CN116819546A - Symmetrical double-sideband modulation differential frequency modulation continuous wave laser radar method and device - Google Patents

Symmetrical double-sideband modulation differential frequency modulation continuous wave laser radar method and device Download PDF

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CN116819546A
CN116819546A CN202310044822.9A CN202310044822A CN116819546A CN 116819546 A CN116819546 A CN 116819546A CN 202310044822 A CN202310044822 A CN 202310044822A CN 116819546 A CN116819546 A CN 116819546A
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signal
frequency
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phi
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职亚楠
孙玉娇
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
    • 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
    • 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
    • G01S17/06—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
    • G01S17/36—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated with phase comparison between the received signal and 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
    • 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
    • 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
    • G01S7/4808—Evaluating distance, position or velocity data
    • 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

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Electromagnetism (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Optical Radar Systems And Details Thereof (AREA)

Abstract

The invention discloses a symmetrical double-sideband modulated differential frequency modulation continuous wave laser radar method and a device, which adopt a unified modulation and symmetrical order filtering method to synchronously generate positive and negative double-chirp orthogonal polarization laser signals modulated by symmetrical sidebands, respectively generate orthogonal beat signals through respective coherent reception, perform analog signal processing on the double-orthogonal beat signals to realize differential elimination of phase noise, and then realize parallel synchronous measurement of distance and vector speed between a radar platform and a target through ADC sampling and digital signal processing. The invention can effectively eliminate the phase noise caused by factors such as line width of a laser light source, and the like, can effectively overcome the influence of the phase noise caused by factors such as atmospheric turbulence, speckle, optical machine structural vibration, and the like, can improve the ranging precision, the ranging sensitivity, the ranging range and the emission repetition frequency, can realize parallel synchronous ranging and speed measurement, and has the advantages of high detection sensitivity and strong anti-interference capability.

Description

Symmetrical double-sideband modulation differential 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 symmetrical double-sideband modulated differential frequency modulation continuous wave laser radar method and device.
Background
The Frequency Modulation Continuous Wave (FMCW) laser radar combines the frequency modulation continuous wave technology and the laser radar technology, adopts a linear frequency modulation signal to carry out linear modulation on the frequency of the emitted laser, obtains target distance information by calculating the instantaneous beat frequency of an echo optical signal and a local oscillation optical signal, simultaneously utilizes the Doppler effect to carry out speed measurement on a target, has the advantages of high detection sensitivity, high distance measurement and speed measurement resolution, strong anti-interference capability, on-chip integration and the like, and has been widely applied in the fields of high-precision three-dimensional imaging, remote sensing mapping, automatic driving and the like. The core component in the frequency modulation continuous wave laser radar system is a laser light source capable of generating a linear frequency modulation optical 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 signals are split through 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 target surface through an optical collimation system. The reflected light signal of the target to be measured is received by the optical collimating system, is mixed with the local oscillation light signal after passing through the optical circulator and the optical mixer, and enters the photoelectric detector to perform coherent beat frequency. Finally, the signal processing system extracts information such as target distance and speed from the photocurrent signal of the photodetector.
The speed measurement and the distance measurement of the frequency modulation continuous wave laser radar are both dependent on the beat frequency signal spectrum extraction of the echo optical signal and the local oscillation optical signal, and are very sensitive to random phase noise. In an ideal case, the constant velocity moving object beat signal spectrum at a distance should be a narrow spectral line. However, the random frequency modulation nonlinearity is generated under the influence of the random phase noise, so that the frequency of the beat frequency signal is not single frequency any more, but has a certain frequency spectrum broadening, which leads to the reduction of the measurement signal-to-noise ratio and the intermediate frequency jitter, and finally leads to the degradation of the measurement accuracy and the resolution of the system. The source of random phase noise has two aspects, one is internal noise, and the internal noise is generated in the FMCW laser radar and is phase disturbance introduced by the factors of spontaneous emission of a laser light source, frequency modulation nonlinearity, environmental temperature fluctuation, a radio frequency device, coherent detection, data acquisition and the like; the other is external noise, which is introduced by external factors such as atmospheric turbulence, target speckle, optical-mechanical structure vibration, and the like.
Phase noise becomes an important influencing factor of key performance indexes such as detection sensitivity, detection precision and the like of the FMCW laser radar. Therefore, how to compensate for phase noise in real time is one of the important issues in frequency modulated continuous wave lidar.
