one of the mixed light 114 of two sidebands and the interfering CW laser (not shown) by a photodetector. Note that the interfering CW laser (not shown) for interfering with the CW laser 113 and the interfering CW laser (not shown) for interfering with one of the mixed light 114 of two sidebands may be different lasers or may be the same laser. When they are the same laser, an interference CW laser (not shown) is split into two, one of which is made to interfere with the CW laser 113 and the other is made to interfere with the sideband.

[0060] 2(a), since the sweep of the oscillation frequency of the RF oscillator 103 and the sweep of the frequency of the CW laser 113 must be performed in the same cycle, the controls by the first control device 105 and the second control device 106 are executed in synchronization with each other. The control of the current controller 104 by the first control device 105 and the control of the RF oscillator 103 by the second control device 106 are executed so that the frequency of the CW laser 113 and the oscillation frequency of the RF oscillator 1102 have, for example, a sawtooth waveform.

[0061] As described above, the distance and speed measuring device and distance and speed measuring method of this embodiment can shorten the time required to measure the distance to an object when the object is stationary, and the time required to measure the distance to the object and the speed of the object when the object is moving.

[0062] Second Embodiment In the first embodiment, a CW laser is input from a CW laser light source device to the electro-optic modulator. In this embodiment, an optical frequency comb is input to the electro-optic modulator instead of a CW laser, thereby further shortening the measurement time of distance and velocity.

[0063] An example of the configuration of the distance / speed measuring device 30 according to this embodiment is shown in Fig. 3. As shown in Fig. 3, the distance / speed measuring device 30 according to this embodiment is composed of a CW laser source device 301, an optical frequency comb generator 302, an electro-optic modulator 303, an RF oscillator 304, a current controller 305, a first control device 306, a second control device 307, a first optical directional coupler 308, a second optical directional coupler 309, a LIDAR unit 310, and a frequency change measuring unit 311.

[0064] Examples of the optical frequency comb generator 302 include an electro-optic modulator and a microresonator. When an electro-optic modulator is used as the optical frequency comb generator 302, a CW laser is input from the CW laser source device 301 to the electro-optic modulator and modulated to generate a sideband, i.e., an optical frequency comb. When a microresonator is used as the optical frequency comb generator 302, a CW laser is input from the CW laser source device 301 through a waveguide to a microresonator optically coupled to the waveguide to generate an optical frequency comb.

[0065] An optical frequency comb using an electro-optic modulator or a microresonator has a comb mode frequency interval of about 10 GHz to 1 THz, which is wider than the comb interval of about 100 MHz to 1 GHz of conventional optical frequency combs such as mode-locked fiber lasers. In this embodiment, as described later, each comb mode of the optical frequency comb is separated from the others, and each comb mode is used as a plurality of CW lasers, and the comb mode frequency of each comb mode is swept. Therefore, it is desirable that the comb interval of the optical frequency comb is wider, and from the viewpoint of the comb interval, it is desirable to use an electro-optic modulator or a microresonator as the optical frequency comb generator 302.

[0066] CW laser 312 is input from CW laser light source device 301 to optical frequency comb generator 302 to generate optical frequency comb 313. Optical frequency comb 313 generated in optical frequency comb generator 302 is separated into optical frequency comb 314 and optical frequency comb 317 by first optical directional coupler 308, and optical frequency comb 314 is input to electro-optic modulator 303. As in the first embodiment, electro-optic modulator 303 has a modulation frequency of f m The electro-optic modulator 303 is driven by an RF oscillator 304, which is set to perform carrier suppression double sideband modulation. When an optical frequency comb 314 is input to the electro-optic modulator 303, the optical frequency comb 314, which is a carrier light source, is suppressed, and for each of the multiple comb modes of the optical frequency comb 314, f is generated on the high-frequency side and low-frequency side of the comb mode frequency of each comb mode. m Assuming that the optical frequency comb 314 is composed of n comb modes, the n comb modes are suppressed by the electro-optic modulator 303, and two sidebands are generated for each of the n comb modes, that is, 2n sidebands are generated. The 2n sidebands generated by the electro-optic modulator 303 are input to the second optical directional coupler 309 as the reference light 315 and separated into the reference light 316 and the reference light 318, and the reference light 316 is input to the LIDAR unit 310.

