JP2022145268A - Distance and speed measuring device and distance and speed measuring method - Google Patents

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

The present invention relates to a distance, speed measuring device and distance, speed measuring method, and more particularly to a distance, speed measuring device and distance, speed measuring method by an FMCW lidar.

“Light Detection and Ranging (LiDAR)” is a technology for irradiating a target object with a laser to detect scattered light and measuring the distance to the target object. One such technique is frequency-modulated cw LiDAR (FMCW LiDAR). The FMCW lidar is a method for detecting the distance and velocity to a target by irradiating the target with a frequency-modulated CW laser and measuring the frequency of beat signals generated by interference between reference light and scattered light.

10, 11 and 11, a method for detecting the distance to the object and the speed of the object by the FMCW lidar will be described. FIG. 10 shows an example of the configuration of a conventional distance measuring device 100 using an FMCW lidar. CW laser 1009 irradiated from CW laser light source device 1001 is separated into reference light 1010 and reference light 1016 at optical directional coupler 1002 . The reference beam 1010 enters the angle sweeping mechanism 1004 via the circulator 1003 and is irradiated in the direction of the angle α by the angle sweeping mechanism 1004 . The irradiated reference beam 1012 is scattered by the object 1005 located in the direction of the angle α, and the scattered beam 1013 is incident on the angle sweeping mechanism 1004 . Scattered light 1013 incident on the angle sweeping mechanism 1004 is directly input to the circulator as scattered light 1014 and output as scattered light 1015 . Scattered light 1015 is combined with reference light 1016 by optical directional coupler 1006 and output as output light 1017 . The interference signal of output light 1017 is detected by photodetector 1007 and detected interference signal 1018 is input to computing device 1008 . The distance to the object 1005 is calculated by sweeping the frequency of the CW laser 1009 with the CW laser light source device 1001 while the angle sweep mechanism 1004 irradiates the reference light 1012 in the direction of the angle α.

As an example of sweeping the frequency of the CW laser 1009, as shown in FIGS. 11A and 12A, the frequency of the CW laser 1009 is changed with time in a triangular waveform. When the target object 1005 is stationary, the scattered light 1015 propagates behind the reference light 1016, so the frequency change amount when the frequency of the output light 1017 is swept is expressed as shown in FIG. 11(b). be done. Interference between the scattered light 1015 and the reference light 1016 generates a beat signal, and the photodetector 1007 can detect the frequency f _beat of the beat signal as shown in FIG. 11(c). The beat signal frequency is

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。

, the distance L to the object 1005 can be calculated. Here, c is the speed of light, T is the half period of the triangular waveform shown in FIGS. 11 and 12, and Δ is the maximum value of the frequency variation shown in FIGS.

When the object 1005 is moving, the scattered light 1015 propagates behind the reference light 1016, but its frequency also changes due to the Doppler shift. In the example shown in FIG. 12(b), the frequency is shifted 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 velocity V of the object can be calculated by the following equations.

In the method of detecting the distance and speed to the target object by such an FMCW lidar, it is necessary to sweep the CW laser frequency at all sweeping irradiation angles while sweeping the irradiation angle of the CW laser, so the measurement time is becomes longer. On the other hand, for example, Non-Patent Document 1 and Non-Patent Document 2 disclose methods for shortening the measurement time when detecting the distance and speed to a target object using an FMCW lidar.

Non-Patent Document 1 discloses a method of shortening the angle sweep time by using a microcomb as a light source and using a CW laser light source for each comb mode of the microcomb. 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 angular sweep time can be reduced by frequency sweeping the microcomb by simultaneously sweeping the resonance frequency of the microcomb.

According to the method described with reference to FIG. 12, in order to calculate the distance and velocity of a moving object, when the frequency is swept in a triangular waveform as shown in FIG. Distance and velocity can be calculated by increasing the frequency from 0 to T and then decreasing the frequency from time T to 2T. According to the method disclosed in Non-Patent Document 2, distance and velocity can be measured at the same time by using carrier-suppressed double-sideband modulation as the light source, thus shortening the sweep time.

FIG. 13 shows an example of the configuration of a distance and speed measuring device 130 according to the method disclosed in Non-Patent Document 2. As shown in FIG. A velocity measuring device 130 shown in FIG. 13 has the same configuration as the distance measuring device 100 using the FMCW lidar shown in FIG. Suppose the electro-optic modulator 1301 is tuned to suppress the carrier, ie the CW laser 1009, to output only the two sidebands, and is driven by an RF oscillator 1302 with a modulation frequency of f _m .