At present, the real-time compensation of the phase noise of the FMCW laser radar mainly comprises the following methods:
(1) Photoelectric feedforward/feedback compensation method: phase noise is extracted by using an auxiliary reference interferometer and coherent detection, and is suppressed by feedforward or feedback (such as a photoelectric phase-locked loop). This is the method that is currently being used more widely. Prior art 1 (Jiayi Ke, ziqi Song, "Phase noise compensation experiment with frequency modulated continuous wave laser in atmospheric propagation," Optical Engineering, vol.61, issue 7, pp.073101-1,2022) implements phase noise compensation, improving the signal-to-noise ratio of FMCW lidar under long range detection and atmospheric propagation conditions. Prior art 2 (Jia-Yi Ke, zi-Qi Song, pei-Si Wang, zhong-Ming Cui, di Mo, miao Lin, ran Wang, and Jin Wu, long distance high resolution FMCW laser ranging with phase noise compensation and 2D signal processing,Applied Optics,Vol.61,Issue 12,pp.3443-3454,2022) employs an auxiliary reference interferometer for recording phase noise from a laser source to compensate for phase errors induced in the target return light. However, the method has relatively complex structure, more adjustment parameters, higher requirements on hardware and more severe requirements on environment.
(2) The differential detection method of fixed frequency carrier and frequency modulation subcarrier comprises the following steps: in prior art 3 (h.tsuchida, "Differential FMCW-LiDAR for breaking the limit of laser coherence," Electronics Letters,56 (12), 614-616, 2020), electro-optical intensity modulation is used to simultaneously generate a fixed frequency carrier and a frequency modulated subcarrier, the carrier and the subcarrier are sent to a heterodyne interferometer, the output beat signals are detected after division multiplexing, and the frequency difference between the two beat signals is used to eliminate laser frequency modulation noise. But the implementation of this method is relatively difficult.
(3) Dual wavelength dual heterodyne mixing method: prior art 4 (Minglong Pu, weilin Xie, "Dual-Heterodyne Mixing Based Phase Noise Cancellation for Long Distance Dual-Wavelength FMCW Lidar," Optical Fiber Communications Conference and Exhibition, 2020) proposes a coherent Dual-wavelength FMCW laser radar scheme, which uses the laser phase correlation characteristic to compensate the linewidth phase noise of the laser light source by using a phase noise cancellation technique based on Dual heterodyne mixing. However, this solution cannot eliminate noise introduced during the frequency modulation process, and the implementation difficulty of this method is relatively high.
(4) Post data processing method: the method has good phase noise compensation effect, does not need a complex system, and has low cost. But the phase noise compensation effect is deteriorated when the target object moves.
The method can only eliminate the influence of internal noise to a certain extent, but cannot eliminate the influence of atmospheric turbulence noise and target speckle noise.
Disclosure of Invention
The invention aims to provide a symmetrical double-sideband modulated differential frequency modulation continuous wave laser radar method and device. The invention can effectively eliminate the phase noise caused by factors such as line width of a laser light source, and the like, can effectively overcome the influence of the phase noise caused by factors such as atmospheric turbulence, speckle, optical machine structural vibration, and the like, can improve the ranging precision, the ranging sensitivity, the ranging range and the emission repetition frequency, can realize parallel synchronous ranging and speed measurement, and has the advantages of high detection sensitivity and strong anti-interference capability.
The technical scheme of the invention is as follows: in the method, at the transmitting end of a radar platform, an optical signal generated by a single-frequency continuous laser source firstly passes through an optical phase modulator and is mixed with a fundamental frequency signal to obtain a radio frequency mixing signal, and the radio frequency mixing signal is used as a driving signal of the optical phase modulator to carry out phase modulation on the optical signal to generate a modulated laser signal; the modulated laser signals are divided into a first modulated optical signal and a second modulated optical signal through a first optical beam splitter, the first modulated optical signal and the second modulated optical signal are respectively subjected to optical bandpass filtering and then respectively synchronously generate positive and negative double-chirp laser signals modulated by symmetrical sidebands, and the positive and negative double-chirp laser signals respectively generate two modulated lights in orthogonal polarization states through a polarization controller; the two modulated light beams are respectively split to respectively obtain a first transmitting light signal and a first local oscillator light signal and a second transmitting light signal and a second local oscillator light signal; the first emission optical signal and the second emission optical signal enter a laser amplifier after polarization beam combination, and the two amplified emission optical signals are emitted to a target through a common optical device and two echo beams are received; at the receiving end of the radar platform, the returned two paths of echo light beams are respectively subjected to coherent mixing with the corresponding first local oscillator optical signals and second local oscillator optical signals after passing through the polarization diversity circulator, then the four-channel photoelectric balance detector is respectively used for receiving and obtaining orthogonal beat frequency signals containing target distance and vector speed information, the two paths of orthogonal beat frequency signals are subjected to analog signal processing to realize differential elimination of phase noise, and then the parallel synchronous measurement of the distance and the vector speed between the radar platform and the target is realized through ADC sampling and digital signal processing.
