CN114035174A - Double-channel double-chirp linear frequency modulation continuous wave laser radar method and device - Google Patents

Double-channel double-chirp linear frequency modulation continuous wave laser radar method and device Download PDF

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CN114035174A
CN114035174A CN202111534810.1A CN202111534810A CN114035174A CN 114035174 A CN114035174 A CN 114035174A CN 202111534810 A CN202111534810 A CN 202111534810A CN 114035174 A CN114035174 A CN 114035174A
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frequency
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职亚楠
邹瑜
徐弼军
田克汉
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Zhejiang Lover Health Science and Technology Development Co Ltd
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Zhejiang Lover Health Science and Technology Development Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/481—Constructional features, e.g. arrangements of optical elements
    • G01S7/4814—Constructional features, e.g. arrangements of optical elements of transmitters alone
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/08—Systems determining position data of a target for measuring distance only
    • G01S17/32—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
    • G01S17/34—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/50—Systems of measurement based on relative movement of target
    • G01S17/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/491—Details of non-pulse systems
    • G01S7/4911—Transmitters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/491—Details of non-pulse systems
    • G01S7/493—Extracting wanted echo signals

Abstract

The invention discloses a dual-channel dual-chirp linear frequency modulation continuous wave laser radar method and a device, wherein an optical signal is divided into two orthogonal polarized optical signals which respectively enter two modulation channels; the two orthogonal polarized lights are respectively modulated by different optical phase modulators and filtered by an optical band-pass filter to synchronously generate positive and negative double-chirp optical signals with different fundamental frequencies, and then are respectively split to be transmitted to a target by an optical antenna and receive a target echo signal; at a receiving end, carrying out coherent mixing detection on a target echo signal of a first modulation optical channel and a first local oscillator signal, carrying out coherent mixing detection on a target echo signal of a second modulation optical channel and a second local oscillator signal to obtain a beat frequency signal containing target distance and speed information, and carrying out filtering, sampling and digital signal processing on the beat frequency signal to obtain the distance and the vector speed between a radar platform and a target. The invention can realize the real parallel synchronous measurement of the distance and the vector speed and has the advantages of high repetition frequency, high detection precision, high sensitivity and strong anti-interference capability.

Description

Double-channel double-chirp linear frequency modulation continuous wave laser radar method and device
Technical Field
The invention relates to the technical field of laser radars, in particular to a dual-channel dual-chirp linear frequency modulation continuous wave laser radar method and a dual-channel dual-chirp linear frequency modulation continuous wave laser radar device.
Background
The frequency modulation continuous wave laser radar adopts a linear frequency modulation signal to carry out linear modulation on the frequency of transmitting laser, obtains target distance information by comparing the instantaneous frequency difference of an echo optical signal and a local oscillator optical signal, simultaneously carries out speed measurement on a target by utilizing a Doppler effect, has the advantages of high detection sensitivity, high distance measurement and speed measurement resolution ratio, favorability for on-chip integration and the like, and is applied to the fields of high-precision three-dimensional imaging, remote sensing mapping, automatic driving and the like.
The core assembly in a frequency modulated continuous wave lidar system is a laser light source capable of producing a chirped light signal. The light source can be an internal modulation laser light source, a chirped pulse laser light source, an external modulation laser light source and the like. The linear frequency modulation optical signal is split by an optical beam splitter, wherein one path is used as a local oscillation optical signal, and the other path is used as a detection signal and is irradiated to the surface of a target by an optical collimation system. The reflected light signal of the target to be measured is received by the optical collimating system, passes through the optical circulator and the optical mixer, is combined with the local oscillator light signal, and is introduced into the photoelectric detector for coherent beat frequency. Finally, the signal processing system extracts information such as the target distance and speed from the photocurrent signal of the photodetector.
In the frequency modulated continuous wave lidar, the doppler frequency shift of the optical signal is high, which will seriously affect the performance of the frequency modulated continuous wave lidar. Therefore, decoupling of distance and velocity is one of the important issues in frequency modulated continuous wave lidar.
A first effective solution is to generate triangular waveform chirped optical signals in frequency modulated continuous wave lidar (d.pierrett, f.amzajerdian, l.petway, b.barnes, g.lockard, and m.rubio, "linear fmcw laser radar for precision range and vector linearity measures, proc.mater.res.soc.symp.,1076, K04-06 (2008)). In the positive chirp stage and the negative chirp stage, two beat frequency signals are respectively obtained, and the target distance and speed information can be respectively obtained by calculating the sum and the difference of the two beat frequency signals. However, under the triangular waveform chirp signal, two single-frequency signals are actually located at different time intervals, so that real parallel synchronous measurement cannot be realized, the repetition frequency is reduced, and noise point clouds may be generated at the target edge.
The second effective solution (Frequency-modulated connected-wave laser emitting dual-surface-emitting laser diodes for real-time measurement of distance and radial velocity, opt.rev.vol.24, No.1, 39-46 (2017)) is to generate positive and negative dual chirp signals respectively by using dual VCSEL laser diodes, obtain two beat signals simultaneously by dual channel transmission and reception, and obtain target distance and speed information respectively by calculating the sum and difference of the two beat signals. But a phase locked loop is required to synchronize the twin lasers.
A third effective solution (simultane real-time ranging and velocimetry video a dual-side band modulated lidar, IEEE photon. Double sideband modulation, however, requires an electro-optic I/Q modulator in the mach-zehnder interferometer configuration and does not achieve vector velocity.
Disclosure of Invention
The invention aims to provide a dual-channel dual-chirp continuous wave laser radar method and a dual-channel dual-chirp continuous wave laser radar device. The invention can realize the parallel synchronous measurement of the distance and the vector speed, and has the advantages of high repetition frequency, high detection precision, high sensitivity and strong anti-interference capability.
The technical scheme of the invention is as follows: in the dual-channel dual-chirp linear frequency modulation continuous wave laser radar method, at the transmitting end of a radar platform, an optical signal generated by a narrow-linewidth single-frequency continuous laser light source is divided into two orthogonal polarized optical signals by a first polarized beam splitter, and the two orthogonal polarized optical signals respectively enter two modulation channels; in the two modulation channels, two orthogonal polarization state lights are respectively modulated by different optical phase modulators and filtered by an optical band pass filter to synchronously generate optical signals with positive and negative double chirps, and then are respectively split to respectively obtain a first transmitting signal and a first local oscillator signal as well as a second transmitting signal and a second local oscillator signal; the first transmitting signal and the second transmitting signal are combined through a second polarization beam splitter, enter a polarization diversity optical circulator after being amplified by laser, and are transmitted to a target through an optical antenna and target echo signals are received; at a receiving end, a target echo signal of a first modulation optical channel passes through a polarization diversity optical circulator and then is subjected to coherent frequency mixing detection with a first local oscillator signal, a target echo signal of a second modulation optical channel passes through the polarization diversity optical circulator and then is subjected to coherent frequency mixing detection with a second local oscillator signal, then a photoelectric balance detector receives beat frequency signals containing target distance and vector speed information, and the beat frequency signals are subjected to filtering, sampling and digital signal processing to realize parallel synchronous measurement of the distance and the vector speed between a radar platform and a target.
In the above two-channel dual chirp chirped continuous wave laser radar method, in the radar platform, the narrow-linewidth single-frequency continuous laser light source generates unmodulated single-frequency single-mode continuous laser light as an output optical signal, which is expressed as:
E0(t)＝E0exp[j2πf0t+jφN0+jφ0]；
in the formula (f)0The frequency of the narrow-linewidth single-frequency continuous laser light source; phi is a0Is the initial phase of the optical signal; phi is aN0Is the noise phase of the optical signal; e0Is the optical signal amplitude, t is the time,
Figure BDA0003412218750000031
exp is an exponential function with a natural constant e as the base.