[0067] An example of the configuration of the LIDAR section 310 is shown in Fig. 4. The LIDAR section 310 shown in Fig. 4 is composed of a third optical directional coupler 401, a circulator 402, a first wavelength division multiplexing (WDM) device 403, a fourth optical directional coupler 404, a second wavelength division multiplexing (WDM) device 405, first to n-th photodetectors 4061 to 406n, and a calculation device 407.

[0068] The reference light 316 is separated into reference light 408 and reference light 409 in the third optical directional coupler 401. The reference light 408 is input to the first wavelength division multiplexing transmission device 403 via the circulator 402. In the first wavelength division multiplexing transmission device 403, the 2n sidebands are separated into n sideband sets, with an upper sideband and a lower sideband of each comb mode as one set, and are irradiated in an angular direction according to the frequency of each sideband.

[0069] Each sideband is scattered by an object 410 located in an angular direction according to the respective frequency. The scattered light of each sideband is combined as scattered light 411 by the first wavelength division multiplexing transmission device 403, combined with the reference light 409 by the circulator 402 and the fourth optical directional coupler 404, and output as output light 412. The output light 412 is again separated into n sideband sets by the second wavelength division multiplexing transmission device 405. Interference signals 4131-413n of each sideband set are detected by the first to n-th photodetectors 4061-406n and input to the calculation device 407.

[0070] In this embodiment, the oscillation frequency of the RF oscillator 304 is f m From f m +Δ m At the same time, we sweep each comb mode frequency of the optical frequency comb 313 to ν p From ν p +Δ p where ν p is the comb mode frequency of the p-th comb mode. Since the sweep of the oscillation frequency of RF oscillator 304 and the sweep of each comb mode frequency of optical frequency comb 313 must have the same period, the controls by first controller 306 and second controller 307 are executed in synchronization with each other.

[0071] When an electro-optical modulator is used as the optical frequency comb generator 302, the frequency sweep of the optical frequency comb 313 is performed by controlling the current controller 305 by the first control device 306 to sweep the frequency of the CW laser input from the CW laser light source device 301 connected to the current controller 305 to the electro-optical modulator. When a microresonator is used as the optical frequency comb generator 302, the resonant frequency of the microresonator is controlled by a microheater, a piezoelectric element, or the like, and the first control device 306 controls the current controller 305 in synchronization with the control of the resonant frequency of the microresonator to control the frequency of the CW laser, thereby sweeping the frequency of the optical frequency comb 313. However, when the frequency sweep range is small, it is sufficient to control only the frequency of the CW laser by controlling the current controller 305.

[0072] The frequency sweep amount of the optical frequency comb 313 is measured using a frequency change measurement unit 311. Since each comb mode is used as an optical carrier for the FMCW lidar, it is necessary to simultaneously measure the frequency sweep amounts of all comb modes being frequency swept.

[0073] The frequency sweep amount of the swept comb mode can be measured, for example, by using an unbalanced Mach-Zehnder interferometer or by using an interfering CW laser for interference with the comb mode. When the frequency sweep amount of the swept comb mode is measured using an interfering CW laser, an interfering CW laser for interference with the comb mode is prepared, the interfering CW laser is made to interfere with the comb mode, the interference signal is detected by a photodetector, and the amount of change in phase of the interference signal due to a frequency change in the frequency of the comb mode is measured to measure the frequency sweep amount. In this embodiment, the frequency sweep amount of the comb mode is measured using an unbalanced Mach-Zehnder interferometer.

[0074] In this embodiment, when measuring the frequency sweep amount of the comb mode using an unbalanced Mach-Zehnder interferometer, the measurement method is different between using an electro-optic modulator as the optical frequency comb generator 302 and using a microresonator.

