JP7654246B2 - Distance and speed measuring device and distance and speed measuring method - Google Patents

Description

The present invention relates to a distance and speed measurement device and a distance and speed measurement method, and in particular to a distance and speed measurement device and a distance and speed measurement method using FMCW lidar.

"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 to 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.

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 Figures 10, 11, and 11. Figure 10 shows an example of the configuration of a distance measuring device 100 using a conventional FMCW lidar. A CW laser 1009 irradiated from a CW laser light 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 is incident on 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 angle α, and the scattered light 1013 is incident on the angle sweep mechanism 1004. The scattered light 1013 incident on the angle sweep mechanism 1004 is input to the circulator as scattered light 1014 as it is and 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 the output light 1017. The 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 source device 1001 sweeps the frequency of the CW laser 1009, thereby calculating the distance to the target object 1005.

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 _beat of the beat signal can be detected by the photodetector 1007 as shown in Figure 11(c). The frequency of the beat signal is expressed by the following equation:

のように表されることから、対象体１００５までの距離Ｌを算出することが出来る。ここで、ｃは光速、Ｔは図１１及び図１２に示す三角波形の半周期、Δは図１１及び図１２に示す周波数変化量の最大値である。

From the above, it is possible to calculate the distance L to the target object 1005. Here, c is the speed of light, T is the half period of the triangular waveform shown in Figures 11 and 12, and Δ is the maximum value of the frequency change amount shown in Figures 11 and 12.

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 higher 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 velocity V of the object can be calculated by the following equation.

This method of detecting the distance and speed of a target object using FMCW LIDAR requires sweeping the frequency of the CW laser at every irradiation angle while sweeping the irradiation angle of the CW laser, which results in long measurement times. In response to this, methods for shortening the measurement time when detecting the distance and speed of a target object using FMCW LIDAR are disclosed, for example, in Non-Patent Documents 1 and 2.

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 corresponding 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 resonant frequency of the microcomb are swept simultaneously to perform frequency sweep of the microcomb, thereby shortening the angle sweep time.

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), in FIG. 12, the frequency is increased from time 0 to T, and then decreased from time T to 2T, thereby allowing the distance and speed to 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, thereby shortening the sweep time.

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 the 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 is driven by an RF oscillator 1302 with a modulation frequency of _fm .

The CW laser 1009 having a frequency of v _c emitted from the CW laser light source device 1001 is modulated by the electro-optic modulator 1301, the CW laser 1009 is suppressed, and two sidebands having frequencies of v _c +f _m and v _c -f _m are generated. By shifting the oscillation frequency of the RF oscillator 1302 from f _m to f _m +Δ, the frequency of the upper sideband (A) can be shifted from v _c +f _m to v _c +f _m +Δ and the frequency of the lower sideband (B) can be shifted from v _c -f _m to v _c -(f _m +Δ) as shown in Fig. 14(a).

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 shifts in frequency due to 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 speed can be calculated simultaneously.

J. Riemensberger, et al. , Nature, 581, 164 (2020) Z. Xu, et al. , IEEE Photonics Technology Letters, Vol. 29, No. 24, December 15, pp. 2254-2257 (2017)

According to the method disclosed in Non-Patent Document 2, when an upper sideband (A) and a lower sideband (B) are irradiated onto a moving object, the beat frequency (G) and the beat frequency (H) are different values 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 sideband (A) and the scattered light (C) and the beat frequency between the lower sideband (B) and the scattered light (D) are the same value, and the scattered light from the upper sideband (A) and the scattered light from the lower sideband (B) interfere with each other and cancel each other out, so that the photodetector cannot detect the signal and the distance cannot be calculated.

In consideration of the above problems, the present invention aims to provide a distance and speed measurement device and a distance and speed measurement method using FMCW lidar that shortens the measurement time for both distance and speed measurement of stationary and moving objects.