A CW laser 1009 with a frequency ν _c emitted from a CW laser light source device 1001 is modulated by an electro-optic modulator 1301, the CW laser 1009 is suppressed, and two frequencies of ν _c +f _m and ν _c −f _m are obtained. Sidebands 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) is shifted from ν _c +f _m to ν _c +f _m +Δ, as shown in FIG. The frequency of the lower sideband (B) can be shifted from ν _c −f _m to ν _c −(f _m +Δ).

Scattered light when a stationary object is irradiated with the upper side band (A) and the lower side band (B) is like scattered light (C) and scattered light (D) in FIG. , propagates behind the upper sideband (A) and the lower sideband (B). When the upper sideband (A) and the lower sideband (B) are irradiated to a moving object, the scattered light is as scattered light (E) and scattered light (F) in FIG. 14(b). Doppler shift shifts the frequency. The photodetector 907 detects the beat frequency (G) between the upper sideband (A) and the scattered light (E), and the lower sideband (B) and the scattered light (F) By detecting the beat frequency (H) between and, the distance and velocity can be calculated at the same time.

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 the moving object is irradiated with the upper side band (A) and the lower side band (B), the beat frequency Since (G) and the beat frequency (H) are different values, distance and velocity can be calculated. However, for stationary objects, the beat frequencies of the upper sideband (A) and scattered light (C) are the same as the beat frequencies of the lower sideband (B) and scattered light (D). The scattered light from the upper side band (A) and the scattered light from the lower side band (B) interfere and cancel each other, so that the signal cannot be detected by the photodetector and the distance cannot be calculated. There are situations where this is not possible.

In view of the above problems, the present invention provides a distance, speed measurement device and distance by FMCW lidar, which shortens the measurement time for both distance and speed measurement of stationary and moving objects. The object is to provide a speed measurement method.

A first aspect of the present invention is a distance and velocity measuring device that controls a laser light source device that emits continuous wave excitation light, a current controller that controls the oscillation frequency of the excitation light, and a current controller. A first control device, an RF oscillator that oscillates a modulated signal at a modulated frequency, and a carrier light source obtained from excitation light are input, driven by the modulated signal of the RF oscillator, suppressing the carrier light source, and increasing the frequency side of the carrier light source. An electro-optic modulator that generates an upper sideband shifted by the modulation frequency and a lower sideband shifted by the modulation frequency to the low frequency side of the carrier light source, and outputs mixed light of the upper sideband and the lower sideband as reference light. and a second controller 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 object is irradiated with the reference light, and detected by the photodetector a calculator for calculating the distance and velocity of the object from the interference signal, sweeping the frequency of the reference light from ν _c to ν _c +Δ _CW under the control of the current controller by the first controller; The control of the RF oscillator by the controller sweeps the oscillation frequency of the RF oscillator from _fm to _fm + _Δm , and the control of the current controller by the first controller and the control of the RF oscillator by the second controller are synchronized with each other. the computing device computes 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 is to calculate the distance τ to the object and the velocity V of the object by the following equation.

The first aspect of the present invention may further include an angle sweeping mechanism for sweeping the angle of the reference light with which the object is irradiated.

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

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

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

In the first aspect of the present invention, an optical frequency comb generator that generates an optical frequency comb as a carrier light source from excitation light and a sweep amount of the comb mode frequency of the optical frequency comb controlled by a current controller by a first control device are measured. and an optical frequency comb input to an electro-optic modulator, and the mixed light of the upper sideband and lower sideband generated for each comb mode of the optical frequency comb is measured for each mode of each comb mode. A first wavelength division multiplexing transmission device for separating and irradiating each of the mixed lights separated for each mode at an angle corresponding to the mode frequency of each comb mode may be further provided.

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

In a first aspect of the invention, the optical frequency comb generator may consist of a microresonator.

In the first aspect of the invention, the frequency change measuring section may consist of an unbalanced Mach-Zehnder interferometer.

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

In a first aspect of the invention, the intensity modulator may be tuned to carrier-suppressed double sideband modulation by adjusting the DC bias voltage.

A second aspect of the present invention is a method for measuring distance and velocity, comprising the steps of irradiating excitation light that is a continuous wave, obtaining a carrier light source from the excitation light, and an RF oscillator that oscillates a modulated signal at a modulation frequency. and the carrier light source is suppressed, producing an upper sideband shifted by the modulation frequency to the high frequency side of the carrier light source and a lower sideband shifted by the modulation frequency to the low frequency side of the carrier light source. generating and outputting mixed light of the upper side band and the lower side band as reference light; measuring an interference signal between the scattered light and the reference light when the reference light is applied to the target; sweeping the frequency of from ν _c to ν _c +Δ _CW , sweeping the oscillation frequency of the RF oscillator from f _m to f _m +Δ _m , 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。

calculating the distance τ to the object and the velocity V of the object using the above equations.