In the method for symmetric double-sideband modulated differential frequency modulation continuous wave laser radar, the single-frequency continuous laser light source generates an unmodulated laser signal, which is expressed as:
E 0 (t)＝E 0 exp[j2πf 0 t+jφ N_SR (t)+jφ 0 ]；
in the formula ,f0 Is the carrier frequency of the laser light source; phi (phi) N_SR (t) is the noise phase of the laser source; phi (phi) 0 Initial phase for the output beam; e (E) 0 Is the output beam amplitude, t is the time,exp is an exponential function based on a natural constant e.
In the method for symmetric double-sideband modulated differential frequency modulation continuous wave laser radar, the frequency modulation signal generated by the frequency modulation signal generator, the fundamental frequency signal generated by the fundamental frequency signal generator are used, the frequency modulation signal and the fundamental frequency signal are mixed to obtain a radio frequency mixed signal, and the radio frequency mixed signal is amplified by radio frequency and then expressed as:
wherein M is the amplification factor of the radio frequency circuit, V RF_M Is the amplitude of the frequency modulated signal, V RF_B Is the amplitude of the fundamental frequency signal,is the frequency modulation rate of the frequency modulated signal, denoted +.>f RF_B Is the frequency of the fundamental frequency signal, f RF_H Is the high frequency cut-off frequency of the frequency modulated signal, f RF_L Is the low frequency cut-off frequency of the frequency-modulated signal, T is the period of the frequency-modulated signal, B is the frequency-modulated bandwidth, phi N_RF (t) is the noise phase of the mixed signal; t is time;
the radio frequency mixed signal after radio frequency amplification is used as a radio frequency driving signal of an optical phase modulator to carry out phase modulation on an incident laser signal, and the generated modulated laser signal is:
wherein ,E0_PM Is the amplitude of the modulated laser signal output by the optical phase modulator; f (f) 0 Is the carrier frequency of the laser source; phi (phi) N_SR (t) isNoise phase introduced by line width of laser source; phi (phi) 0 Is the initial phase of the laser source output;is the frequency modulation rate of the frequency modulated signal; phi (phi) N_PM (t) is the phase of noise introduced by the optical phase modulator; phi (phi) N_RF (t) is the phase of noise introduced by the rf driver; beta is the phase modulation factor of the optical phase modulator, denoted +.>V π Is the half-wave voltage of the optical phase modulator; t is time, < >>exp is an exponential function based on a natural constant e;
the above equation is developed by the Bessel function:
wherein ,Jn Is a first class of n-order bessel functions, n=0, 1,2 …; wherein J 0 Representing the optical carrier, the rest J n The term then represents a modulated sideband optical signal comprising a positive sideband and a negative sideband; the power of a single frequency continuous laser source is spread over n modulation sidebands whose amplitudes are controlled by the respective orders of the Bessel function of the first type with parameter beta, and carrier suppression is achieved by varying the amplitudes of the frequency modulated signal and the fundamental frequency signal.