[0075] 5 shows an example of frequency change measurement unit 311 according to this embodiment when an electro-optic modulator is used as optical frequency comb generator 302, as frequency change measurement unit 3111. Frequency change measurement unit 311 shown in Fig. 5 is composed of a two-wavelength unbalanced Mach-Zehnder interferometer 501, a first optical bandpass filter (BPF) 502, a second optical bandpass filter (BPF) 503, a first photodetector 504, and a second photodetector 505. Two-wavelength unbalanced Mach-Zehnder interferometer 501 is composed of a first waveguide 506, a second waveguide 507, a fifth optical directional coupler 508, and a sixth optical directional coupler 509, which have different optical path lengths.

[0076] The optical frequency comb 313 generated in the optical frequency comb generator 302 is input to the first optical directional coupler 308 and separated into the optical frequency comb 314 and the optical frequency comb 317, and the optical frequency comb 317 is input to the frequency change measurement unit 311. The optical frequency comb 317 propagates through the first waveguide 506 as reference light 510 and through the second waveguide 507 as reference light 511, and is merged at the sixth optical directional coupler 509, and output light 512 is output. Only the p-th comb mode of the output light 512 is transmitted by the first optical bandpass filter (BPF) 502 as the output light 513, and an interference signal of the output light 513 is detected by the first optical detector 504.

[0077] The 2n sidebands generated by the electro-optical modulator 303 are input to the second optical directional coupler 309 as the reference light 315, and are separated into the reference light 316 and the reference light 318, and the reference light 318 is input to the frequency change measuring unit 311. The reference light 318, like the optical frequency comb 317, propagates through the first waveguide 506 and the second waveguide 507, and is output from the first optical directional coupler 308 as the output light 516. The second optical bandpass filter (BPF) 503 transmits only the upper sideband of the q-th comb mode of the output light 516 as the output light 517, and the second optical detector 505 detects an interference signal of the output light 517. The second optical bandpass filter (BPF) 503 is set to transmit only the upper sideband of the q-th comb mode of the output light 516, but may be set to transmit the lower sideband of the q-th comb mode of the output light 516.

[0078] Assuming that the optical frequency comb 313 is composed of n combs, among the 2n sidebands generated by inputting the optical frequency comb 313 to the electro-optic modulator 303, the frequency of the upper sideband of the sideband generated from the q-th comb counted from the CW laser 312 of the optical frequency comb 313 is ν q+ and the frequency of the lower sideband ν q― teeth,

[0079]

number

[0080]

number

[0081] When the frequency change measurement unit 3111 shown in FIG. 5 is used, the frequency of the s-th comb mode of the optical frequency comb 317 is given by

[0082]

number

[0083]

number

[0084] The frequency ν of the upper sideband of the sideband generated from the q-th comb counted from the CW laser 312 of the reference light 318 q+ Since is expressed as (Equation 12), the frequency change amount Δν s , that is, Δ CW The frequency change amount Δ CW +Δ m , that is, Δ m It is possible to ask for:

[0085] Fig. 6 shows an example of frequency change measurement unit 311 according to this embodiment as frequency change measurement unit 3112 when a microresonator is used as optical frequency comb generator 302. Compared to frequency change measurement unit 3111 shown in Fig. 5, frequency change measurement unit 3112 shown in Fig. 6 differs in that fifth optical directional coupler 508 is connected to fifth optical bandpass filter (BPF) 603 and fifth optical detector 606, and sixth optical directional coupler 509 is connected to third optical bandpass filter (BPF) 601, fourth optical bandpass filter (BPF) 602, third optical detector 604 and fourth optical detector 605.

[0086] The optical frequency comb 317 is separated into reference light 510 and reference light 511 by the fifth optical directional coupler 508, the reference light 510 propagates through the first waveguide 506, and the reference light 511 propagates through the second waveguide 507, and these are merged at the sixth optical directional coupler 509, and output light 606 and output light 607 are output. The output light 606 is input to a third optical bandpass filter (BPF) 601, and the output light 607 is input to a fourth optical bandpass filter (BPF) 602. The third optical bandpass filter (BPF) 601 transmits only the p-th comb mode of the output light 606 as output light 609, and the third optical detector 604 detects an interference signal of the output light 609. A fourth optical bandpass filter (BPF) 602 transmits only the q-th comb mode of the output light 607 as output light 610, and a fourth optical detector 605 detects an interference signal of the output light 610, where p≠q.