The second aspect of the present invention may further comprise the step of sweeping the angle of the reference light with which the object is irradiated.

In the second aspect of the invention, the excitation light and the carrier light source may be identical to each other.

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 may be further included.

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 a CW laser for interference may be further provided.

In the second aspect of the present invention, the step of generating an optical frequency comb as the carrier light source from the excitation light, 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 measuring the sweep amount of the comb mode frequency of the optical frequency comb in the step of sweeping to f _m +Δ _m ; A step of separating each comb mode for each mode and irradiating each of the mixed lights separated for each mode at an angle according to the mode frequency of each comb mode may be further included.

According to the present invention, the distance, speed measurement device, and distance by FMCW lidar, which enable measurement in a short time for both the distance and speed measurement of a stationary object or a moving object, A speed measurement method can be provided.

1 is a block diagram showing an example of a configuration of a distance and speed measuring device according to a first embodiment; FIG. 7A and 7B are graphs showing temporal changes in the upper sideband frequency, the lower sideband frequency, and the beat frequency of the reference light and the scattered light obtained by the distance and velocity measuring device according to the first embodiment; Sideband frequency, lower sideband frequency, (c) is plotted against 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 the rider section of the distance and speed measuring device according to the second embodiment; FIG. 4 is a block diagram showing an example of the configuration of a frequency change measuring section when an electro-optic modulator is used as an optical frequency comb generator; FIG. 4 is a block diagram showing an example of the configuration of a frequency change measuring section when using a microresonator as an optical frequency comb generator; It is a block diagram which shows the structure of the distance and speed measuring apparatus which experimented. It is a graph which shows the time change of the frequency of the upper side band and the lower side band which were observed. Fig. 10 is a graph showing an observed beat signal; 1 is a block diagram showing an example of the configuration of a conventional distance measuring device using an FMCW lidar; FIG. 1 is a graph showing changes in reference light, scattered light, and beat frequency by a conventional FMCW lidar when the target object is stationary, where (a) is the reference light, (b) is the reference light and the scattered light, and (c ) is a graph against beat frequency. 1 is a graph showing changes in reference light, scattered light, and beat frequency by a conventional FMCW lidar when an object is moving, where (a) is the reference light, (b) is the reference light and the scattered light, and (c ) is a graph against beat frequency. 1 is a block diagram showing an example of the configuration of a distance and speed measuring device according to the method disclosed in Non-Patent Document 2; FIG. Graphs showing temporal changes in the distance, the reference light of the velocity measuring device, the upper sideband frequency of the scattered light, the lower sideband frequency, and the beat frequency according to the method disclosed in Non-Patent Document 2, (a) and (b) ) is a graph for the upper sideband frequency and the lower sideband frequency, and (c) is a graph for the beat frequency.

Next, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings according to the embodiments, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and that the relationship between thickness and planar dimension, the ratio of thickness of each member, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined with reference to the following description. In addition, it is a matter of course that there are portions with different dimensional relationships and ratios between the drawings.

Further, the embodiments illustrate devices and methods for embodying the technical idea of the present invention. It does not specify anything. Various modifications can be made to the technical idea of the present invention within the technical scope defined by the claims.

(First embodiment)
A distance/velocity measuring device and a distance/velocity measuring method according to a first embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, the distance/velocity measuring device 10 according to the present embodiment includes a CW laser light source device 101, an electro-optic modulator 102, an RF oscillator 103, a current controller 104, and a first control device 105. , a second controller 106, a first optical directional coupler 107, a circulator 108, an angle sweeping mechanism 109, a second optical directional coupler 110, a photodetector 111, and a computing device 112. be done.

From the CW laser light source device 101, a CW laser 113 having a frequency of _νc is incident on an electro-optic modulator 102 which is set to perform carrier suppression double sideband modulation. The electro-optic modulator 102 is driven by an RF oscillator 103 whose modulation frequency is _fm . Carrier-suppressed double-sided sideband modulation means that 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. It is a modulation that Electro-optic modulator 102 is particularly suitable as an intensity modulator, in which case it is tuned for carrier-suppressed double sideband modulation by adjusting the DC bias voltage. The electro-optic modulator 102 suppresses the CW laser 113, which is the carrier light source, and generates two sidebands having frequencies shifted by f _m to the high and low frequencies of the frequency ν _c of the CW laser 113 .

The two sideband mixed light 114 generated by the electro-optic modulator 102 is split into two reference beams 115 and 116, the reference beam 115 is irradiated onto the object 124, and the interference between the scattered light and the reference beam is photodetected. As described below, it is the same as the conventional FMCW lidar in that the distance to the object is calculated by detecting it with a device.