A first aspect of the present invention is a distance/velocity measuring device, comprising: a laser light source device that irradiates excitation light which is a continuous wave; a current controller for controlling the oscillation frequency of the excitation light; a first control device that controls the current controller; an RF oscillator that oscillates a modulated signal at a modulation frequency; an electro-optic modulator that receives a carrier light source obtained from the excitation light and 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 that controls the modulation frequency of the RF oscillator; a photodetector that measures an interference signal between the scattered light and the reference light when the reference light is irradiated onto an object; and a calculation device that calculates a distance to the object and a velocity of the object from the interference signal detected by the photodetector. The first control device controls the current controller to sweep the frequency of the reference light from ν _c to ν _c + Δ _CW , and the second control device controls the RF oscillator to change the oscillation frequency of the RF oscillator to f _m to f _m + _Δm , the control of the current controller by the first control device and the control of the RF oscillator by the second control device are executed in synchronization with each other, and the calculation device calculates beat signals f _beat+ and f _beat− from the interference signal,

の式により対象体までの距離τ及び対象体の速度Ｖを算出することを要旨とする。

The gist of the present invention is to calculate the distance τ to the target object and the velocity V of the target object using the following equation.

The first aspect of the present invention may further include an angle sweep mechanism that sweeps the angle of the reference light irradiated onto the target object.

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

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

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

In the 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 the 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 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 irradiates each of the mixed light separated for each mode at an angle corresponding to the mode frequency of each comb mode.

In a first aspect of the present invention, the optical frequency comb generator may be comprised of an electro-optic modulator.

In a first aspect of the present invention, the optical frequency comb generator may be comprised of a microresonator.

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

In the first aspect of the present invention, the frequency change measurement unit may be composed of an interferometer between an optical frequency comb and an interfering CW laser.

In a first aspect of the present invention, the intensity modulator may be adjusted to provide carrier suppression double sideband modulation by adjusting the DC bias voltage.

A second aspect of the present invention is a distance/speed measuring 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, sweeping the frequency of the reference light from ν _c to ν _c +Δ _CW and sweeping the oscillation frequency of the RF oscillator from f _m to f _m +Δ _m , and calculating beat signals f _beat+ and f _beat− from the interference signal,

上式により対象体までの距離τ及び対象体の速度Ｖを算出するステップとを備えることを要旨とする。

The method further comprises a step of calculating a distance τ to the object and a velocity V of the object using the above formula.

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

In a second aspect of the present invention, the excitation light and the carrier light source may be the same.

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

The method may further include a step of measuring the sweep amount of the reference light frequency and the sweep amount of the RF oscillator oscillation frequency using an interference CW laser.

In a second aspect of the present invention, the method may further include a step of measuring a sweep amount of the comb mode frequency of the optical frequency comb in the step of generating an optical frequency comb from excitation light as the carrier light source, _sweeping the frequency of the reference light from ν _c to ν _c + Δ _CW and sweeping the oscillation frequency of the RF oscillator from f m to f _m + Δ _m , 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.

The present invention provides a distance and speed measurement device and method using FMCW lidar that enables measurements in a short time for both stationary and moving object distance and speed measurements.

1 is a block diagram showing an example of a configuration of a distance and speed measuring device according to a first embodiment. 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 a graph for the beat frequency. FIG. 11 is a block diagram showing an example of the configuration of a distance and speed measuring device according to a second embodiment. 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. 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. 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. FIG. 2 is a block diagram showing the configuration of a distance and speed measuring device used in the experiment. 1 is a graph showing the change over time in the observed frequencies of the upper sideband and the lower sideband. 1 is a graph showing an observed beat signal. FIG. 1 is a block diagram showing an example of the configuration of a distance measurement device using a conventional FMCW LIDAR. 1A and 1B are graphs showing the changes 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. 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. FIG. 1 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. 13 is a graph showing the time variations in 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 a graph for the beat frequency.