In the symmetrical double-sideband modulated differential frequency modulation continuous wave laser radar method, the modulated laser signal is divided into a first modulated optical signal and a second modulated optical signal through a first optical beam splitter;
The first modulated optical signal filters the residual carrier and the sidebands by using a first optical bandpass filter, so that +k-order sideband optical signals pass through, and the method is expressed as follows:
wherein ,E1 Is the first modulated optical signal amplitude, denoted E 1 ＝J k (β)E 0_PM ，E 0_PM Is the amplitude of the modulated laser signal output by the optical phase modulator, J k (β) is a first class Bessel function representing k-th order, +k is the first bandpass filtered single sideband order, and β is the phase modulation factor of the optical phase modulator; t is time; f (f) 0 Is the carrier frequency of the laser light source;is the frequency modulation rate; t is a frequency modulation period; b is the frequency modulation bandwidth; phi (phi) N_SR (t) is the noise phase introduced by the linewidth of the laser source; phi (phi) N_PM (t) is the phase of noise introduced by the optical phase modulator; phi (phi) N_RF (t) is the noise phase introduced by the rf drive circuit; />exp is an exponential function based on a natural constant e;
with phi N1 (t) represents the noise phase of the first modulated optical signal:
φ N1 (t)＝φ N_SR (t)+φ N_PM (t)+kφ N_RF (t)；
the first modulated optical signal after optical filtering is divided into a first transmitted optical signal and a first local oscillation optical signal by a first polarization controller and a second optical beam splitter, wherein a small part of energy is used as the first local oscillation optical signal, and the first local oscillation optical signal is time delay tau L1 The optical field is denoted as:
wherein ,ELO1 Is the first local oscillator optical signal amplitude;
the majority of energy of the first modulated optical signal with the adjusted polarization state is taken as a first transmitted optical signal, and the first modulated optical signal and a second transmitted optical signal with the orthogonal polarization state are combined and excited by a polarization beam combinerAfter the light is amplified, the light is transmitted to a target through a polarization diversity optical circulator and an optical scanner and a transmitting/receiving optical telescope, and a first target echo signal returned from the target is a time delay tau S1 The optical field is denoted as:
wherein ,ES1 Is the amplitude phi of the first echo optical signal N1_OA Is the noise phase of the first transmitted light signal due to the optical amplifier; phi (phi) NS1 The noise phase of the first echo optical signal is caused by factors such as target speckle, atmospheric turbulence, optical-mechanical structure vibration and the like;
time delay τ of first echo signal S1 Time delay τ with first local oscillator optical signal L1 Expressed as:
wherein c is the speed of light, R is the target distance, and V is the radial speed of relative movement of the radar platform and the target;
the second modulated optical signal filters the residual carrier and sidebands using a second optical bandpass filter to pass the-k order sideband optical signal, expressed as:
wherein ,E2 Is the second modulated optical signal amplitude, denoted E 2 ＝J k (β)E 0_PM ，E 0_PM Is the amplitude of the modulated laser signal output by the optical phase modulator, J k (β) is a first class Bessel function representing the k-th order, -k is the second bandpass filtered single sideband order, and β is the phase modulation factor of the optical phase modulator; t is time; f (f) 0 Is the carrier frequency of the laser light source;is the frequency modulation rate; t is a frequency modulation period; b is the frequency modulation bandwidth; phi (phi) N_SR (t) is the noise phase introduced by the linewidth of the laser source; phi (phi) N_PM (t) is the phase of noise introduced by the optical phase modulator; phi (phi) N_RF (t) is the noise phase introduced by the rf drive circuit; />exp is an exponential function based on a natural constant e;
with phi N2 (t) represents the noise phase of the second modulated optical signal:
φ N2 (t)＝φ N_SR (t)+φ N_PM (t)-kφ N_RF (t)；
the second modulated optical signal after optical filtering is divided into a second transmitted optical signal and a second local oscillation optical signal by a second polarization controller and a third optical beam splitter, wherein a small part of energy is used as the second local oscillation optical signal, and the second local oscillation optical signal is time delay tau L2 The optical field is denoted as:
wherein ,ELO2 Is the first local oscillator optical signal amplitude;
the majority of energy of the second modulated optical signal with the adjusted polarization state is used as a second transmitted optical signal, the second transmitted optical signal with the orthogonal polarization state and the first transmitted optical signal are combined and amplified by a polarization beam combiner, and then transmitted to a target through an optical scanner and a transmitting/receiving optical telescope by a polarization diversity optical circulator, and a second target echo signal returned from the target is time delay tau S2 The optical field is denoted as:
wherein ,ES2 Is the amplitude phi of the second echo optical signal N2_OA (t) is a second hairNoise phase of the light emission signal due to the optical amplifier; phi (phi) NS2 The second echo optical signal is noise phase caused by factors such as target speckle, atmospheric turbulence, optical-mechanical structure vibration and the like;
time delay τ of second echo optical signal S2 Time delay τ with second local oscillator optical signal L2 Expressed as:
since the first and second transmitted optical signals are transmitted and received coaxially, i.e. τ S1 ＝τ S2 ，τ L1 ＝τ L2 Then
The first and second transmitted optical signals pass through the same optical amplifier and the introduced phase noise is the same, i.e. N_OA ＝φ N1_OA ＝φ N2_OA The method comprises the steps of carrying out a first treatment on the surface of the The two echo optical signals are affected by target speckle, atmospheric turbulence, optical-mechanical structure vibration and other factors approximately the same, namely phi NS ＝φ NS1 ＝φ NS2 。
In the aforementioned symmetric double-sideband modulated differential frequency modulation continuous wave laser radar method, the coherent mixing is that a first beam combining light obtained by combining the first echo optical signal and the first local oscillation optical signal is expressed as:
the 4 paths of output of the first combined light after being mixed by the first optical bridge are respectively:
wherein ,indicating lightningAchieving Doppler shift caused by relative motion between the platform and the target;
Then the first photoelectric balance detector receives the signal, and after band-pass filtering, a first orthogonal beat frequency signal is obtained:
wherein ,σin_1 The response of the first photodetector, σ, being the I-channel qu_1 The response rate of the first photodetector, which is the Q channel;
and the second combined beam light obtained by combining the second echo signal and the second local oscillation optical signal is expressed as:
the 4 paths of output of the second combined light after being mixed by the second optical bridge are respectively:
wherein ,representing Doppler shift caused by relative motion of the radar platform and the target;
the second photoelectric balance detector receives the second orthogonal beat signal, and the second orthogonal beat signal is obtained after band-pass filtering:
wherein ,σin_2 The response of the second photodetector, σ, being the I-channel qu_2 The response rate of the second photodetector, which is the Q channel;
due to polarization diversity, crosstalk isolation is realized between the first modulated optical signal and the second modulated optical signal through polarization, and if the fundamental frequency difference of the two modulated optical signals is far greater than Doppler frequency shift, crosstalk suppression is realized through low-pass filtering.
The method for symmetric double-sideband modulated differential frequency modulation continuous wave laser radar comprises the following steps of:
First, the four-channel beat signal performs analog multiplication operation in pairs, expressed as:
let sigma in_1 σ in_2 ＝σ qu_1 σ qu_2 ＝σ in_1 σ qu_2 ＝σ qu_1 σ in_2 =Λ, and then performing a two-by-two analog addition and subtraction operation to obtain three analog channel output signals:
in the above, I a1 (t) is an amount including the target distance, I a2(t) and Ia3 (t) is the amount containing target Doppler information;
at I a1 In (t), through symmetrical double-sideband modulation differential processing, the noise phase introduced by the linewidth of the laser light source, the noise phase introduced by the optical phase modulator, the noise phase output by the radio frequency amplifier, the target speckle noise, the atmospheric turbulence noise and the vibration noise of the optical machine structure are completely eliminated; the remaining noise phase introduced by the rf driver circuit is suppressed by optimizing the rf device.
In the method for the symmetrical double-sideband modulated differential frequency modulation continuous wave laser radar, the parallel synchronous measurement of the distance and the vector speed between the radar platform and the target is as follows:
performing fast Fourier transform on the beat frequency signal of the first analog channel, and extracting the position of a frequency spectrum peak value by a gravity center method to obtain an intermediate frequency f IF1 ；
The second analog channel and the third analog channel are obtained by multiplexing:
the complex beat frequency signal is subjected to fast Fourier transformation, and the position of a frequency spectrum peak value is extracted through a gravity center method to obtain an intermediate frequency f IF2 ；
The two intermediate frequencies are respectively expressed as:
the magnitude and direction of the radial velocity of the relative motion of the radar platform and the target are obtained by the method, and are expressed as follows:
wherein positive values represent the radar platform moving towards the target and negative values represent the radar platform moving away from the target;
the distance between the laser radar and the target point is also obtained by the following steps:
while ranging resolution is expressed as:
the speed measurement resolution is expressed as:
the device for realizing the symmetrical double-sideband modulated differential frequency modulation continuous wave laser radar method comprises a single-frequency connection laser source, wherein the single-frequency connection laser source is connected with an optical phase modulator; the optical phase modulator is respectively connected with a first optical beam splitter and a radio frequency amplifier; the radio frequency amplifier is connected with a radio frequency mixer, and the radio frequency mixer is connected with a frequency modulation signal generator and a fundamental frequency signal generator; the first optical beam splitter is respectively connected with a first optical band-pass filter and a second optical band-pass filter; the first optical band-pass filter is connected with a second optical beam splitter through a first polarization controller; the second optical band-pass filter is connected with a third optical beam splitter through a second polarization controller; the second optical beam splitter and the third optical beam splitter are connected with a polarization beam combiner together, the polarization beam combiner is connected with a polarization diversity optical circulator through a laser amplifier, and the polarization diversity optical circulator is connected with a transmitting and receiving telescope through an optical scanner; the second optical beam splitter and the polarization diversity optical circulator are connected with a first optical bridge, and the first optical bridge is connected with a first band-pass filter through a first photoelectric balance detector; the third optical beam splitter and the polarization diversity optical circulator are connected with a second optical bridge, and the second optical bridge is connected with a second band-pass filter through a second photoelectric balance detector; the first band-pass filter and the second band-pass filter are connected with an analog signal processing unit together, the analog signal processing unit is connected with three analog-to-digital converters, the three analog-to-digital converters are connected with a digital signal processing unit together, and the digital signal processing unit is connected with an upper computer; the digital signal processing unit is connected with an external trigger circuit which is respectively connected with the frequency modulation signal generator and the fundamental frequency signal generator; the digital signal processing unit is also connected with the optical scanner.