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

In the method disclosed in Non-Patent Document 2, the oscillation frequency of the RF oscillator 1202 is swept from f _m to f _m +Δ, and as shown in FIG. ) and the beat frequency (H) of the lower sideband (B) and the scattered light (F) are detected, and the distance and velocity are calculated simultaneously. According to this method, for a stationary object, the beat frequencies of the upper sideband (A) and scattered light (C) and the beat frequencies of the lower sideband (B) and scattered light (D) are becomes the same value, and there is a situation where the distance cannot be calculated.

In this embodiment, the oscillation frequency of the RF oscillator 103 is swept from f _m to f _m +Δ _m , and at the same time, the frequency of the CW laser 113 emitted from the CW laser light source device 101 is swept from ν _c to ν _c +Δ _CW . As shown in FIG. 2(a), the frequency of the upper sideband (I) generated by the electro-optic modulator 102 ranges from ν _c +f _m to ν _c +f _m +Δ+Δ _CW , and the frequency of the lower sideband (J) is varies from ν _c −f _m to ν _c −(f _m +Δ)+Δ _CW . Scattered light when a stationary object is irradiated with the upper side band (I) and the lower side band (J) is scattered light (K) and scattered light (L) in FIG. Scattered light when the object is irradiated becomes scattered light (M) and scattered light (N) in FIG. 2(b).

In the method disclosed in Non-Patent Document 2, the beat frequency of the upper sideband (A) and the scattered light (C) and the beat frequency of the lower sideband (B) and the scattered light (D) are the same value. In this embodiment, the beat frequencies of the upper side band (I) and the lower side band (J) are different from each other. It is possible to calculate the distance even when

As shown in FIG. 2(c), the beat frequency (O) of the upper side band and the beat frequency (P) of the lower side band both when the object is stationary and when it is moving. They are different from each other 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 object is stationary, the distance to the object can be calculated, and when the object is moving, the distance to the object and the speed of the object can be calculated from the following equations.

The distance and speed obtained by the above equations are the distance from the angle sweeping mechanism 109 to the object positioned in the direction of the prescribed angle when the reference beam 115 is irradiated in the direction of the prescribed angle by the angle sweeping mechanism 109 and the object is the speed of A series of distance and velocity measurements in this embodiment are performed by sweeping the irradiation angle of the reference light 115 by the angle sweeping mechanism 109, and measuring the distance and velocity according to the above equations at each angle.

In this embodiment, an intensity modulator is particularly used as the electro-optic modulator 102, and the DC bias voltage is adjusted so as to enable carrier-suppressed double sideband modulation. A voltage-controlled oscillator, for example, is used as the RF oscillator 103 . A second controller 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 connected to the current controller 104 . The current controller 104 is controlled by the first controller 105 to sweep the frequency of the CW laser 113 emitted from the CW laser light source device 101 from ν _c to ν _c +Δ _CW .

As a method for measuring the frequency sweep amount of the CW laser and the frequency sweep amount of the RF oscillator, for example, a method using an unbalanced Mach-Zehnder interferometer, or a CW laser for interference for interfering with the CW laser and the upper sideband. A photodetector detects the interference between the CW laser for interference and the CW laser and the interference between the CW laser for interference and the upper sideband, respectively, and measures the frequency difference.

When measuring the frequency sweep amount of the CW laser and the frequency sweep amount of the RF oscillator using an unbalanced Mach-Zehnder interferometer, in the present embodiment, the CW laser 113 is used as an unbalanced Mach-Zehnder for measuring the frequency sweep amount (not shown). An interferometer is used to split the two optical paths, which are propagated through two optical paths having different optical path lengths, and are then superimposed. The amount of frequency sweep of the CW laser is measured by measuring the change. Similarly, for the measurement of the frequency sweep amount of the RF oscillator, an interference signal of interference generated by an unbalanced Mach-Zehnder interferometer (not shown) of one of the sidebands of the mixed light 114 of two sidebands is detected by a photodetector. The detection measures the amount of frequency sweep of the RF oscillator. 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 are different interferometers. There may be, or they may be identical interferometers. In the case of the same interferometer, the CW laser 113 and one of the sidebands of the mixed light 114 of the two sidebands are respectively opposed to the unbalanced Mach-Zehnder interferometer for measuring the amount of frequency sweep. Input from the input terminal.

When the frequency sweep amount of the CW laser and the frequency sweep amount of the RF oscillator are measured using a CW laser for interference, in the present embodiment, an illustrated A CW laser for interference is prepared, and an interference signal due to interference between the CW laser 113 and the CW laser for interference is detected by a photodetector. Measure the frequency sweep amount of the laser. Similarly, for the measurement of the frequency sweep amount of the RF oscillator, an interference signal of interference between one sideband of the mixed light 114 of two sidebands and an interference CW laser (not shown) is detected by a photodetector. The amount of frequency sweep of the RF oscillator is thereby measured. Note that the interference CW laser (not shown) for interfering with the CW laser 113 and the interference CW laser (not shown) for interfering with one of the sidebands of the mixed light 114 of the two sidebands are different from each other. They may be lasers, or they may be the same lasers. If they are the same laser, a CW laser for interference (not shown) is split into two, one of which interferes with the CW laser 113, and the other of which interferes with the sideband.