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 component, etc., differ from the actual ones. Therefore, the specific thickness and dimensions should be determined with reference to the following explanation. In addition, it goes without saying that the drawings include parts with different dimensional relationships and ratios.

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.

(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.

A CW laser 113 having a frequency of ν _c is input from a CW laser light source device 101 to an electro-optical modulator 102 set to perform carrier suppression double-sided sideband modulation. The electro-optical modulator 102 is driven by an RF oscillator 103 having a modulation frequency of f _m . The carrier suppression double-sided sideband modulation is a 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 high-frequency side and the low-frequency side by the modulation frequency are generated and output. An intensity modulator is particularly suitable as the electro-optical modulator 102, and in this case, the DC bias voltage is adjusted to perform carrier suppression double-sided sideband modulation. The CW laser 113, which is a carrier light source, is suppressed by the electro-optical modulator 102, and two sidebands having frequencies shifted by f _m to the high-frequency side and the low-frequency side of the frequency ν _c of the CW laser 113 are generated.

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

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 seen from the output hole of the angle sweep mechanism 109, the irradiated reference light 118 is scattered by the 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 output as output light 122. The 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.

In the method disclosed in Non-Patent Document 2, the oscillation frequency of RF oscillator 1202 is swept from _fm to _fm + Δ, and the beat frequency (G) between the upper side band (A) and scattered light (E) and the beat frequency (H) between the lower side band (B) and scattered light (F) are detected as shown in Fig. 13(c), and distance and speed are calculated simultaneously. According to this method, for a stationary target, there are situations in which the beat frequency between the upper side band (A) and scattered light (C) and the beat frequency between the lower side band (B) and scattered light (D) have the same value, making it impossible to calculate the distance.

In this embodiment, the oscillation frequency of the RF oscillator 103 is swept from _fm to _fm + _Δm , and at the same time, the frequency of the CW laser 113 irradiated from the CW laser light source device 101 is swept from _νc to _νc + _ΔCW . As shown in Fig. 2(a), the frequency of the upper sideband (I) generated by the electro-optic modulator 102 changes from _νc + _fm to _νc + _fm + Δ + _ΔCW , and the frequency of the lower sideband (J) changes from _νc - _fm to _νc - ( _fm + Δ) + _ΔCW . The scattered light when the upper sideband (I) and the lower sideband (J) are irradiated on a stationary target becomes the scattered light (K) and scattered light (L) in Fig. 2(b), and the scattered light when they are irradiated on a moving target becomes the scattered light (M) and scattered light (N) in Fig. 2(b).

In the method disclosed in Non-Patent Document 2, the beat frequency between the upper sideband (A) and the scattered light (C) and the beat frequency between the lower sideband (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 sideband (I) and the lower sideband (J) are different from each other, so that the distance can be calculated even when the target object is stationary.

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 and can be expressed as follows:

したがって、対象体が静止しているときは対象体までの距離を、対象体が移動しているときは対象体までの距離及び対象体の速度を次式より算出することが出来る。

Therefore, when the target object is stationary, the distance to the target object can be calculated from the following equation, and when the target object is moving, the distance to the target object and the speed of the target object can be calculated from the following equation.

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 a direction at a predetermined angle by the angle sweep mechanism 109. In this embodiment, a series of distance and velocity measurements are performed by sweeping the irradiation angle of the reference light 115 by the angle sweep mechanism 109, and measuring the distance and velocity at each angle using the above formula.

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. For example, a voltage controlled oscillator is used as the RF oscillator 103. The second control device 106 controls the RF oscillator 103 to sweep the oscillation frequency from _fm to _fm + _Δm . A current controller 104 is connected to the CW laser light source device 101, and a first control device 105 is further connected to the current controller 104. The first control device 105 controls the current controller 104 to sweep the frequency of the CW laser 113 irradiated from the CW laser light source device 101 from _νc to _νc + _ΔCW .