In the dual-channel dual-chirp continuous wave laser radar method, in two modulation channels, two orthogonal polarized lights are respectively modulated by different optical phase modulators, specifically,
in the first modulated optical channel, a first mixing signal of a first frequency modulation signal generated by a first frequency modulation signal generator and a first fundamental frequency signal generated by a first fundamental frequency signal generator is used as a first radio frequency driving signal of a first optical phase modulator:
Figure BDA0003412218750000032
in the formula: m1Is the amplification factor, V, of the first RF driving circuitRF1_MIs the amplitude, V, of the first frequency-modulated signalRF1_BIs the amplitude of the first fundamental frequency signal, fRF1_BIs the frequency of the first fundamental frequency signal, fRF1_HIs the high-frequency cut-off frequency, f, of the first frequency-modulated signalRF1_LIs the low-frequency cut-off frequency, T, of the first frequency-modulated signal1Is the period of the first frequency-modulated signal, phiN_RF1(t) is the noise phase after the first mixing,
Figure BDA0003412218750000033
is the frequency modulation rate of the first microwave chirp signal expressed as:
Figure BDA0003412218750000034
B1is a first bandwidth of modulation; t is time;
the first radio frequency driving signal drives the first optical phase modulator, and the optical signal output by the first optical phase modulator is:
Figure BDA0003412218750000041
in the formula (I), the compound is shown in the specification,
Figure BDA0003412218750000042
E0_PM1is the optical signal output by the first optical phase modulatorAmplitude of sign, f0Is the laser carrier frequency phi0Is the initial phase of the optical signal, phiN_PM1(t) is the noise phase, β, of the first optical phase modulator output1Is the phase modulation index of the first optical phase modulator,
Figure BDA0003412218750000043
Vπ1is the half-wave voltage of the first optical phase modulator;
in the second modulated optical channel, a second mixing signal of the second frequency modulation signal generated by the second frequency modulation signal generator and the second fundamental frequency signal generated by the second fundamental frequency signal generator is used as a second radio frequency driving signal of the second optical phase modulator:
Figure BDA0003412218750000044
；
in the formula: m2Is the amplification factor, V, of the second RF driving circuitRF2_MIs the amplitude, V, of the second frequency-modulated signalRF2_BIs the amplitude of the second fundamental frequency signal, fRF2_BIs the frequency of the second fundamental frequency signal, fRF2_HIs the high-frequency cut-off frequency, f, of the second frequency-modulated signalRF2_LIs the low-frequency cut-off frequency, T, of the second frequency-modulated signal2Is the period of the second frequency-modulated signal, phiN_RF2(t) is the noise phase after the second mixing,
Figure BDA0003412218750000045
is the frequency modulation rate of the second microwave chirp signal expressed as:
Figure BDA0003412218750000046
B2is a second bandwidth of modulation; t is time.
The second radio frequency driving signal drives a second optical phase modulator, and an optical signal output by the second optical phase modulator is:
Figure BDA0003412218750000051
in the formula (I), the compound is shown in the specification,
Figure BDA0003412218750000052
E0_PM2is the amplitude of the optical signal output by the second optical phase modulator, f0Is the laser carrier frequency phi0Is the initial phase of the optical signal, phiN_PM2(t) is the noise phase, β, of the second optical phase modulator output2Is the phase modulation factor of the second optical phase modulator,
Figure BDA0003412218750000053
Vπ2is the half-wave voltage of the second optical phase modulator.
The dual-channel dual-chirp continuous wave laser radar method performs optical band-pass filtering on two modulation channels respectively, synchronously generates positive and negative dual-chirp laser signals with different fundamental frequencies, performs beam splitting respectively, and obtains a first transmitting signal and a first local oscillation signal and a second transmitting signal and a second local oscillation signal respectively,
and expanding the optical signal output by the first optical phase modulator through a Bessel function:
Figure BDA0003412218750000054
wherein, JnIs a first class of n-order bessel function, n being 0,1, 2; the first term of the above equation represents the optical carrier, and the remaining terms represent the modulated sideband optical signal, including the positive sideband and the negative sideband;
the power of the first modulated optical channel is spread over n modulation sidebands, the amplitude of which is given by a parameter beta1The corresponding order of the Bessel function of the first kind is controlled, and the carrier suppression can be realized by changing the amplitudes of the microwave frequency modulation signal and the microwave base frequency signal;
filtering the residual carrier and sideband with a first optical bandpass filter to k1The order single-sideband optical signal passes through:
Figure BDA0003412218750000061
the output optical signal of the first modulation optical channel is continuous coherent laser with linearly modulated frequency, the continuous coherent laser adopts sawtooth wave linear modulation, the frequency of the modulation signal changes in a sawtooth mode along with time, the modulation signal is positive chirp in a period, and the modulation signal is expressed as:
Figure BDA0003412218750000062
wherein E is1Is the first modulated optical channel output optical amplitude, expressed as:
E1＝Jk1(β1)E0_PM1；φN1(t) is the noise phase of the output optical signal of the first modulated optical channel, expressed as:
Figure BDA0003412218750000063
t is time, k1Is the single sideband order of the first optical bandpass filter, T1Is the period of the first frequency-modulated signal, f0In order to frequency-modulate the initial frequency,
Figure BDA0003412218750000064
is a first frequency modulation rate, k1B1A first bandwidth of modulation;
the signal is divided into a first local oscillator signal and a first transmission signal by a 1 x 2 optical splitter, wherein a small part of energy is used as the first local oscillator signal, and the first local oscillator signal is time delay tauL1The optical field is represented as:
Figure BDA0003412218750000065
wherein E isLO1Is the local oscillator optical amplitude of the first modulated optical channel;
most of the energy is taken as a first transmission signal, which is expressed as:
Figure BDA0003412218750000066
wherein eta is1An amplitude splitting ratio for the first transmit signal;
and expanding the optical signal output by the second optical phase modulator through a Bessel function:
Figure BDA0003412218750000071
；
the power of the second modulated optical channel is spread over n modulated sidebands whose amplitude is given by a parameter beta2The corresponding order of the Bessel function of the first kind is controlled, and the carrier suppression can be realized by changing the amplitudes of the microwave frequency modulation signal and the microwave base frequency signal;
filtering the residual carrier and sideband with a second optical bandpass filter to k2The order single-sideband optical signal passes through:
Figure BDA0003412218750000072
the output optical signal of the second modulation optical channel is continuous coherent laser with linearly modulated frequency, the continuous coherent laser adopts sawtooth wave linear modulation, the frequency of the modulation signal changes in a sawtooth mode along with time, negative chirp is obtained in one period, and the negative chirp is expressed as:
Figure BDA0003412218750000073
wherein E is2Is the first modulated optical channel output optical amplitude, expressed as:
E2＝Jk2(β2)E0_PM2；φN2(t) is the noise phase of the output optical signal of the second modulated optical channel, expressed as:
Figure BDA0003412218750000074
t is time, k2Is the single sideband order, T, of the second optical bandpass filter2Is the period of the second frequency-modulated signal, f0In order to frequency-modulate the initial frequency,
Figure BDA0003412218750000075
at a second frequency modulation rate, k2B2A second bandwidth of modulation;
the optical signal is divided into a second local oscillation signal and a second transmitting signal by a 1 x 2 optical splitter, wherein a small part of energy is used as the second local oscillation signal, and the second local oscillation signal is time delay tauL2The optical field is represented as:
Figure BDA0003412218750000081
；
wherein E isLO2Is the local oscillator optical amplitude of the second modulated optical channel.
Most of the energy is taken as a second transmission signal, which is expressed as:
Figure BDA0003412218750000082
wherein eta is2Is the amplitude splitting ratio of the second transmit signal.
According to the double-channel double-chirp continuous wave laser radar method, the first driving signal and the second driving signal are synchronously triggered by the external trigger circuit to ensure that the frequency modulation periods of the two modulation optical channels are the same, namely T1＝T2T and the modulation is phase synchronized.
According to the double-channel double-chirp continuous wave laser radar method, a first transmitting signal and a second transmitting signal are combined through a second polarization beam splitter, enter a polarization diversity optical circulator after being subjected to laser amplification, are transmitted to a target through an optical antenna and receive a target echo signal, and specifically, the method comprises the following steps of:
most of the energy of the first modulated optical channel is separated as a first emission signal and a second emission signal of the second modulated optical channel through a second polarized lightThe beam combining device combines beams and amplifies laser, and then the beams are transmitted to a target through the polarization diversity optical circulator and the optical telescope and the optical scanner. The target echo signal of the first modulated optical channel is time delayed by tauS1The optical field is represented as:
Figure BDA0003412218750000083
wherein E isS1Is the signal light amplitude, phi, of the first modulated optical channelNS1The first modulation optical channel is a noise phase of a first transmission signal caused by target speckle or atmospheric turbulence;
time delay tau of echo signal of first modulated optical channelS1Time delay tau from local oscillator signalL1Expressed as:
Figure BDA0003412218750000084
wherein c is the speed of light, R is the distance of the target, and V is the relative movement radial speed of the radar platform and the target;
most energy of the second modulation optical channel is used as a transmitting signal, and the transmitting signal of the first modulation optical channel is subjected to beam combination and laser amplification through the second polarization beam splitter, then passes through the polarization diversity optical circulator, and is transmitted to a target through the transmitting/receiving optical telescope and the optical scanner. Target echo signal time delay tau of second modulated optical channelS2The optical field is represented as:
Figure BDA0003412218750000091
；
wherein E isS2Is the signal light amplitude, phi, of the second modulated optical channelNS2The phase of the noise of the second modulation optical channel emission signal caused by target speckle or atmospheric turbulence and the like;
time delay of target echo signal of second modulation optical channelRetardation τS2Time delay tau from a second local oscillator signalL2Expressed as:
Figure BDA0003412218750000092
where c is the speed of light, R is the target distance, and V is the relative radial velocity of the radar platform and the target.