As shown in FIG. 2A, 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 at the same period. , are executed synchronously 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 performed so that the frequency of the CW laser 113 and the oscillation frequency of the RF oscillator 1102 have, for example, a sawtooth waveform. be.

As described above, according to the distance/velocity measuring device and the distance/velocity measuring method according to the present embodiment, when the object is stationary, the distance to the object is measured, and when the object is moving, can shorten the time to measure the distance to the object and the velocity of the object.

(Second embodiment)
In the first embodiment, the CW laser was incident on the electro-optic modulator from the CW laser light source device. In this embodiment, an optical frequency comb is incident on the electro-optic modulator instead of a CW laser, thereby further shortening the distance and velocity measurement time.

FIG. 3 shows an example of the configuration of the distance and speed measuring device 30 according to this embodiment. As shown in FIG. 3, the distance/velocity measuring device 30 according to this embodiment includes a CW laser light source device 301, an optical frequency comb generator 302, an electro-optic modulator 303, an RF oscillator 304, and a current controller 305. , a first controller 306, a second controller 307, a first optical directional coupler 308, a second optical directional coupler 309, a lidar section 310, and a frequency change measuring section 311. be.

Optical frequency comb generator 302 may include, for example, an electro-optic modulator or a microresonator. When an electro-optic modulator is used as the optical frequency comb generator 302, the CW laser from the CW laser light source device 301 is input to the electro-optic modulator and modulated to generate a sideband, that is, an optical frequency comb. When a microresonator is used as the optical frequency comb generator 302, the CW laser from the CW laser light source device 301 is input via a waveguide into the 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 interval of about 10 GHz-1 THz, compared to the comb interval of a conventional optical frequency comb such as a mode-locked fiber laser, which is about 100 MHz-1 GHz. and wide. In this embodiment, as will be described later, each comb mode of the optical frequency comb is separated from each other, each comb mode is used as a plurality of CW lasers, and the comb mode frequency of each comb mode is swept. It is desirable that the comb interval of the optical frequency comb is wide, 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 .

A CW laser 312 is input from a CW laser light 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 the optical frequency comb 314 and the optical frequency comb 317 by the first optical directional coupler 308, and the optical frequency comb 314 is input to the electro-optic modulator 303. be done. The electro-optic modulator 303 is driven by an RF oscillator 304 having a modulation frequency of _fm , and is set for carrier-suppressed double-sideband modulation, as in the first embodiment. When the optical frequency comb 314 is input to the electro-optic modulator 303, the optical frequency comb 314, which is the carrier light source, is suppressed, and for each of the multiple comb modes of the optical frequency comb 314, the high frequencies of the comb mode frequency of each comb mode are generated. Two sidebands are generated with frequencies shifted by f _m to the side and to the lower frequency side. Assuming that the optical frequency comb 314 consists of n comb modes, the electro-optic modulator 303 suppresses the n comb modes, two for each of the n comb modes, i.e., 2n comb modes. Sidebands are generated. The 2n sidebands generated by electro-optic modulator 303 are input to second optical directional coupler 309 as reference light 315 and separated into reference light 316 and reference light 318 . is entered in

An example of the configuration of the rider section 310 is shown in FIG. The lidar unit 310 shown in FIG. 4 includes a third optical directional coupler 401, a circulator 402, a first wavelength division multiplexing (WDM) device 403, a fourth optical directional coupler 404, It comprises a second wavelength division multiplexing (WDM) device 405 , first to nth photodetectors 406 1 to 406 n and a computing device 407 .

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

Each sideband is scattered by the object 410 located at an angular direction corresponding to its respective frequency. 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 the output light 412. . The output light 412 is separated again into a set of n sidebands by the second wavelength division multiplexing transmission device 405 . Interference signals 413 1 - 413 n for each sideband set are detected by first through nth photodetectors 406 1 - 406 n and input to computing device 407 .

In this embodiment, the oscillation frequency of the RF oscillator 304 is swept from _fm to _fm + _Δm , and each comb mode frequency of the optical frequency comb 313 is swept from _νp to _νp + _Δp . where ν _p 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 need to have the same period, the control by the first controller 306 and the second controller 307 are synchronized with each other. executed.