Compared with the prior art, the method of unified modulation and symmetrical order filtering is adopted, positive and negative double-chirp orthogonal polarization laser signals modulated by symmetrical sidebands are synchronously generated, orthogonal beat signals are respectively generated through respective coherent reception, and analog signal processing is carried out on the double-orthogonal beat signals, so that the method can completely eliminate noise phases introduced by line widths of laser light sources, noise phases introduced by optical phase modulators, noise phases output by radio frequency amplifiers, target speckle noise, atmospheric turbulence noise and vibration noise of optical machine structures through differential processing, can improve the ranging precision, the ranging sensitivity, the ranging range and the emission repetition frequency, and can realize parallel synchronous ranging and speed measurement. Therefore, the invention has the advantages of high ranging precision, good sensitivity and strong anti-interference capability, can realize the high-precision ranging of a long-distance scattering target, and has the function of speed measurement. Has good development prospect in the fields of airborne and spaceborne surveying and mapping radars and the like.
Drawings
FIG. 1 is a schematic view of the apparatus of the present invention;
fig. 2 shows a schematic diagram of the frequency modulated carrier and sideband signal output by the optical phase modulator.
Fig. 3 shows schematic diagrams of the positive and negative double chirps of the output of the first modulated optical channel and the second modulated optical channel, respectively.
Fig. 4 shows a schematic diagram of filtering the residual carrier and sidebands using a first optical bandpass filter to pass the +k order single sideband optical signal.
Fig. 5 shows a schematic diagram of filtering the residual carrier and sidebands using a second optical bandpass filter to pass the-k order single sideband optical signal.
Fig. 6 shows the + -1-order symmetric double-sideband spectral distribution measured by a spectrometer.
Fig. 7 shows a schematic diagram of a mach-zehnder structure polarization diversity optical circulator.
The marks in the drawings are:
1. the single frequency is connected with a laser source; 2. an optical phase modulator; 3. a first optical beam splitter; 4. a radio frequency amplifier; 5. a radio frequency mixer; 6. a frequency modulated signal generator; 7. a baseband signal generator; 8. a first optical bandpass filter; 9. a second optical bandpass filter; 10. a first polarization controller; 11. a second optical beam splitter; 12. a second polarization controller; 13. a third optical beam splitter; 14. a polarizing beam combiner; 15. a laser amplifier; 16. a polarization diversity optical circulator; 17. an optical scanner; 18. a transmitting-receiving telescope; 19. a first optical bridge; 20. a first photo balance detector; 21. a first band-pass filter; 22. a second optical bridge; 23. a second photo balance detector; 24. a second band-pass filter; 25. an analog signal processing unit; 26. an analog-to-digital converter; 27. a digital signal processing unit; 28. an upper computer; 29. an external trigger circuit.
Detailed Description
The invention is further illustrated by the following figures and examples, which are not intended to be limiting.