In the dual-channel dual-chirp continuous wave laser radar method, at a receiving end, a target echo signal of a first modulation optical channel is subjected to coherent frequency mixing detection with a first local oscillator signal after passing through a polarization diversity optical circulator, a target echo signal of a second modulation optical channel is subjected to coherent frequency mixing detection with a second local oscillator signal after passing through the polarization diversity optical circulator, and beat frequency signals containing target distance and vector velocity information are respectively received by a photoelectric balance detector,
after a target echo signal of the first modulation optical channel passes through the polarization diversity optical circulator and is combined with the first local oscillator signal, the optical field is expressed as:
Figure BDA0003412218750000093
the 4 outputs of the first modulated optical channel after being mixed by the 2 × 490 ° optical bridge are respectively:
Figure BDA0003412218750000101
wherein the content of the first and second substances,
Figure BDA0003412218750000102
representing Doppler frequency shift caused by relative motion of the radar platform and the target;
receiving by a photoelectric balance detector, and after filtering, acquiring a beat frequency signal of a first modulation optical channel as follows:
Figure BDA0003412218750000103
the complex number can be obtained:
Figure BDA0003412218750000104
；
wherein the content of the first and second substances,
Figure BDA0003412218750000105
kinresponsivity, k, of a photodetector of the I channelquIs the responsivity, phi, of the photodetector of the Q channeli1_nAnd phiq1_nNoise phases of the I channel and the Q channel, respectively;
after the target echo signal of the second modulation optical channel passes through the polarization diversity optical circulator and is combined with the second local oscillator signal, the optical field is expressed as:
Figure BDA0003412218750000106
the 4 outputs of the second modulated optical channel after being mixed by the 2 × 490 ° optical bridge are respectively:
Figure BDA0003412218750000111
；
receiving by the photoelectric balance detector, and acquiring the beat frequency signal of the second modulation optical channel:
Figure BDA0003412218750000112
the complex number can be obtained:
Figure BDA0003412218750000113
wherein the content of the first and second substances,
Figure BDA0003412218750000114
kinresponsivity, k, of a photodetector of the I channelquIs the responsivity, phi, of the photodetector of the Q channeli2_nAnd phiq2_nThe noise phases of the I and Q channels, respectively.
In the dual-channel dual-chirp continuous wave laser radar method, the output signal of coherent reception contains an intermediate frequency of | k2fRF2_B-k1fRF1_BIf the fundamental frequency difference of the two channels is far larger than the intermediate frequency, the low-pass filtering is adopted to eliminate the fundamental frequency difference, and the cross talk suppression between the channels is realized.
In the double-channel double-chirp continuous wave laser radar method, the beat frequency signals are filtered, sampled and processed by digital signals to realize the parallel and synchronous measurement of the distance and the vector speed between a radar platform and a target,
carrying out fast Fourier transform on the complex beat frequency signal of the first modulation optical channel, and extracting the position of a frequency spectrum peak value by a gravity center method to obtain an intermediate frequency f in the forward frequency modulation (positive chirp) processIF1；
The complex beat frequency signal of the second modulation optical channel is subjected to fast Fourier transform, and the frequency spectrum peak position is extracted by a gravity center method to obtain the intermediate frequency f in the negative frequency modulation (negative chirp) processIF2；
The intermediate frequencies of the two modulation channels are respectively expressed as:
Figure BDA0003412218750000121
and obtaining the magnitude and the direction of the radial speed of the relative motion of the radar platform and the target according to the formula, wherein the magnitude and the direction are expressed as follows:
Figure BDA0003412218750000122
the positive value represents that the radar platform and the target move oppositely, and the negative value represents that the radar platform and the target move oppositely;
the distance between the laser radar and the target point is also obtained by the formula:
Figure BDA0003412218750000123
the simultaneous ranging resolution is expressed as:
Figure BDA0003412218750000124
the velocimetry resolution is expressed as:
Figure BDA0003412218750000125
where T is the frequency modulation period of the two modulated optical channels.
The device of the double-channel double-chirp continuous wave laser radar method comprises a narrow-linewidth single-frequency continuous laser light source, wherein the output end of the narrow-linewidth single-frequency continuous laser light source is connected with a first polarization beam splitter, and the output end of the first polarization beam splitter is connected with a first optical phase modulator and a second optical phase modulator; the first optical phase modulator is connected with a first radio frequency mixer through a first radio frequency amplifier, and the first radio frequency mixer is connected with a first frequency modulation signal generator and a first base frequency signal generator; the second optical phase modulator is connected with a second radio frequency mixer through a second radio frequency amplifier, and the second radio frequency mixer is connected with a second frequency modulation signal generator and a second frequency modulation signal generator; the first frequency modulation signal generator, the first base frequency signal generator, the second frequency modulation signal generator and the second frequency modulation signal generator are connected with an external trigger circuit together; the output end of the first optical phase modulator is connected with a first optical beam splitter through a first optical band-pass filter; the output end of the second optical phase modulator is connected with a second optical beam splitter through a second optical band-pass filter; the first beam splitter and the second beam splitter are connected with a second polarization beam splitter together, the output end of the second polarization beam splitter is connected with a polarization diversity optical circulator through a laser amplifier, and the output end of the polarization optical circulator is connected with an optical telescope through an optical scanner; the first optical beam splitter and the polarization diversity optical circulator are connected with a first optical bridge, the output end of the first optical bridge is connected with a first low-pass filter through a first photoelectric balance detector, and the output end of the first low-pass filter is connected with a first analog-to-digital converter; the second optical beam splitter and the polarization diversity optical circulator are connected with a second optical bridge, the output end of the second optical bridge is connected with a second low-pass filter through a second photoelectric balance detector, and the output end of the second low-pass filter is connected with a second analog-to-digital converter; the first analog-to-digital converter and the second analog-to-digital converter are connected with a digital signal processing unit together, and the digital signal processing unit is connected with an upper computer.
Compared with the prior art, the invention divides the optical signal generated by the narrow-linewidth single-frequency continuous laser light source into two orthogonal polarized optical signals through the first polarization beam splitter, and the two orthogonal polarized optical signals respectively enter the two modulation channels; in the two modulation channels, two orthogonal polarization state lights are respectively modulated by different optical phase modulators and filtered by an optical band pass filter to synchronously generate optical signals with positive and negative double chirps, and then are respectively split to respectively obtain a first transmitting signal and a first local oscillator signal as well as a second transmitting signal and a second local oscillator signal; the first transmitting signal and the second transmitting signal are combined through a second polarization beam splitter, enter a polarization diversity optical circulator after being amplified by laser, and are transmitted to a target through an optical antenna and target echo signals are received; at a receiving end, a target echo signal of a first modulation optical channel passes through a polarization diversity optical circulator and then is subjected to coherent frequency mixing detection with a first local oscillator signal, a target echo signal of a second modulation optical channel passes through the polarization diversity optical circulator and then is subjected to coherent frequency mixing detection with a second local oscillator signal, then a photoelectric balance detector receives beat frequency signals containing target distance and vector speed information, and the beat frequency signals are subjected to filtering, sampling and digital signal processing to realize parallel synchronous measurement of the distance and the vector speed between a radar platform and a target. Therefore, the invention can effectively overcome the defects of the prior art by adopting the double-channel double chirp, realize the parallel synchronous measurement of the distance and the vector speed in the real sense, simultaneously has the advantages of high repetition frequency, high detection precision, high sensitivity and strong anti-interference capability, and has good development prospect in the fields of airborne and satellite-borne surveying and mapping radars and the like.
Drawings
FIG. 1 is a schematic diagram of a frame structure of a radar system of the present invention;
fig. 2 is a schematic diagram of positive and negative double chirps of different fundamental frequencies output by a first modulated optical channel and a second modulated optical channel;
FIG. 3 is a schematic diagram of the frequency modulated carrier and sideband signals output by the optical phase modulator;
FIG. 4 is a diagram of a first optical bandpass filter for filtering the residual carrier and sidebands, resulting in k1Schematic diagram of order single-side band optical signal passing;
FIG. 5 is a diagram of a second band pass filter for filtering the residual carrier and sidebands to k2A step single sideband optical signal pass schematic diagram;
fig. 6 is a schematic diagram showing the relationship between the waveforms and the frequency difference between the positive and negative dual chirp echoes and the local oscillation signal.