The frequency sweep of the optical frequency comb 313 is performed by controlling the current controller 305 by the first controller 306 when using an electro-optic modulator as the optical frequency comb generator 302, so that the CW laser source connected to the current controller 305 is operated. This is done by sweeping the frequency of the CW laser input from device 301 to the electro-optic modulator. When a microresonator is used as the optical frequency comb generator 302, the resonance frequency of the microresonator is controlled by a microheater, a piezoelectric element, or the like, and the first controller 306 controls the resonance frequency of the microresonator in synchronization with the control of the resonance frequency of the microresonator. By controlling the current controller 305 with , the frequency of the CW laser is controlled, and the frequency of the optical frequency comb 313 is swept. However, when the frequency sweep range is small, it is sufficient to control 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 measuring section 311 . Since each comb mode is used as an optical carrier for the FMCW lidar, it is necessary to simultaneously measure the frequency sweep amount of all comb modes that are frequency swept.

Measurement of the frequency sweep amount of the swept comb mode includes, for example, a method using an unbalanced Mach-Zehnder interferometer and a method using an interfering CW laser for interfering with the comb mode. When the frequency sweep amount of the swept comb mode is measured using a CW laser for interference, a CW laser for interference is prepared to interfere with the comb mode, and the CW laser for interference and the comb mode interfere with each other, The interference signal is detected by a photodetector, and the amount of frequency sweep is measured by measuring the phase change amount of the interference signal due to the frequency change of the comb mode frequency. In this embodiment, an unbalanced Mach-Zehnder interferometer is used to measure the comb-mode frequency sweep amount.

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

FIG. 5 shows an example of frequency change measuring section 3111 as frequency change measuring section 3111 in the case of using an electro-optic modulator as optical frequency comb generator 302 . 5 includes 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 . A two-wavelength unbalanced Mach-Zehnder interferometer 501 comprises a first waveguide 506 having different optical path lengths, a second waveguide 507, a fifth optical directional coupler 508, and a sixth optical directional coupler 509. Configured.

Optical frequency comb 313 generated in optical frequency comb generator 302 is input to first optical directional coupler 308 and separated into optical frequency comb 314 and optical frequency comb 317. Optical frequency comb 317 is frequency change measuring unit. 311. The optical frequency comb 317 propagates through the first waveguide 506 as the reference light 510 and through the second waveguide 507 as the reference light 511 , joins at the sixth optical directional coupler 509 , and outputs the output light 512 . 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 the interference signal of the output light 513 is detected by the first photodetector 504 .

The 2n sidebands generated by electro-optic modulator 303 are input to second optical directional coupler 309 as reference beam 315 and separated into reference beam 316 and reference beam 318, reference beam 318 being used for frequency change measurement. It is input to the part 311 . The reference light 318 propagates through the first waveguide 506 and the second waveguide 507 similarly to the optical frequency comb 317 and is output as the output light 516 from the first optical directional coupler 308 . Only the upper sideband of the q-th comb mode of the output light 516 is transmitted by the second optical bandpass filter (BPF) 503 as the output light 517, and the interference signal of the output light 517 is detected by the second photodetector 505. . A second optical bandpass filter (BPF) 503 was set to transmit only the upper sideband of the qth comb mode of the output light 516, whereas the lower sideband of the qth comb mode of the output light 516 It may be set so as to transmit the side band.

Assuming that the optical frequency comb 313 is composed of n combs, the CW laser 312 of the optical frequency comb 313 is The upper sideband frequency ν _q+ and the lower sideband frequency ν _q− of the sidebands generated from the q-th comb counting from

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。

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

When the frequency change measuring 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、

is represented by 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

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。

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

The frequency ν _q+ of the upper sideband of the sideband generated from the q-th comb counting from the CW laser 312 of the reference beam 318 is expressed as in (Equation 12), so the frequency change of the optical frequency comb 317 is The frequency change amount _ΔCW + _Δm of the reference light 318, ie, _Δm , can be obtained by the same procedure as the procedure for obtaining the amount Δν _s , that is, _ΔCW .

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

The optical frequency comb 317 is separated into the reference light 510 and the 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 output light 606 and the output light 607 are output, the output light 606 is sent to the third optical bandpass filter (BPF) 601, and the output light 607 is sent to the fourth optical bandpass filter (BPF) 601. BPF) 602 . Only the p-th comb mode of the output light 606 is transmitted by the third optical bandpass filter (BPF) 601 as the output light 609 , and the interference signal of the output light 609 is detected by the third photodetector 604 . A fourth optical bandpass filter (BPF) 602 transmits only the q-th comb mode of the output light 607 as an output light 610 , and an interference signal of the output light 610 is detected by a fourth photodetector 605 . However, p≠q.