[0087] As with the optical frequency comb 317, the fifth optical bandpass filter (BPF) 603 transmits only the upper sideband of the r-th comb mode of the output light 608 as the output light 611 for the reference light 318, and the fifth optical detector 606 detects an interference signal of the output light 611.

[0088] Of the 2n sidebands generated by inputting the optical frequency comb 313 to the electro-optic modulator 303, the frequency of the upper sideband of the sideband generated by the r-th comb counted from the CW laser 312 of the optical frequency comb 313 is ν r+and the frequency of the lower sideband ν r― teeth,

[0089]

number

[0090]

number

[0091] When the frequency change measuring unit 3112 shown in FIG. 6 is used, Δ CW and Δ rep Furthermore, from the interference signal of the output light 611, Δ m It is possible to ask for:

[0092] The oscillation frequency of the RF oscillator 304 is f m From f m +Δ m At the same time, we sweep each comb mode frequency of the optical frequency comb 313 to ν p From ν p +Δ p and from the interference signals 4131 to 413n detected by the first to n-th photodetectors 4061 to 406n of the LIDAR unit 310, the distance from the first wavelength division multiplexing transmission device 403 to an object located in an angular direction corresponding to the frequency of each sideband of the optical frequency comb 313 and the velocity of the object can be calculated, as in the first embodiment.

[0093] The distance and velocity obtained as above are the distance to and the velocity of an object located in an angular direction according to the frequency of each sideband of optical frequency comb 313. In this embodiment, a series of distance and velocity measurements is performed by sweeping the comb mode frequency of optical frequency comb 313 to perform an angle sweep of the irradiation angle of reference light 408, and measuring the distance and velocity at each angle according to the above formula.

[0094] Using the distance and speed measurement device of this embodiment, the distance and speed of a stationary target object and a moving target object were actually calculated. Part of the configuration of this experiment is shown in FIG. 7. In this experiment, a microresonator 702 was used as the optical frequency comb generator 302 shown in FIG. 3. For simplicity, only one comb mode 716 out of n comb modes of the optical frequency comb 715 generated in the microresonator 702 was extracted by an optical bandpass filter (BPF) 711, and the distance and speed were calculated only for the comb mode 616. The lidar unit 310 and the frequency change measurement unit 311 shown in FIG. 3 are not shown in FIG. 7. Furthermore, a mechanism such as a microheater for changing the resonance frequency of the microresonator 702 is not shown in FIG. 7.

[0095] Figure 8 shows the time changes in the observed frequencies of the upper and lower sidebands. Figure 9 shows the beat signals observed for a stationary target and a moving target. As shown in Figure 9, beat frequencies were observed for both stationary and moving targets. Also, as shown in Figure 8, different frequency changes were observed for the upper and lower sidebands.

[0096] The following table shows the distance and speed calculated using the beat frequency of a stationary object and a moving object. The distances of the stationary object and the moving object were almost the same, and the speed values ​​differed by about 50 times. Therefore, the distance and speed measuring device of this embodiment was able to recognize that the stationary object was in a stationary state and that the moving object was in a moving state. In addition, the values ​​were able to be calculated quantitatively.