The labels in the figures are: 1. a narrow linewidth single-frequency continuous laser light source; 2. a first polarization beam splitter; 3. a first optical phase modulator; 4. a second optical phase modulator; 5. a first radio frequency amplifier; 6. a first radio frequency mixer; 7. a first frequency-modulated signal generator; 8. a first baseband signal generator; 9. a second radio frequency amplifier; 10. a second radio frequency mixer; 11. a second frequency-modulated signal generator; 12. a second frequency-modulated signal generator; 13. an external trigger circuit; 14. a first optical band-pass filter; 15. a second optical band-pass filter; 16. a second optical splitter; 17. a second polarization beam splitter; 18. a laser amplifier; 19. a polarization diversity optical circulator; 20. an optical scanner; 21. an optical telescope; 22. a first optical bridge; 23. a first photoelectric balance detector; 24. a first low-pass filter; 25. a first analog-to-digital converter; 26. a second optical bridge; 27. a second photoelectric balance detector; 28. a second low-pass filter; 29. a second analog-to-digital converter; 30. a digital signal processing unit; 31. and (4) a host computer.
Detailed Description
The invention is further illustrated by the following figures and examples, which are not to be construed as limiting the invention.
Example 1: the double-channel double-chirp continuous wave laser radar method is characterized by comprising the following steps of: at the transmitting end of the radar platform, an optical signal generated by a narrow-linewidth single-frequency continuous laser light source is divided into two orthogonal polarized optical signals by a first polarized beam splitter, and the two orthogonal polarized optical signals respectively enter two modulation channels; in the two modulation channels, two orthogonal polarization state lights are respectively modulated by different optical phase modulators and filtered by an optical band pass filter to synchronously generate optical signals with positive and negative double chirps, and then are respectively split to respectively obtain a first transmitting signal and a first local oscillator signal as well as a second transmitting signal and a second local oscillator signal; the first transmitting signal and the second transmitting signal are combined through a second polarization beam splitter, enter a polarization diversity optical circulator after being amplified by laser, and are transmitted to a target through an optical antenna and target echo signals are received; at a receiving end, a target echo signal of a first modulation optical channel passes through a polarization diversity optical circulator and then is subjected to coherent frequency mixing detection with a first local oscillator signal, a target echo signal of a second modulation optical channel passes through the polarization diversity optical circulator and then is subjected to coherent frequency mixing detection with a second local oscillator signal, then a photoelectric balance detector receives beat frequency signals containing target distance and vector speed information, and the beat frequency signals are subjected to filtering, sampling and digital signal processing to realize parallel synchronous measurement of the distance and the vector speed between a radar platform and a target.
The device for realizing the method comprises a narrow-linewidth single-frequency continuous laser light source 1, as shown in fig. 1, wherein the output end of the narrow-linewidth single-frequency continuous laser light source 1 is connected with a first polarization beam splitter 2, and the output end of the first polarization beam splitter 2 is connected with a first optical phase modulator 3 and a second optical phase modulator 4; the first optical phase modulator 3 is connected with a first radio frequency mixer 6 through a first radio frequency amplifier 5, and the first radio frequency mixer 6 is connected with a first frequency modulation signal generator 7 and a first base frequency signal generator 8; the second optical phase modulator 4 is connected with a second radio frequency mixer 10 through a second radio frequency amplifier 9, and the second radio frequency mixer 10 is connected with a second frequency modulation signal generator 11 and a second frequency modulation signal generator 12; the first frequency modulation signal generator 7, the first base frequency signal generator 8, the second frequency modulation signal generator 11 and the second frequency modulation signal generator 12 are connected with an external trigger circuit 13 together; the output end of the first optical phase modulator 3 is connected with a first optical beam splitter 15 through a first optical band-pass filter 14; the output end of the second optical phase modulator 4 is connected with a second optical beam splitter 16 through a second optical band-pass filter 32; the first beam splitter 15 and the second beam splitter 16 are connected with a second polarization beam splitter 17 together, the output end of the second polarization beam splitter 17 is connected with a polarization diversity optical circulator 19 through a laser amplifier 18, and the output end of the polarization optical circulator 19 is connected with an optical telescope 21 through an optical scanner 20; the first optical beam splitter 15 and the polarization diversity optical circulator 19 are connected together with a first optical bridge 22, the output end of the first optical bridge 22 is connected with a first low-pass filter 24 through a first photoelectric balance detector 23, and the output end of the first low-pass filter 24 is connected with a first analog-to-digital converter 25; the second optical beam splitter 16 and the polarization diversity optical circulator 19 are connected together with a second optical bridge 26, the output end of the second optical bridge 26 is connected with a second low-pass filter 28 through a second photoelectric balance detector 27, and the output end of the second low-pass filter 28 is connected with a second analog-to-digital converter 29; the first analog-to-digital converter 25 and the second analog-to-digital converter 29 are connected together with a digital signal processing unit 30, and the digital signal processing unit 30 is connected with an upper computer 31.
Example 2: on the basis of the embodiment 1, as shown in fig. 1, the optical fiber comprises a chirped continuous wave laser light source, a human-eye-safe 1550.148nm (corresponding to 193396.02GHz) single-mode narrow-linewidth continuous wave fiber laser is adopted, the linewidth of the laser is 10kHz, the output power is 20mW, and the output of the fiber has isolation protection. The narrow-linewidth single-frequency continuous laser light source generates unmodulated single-frequency single-mode continuous coherent laser as an output optical signal, which is expressed as follows:
E0(t)＝E0exp[j2πf0t+jφN0+jφ0]；
in the formula (f)0The frequency of the narrow-linewidth single-frequency continuous laser light source; phi is a0Is the initial phase of the optical signal; phi is aN0Is the noise phase of the optical signal; e0Is the optical signal amplitude, t is the time,
Figure BDA0003412218750000161
exp is an exponential function with a natural constant e as the base.
The optical signal firstly passes through an online polarizer/controller, and the polarization extinction ratio is more than 25 dB. Then, the first polarization beam splitter 2(1 × 2 polarization beam splitter) performs 50/50 beam splitting, and enters two orthogonally polarized optical signals of two modulation channels, respectively.
In the two modulation channels, two orthogonal polarized lights are modulated by different optical phase modulators, specifically:
as shown in fig. 2, in the first modulated optical channel, a first mixing signal of the first frequency modulation signal generated by the first frequency modulation signal generator and the first fundamental frequency signal generated by the first fundamental frequency signal generator is used as the first rf driving signal of the first optical phase modulator (where the first frequency modulation signal generator has a signal bandwidth of 1.2GHz, the first fundamental frequency signal generator has a frequency of 9.4GHz, and the output rf signal drives the lithium niobate electro-optical modulator with a bandwidth of 10 GHz):
Figure BDA0003412218750000171
in the formula: m1Is the amplification factor, V, of the first RF driving circuitRF1_MIs the amplitude, V, of the first frequency-modulated signalRF1_BIs the amplitude of the first fundamental frequency signal, fRF1_BIs the frequency of the first fundamental frequency signal, fRF1_HIs the high-frequency cut-off frequency, f, of the first frequency-modulated signalRF1_LIs the low-frequency cut-off frequency, T, of the first frequency-modulated signal1Is the period of the first frequency-modulated signal, phiN_RF1(t) is the noise phase after the first mixing,
Figure BDA0003412218750000172
is the frequency modulation rate of the first microwave chirp signal expressed as:
Figure BDA0003412218750000173
B1is a first bandwidth of modulation; t is time;
the first radio frequency driving signal drives the first optical phase modulator, and the optical signal output by the first optical phase modulator is, without considering the phase noise introduced by the frequency modulation nonlinearity:
Figure BDA0003412218750000174
in the formula (I), the compound is shown in the specification,
Figure BDA0003412218750000175
E0_PM1is the amplitude of the optical signal output by the first optical phase modulator, f0Is the laser carrier frequency phi0Is the initial phase of the optical signal, phiN_PM1(t) is the noise phase, β, of the first optical phase modulator output1Is the phase modulation index of the first optical phase modulator,
Figure BDA0003412218750000176
Vπ1is the half-wave voltage of the first optical phase modulator;
in the second modulation optical channel, a second mixing signal of a second frequency modulation signal generated by a second frequency modulation signal generator and a second fundamental frequency signal generated by a second fundamental frequency signal generator is used as a second radio-frequency driving signal of the second optical phase modulator (wherein the frequency modulation signal generator has a signal bandwidth of 1.2GHz, the fundamental frequency signal generator has a frequency of 9.9GHz, and the output radio-frequency signal drives the lithium niobate electro-optical modulator with a bandwidth of 10 GHz):
Figure BDA0003412218750000181
；
in the formula: m2Is amplified by the second radio frequency drive circuitNumber, VRF2_MIs the amplitude, V, of the second frequency-modulated signalRF2_BIs the amplitude of the second fundamental frequency signal, fRF2_BIs the frequency of the second fundamental frequency signal, fRF2_HIs the high-frequency cut-off frequency, f, of the second frequency-modulated signalRF2_LIs the low-frequency cut-off frequency, T, of the second frequency-modulated signal2Is the period of the second frequency-modulated signal, phiN_RF2(t) is the noise phase after the second mixing,
Figure BDA0003412218750000182
is the frequency modulation rate of the second microwave chirp signal expressed as:
Figure BDA0003412218750000183
B2is a second bandwidth of modulation; t is time.