Example 1: in the method, at the transmitting end of a radar platform, an optical signal generated by a single-frequency continuous laser source is firstly subjected to an optical phase modulator, a frequency modulation signal is mixed with a fundamental frequency signal to obtain a radio frequency mixing signal, and the radio frequency mixing signal is used as a driving signal of the optical phase modulator to carry out phase modulation on the optical signal to generate a modulated laser signal; the modulated laser signals are divided into a first modulated optical signal and a second modulated optical signal through a first optical beam splitter, the first modulated optical signal and the second modulated optical signal are respectively subjected to optical bandpass filtering and then respectively synchronously generate positive and negative double-chirp laser signals modulated by symmetrical sidebands, and the positive and negative double-chirp laser signals respectively generate two modulated lights in orthogonal polarization states through a polarization controller; the two modulated light beams are respectively split to respectively obtain a first transmitting light signal and a first local oscillator light signal and a second transmitting light signal and a second local oscillator light signal; the first emission optical signal and the second emission optical signal enter a laser amplifier after polarization beam combination, and the two amplified emission optical signals are emitted to a target through a common optical device and two echo beams are received; at the receiving end of the radar platform, the returned two paths of echo light beams are respectively subjected to coherent mixing with the corresponding first local oscillator optical signals and second local oscillator optical signals after passing through the polarization diversity circulator, then the four-channel photoelectric balance detector is respectively used for receiving and obtaining orthogonal beat frequency signals containing target distance and vector speed information, the two paths of orthogonal beat frequency signals are subjected to analog signal processing to realize differential elimination of phase noise, and then the parallel synchronous measurement of the distance and the vector speed between the radar platform and the target is realized through ADC sampling and digital signal processing.
The device for realizing the method comprises a single-frequency connection laser light source 1, wherein the single-frequency connection laser light source 1 is connected with an optical phase modulator 2 as shown in fig. 1; the optical phase modulator 2 is respectively connected with a first optical beam splitter 3 and a radio frequency amplifier 4; the radio frequency amplifier 4 is connected with a radio frequency mixer 5, and the radio frequency mixer 5 is connected with a frequency modulation signal generator 6 and a fundamental frequency signal generator 7; the first optical beam splitter 3 is respectively connected with a first optical band-pass filter 8 and a second optical band-pass filter 9; the first optical bandpass filter 8 is connected with a second optical beam splitter 11 through a first polarization controller 10; the second optical bandpass filter 9 is connected with a third optical beam splitter 13 through a second polarization controller 12; the second optical beam splitter 11 and the third optical beam splitter 13 are connected with a polarization beam combiner 14 together, the polarization beam combiner 14 is connected with a polarization diversity optical circulator 16 through a laser amplifier 15, and the polarization diversity optical circulator 16 is connected with a transmitting and receiving telescope 18 through an optical scanner 17; the second optical beam splitter 11 and the polarization diversity optical circulator 16 are connected together with a first optical bridge 19, and the first optical bridge 19 is connected with a first band-pass filter 21 through a first photoelectric balance detector 20; the third optical beam splitter 13 and the polarization diversity optical circulator 16 are connected with a second optical bridge 22, and the second optical bridge 22 is connected with a second band-pass filter 24 through a second photoelectric balance detector 23; the first band-pass filter 21 and the second band-pass filter 24 are connected with an analog signal processing unit 25 together, the analog signal processing unit 25 is connected with three analog-to-digital converters 26, the three analog-to-digital converters 26 are connected with a digital signal processing unit 27 together, and the digital signal processing unit 27 is connected with an upper computer 28; the digital signal processing unit 27 is connected with an external trigger circuit 29, and the external trigger circuit 29 is respectively connected with the frequency modulation signal generator 6 and the fundamental frequency signal generator 7; the digital signal processing unit 25 is also connected to the optical scanner 17.
Example 2: based on the embodiment 1, a 1550.148nm (corresponding frequency is 193397.0 GHz) single-mode continuous fiber laser source with a linewidth of 100kHz, an output power of 20mW and an optical fiber output with isolation protection is adopted. The single frequency continuous laser source generates an unmodulated laser signal, represented as:
E 0 (t)＝E 0 exp[j2πf 0 t+jφ N_SR (t)+jφ 0 ]；
in the formula ,f0 Is the carrier frequency of the laser light source; phi (phi) N_SR (t) is the noise phase of the laser source; phi (phi) 0 Initial phase for the output beam; e (E) 0 Is the output beam amplitude, t is the time,exp is an exponential function based on a natural constant e.