[0097] [Table 1]

[0098] As described above, the present invention naturally includes various embodiments not described here. Therefore, the technical scope of the present invention is defined only by the invention-specifying matters related to the scope of the claims appropriate from the above description. [Explanation of symbols]

[0099] 10, 30, 90, 130 distance and speed measuring devices 101, 301, 701, 1001 CW laser light source device 102, 303, 703, 1301 Electro-optic modulator 103, 304, 704, 1302 RF Oscillators 104, 305, 705 Current Controller 105, 306, 706 First control device 106, 307, 707 Second control device 107, 308 1st optical directional coupler 108, 402, 1003 Circulator 109, 1004 Angle sweep mechanism 110, 309 Second optical directional coupler 111, 712, 1007 Photodetector 112, 407, 713, 1008 Computing equipment 113, 312, 714, 1009 CW laser 114 Mixed light 115~118, 315, 316, 318, 408, 409, 510, 511, 1010~1012, 1016 Reference light 119~121, 411, 1013, 1014 Scattered light 122, 412, 512, 513, 516, 517, 606~611, 1017 Output light 123, 4131~413n, 1018 Interference signal 124, 410, 1005 Target 302 Optical Frequency Comb Generator 310 Rider Club 311, 3111, 3112 Frequency change measurement section 313, 314, 317, 615 Optical frequency comb 401 Third optical directional coupler 403 1st Wavelength Division Multiplexing Transmission Device 404 4th optical directional coupler 405 2nd Wavelength Division Multiplexing Transmission Device 4061~406n 1st to nth photodetectors 501 Two-wavelength unbalanced Mach-Zehnder interferometer 502 1st Optical Bandpass Filter (BPF) 503 Second Optical Bandpass Filter (BPF) 504 First Photodetector 505 Second Photodetector 506 First Waveguide 507 Second Waveguide 508 5th optical directional coupler 509 6th optical directional coupler 601 3rd Optical Bandpass Filter (BPF) 602 4th Optical Bandpass Filter (BPF) 603 5th Optical Bandpass Filter (BPF) 604 3rd Photodetector 605 4th Photodetector 606 5th Photodetector 702 Microresonator 711 Com Mode 1002, 1006 Optical directional coupler

Claims

1. A laser light source device that irradiates excitation light that is a continuous wave; a current controller for controlling an oscillation frequency of the excitation light; a first control device for controlling the current controller; an RF oscillator that oscillates a modulating signal at a modulating frequency; an electro-optical modulator that receives a carrier light source obtained from the excitation light, is driven by the modulation signal of the RF oscillator, suppresses the carrier light source, generates an upper side band shifted to the high frequency side of the carrier light source by the modulation frequency and a lower side band shifted to the low frequency side of the carrier light source by the modulation frequency, and outputs a mixed light of the upper side band and the lower side band as a reference light; a second control device for controlling the modulation frequency of the RF oscillator; a photodetector that measures an interference signal between the reference light and scattered light when the reference light is irradiated onto an object; a calculation device for calculating a distance to the object and a velocity of the object from the interference signal detected by the optical detector; The first control device controls the current controller to change the frequency of the reference light to v ｃ From ν ｃ +Δ ＣＷ and sweeping the oscillation frequency of the RF oscillator to f by controlling the RF oscillator by the second control device. ｍ From f ｍ +Δ ｍ Sweep up to the control of the current controller by the first control device and the control of the RF oscillator by the second control device are performed in synchronization with each other; The computing device extracts the upper sideband beat signal frequency f ｂｅａｔ＋ , and the frequency f of the beat signal of the lower sideband ｂｅａｔ－ The following formula [0010] [0025] Calculate from and further [0030] [0045] (c is the speed of light, T is the frequency of the reference light v ｃ From ν ｃ +Δ ＣＷ where Δ is the sweep time from the frequency of the target to the frequency of the target, and Δ is the maximum frequency change.

2. 2. The distance / speed measuring device according to claim 1, further comprising an angle sweeping mechanism for sweeping an angle of the reference light irradiated onto the target object.

3. 3. The distance and speed measuring device according to claim 1, wherein the excitation light and the carrier light source are the same.

4. 4. The distance / speed measuring device according to claim 1, wherein the frequency sweep amount of the reference light and the oscillation frequency sweep amount of the RF oscillator are measured using an unbalanced Mach-Zehnder interferometer.

5. 4. The distance / velocity measuring device according to claim 1, wherein the sweep amount of the frequency of the reference light and the sweep amount of the oscillation frequency of the RF oscillator are measured using an interference CW laser.