Methods for measuring the frequency sweep amount of a CW laser and the frequency sweep amount of an RF oscillator include, for example, using an unbalanced Mach-Zehnder interferometer, and preparing an interfering CW laser for interference with the CW laser and the upper sideband, detecting the interference between the interfering CW laser and the CW laser and the interference between the interfering CW laser and the upper sideband with a photodetector, and measuring the frequency difference.

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. The 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 the interference signal of the interference generated by an unbalanced Mach-Zehnder interferometer (not shown) of one of the mixed light 114 of the two sidebands using a photodetector. In addition, 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, or may be the same interferometer. If they are the same interferometer, the CW laser 113 and one of the two sidebands of the mixed light 114 of the sidebands are input from opposing input terminals of the unbalanced Mach-Zehnder interferometer for measuring the frequency sweep amount.

When the frequency sweep amount of the CW laser and the frequency sweep amount of the RF oscillator are measured using an interference CW laser, in this embodiment, a non-illustrated interference CW laser is prepared for interference with the CW laser 113, and an interference signal caused by interference between the CW laser 113 and the interference 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, for measuring the frequency sweep amount of the RF oscillator, an interference signal caused by interference between one of the two sidebands of the mixed light 114 and the interference CW laser (not shown) is detected by a photodetector, thereby measuring the frequency sweep amount of the RF oscillator. Note that the interference CW laser (not shown) for interference with the CW laser 113 and the interference CW laser (not shown) for interference with one of the two sidebands of the mixed light 114 may be different lasers from each other, or may be the same laser. If 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.

As shown in FIG. 2(a), 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, so 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 wave shape.

As described above, the distance and speed measurement device and distance and speed measurement method according to this embodiment can reduce 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.

Second Embodiment
In the first embodiment, a CW laser is input from a CW laser light source device to the electro-optic modulator. In the present 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.

An example of the configuration of the distance and speed measurement device 30 according to this embodiment is shown in FIG. 3. As shown in FIG. 3, the distance and speed measurement device 30 according to this embodiment is composed of a CW laser light source device 301, an optical frequency comb generator 302, an electro-optical 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 measurement unit 311.

The optical frequency comb generator 302 may be, for example, an electro-optical modulator or a microresonator. When an electro-optical 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-optical 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 via a waveguide to a microresonator optically coupled to the waveguide to generate an optical frequency comb.

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

A CW laser 312 is input from a CW laser source device 301 to an optical frequency comb generator 302 to generate an optical frequency comb 313. The optical frequency comb 313 generated in the optical frequency comb generator 302 is separated into an optical frequency comb 314 and an optical frequency comb 317 by a first optical directional coupler 308, and the optical frequency comb 314 is input to an electro-optical modulator 303. As in the first embodiment, the electro-optical modulator 303 is driven by an RF oscillator 304 having a modulation frequency of _fm , and is set to perform carrier suppression double sideband modulation. When the optical frequency comb 314 is input to the electro-optical modulator 303, the optical frequency comb 314, which is a carrier light source, is suppressed, and two sidebands having frequencies shifted by _fm to the higher and lower frequency sides of the comb mode frequency of each comb mode are generated for each of the multiple comb modes of the optical frequency comb 314. If 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, i.e., 2n sidebands are generated. The 2n sidebands generated by the electro-optic modulator 303 are input to the second optical directional coupler 309 as reference light 315 and separated into reference light 316 and reference light 318, and the reference light 316 is input to the LIDAR section 310.

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 nth photodetectors 4061 to 406n, and a calculation device 407.

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 sets of sidebands, with the upper sideband and the lower sideband of each comb mode being one set, and are irradiated in an angular direction according to the frequency of each sideband.

Each sideband is scattered by an object 410 located in an angular direction corresponding 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 sets of sidebands by the second wavelength division multiplexing transmission device 405. The interference signals 4131 to 413n of each set of sidebands are detected by the first to nth photodetectors 4061 to 406n and input to the calculation device 407.