The second radio frequency driving signal drives the second optical phase modulator, and the optical signal output by the second optical phase modulator is, without considering the phase noise introduced by the frequency modulation nonlinearity:
Figure BDA0003412218750000184
in the formula (I), the compound is shown in the specification,
Figure BDA0003412218750000185
E0_PM2is the amplitude of the optical signal output by the second optical phase modulator, f0Is the laser carrier frequency phi0Is the initial phase of the optical signal, phiN_PM2(t) is the noise phase, β, of the second optical phase modulator output2Is the phase modulation factor of the second optical phase modulator,
Figure BDA0003412218750000186
Vπ2is the half-wave voltage of the second optical phase modulator.
The two modulation channels are respectively subjected to optical band-pass filtering to synchronously generate laser signals with positive and negative double chirps of different fundamental frequencies, and then are respectively subjected to beam splitting to respectively obtain a first transmitting signal and a first local oscillator signal as well as a second transmitting signal and a second local oscillator signal,
and expanding the optical signal output by the first optical phase modulator through a Bessel function:
Figure BDA0003412218750000191
；
wherein, JnIs a first class of n-order bessel function, n being 0,1, 2; the first term of the above equation represents the optical carrier, and the remaining terms represent the modulated sideband optical signal, including the positive sideband and the negative sideband;
the power of the first modulated optical channel is spread over n modulation sidebands, the amplitude of which is given by a parameter beta1And the respective orders of the first-type bessel functions are controlled, and carrier suppression can be realized by changing the amplitudes of the microwave frequency modulation signal and the microwave fundamental frequency signal.
Filtering the residual carrier and the sideband by using a first optical band-pass filter (the first optical band-pass filter adopts a thermal tuning fiber bragg grating filter in a reflection mode, the center wavelength of the first optical band-pass filter is set to be 1549.9877nm (the corresponding frequency is 193416.023GHz), the 3dB passband bandwidth of the first optical band-pass filter is about 5GHz, and the sideband suppression ratio is greater than 20dB), so that a + 2-order single-sideband optical signal passes through, as shown in fig. 4:
Figure BDA0003412218750000192
the output optical signal of the first modulation optical channel is continuous coherent laser with frequency linear modulation, which adopts sawtooth wave linear modulation (frequency modulation bandwidth 2.4GHz, frequency modulation period 5 mus, repetition frequency 200kHz), the frequency of the modulation signal changes in sawtooth mode with time, and within a period, the modulation signal is positive direction frequency modulation (positive chirp), which is expressed as:
Figure BDA0003412218750000193
wherein E is1Is the first modulated optical channel output lightAmplitude, expressed as:
E1＝Jk1(β1)E0_PM1；φN1(t) is the noise phase of the output optical signal of the first modulated optical channel, expressed as:
Figure BDA0003412218750000201
t is time, k1Is the single sideband order of the first optical bandpass filter, T1For a frequency-modulated period, f0In order to frequency-modulate the initial frequency,
Figure BDA0003412218750000202
is a first frequency modulation rate, k1B1A first bandwidth of modulation;
the signal is divided into a first local oscillator signal and a first transmission signal by a 1 x 2 optical splitter, wherein a small part of energy is used as the first local oscillator signal, and the first local oscillator signal is time delay tauL1The optical field is represented as:
Figure BDA0003412218750000203
wherein E isLO1Is the local oscillator optical amplitude of the first modulated optical channel;
most of the energy is taken as a first transmission signal, which is expressed as:
Figure BDA0003412218750000204
wherein eta is1Is the amplitude splitting ratio of the first modulated optical channel.
And expanding the optical signal output by the second optical phase modulator through a Bessel function:
Figure BDA0003412218750000205
；
the power of the second modulated optical channel is spread over n modulated sidebands whose amplitude is given by a parameter beta2First ofThe corresponding order of the Bessel-like function is controlled, and the carrier suppression can be realized by changing the amplitudes of the microwave frequency modulation signal and the microwave base frequency signal.
In the second modulation optical channel, a second band-pass filter is used for filtering the residual carrier and the sideband (the second optical band-pass filter adopts a thermal tuning fiber bragg grating filter in a reflection mode, the center wavelength of the second optical band-pass filter is set to be 1549.9877nm (the corresponding frequency is 193416.023GHz), the 3dB passband bandwidth of the filter is about 5GHz, and the sideband suppression ratio is greater than 20dB), so that a + 2-order single-sideband optical signal passes through, as shown in fig. 5;
in the embodiment, the field-programmable gate array (FPGA) is used to synchronously trigger the first and second rf driving signals, so as to implement the modulation phase synchronization of the two modulation channels. The output optical signal of the second modulation optical channel is continuous coherent laser with frequency linear modulation, sawtooth wave linear modulation is adopted (the frequency modulation bandwidth is 2.4GHz, the frequency modulation period is 5 mu s, and the repetition frequency is 200kHz), the frequency of the modulation signal changes in a sawtooth mode along with time, and negative frequency modulation (negative chirp) is carried out in one period. The output light field is represented as:
Figure BDA0003412218750000211
the output optical signal of the second modulation optical channel is continuous coherent laser with frequency linear modulation, sawtooth wave linear modulation is adopted, the frequency of the modulation signal changes in a sawtooth mode along with time, negative frequency modulation (negative chirp) is achieved in one period, and simplified expression is as follows:
Figure BDA0003412218750000212
wherein E is2Is the second modulated optical channel output optical amplitude, expressed as:
E2＝Jk2(β2)E0_PM2；φN2(t) is the noise phase of the output optical signal of the second modulated optical channel, expressed as:
Figure BDA0003412218750000213
t is time, k2Is the single sideband order of the first optical bandpass filter, T2For a frequency-modulated period, f0In order to frequency-modulate the initial frequency,
Figure BDA0003412218750000214
at a second frequency modulation rate, k2B2A second bandwidth of modulation;
the optical signal is divided into a second local oscillation signal and a second transmitting signal by a 1 x 2 optical splitter, wherein a small part of energy is used as the second local oscillation signal, and the second local oscillation signal is time delay tauL2The optical field is represented as:
Figure BDA0003412218750000221
wherein E isLO2Is the local oscillator optical amplitude of the second modulated optical channel.
Most of the energy is taken as a second transmission signal, which is expressed as:
Figure BDA0003412218750000222
wherein eta is2Is the amplitude splitting ratio of the second modulated optical channel.
In this embodiment, the first and second rf driving signals are synchronously triggered by the external trigger circuit, so that the same frequency modulation period, i.e. T, of the two modulated optical channels can be ensured1＝T2T and the modulation is phase synchronized.
