Distance and speed measuring apparatus
To provide a distance and velocity measurement apparatus that can be adopted preferably in a LiDAR or a sensor for a robot, wherein the apparatus can prevent deterioration of SN ratio even in a case where an object in an external environment vibrates. A LiDAR 20 according to the present embodiment includes a first laser apparatus 1 a , a second laser apparatus 1 b , a polarization-maintaining type optical fiber 2 , a WDM filter 6 , an optical fiber coupler 3 a , an optical amplifier 11 , an input/output unit 4 , an optical scanner 5 , a second optical fiber coupler 3 b , a balanced photodetector 7 , and a square-law detector 9 . Further, a delay line 10 composed of a polarization-maintaining optical fiber is provided on the local port 2 b . The first laser apparatus 1 a includes a device for generating a first laser light having a first wavelength and a first chirp rate in an interior thereof, and the second laser apparatus 1 b includes a device for generating a second laser light having a second wavelength that differs from the first wavelength and a second chirp rate that differs from the first chirp rate.
1 . A distance and velocity measurement apparatus for measuring a distance to a target and a velocity of the target by a laser light, the apparatus comprising:
a first laser apparatus configured to irradiate a first laser light having a first wavelength and a first chirp rate;
a second laser apparatus configured to irradiate a second laser light having a second wavelength of a wavelength that differs from the first wavelength and a second chirp rate of a chirp rate that differs from the first chirp rate;
an irradiation-side multiplexer configured to subject the first laser light and the second laser light to multiplexing;
a optical splitter configured to spectrally separate a laser light having been subjected to multiplexing by the irradiation-side multiplexer to an irradiation light to be irradiated to the target and a reference light serving as a reference for measurement;
an irradiated light receiving device configured to irradiate the irradiation light to the target and receive a reflected light from the target;
a light receiving-side multiplexer configured to subject the reflected light transmitted from the irradiated light receiving device and the reference light to multiplexing;
a photodetector configured to convert a synthesized light having been subjected to multiplexing by the light receiving-side multiplexer to an electric signal; and
a wave detector configured to perform detection of the conversion signal having been converted by the photodetector,
wherein the wave detector is configured to detect the conversion signal to acquire a beat signal, and to analyze the distance to the target and the velocity of the target by subjecting the beat signal to frequency analysis, and
wherein a difference between the first chirp rate and the second chirp rate (AZ) satisfies a following relationship:
Δζ×2Rmax/C<10 MHz (wherein C is a velocity of light in vacuum),
wherein Rmax represents a maximum distance for performing measurement.
2 . The distance and velocity measurement apparatus according to claim 1 ,
wherein a difference between the first wavelength and the second wavelength is 1 to 35 nm.
3 . The distance and velocity measurement apparatus according to claim 1 ,
wherein the photodetector is a balanced photodetector.
4 . The distance and velocity measurement apparatus according to claim 1 ,
wherein a delay line of a distance corresponding to a coherence length of the reference light or a maximum distance to be measured is provided between the optical splitter and the light receiving-side multiplexer.
5 . The distance and velocity measurement apparatus according to claim 1 ,
wherein an optical fiber used in the distance and velocity measurement apparatus is a polarization-maintaining optical fiber, and a polarizing axis thereof is made to correspond between members being connected.
6 . The distance and velocity measurement apparatus according to claim 1 ,
wherein the irradiated light receiving device comprises a second optical splitter configured to spectrally separate the irradiation light into a plurality of lights, and a plurality of irradiation ports configured to irradiate the separated irradiation lights through a plurality of different irradiation surfaces, and
wherein refraction members having different irradiation angles are attached to the plurality of irradiation ports.
7 . The distance and velocity measurement apparatus according to claim 1 ,
wherein the irradiated light receiving device comprises an irradiation port configured to irradiate the irradiation light from an irradiation surface, and a plurality of light receiving ports configured to receive the reflected light,
wherein the light receiving ports are arranged around the irradiation port,
wherein wo represents a radius of a light beam of the irradiation light,
wherein wr represents a radius of a light beam of the reflected light, and
wherein wr is set to be double the value of wo or greater.
8 . The distance and velocity measurement apparatus according to claim 1 ,
wherein at least a part of the first laser apparatus, the second laser apparatus, the irradiation-side multiplexer, the optical splitter, the light receiving-side multiplexer, the photodetector, and the wave detector is integrated on a substrate.