In this embodiment, the oscillation frequency of the RF oscillator 304 is swept from _fm to _fm + _Δm , and at the same time, each comb mode frequency of the optical frequency comb 313 is swept from _νp to _νp + _Δp , where _νp is the comb mode frequency of the p-th comb mode. Since the sweep of the oscillation frequency of the RF oscillator 304 and the sweep of each comb mode frequency of the optical frequency comb 313 must have the same period, the controls by the first control device 306 and the second control device 307 are executed in synchronization with each other.

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 with 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, etc., 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 performing the frequency sweep 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.

The frequency sweep amount of the optical frequency comb 313 is measured using the 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 that are being frequency swept.

Measurements of the frequency sweep amount of the swept comb mode include, for example, a method using an unbalanced Mach-Zehnder interferometer and a method using an interfering CW laser for interference with the comb mode. When measuring the frequency sweep amount of the swept comb mode 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, an unbalanced Mach-Zehnder interferometer is used to measure the frequency sweep amount of the comb mode.

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

FIG. 5 shows an example of the frequency change measurement unit 311 according to this embodiment when an electro-optical modulator is used as the optical frequency comb generator 302, as the frequency change measurement unit 3111. The 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. The 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, each of which has a different optical path length.

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 the output light 512 is output. The first optical bandpass filter (BPF) 502 transmits only the p-th comb mode of the output light 512 as the output light 513, and the first photodetector 504 detects the interference signal of the output light 513.

The 2n sidebands generated by the electro-optical modulator 303 are input to the second optical directional coupler 309 as reference light 315, separated into reference light 316 and reference light 318, and the reference light 318 is input to the frequency change measurement unit 311. The reference light 318 propagates through the first waveguide 506 and the second waveguide 507, similar to the optical frequency comb 317, and is output from the first optical directional coupler 308 as 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 output light 517, and the second optical detector 505 detects the 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 it may also be set to transmit the lower sideband of the q-th comb mode of the output light 516.

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 v _{q+ and the frequency of the lower sideband v q−} of the sideband generated from the q-th comb of the optical frequency comb 313 counting from the CW laser 312 are expressed as _follows :

で表すことが出来る。Δ_ＣＷとΔ_ｍを求めることによって、電気光学変調器３０３によって生成された２ｎ個のサイドバンドのうち、全てのサイドバンドの周波数を算出することが出来る。

By determining Δ _CW and Δ _m , the frequencies of all of the 2n sidebands generated by the electro-optic modulator 303 can be calculated.

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

で表される。光周波数コム３１７の周波数変化量Δν_ｓと、第１光検出器５０４によって検出された出力光５１３の干渉信号の位相の変化量Δφは、

The frequency change amount Δν _s of the optical frequency comb 317 and the phase change amount Δφ of the interference signal of the output light 513 detected by the first photodetector 504 are expressed as follows:

で表されることから、出力光５１３の干渉信号の位相の変化量Δφを計測することで、光周波数コム３１７の周波数変化量Δν_ｓ、即ちΔ_ＣＷを求めることが出来る。ここで、τは、２波長アンバランスマッハツェンダ―干渉計５０１による、参照光３１８の光周波数コム３１７に対する遅延時間である。

Since it is expressed as above, the frequency change amount Δν _s of the optical frequency comb 317, i.e., Δ _CW , can be obtained by measuring the phase change amount Δφ of the interference signal of the output light 513. Here, τ is the delay time of the reference light 318 with respect to the optical frequency comb 317, caused by the two-wavelength unbalanced Mach-Zehnder interferometer 501.

Since the frequency ν _q+ of the upper sideband of the sideband generated from the q-th comb of the reference light 318 counting from the CW laser 312 is expressed as (Equation 12), the frequency change Δ CW +Δ m of the reference light 318, i.e., Δ _m , can be obtained in a similar manner to the procedure for obtaining the frequency change Δν _s of _the optical frequency comb ₃₁₇ , i.e., Δ _CW .