The first transmitting signal and the second transmitting signal are combined by a second polarization beam splitter, enter a polarization diversity optical circulator after laser amplification (the laser amplifier is an erbium-doped fiber amplifier and is amplified to 600mW), are transmitted to a target by an optical antenna and receive a target echo signal, specifically,
the majority of the energy of the first modulated optical channel is used as the first transmit signal and the second transmit signal of the second modulated optical channelAfter beam combination and laser amplification are carried out by the second polarization beam splitter, the signal is transmitted to a target through the polarization diversity optical circulator, the optical telescope and the optical scanner, and as shown in fig. 6, the target echo signal is time delay tauS1The optical field is represented as:
Figure BDA0003412218750000223
wherein E isS1Is the signal light amplitude, phi, of the first modulated optical channelNS1The first modulation optical channel is a noise phase of a first transmission signal caused by target speckle or atmospheric turbulence;
time delay tau of echo signal of first modulated optical channelS1Time delay tau from local oscillator signalL1Expressed as:
Figure BDA0003412218750000224
wherein c is the speed of light, R is the distance of the target, and V is the relative movement radial speed of the radar platform and the target;
most energy of the second modulation optical channel is used as a transmitting signal, the transmitting signal of the first modulation optical channel is subjected to beam combination and laser amplification by the second polarization beam splitter, then passes through the polarization diversity optical circulator and is transmitted to a target by the transmitting/receiving optical telescope and the optical scanner, and as shown in fig. 6, the time delay tau of a target echo signal isS2The optical field is represented as:
Figure BDA0003412218750000231
；
wherein E isS2Is the signal light amplitude, phi, of the second modulated optical channelNS2The phase of the noise of the second modulation optical channel emission signal caused by target speckle or atmospheric turbulence and the like;
of target echo signals of the second modulated optical channelTime delay tauS2Time delay tau from a second local oscillator signalL2Expressed as:
Figure BDA0003412218750000232
where c is the speed of light, R is the target distance, and V is the relative radial velocity of the radar platform and the target.
At a receiving end, a target echo signal of a first modulation optical channel enters a polarization diversity optical circulator (Mach-Zehnder structure polarization diversity optical circulator) and then is subjected to coherent frequency mixing detection with a first local oscillator signal, a target echo signal of a second modulation optical channel passes through the polarization diversity optical circulator and then is subjected to coherent frequency mixing detection with a second local oscillator signal, and then beat frequency signals containing target distance and speed information are respectively obtained by receiving through a photoelectric balance detector,
after a target echo signal of the first modulation optical channel passes through the polarization diversity optical circulator and is combined with the first local oscillator signal, the optical field is expressed as:
Figure BDA0003412218750000233
the 4 outputs of the first modulated optical channel after being mixed by the 2 × 490 ° optical bridge are respectively:
Figure BDA0003412218750000241
wherein, the Doppler frequency shift caused by the relative motion of the radar platform and the target
Figure BDA0003412218750000242
Receiving by a photoelectric balance detector, and acquiring a beat frequency signal of a first modulation optical channel as follows:
Figure BDA0003412218750000243
can be obtained by repeating
Figure BDA0003412218750000244
Wherein the content of the first and second substances,
Figure BDA0003412218750000245
kinresponsivity, k, of a photodetector of the I channelquIs the responsivity, phi, of the photodetector of the Q channeli1_nAnd phiq1_nThe noise phases of the I and Q channels, respectively.
After the target echo signal of the second modulation optical channel passes through the polarization diversity optical circulator and is combined with the second local oscillator signal, the optical field is expressed as:
Figure BDA0003412218750000246
the 4 outputs of the second modulated optical channel after being mixed by the 2 × 490 ° optical bridge are respectively:
Figure BDA0003412218750000251
；
receiving by the photoelectric balance detector, and acquiring the beat frequency signal of the second modulation optical channel:
Figure BDA0003412218750000252
can be obtained by repeating
Figure BDA0003412218750000253
Wherein the content of the first and second substances,
Figure BDA0003412218750000254
kinresponsivity, k, of a photodetector of the I channelquIs the responsivity, phi, of the photodetector of the Q channeli2_nAnd phiq2_nThe noise phases of the I and Q channels, respectively.
Due to polarization diversity, crosstalk isolation between the first modulated optical channel and the second modulated optical channel can be achieved through polarization. Even for some of the same polarization components, such as: the first channel crosstalk signal entering the second channel may be represented as:
Figure BDA0003412218750000255
；
the output signal of coherent reception must contain the frequency of | k2fRF2_B-k1fRF1_BIn the item, the difference of the fundamental frequencies of the two channels is far greater than the intermediate frequency by 500MHz, and then the low-pass filtering (low-pass filtering of 450MHz) can be used for eliminating, so that the crosstalk suppression between the channels is realized.
Finally, the beat frequency signal is filtered, sampled and processed by digital signals to realize the parallel synchronous measurement of the distance and the vector speed between the radar platform and the target,
carrying out fast Fourier transform on the complex beat frequency signal of the first modulation optical channel, and extracting the position of a frequency spectrum peak value by a gravity center method to obtain an intermediate frequency f in the forward frequency modulation (positive chirp) processIF1；
The complex beat frequency signal of the second modulation optical channel is subjected to fast Fourier transform, and the frequency spectrum peak position is extracted by a gravity center method to obtain the intermediate frequency f in the negative frequency modulation (negative chirp) processIF2；
The intermediate frequencies of the two modulation channels are respectively expressed as:
Figure BDA0003412218750000261
and obtaining the magnitude and the direction of the radial speed of the relative motion of the radar platform and the target according to the formula, wherein the magnitude and the direction are expressed as follows:
Figure BDA0003412218750000262
the positive value represents that the radar platform and the target move oppositely, and the negative value represents that the radar platform and the target move oppositely;
the distance between the laser radar and the target point is also obtained by the formula:
Figure BDA0003412218750000263
the simultaneous ranging resolution is expressed as:
Figure BDA0003412218750000264
the velocimetry resolution is expressed as:
Figure BDA0003412218750000271
where T is the frequency modulation period of the two modulated optical channels.
In the embodiment, the ranging resolution of the laser radar system is 6.25cm, the speed measurement resolution is 0.155m/s, the emission repetition frequency is 200kHz, and the detection distance is 150 meters.
In conclusion, the invention can realize the parallel synchronous measurement of the distance and the vector speed in the true sense by adopting the double-channel double chirp, has the advantages of high repetition rate, high laser detection precision, high sensitivity and strong anti-interference capability, and has good development prospect in the fields of airborne and satellite-borne surveying and mapping radars and the like.

Claims (10)

1. The double-channel double-chirp continuous wave laser radar method is characterized by comprising the following steps of: at the transmitting end of the radar platform, an optical signal generated by a narrow-linewidth single-frequency continuous laser light source is divided into two orthogonal polarized optical signals by a first polarized beam splitter, and the two orthogonal polarized optical signals respectively enter two modulation channels; in the two modulation channels, two orthogonal polarization state lights are respectively modulated by different optical phase modulators and filtered by an optical band pass filter to synchronously generate optical signals with positive and negative double chirps, and then are respectively split to respectively obtain a first transmitting signal and a first local oscillator signal as well as a second transmitting signal and a second local oscillator signal; the first transmitting signal and the second transmitting signal are combined through a second polarization beam splitter, enter a polarization diversity optical circulator after being amplified by laser, and are transmitted to a target through an optical antenna and target echo signals are received; at a receiving end, a target echo signal of a first modulation optical channel passes through a polarization diversity optical circulator and then is subjected to coherent frequency mixing detection with a first local oscillator signal, a target echo signal of a second modulation optical channel passes through the polarization diversity optical circulator and then is subjected to coherent frequency mixing detection with a second local oscillator signal, then a photoelectric balance detector receives beat frequency signals containing target distance and vector speed information, and the beat frequency signals are subjected to filtering, sampling and digital signal processing to realize parallel synchronous measurement of the distance and the vector speed between a radar platform and a target.
2. The dual channel dual chirp chirped continuous wave lidar method of claim 1, wherein: in the radar platform, a narrow-linewidth single-frequency continuous laser light source generates unmodulated single-frequency single-mode continuous laser as an output optical signal, which is expressed as:
E0(t)＝E0exp[j2πf0t+jφN0+jφ0]；
in the formula (f)0The frequency of the narrow-linewidth single-frequency continuous laser light source; phi is a0Is the initial phase of the optical signal; phi is aN0Is the noise phase of the optical signal; e0Is the optical signal amplitude, t is the time,
Figure FDA0003412218740000011
exp is an exponential function with a natural constant e as the base.