6. an optical frequency comb generator that generates an optical frequency comb from the excitation light as the carrier light source; a frequency change measurement unit that measures a sweep amount of a comb mode frequency of the optical frequency comb under control of the current controller by the first control device; a first wavelength division multiplexing transmission device for inputting the optical frequency comb to the electro-optical modulator, separating mixed light of the upper sideband and the lower sideband generated for each comb mode of the optical frequency comb for each mode of each of the comb modes, and irradiating each of the mixed light separated for each mode at an angle corresponding to a mode frequency of each of the comb modes; 3. The distance and speed measuring device according to claim 1, further comprising:

7. 7. The distance and speed measuring device according to claim 6, wherein the optical frequency comb generator comprises an electro-optic modulator.

8. 7. The distance and speed measuring device according to claim 6, wherein the optical frequency comb generator is composed of a microresonator.

9. 9. The distance / speed measuring device according to claim 6, wherein the frequency change measuring section is composed of an unbalanced Mach-Zehnder interferometer.

10. 9. The distance / speed measuring device according to claim 6, wherein the frequency change measuring section is composed of an interferometer between the optical frequency comb and an interferometric CW laser.

11. 11. The distance and speed measuring device according to claim 1, wherein the electro-optic modulator is an intensity modulator and is adjusted to perform carrier suppression double sideband modulation by adjusting a DC bias voltage.

12. Irradiating the device with continuous wave excitation light; obtaining a carrier light source from the excitation light; inputting the modulated signal to an electro-optic modulator driven by an RF oscillator that oscillates the modulated signal at a modulation frequency, suppressing the carrier light source, generating an upper sideband shifted to the high frequency side of the carrier light source by the modulation frequency and a lower sideband shifted to the low frequency side of the carrier light source by the modulation frequency, and outputting a mixed light of the upper sideband and the lower sideband as a reference light; measuring an interference signal between the reference light and scattered light when the reference light is irradiated onto an object; The frequency of the reference light is v ｃ From ν ｃ +Δ ＣＷ and the oscillation frequency of the RF oscillator is swept to f ｍ From f ｍ +Δ ｍ and sweeping to The frequency f of the beat signal of the upper sideband from the interference signal ｂｅａｔ＋ , and the frequency f of the beat signal of the lower sideband ｂｅａｔ－ The following formula [0050] [006] and calculating the [0070] [0080] In the above formula (c is the speed of light, T is the frequency of the reference light v ｃ From ν ｃ +Δ ＣＷ Calculating a distance τ to the object and a velocity V of the object based on the sweep time τ, Δ being the maximum value of the frequency change amount; A distance and speed measuring method comprising:

13. 13. The distance and speed measuring method according to claim 12, further comprising the step of sweeping an angle of the reference light irradiated onto the target object.

14. 14. The distance and velocity measuring method according to claim 12, wherein the excitation light and the carrier light source are the same.

15. 15. The distance / velocity measurement method according to claim 12, further comprising a step of measuring the frequency sweep amount of the reference light and the oscillation frequency sweep amount of the RF oscillator using an unbalanced Mach-Zehnder interferometer.

16. 15. The distance / velocity measuring method according to claim 12, further comprising a step of measuring the frequency sweep amount of the reference light and the oscillation frequency sweep amount of the RF oscillator using an interference CW laser.

17. generating an optical frequency comb from the excitation light as the carrier light source; The frequency of the reference light is v ｃ From ν ｃ +Δ ＣＷ and sweeping the oscillation frequency of the RF oscillator to f ｍ From f ｍ +Δ ｍ measuring a sweep amount of a comb mode frequency of the optical frequency comb in the step of sweeping to separating the mixed light of the upper sideband and the lower sideband generated for each comb mode of the optical frequency comb into each mode of each comb mode, and irradiating each of the mixed light separated for each mode at an angle corresponding to the mode frequency of each comb mode; 14. The distance and speed measuring method according to claim 12 or 13, further comprising:

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