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

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. The sixth optical directional coupler 509 merges the reference light 510 and the output light 607, which are output. The output light 606 is input to the third optical bandpass filter (BPF) 601, and the output light 607 is input to the 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 the 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. Here, p ≠ q.

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.

Of the 2n sidebands generated by inputting the optical frequency comb 313 to the electro-optic modulator 303, the frequency of the upper sideband v _r+ and the frequency of the lower sideband v _r− generated from the r-th comb of the optical frequency comb 313 counting from the CW laser 312 are given by

で表すことが出来る。ただし、Δ_ｒｅｐはＣＷレーザ３１２の変化に伴って生じるコムモード間隔の変化量である。Δ_ＣＷ、Δ_ｍ、及びΔ_ｒｅｐを求めることによって、電気光学変調器３０３によって生成された２ｎ個のサイドバンドのうち、全てのサイドバンドの周波数を算出することが出来る。

where Δ _rep is the amount of change in the comb mode spacing that occurs with the change in the CW laser 312. By determining Δ _cw , Δ _m , and Δ _rep , the frequencies of all of the 2n sidebands generated by the electro-optic modulator 303 can be calculated.

6, Δ _CW and Δ _rep can be obtained from the interference signal of output light 609 and output light 610. Furthermore, Δ _m can be obtained from the interference signal of output light 611.

While sweeping the oscillation frequency of the RF oscillator 304 from f _m to f _m + Δ _m , each comb mode frequency of the optical frequency comb 313 is swept from ν _p to ν _p + Δ _p , and from the interference signals 4131 to 413n detected by the first to nth photodetectors 4061 to 406n of the LIDAR section 310, the distance from the first wavelength division multiplexing transmission device 403 to a target located in an angular direction corresponding to the frequency of each sideband of the optical frequency comb 313 and the velocity of the target can be calculated, as in the first embodiment.

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

The distance and speed measurement device of this embodiment was used to actually calculate the distance and speed of a stationary object and a moving object. 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. Also, a mechanism such as a microheater for changing the resonant frequency of the microresonator 702 is not shown in FIG. 7.

Figure 8 shows the observed changes in frequency of the upper and lower sidebands over time. Figure 9 shows the beat signals observed for a stationary object and a moving object. As shown in Figure 9, beat frequencies were observed for both stationary and moving objects. Also, as shown in Figure 8, different frequency changes were observed for the upper and lower sidebands.

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, but the speed values differed by about 50 times. Therefore, the distance and speed measuring device of this embodiment was able to recognize that a stationary object is in a stationary state, and that a moving object is in a moving state. It was also possible to calculate the values quantitatively.

The present invention naturally includes various embodiments not described here. Therefore, the technical scope of the present invention is determined only by the invention-specific matters related to the scope of the claims that are appropriate from the above explanation.

10, 30, 90, 130 Distance, speed measuring device 101, 301, 701, 1001 CW laser light source device 102, 303, 703, 1301 Electro-optical modulator 103, 304, 704, 1302 RF oscillator 104, 305, 705 Current controller 105, 306, 706 First control device 106, 307, 707 Second control device 107, 308 First 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 Calculation device 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 Object 302 Optical frequency comb generator 310 LIDAR unit 311, 3111, 3112 Frequency change measurement unit 313, 314, 317, 615 Optical frequency comb 401 Third optical directional coupler 403 First wavelength division multiplexing transmission device 404 Fourth optical directional coupler 405 Second wavelength division multiplexing transmission devices 4061 to 406n First to nth photodetectors 501 Two-wavelength unbalanced Mach-Zehnder interferometer 502 First optical bandpass filter (BPF)
503 Second optical bandpass filter (BPF)
504: First photodetector 505: Second photodetector 506: First waveguide 507: Second waveguide 508: Fifth optical directional coupler 509: Sixth optical directional coupler 601: Third optical bandpass filter (BPF)
602 4th optical bandpass filter (BPF)
603 5th optical bandpass filter (BPF)
604 Third photodetector 605 Fourth photodetector 606 Fifth photodetector 702 Microresonator 711 Comb mode 1002, 1006 Optical directional coupler