3. The dual channel dual chirp chirped continuous wave lidar method of claim 1, wherein: in the two modulation channels, two orthogonal polarized lights are respectively modulated by different optical phase modulators, specifically,
in the first modulated optical channel, a first mixing signal of a first frequency modulation signal generated by a first frequency modulation signal generator and a first fundamental frequency signal generated by a first fundamental frequency signal generator is used as a first radio frequency driving signal of a first optical phase modulator:
Figure FDA0003412218740000021
in the formula: m1Is the amplification factor, V, of the first RF driving circuitRF1_MIs the amplitude, V, of the first frequency-modulated signalRF1_BIs the amplitude of the first fundamental frequency signal, fRF1_BIs the frequency of the first fundamental frequency signal, fRF1_HIs the high-frequency cut-off frequency, f, of the first frequency-modulated signalRF1_LIs the low-frequency cut-off frequency, T, of the first frequency-modulated signal1Is the period of the first frequency-modulated signal, phiN_RF1(t) is the noise phase after the first mixing,
Figure FDA0003412218740000022
is the frequency modulation rate of the first microwave chirp signal expressed as:
Figure FDA0003412218740000023
B1is a first bandwidth of modulation; t is time;
the first radio frequency driving signal drives the first optical phase modulator, and the optical signal output by the first optical phase modulator is:
Figure FDA0003412218740000024
in the formula (I), the compound is shown in the specification,
Figure FDA0003412218740000031
E0_PM1is the amplitude of the optical signal output by the first optical phase modulator, f0Is the laser carrier frequency phi0Is the initial phase of the optical signal, phiN_PM1(t) is the noise phase, β, of the first optical phase modulator output1Is the phase modulation index of the first optical phase modulator,
Figure FDA0003412218740000032
Vπ1is the half-wave voltage of the first optical phase modulator;
in the second modulated optical channel, a second mixing signal of the second frequency modulation signal generated by the second frequency modulation signal generator and the second fundamental frequency signal generated by the second fundamental frequency signal generator is used as a second radio frequency driving signal of the second optical phase modulator:
Figure FDA0003412218740000033
；
in the formula: m2Is the amplification factor, V, of the second RF driving circuitRF2_MIs the amplitude, V, of the second frequency-modulated signalRF2_BIs the amplitude of the second fundamental frequency signal, fRF2_BIs the frequency of the second fundamental frequency signal, fRF2_HIs the high-frequency cut-off frequency, f, of the second frequency-modulated signalRF2_LIs the low-frequency cut-off frequency, T, of the second frequency-modulated signal2Is the period of the second frequency-modulated signal, phiN_RF2(t) is the noise phase after the second mixing,
Figure FDA0003412218740000034
is the frequency modulation rate of the second microwave chirp signal expressed as:
Figure FDA0003412218740000035
B2is a second bandwidth of modulation; t is time;
the second radio frequency driving signal drives a second optical phase modulator, and an optical signal output by the second optical phase modulator is:
Figure FDA0003412218740000036
in the formula (I), the compound is shown in the specification,
Figure FDA0003412218740000037
E0_PM2is the amplitude of the optical signal output by the second optical phase modulator, f0Is the laser carrier frequency phi0Is the initial phase of the optical signal, phiN_PM2(t) is the noise phase, β, of the second optical phase modulator output2Is the phase modulation factor of the second optical phase modulator,
Figure FDA0003412218740000041
Vπ2is the half-wave voltage of the second optical phase modulator.
4. The dual channel dual chirp chirped continuous wave lidar method of claim 3, wherein: the two modulation channels are respectively subjected to optical band-pass filtering to synchronously generate laser signals with positive and negative double chirps of different fundamental frequencies, and then are respectively subjected to beam splitting to respectively obtain a first transmitting signal and a first local oscillator signal as well as a second transmitting signal and a second local oscillator signal,
and expanding the optical signal output by the first optical phase modulator through a Bessel function:
Figure FDA0003412218740000042
；
wherein, JnIs a first class of nth order bessel functions, n being 0,1,2 …; the first term of the above equation represents the optical carrier, and the remaining terms represent the modulated sideband optical signal, including the positive sideband and the negative sideband;
the power of the first modulated optical channel is spread over n modulation sidebands, the amplitude of which is given by a parameter beta1The corresponding order of the Bessel function of the first kind is controlled, and the carrier suppression can be realized by changing the amplitudes of the microwave frequency modulation signal and the microwave base frequency signal;
using a first optical bandpassThe filter filters the residual carrier and the sideband to k1The order single-sideband optical signal passes through:
Figure FDA0003412218740000051
the output optical signal of the first modulation optical channel is continuous coherent laser with linearly modulated frequency, the continuous coherent laser adopts sawtooth wave linear modulation, the frequency of the modulation signal changes in a sawtooth mode along with time, the modulation signal is positive chirp in a period, and the modulation signal is expressed as:
Figure FDA0003412218740000052
wherein E is1Is the first modulated optical channel output optical amplitude, expressed as:
E1＝Jk1(β1)E0_PM1；φN1(t) is the noise phase of the output optical signal of the first modulated optical channel, expressed as:
Figure FDA0003412218740000053
t is time, k1Is the single sideband order of the first optical bandpass filter, T1Is the period of the first frequency-modulated signal, f0In order to frequency-modulate the initial frequency,
Figure FDA0003412218740000054
is a first frequency modulation rate, k1B1A first bandwidth of modulation;
the signal is divided into a first local oscillator signal and a first transmission signal by a 1 x 2 optical splitter, wherein a small part of energy is used as the first local oscillator signal, and the first local oscillator signal is time delay tauL1The optical field is represented as:
Figure FDA0003412218740000055
wherein E isLO1Is the local oscillator optical amplitude of the first modulated optical channel;
most of the energy is taken as a first transmission signal, which is expressed as:
Figure FDA0003412218740000056
wherein eta is1An amplitude splitting ratio for the first transmit signal;
and expanding the optical signal output by the second optical phase modulator through a Bessel function:
Figure FDA0003412218740000061
the power of the second modulated optical channel is spread over n modulated sidebands whose amplitude is given by a parameter beta2The corresponding order of the Bessel function of the first kind is controlled, and the carrier suppression can be realized by changing the amplitudes of the microwave frequency modulation signal and the microwave base frequency signal;
filtering the residual carrier and sideband with a second optical bandpass filter to k2The order single-sideband optical signal passes through:
Figure FDA0003412218740000062
the output optical signal of the second modulation optical channel is continuous coherent laser with linearly modulated frequency, the continuous coherent laser adopts sawtooth wave linear modulation, the frequency of the modulation signal changes in a sawtooth mode along with time, negative chirp is obtained in one period, and the negative chirp is expressed as:
Figure FDA0003412218740000063
wherein E is2Is the first modulated optical channel output optical amplitude, expressed as: e2＝Jk2(β2)E0_PM2；φN2(t) is the noise phase of the output optical signal of the second modulated optical channel, expressed as:
Figure FDA0003412218740000071
t is time, k2Is the single sideband order, T, of the second optical bandpass filter2Is the period of the second frequency-modulated signal, f0In order to frequency-modulate the initial frequency,
Figure FDA0003412218740000072
at a second frequency modulation rate, k2B2A second bandwidth of modulation;
the optical signal is divided into a second local oscillation signal and a second transmitting signal by a 1 x 2 optical splitter, wherein a small part of energy is used as the second local oscillation signal, and the second local oscillation signal is time delay tauL2The optical field is represented as:
Figure FDA0003412218740000073
；
wherein E isLO2Is the local oscillator optical amplitude of the second modulated optical channel.
Most of the energy is taken as a second transmission signal, which is expressed as:
Figure FDA0003412218740000074
wherein eta is2Is the amplitude splitting ratio of the second transmit signal.
5. The dual channel dual chirp chirped continuous wave lidar method of claim 4, wherein: the first and second drive signals are synchronously triggered by an external trigger circuit to ensure that the frequency modulation periods of the two modulated optical channels are the same, namely T1＝T2T and the modulation is phase synchronized.
6. The dual channel dual chirp chirped continuous wave lidar method of claim 4, wherein: the first transmitting signal and the second transmitting signal are combined through a second polarization beam splitter, enter a polarization diversity optical circulator after being amplified by laser, are transmitted to a target through an optical antenna and receive a target echo signal, and the method specifically comprises the following steps:
most energy of the first modulation optical channel is used as a first transmitting signal and a second transmitting signal of the second modulation optical channel, the first transmitting signal is subjected to beam combination and laser amplification through the second polarization beam splitter, and then the first transmitting signal passes through the polarization diversity optical circulator and is transmitted to a target through the optical telescope and the optical scanner. The target echo signal of the first modulated optical channel is time delayed by tauS1The optical field is represented as:
Figure FDA0003412218740000081
wherein E isS1Is the signal light amplitude, phi, of the first modulated optical channelNS1The first modulation optical channel is a noise phase of a first transmission signal caused by target speckle or atmospheric turbulence;
time delay tau of echo signal of first modulated optical channelS1Time delay tau from local oscillator signalL1Expressed as:
Figure FDA0003412218740000082
wherein c is the speed of light, R is the distance of the target, and V is the relative movement radial speed of the radar platform and the target;
most energy of the second modulation optical channel is used as a transmitting signal, and the transmitting signal of the first modulation optical channel is subjected to beam combination and laser amplification through the second polarization beam splitter, then passes through the polarization diversity optical circulator, and is transmitted to a target through the transmitting/receiving optical telescope and the optical scanner. Target echo signal time delay tau of second modulated optical channelS2The optical field is represented as:
Figure FDA0003412218740000083
；
wherein E isS2Is the signal light amplitude, phi, of the second modulated optical channelNS2The phase of the noise of the second modulation optical channel emission signal caused by target speckle or atmospheric turbulence and the like;
time delay tau of target echo signal of second modulated optical channelS2Time delay tau from a second local oscillator signalL2Expressed as:
Figure FDA0003412218740000091
where c is the speed of light, R is the target distance, and V is the relative radial velocity of the radar platform and the target.