As for the reference light 318, as with the optical frequency comb 317, only the upper sideband of the r-th comb mode of the output light 608 is transmitted as the output light 611 by the fifth optical bandpass filter (BPF) 603, and the fifth light detection is performed. An interference signal in the output light 611 is detected by the detector 606 .

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

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。

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

When the frequency change measuring section 3112 shown in FIG. 6 is used, Δ _CW and Δ _rep can be obtained from the interference signal of the output light 609 and the output light 610 . Furthermore, _Δm can be obtained from the interference signal of the output light 611 .

The oscillation frequency of the RF oscillator 304 is swept from _fm to _fm +Δm, and each comb mode frequency of the optical frequency comb 313 is swept from _νp to _νp + _Δp to obtain the first to _n -th light beams of the lidar section 310. From the interference signals 4131 to 413n detected by the detectors 4061 to 406n, as in the first embodiment, from the first wavelength division multiplexing transmission device 403 to the optical frequency comb 313 in the angular direction corresponding to the frequency of each sideband. It is possible to calculate the distance to the target object and the speed of the target object.

The distances and velocities obtained as described above are the distances and the velocities of the target object located in the angular direction corresponding to the frequency of each sideband of the optical frequency comb 313 . A series of distance and velocity measurements in this embodiment are performed by sweeping the comb mode frequency of the optical frequency comb 313 to sweep the irradiation angle of the reference light 408, and at each angle, the distance and velocity measurements according to the above equations are performed. conduct.

Using the distance and speed measuring device of this embodiment, the distance and speed of a stationary object and a moving object were actually calculated. A portion of the setup for this experiment is shown in FIG. In this experiment, a microresonator 702 was used as the optical frequency comb generator 302 shown in FIG. For simplicity, only one comb mode 716 out of n comb modes of the optical frequency comb 715 generated in the microresonator 702 is extracted by an optical bandpass filter (BPF) 711, and the comb mode Distance and velocity calculations were performed only for 616. FIG. 7 does not show the lidar section 310 and the frequency change measuring section 311 shown in FIG. Also not shown in FIG. 7 is a mechanism, such as a microheater, for changing the resonant frequency of the microresonator 702 .

FIG. 8 shows temporal changes in the observed upper sideband and lower sideband frequencies. FIG. 9 also shows the observed beat signals for stationary and moving objects. As shown in FIG. 9, beat frequencies could be observed for both stationary and moving objects. Also, as shown in FIG. 8, different frequency changes were observed between the upper side band and the lower side band.

The following table shows distances and velocities calculated using beat frequencies for stationary and moving objects. The distances of the stationary object and the moving object showed almost the same value, and the difference in speed was about 50 times. Therefore, with the distance and speed measuring device of this embodiment, it was possible to recognize that a stationary object was in a stationary state and that a moving object was in a moving state. Moreover, the value could be calculated quantitatively.

As described above, the present invention naturally includes various embodiments and the like that are not described here. Therefore, the technical scope of the present invention is defined only by the matters specifying the invention according to the valid scope of claims based on the above description.

10, 30, 90, 130 distance and velocity measuring devices 101, 301, 701, 1001 CW laser light source devices 102, 303, 703, 1301 electro-optical modulators 103, 304, 704, 1302 RF oscillators 104, 305, 705 current controllers 105, 306, 706 First controllers 106, 307, 707 Second controllers 107, 308 First optical directional couplers 108, 402, 1003 Circulators 109, 1004 Angle sweep mechanisms 110, 309 Second optical directional couplers 111, 712, 1007 photodetectors 112, 407, 713, 1008 computing devices 113, 312, 714, 1009 CW laser 114 mixed light 115-118, 315, 316, 318, 408, 409, 510, 511, 1010-1012 , 1016 reference beams 119-121, 411, 1013, 1014 scattered beams 122, 412, 512, 513, 516, 517, 606-611, 1017 output beams 123, 4131-413n, 1018 interference signals 124, 410, 1005 object 302 optical frequency comb generator 310 lidar units 311, 3111, 3112 frequency change measuring units 313, 314, 317, 615 optical frequency comb 401 third optical directional coupler 403 first wavelength division multiplex transmission device 404 fourth optical directivity Coupler 405 Second wavelength division multiplex transmission device 4061 to 406n First to n-th 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 fourth optical bandpass filter (BPF)
603 fifth 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 emits excitation light that 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 that oscillates a modulated signal at a modulated frequency;
A carrier light source obtained from the excitation light is input, driven by the modulated signal of the RF oscillator, the carrier light source is suppressed, and an upper sideband and the carrier light source are shifted to a high frequency side of the carrier light source by the modulation frequency. an electro-optic modulator that generates a lower side band shifted by the modulation frequency to the low frequency side of and outputs mixed light of the upper side band and the lower side band as reference light;
a second controller for controlling the modulation frequency of the RF oscillator;
a photodetector that measures an interference signal between scattered light and the reference light when the reference light is applied to an object;
a calculation device for calculating the distance to the object and the velocity of the object from the interference signal detected by the photodetector, wherein the frequency of the reference light is controlled by the current controller by the first control device. is swept from ν _c to ν _c +Δ _CW , and control of the RF oscillator by the second controller sweeps the oscillation frequency of the RF oscillator from f _m to f _m +Δ _m ;
Control of the current controller by the first control device and control of the RF oscillator by the second control device are performed in synchronization with each other,
The computing device computes beat signals f _beat+ and f _beat− from the interference signal, and