Claims (17)

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; and 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 that calculates a distance to the object and a velocity of the object from the interference signal detected by the photodetector, wherein the frequency of the reference light is swept from v _c to v _c + Δ _CW by controlling the current controller by the first control device, and the oscillation frequency of the RF oscillator is swept from f _m to f _m + Δ _m by controlling the RF oscillator by the second control device;
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 calculation device calculates the frequency f _beat+ of the upper sideband beat signal and the frequency f _beat− of the lower sideband beat signal from the interference signal using the following formula:


Calculate from and further



(c is the speed of light, T is the sweep time from v _c to v _c + Δ _CW of the frequency of the reference light, and Δ is the maximum value of the frequency change) The distance/speed measuring device according to claim 1, further comprising an angle sweeping mechanism for sweeping the angle of the reference light irradiated onto the target object. The distance/speed measuring device according to claim 1 or 2, characterized in that the excitation light and the carrier light source are the same. A distance/speed measuring device according to any one of claims 1 to 3, characterized in that 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 unbalanced Mach-Zehnder interferometer. A distance/speed measuring device according to any one of claims 1 to 3, characterized in that 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. 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;
3. The distance/speed measurement device according to claim 1, further comprising: a first wavelength division multiplexing transmission device for inputting the optical frequency comb to the electro-optical modulator, 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 of the comb modes, and irradiating each of the mixed lights separated for each mode at an angle corresponding to the mode frequency of each of the comb modes. The distance and speed measurement device according to claim 6, characterized in that the optical frequency comb generator is composed of an electro-optical modulator. The distance and speed measurement device according to claim 6, characterized in that the optical frequency comb generator is composed of a microresonator. A distance/speed measuring device according to any one of claims 6 to 8, characterized in that the frequency change measuring unit is composed of an unbalanced Mach-Zehnder interferometer. A distance/speed measurement device according to any one of claims 6 to 8, characterized in that the frequency change measurement unit is composed of an interferometer between the optical frequency comb and an interfering CW laser. The distance and speed measurement device according to any one of claims 1 to 10, characterized in that the electro-optical modulator is an intensity modulator and is adjusted to perform carrier suppression double sideband modulation by adjusting the DC bias voltage. 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;
Sweeping the frequency of the reference light from v _c to v _c +Δ _CW and sweeping the oscillation frequency of the RF oscillator from f _m to f _m +Δ _m ;
The frequency f _beat+ of the upper sideband beat signal and the frequency f _beat− of the lower sideband beat signal are calculated from the interference signal by the following formula:




and calculating the




and calculating a distance τ to the object and a velocity V of the object using the above formula (where c is the speed of light, T is the sweep time from v _c to v _c + Δ _CW of the frequency of the reference light, and Δ is the maximum value of the frequency change). The distance/speed measurement method according to claim 12, further comprising a step of sweeping the angle of the reference light irradiated onto the target object. The distance/speed measurement method according to claim 12 or 13, characterized in that the excitation light and the carrier light source are the same. The distance/velocity measurement method according to any one of claims 12 to 14, further comprising a 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. The distance/velocity measurement method according to any one of claims 12 to 14, further comprising a 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 interference CW laser. generating an optical frequency comb from the excitation light as the carrier light source;
a step of sweeping the frequency of the reference light from v _c to v _c +Δ _CW and sweeping the oscillation frequency of the RF oscillator from f _m to f _m +Δ _m , measuring a sweep amount of a comb mode frequency of the optical frequency comb;
14. The distance and velocity measurement method according to claim 12 or 13, further comprising 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 the comb mode, and irradiating each of the mixed lights separated for each mode at an angle corresponding to the mode frequency of each of the comb modes.

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