7. The dual channel dual chirp chirped continuous wave lidar method of claim 6, wherein: at a receiving end, a target echo signal of a first modulation optical channel and a first local oscillator signal are subjected to coherent frequency mixing detection after passing through a polarization diversity optical circulator, a target echo signal of a second modulation optical channel and a second local oscillator signal are subjected to coherent frequency mixing detection after passing through the polarization diversity optical circulator, and beat frequency signals containing target distance and speed information are respectively obtained by receiving the signals by a photoelectric balance detector,
after a target echo signal of the first modulation optical channel passes through the polarization diversity optical circulator and is combined with the first local oscillator signal, the optical field is expressed as:
Figure FDA0003412218740000092
the 4 outputs of the first modulated optical channel after being mixed by the 2 × 490 ° optical bridge are respectively:
Figure FDA0003412218740000101
wherein the content of the first and second substances,
Figure FDA0003412218740000102
representing Doppler frequency shift caused by relative motion of the radar platform and the target;
receiving by a photoelectric balance detector, and after filtering, acquiring a beat frequency signal of a first modulation optical channel as follows:
Figure FDA0003412218740000103
the complex number can be obtained:
Figure FDA0003412218740000104
wherein the content of the first and second substances,
Figure FDA0003412218740000105
kinresponsivity, k, of a photodetector of the I channelquIs the responsivity, phi, of the photodetector of the Q channeli1_nAnd phiq1_nNoise phases of the I channel and the Q channel, respectively;
after the target echo signal of the second modulation optical channel passes through the polarization diversity optical circulator and is combined with the second local oscillator signal, the optical field is expressed as:
Figure FDA0003412218740000106
the 4 outputs of the second modulated optical channel after being mixed by the 2 × 490 ° optical bridge are respectively:
Figure FDA0003412218740000111
receiving by the photoelectric balance detector, and acquiring the beat frequency signal of the second modulation optical channel:
Figure FDA0003412218740000112
the complex number can be obtained:
Figure FDA0003412218740000113
wherein the content of the first and second substances,
Figure FDA0003412218740000114
kinresponsivity, k, of a photodetector of the I channelquIs the responsivity, phi, of the photodetector of the Q channeli2_nAnd phiq2_nThe noise phases of the I and Q channels, respectively.
8. The dual channel dual chirp chirped continuous wave lidar method of claim 7, wherein: coherent received output signal contains intermediate frequency of | k2fRF2_B-k1fRF1_BIf the fundamental frequency difference of the two channels is far larger than the intermediate frequency, the low-pass filtering is adopted to eliminate the fundamental frequency difference, and the cross talk suppression between the channels is realized.
9. The dual channel dual chirp chirped continuous wave lidar method of claim 7, wherein: the beat frequency signal is filtered, sampled and processed by digital signals to realize the parallel synchronous measurement of the distance and the vector speed between the radar platform and the target,
carrying out fast Fourier transform on the complex beat frequency signal of the first modulation optical channel, and extracting the position of a frequency spectrum peak value by a gravity center method to obtain an intermediate frequency f in the positive chirp processIF1；
Second oneModulating the complex beat frequency signal of the optical channel to perform fast Fourier transform, and extracting the position of a frequency spectrum peak value by a gravity center method to obtain an intermediate frequency f in the negative chirp processIF2；
The intermediate frequencies of the two modulation channels are respectively expressed as:
Figure FDA0003412218740000121
and obtaining the magnitude and the direction of the radial speed of the relative motion of the radar platform and the target according to the formula, wherein the magnitude and the direction are expressed as follows:
Figure FDA0003412218740000122
the positive value represents that the radar platform and the target move oppositely, and the negative value represents that the radar platform and the target move oppositely;
the distance between the laser radar and the target point is also obtained by the formula:
Figure FDA0003412218740000123
the simultaneous ranging resolution is expressed as:
Figure FDA0003412218740000124
the velocimetry resolution is expressed as:
Figure FDA0003412218740000131
where T is the frequency modulation period of the two modulated optical channels.
10. The apparatus of the dual channel dual chirped continuous wave lidar method according to any of claims 1 to 9, characterized in that: the device comprises a narrow-linewidth single-frequency continuous laser light source (1), wherein the output end of the narrow-linewidth single-frequency continuous laser light source (1) is connected with a first polarization beam splitter (2), and the output end of the first polarization beam splitter (2) is connected with a first optical phase modulator (3) and a second optical phase modulator (4); the first optical phase modulator (3) is connected with a first radio frequency mixer (6) through a first radio frequency amplifier (5), and the first radio frequency mixer (6) is connected with a first frequency modulation signal generator (7) and a first base frequency signal generator (8); the second optical phase modulator (4) is connected with a second radio frequency mixer (10) through a second radio frequency amplifier (9), and the second radio frequency mixer (10) is connected with a second frequency modulation signal generator (11) and a second frequency modulation signal generator (12); the first frequency modulation signal generator (7), the first base frequency signal generator (8), the second frequency modulation signal generator (11) and the second frequency modulation signal generator (12) are connected with an external trigger circuit (13) together; the output end of the first optical phase modulator (3) is connected with a first optical beam splitter (15) through a first optical band-pass filter (14); the output end of the second optical phase modulator (4) is connected with a second optical beam splitter (16) through a second optical band-pass filter (32); the first beam splitter (15) and the second beam splitter (16) are connected with a second polarization beam splitter (17), the output end of the second polarization beam splitter (17) is connected with a polarization diversity optical circulator (19) through a laser amplifier (18), and the output end of the polarization optical circulator (19) is connected with an optical telescope (21) through an optical scanner (20); the first optical beam splitter (15) and the polarization diversity optical circulator (19) are connected with a first optical bridge (22), the output end of the first optical bridge (22) is connected with a first low-pass filter (24) through a first photoelectric balance detector (23), and the output end of the first low-pass filter (24) is connected with a first analog-to-digital converter (25); the second optical beam splitter (16) and the polarization diversity optical circulator (19) are connected with a second optical bridge (26), the output end of the second optical bridge (26) is connected with a second low-pass filter (28) through a second photoelectric balance detector (27), and the output end of the second low-pass filter (28) is connected with a second analog-to-digital converter (29); the first analog-to-digital converter (25) and the second analog-to-digital converter (29) are connected with a digital signal processing unit (30), and the digital signal processing unit (30) is connected with an upper computer (31).
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CN114690196A (en) * 2022-05-31 2022-07-01 杭州蓝芯科技有限公司 Light double-chirp distance measuring radar system
CN115356742A (en) * 2022-08-08 2022-11-18 深圳市圳阳精密技术有限公司 High-precision externally-adjusted FMCW laser ranging system and method based on phase splicing
CN117572444A (en) * 2024-01-17 2024-02-20 赛丽科技(苏州)有限公司 Frequency modulation continuous wave laser radar ranging and speed measuring system and method
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Cited By (7)

* Cited by examiner, † Cited by third party
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CN114690196A (en) * 2022-05-31 2022-07-01 杭州蓝芯科技有限公司 Light double-chirp distance measuring radar system
CN114690196B (en) * 2022-05-31 2022-08-26 杭州蓝芯科技有限公司 Light double-chirp distance measuring radar system
CN115356742A (en) * 2022-08-08 2022-11-18 深圳市圳阳精密技术有限公司 High-precision externally-adjusted FMCW laser ranging system and method based on phase splicing
CN115356742B (en) * 2022-08-08 2023-09-29 深圳市圳阳精密技术有限公司 High-precision external-adjustment FMCW laser ranging system and method based on phase splicing
WO2024046509A1 (en) * 2022-08-31 2024-03-07 电子科技大学长三角研究院(衢州) Radar high-speed single-target measurement method based on double-sideband lfmcw waveform
CN117572444A (en) * 2024-01-17 2024-02-20 赛丽科技(苏州)有限公司 Frequency modulation continuous wave laser radar ranging and speed measuring system and method
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