(c is the speed of light, T is the sweep time of the frequency of the reference light from ν _c to ν _c +Δ _CW , Δ is the maximum value of the frequency change), the distance τ to the object and the velocity of the object A distance/velocity measuring device characterized by calculating V. 2. The distance/velocity measuring device according to claim 1, further comprising an angle sweeping mechanism for sweeping the angle of the reference light that irradiates the object. 3. The distance/velocity measuring device according to claim 1, wherein the excitation light and the carrier light source are the same. 4. The distance according to any one of claims 1 to 3, wherein the amount of sweep of the frequency of the reference light and the amount of sweep of the oscillation frequency of the RF oscillator are measured using an unbalanced Mach-Zehnder interferometer. Speed measuring device. 4. The distance/velocity measurement 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 a CW laser for interference. Device. an optical frequency comb generator that generates an optical frequency comb as the carrier light source from the excitation light;
a frequency change measuring unit that measures a sweep amount of the comb mode frequency of the optical frequency comb under control of the current controller by the first control device;
The optical frequency comb is input to the electro-optic modulator, and the mixed light of the upper side band and the lower side band generated for each comb mode of the optical frequency comb is separated for each mode of each comb mode. and a first wavelength division multiplexing transmission device for irradiating each of the mixed lights separated for each of the modes at an angle corresponding to the mode frequency of each comb mode. 3. The distance/velocity measuring device according to 1 or 2. 7. The distance/velocity measuring device according to claim 6, wherein said optical frequency comb generator comprises an electro-optic modulator. 7. The distance/velocity measuring device according to claim 6, wherein said optical frequency comb generator comprises a microresonator. 9. The distance/velocity measuring device according to claim 6, wherein said frequency change measuring unit comprises an unbalanced Mach-Zehnder interferometer. 9. The distance/velocity measuring device according to claim 6, wherein said frequency change measuring unit comprises an interferometer comprising said optical frequency comb and an interfering CW laser. 11. A distance as claimed in any preceding claim, wherein the electro-optic modulator is an intensity modulator and is tuned to carrier-suppressed double sideband modulation by adjusting a DC bias voltage. - Velocity measuring device. a step of irradiating excitation light that is a continuous wave;
obtaining a carrier light source from the excitation light;
input to an electro-optic modulator driven by an RF oscillator that oscillates a modulation signal at a modulation frequency, the carrier light source is suppressed, the upper sideband shifted to the high frequency side of the carrier light source by the modulation frequency, and the carrier light source generating a lower sideband shifted by the modulation frequency to the low frequency side, and outputting mixed light of the upper sideband and the lower sideband as reference light;
a step of measuring an interference signal between the scattered light and the reference light when the target is irradiated with the reference light;
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 ;
calculating beat signals f _beat+ and f _beat− from the interference signal;

Distance τ to the object and velocity of the object are obtained by the above equation ( _c is the speed of light, T is the sweep time from νc of the frequency of the reference light to _νc + _ΔCW , and Δ is the maximum value of the frequency change amount). and calculating V. A method for measuring distance and speed, comprising: 13. The distance/velocity measuring method according to claim 12, further comprising the step of sweeping the angle of the reference light with which the object is irradiated. 14. The distance/velocity measuring method according to claim 12, wherein the excitation light and the carrier light source are the same. 15. The method according to any one of claims 12 to 14, further comprising 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. Distance and speed measurement method described in . 15. The method according to any one of claims 12 to 14, further comprising the step of measuring the sweep amount of the frequency of said reference light and the sweep amount of said oscillation frequency of said RF oscillator using a CW laser for interference. distance and speed measurement method. generating an optical frequency comb as the carrier light source from the excitation light;
In the step of 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 , the amount of sweep of the comb mode frequency of the optical frequency comb is a step of measuring;
The mixed light of the upper side band and the lower side band generated for each comb mode of the optical frequency comb is separated for each mode of each comb mode, and each of the mixed lights separated for each mode is separated. 14. The distance/velocity measuring method according to claim 12 or 13, further comprising a step of irradiating at an angle corresponding to the mode frequency of each comb mode.

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