The frequency modulation signal generated by the frequency modulation signal generator and the fundamental frequency signal generated by the fundamental frequency signal generator are adopted, wherein the bandwidth of the frequency modulation signal generator is 1.2GHz, the frequency of the fundamental frequency signal generator is 10GHz, the output radio frequency signal drives the lithium niobate electro-optical modulator with the bandwidth of 10GHz, and the frequency modulation wave pattern is a symmetrical triangle. The frequency modulation signal and the fundamental frequency signal are mixed to obtain a radio frequency mixed signal, and the radio frequency mixed signal is expressed as:
wherein M is the amplification factor of the radio frequency circuit, V RF_M Is the amplitude of the frequency modulated signal, V RF_B Is the amplitude of the fundamental frequency signal,is the frequency modulation rate of the frequency modulated signal, denoted +. >f RF_B Is the frequency of the fundamental frequency signal, f RF_H Is the high frequency cut-off frequency of the frequency modulated signal, f RF_L Is the low frequency cut-off frequency of the frequency-modulated signal, T is the period of the frequency-modulated signal, B is the frequency-modulated bandwidth, phi N_RF (t) is the noise phase of the mixed signal; t is time;
the radio frequency mixed signal after radio frequency amplification is used as a radio frequency driving signal of a phase modulator to carry out phase modulation on an incident laser signal, and the generated modulated laser signal is:
wherein ,E0_PM Is the amplitude of the modulated laser signal output by the optical phase modulator; f (f) 0 Is the carrier frequency of the laser source; phi (phi) N_SR (t) is the noise phase introduced by the linewidth of the laser source; phi (phi) 0 Is the initial phase of the laser source output;is the frequency modulation rate of the frequency modulated signal; phi (phi) N_PM (t) is the phase of noise introduced by the optical phase modulator; phi (phi) N_RF (t) is the phase of noise introduced by the rf driver; beta is the phase modulation factor of the optical phase modulator, denoted +.>V π Is the half-wave voltage of the optical phase modulator; t is time, < >>exp is an exponential function based on a natural constant e;
the above equation is developed by the Bessel function:
wherein ,Jn Is a first class of n-order bessel functions, n=0, 1,2 …; frequency modulated carrier and sideband output by the optical phase modulator of figure 2 Schematic of the signal. Above J 0 Representing the optical carrier, the rest J n The term then represents a modulated sideband optical signal comprising a positive sideband and a negative sideband; the power of a single frequency continuous laser source is spread over n modulation sidebands whose amplitudes are controlled by the respective orders of the Bessel function of the first type with parameter beta, and carrier suppression is achieved by varying the amplitudes of the frequency modulated signal and the fundamental frequency signal.
The modulated laser signal is split into a first modulated optical signal and a second modulated optical signal by a first optical beam splitter (50/50);
as shown in fig. 3, the first modulated optical signal uses a first optical bandpass filter to filter the residual carrier and sidebands, the first optical bandpass filter uses a thermally tuned fiber bragg grating filter with a reflection mode, the center frequency is set to 193417.0GHz, the 3dB passband bandwidth of the filter is about 5GHz, and the side-to-side rejection ratio is greater than 25dB. Therefore, the positive first-order modulation sideband can be obtained, the frequency modulation bandwidth is 1.2GHz, the frequency modulation period is 10 mu s, the repetition frequency is 100kHz, the sawtooth wave linear modulation is adopted, the frequency of a modulation signal changes into sawtooth with time, and the positive frequency modulation is realized in one period. After passing through the first optical bandpass filter, the +k order single sideband optical signal is passed (as shown in fig. 4), denoted as:
wherein ,E1 Is the first modulated optical signal amplitude, denoted E 1 ＝J k (β)E 0_PM ，E 0_PM Is the amplitude of the modulated laser signal output by the optical phase modulator, J k (β) is a first class Bessel function representing k-th order, +k is the first bandpass filtered single sideband order, and β is the phase modulation factor of the optical phase modulator; t is time; f (f) 0 Is the carrier frequency of the laser light source;is the frequency modulation rate; t is a frequency modulation period; b is the frequency modulation bandwidth; phi (phi) N_SR (t) is the noise phase introduced by the linewidth of the laser source; phi (phi) N_PM (t) is the phase of noise introduced by the optical phase modulator; phi (phi) N_RF (t) is the noise phase introduced by the rf drive circuit; />Exp is an exponential function based on a natural constant e;
with phi N1 (t) represents the noise phase of the first modulated optical signal:
φ N1 (t)＝φ N_SR (t)+φ N_PM (t)+kφ N_RF (t)；
the first modulated optical signal after optical filtering is divided into a first transmitted optical signal and a first local oscillation optical signal by a first polarization controller and a second optical beam splitter (1/99), wherein a small part of energy is used as the first local oscillation optical signal, and the first local oscillation optical signal is time delay tau L1 The optical field is denoted as:
wherein ,ELO1 Is the first local oscillator optical signal amplitude;
the majority of energy of the first modulated optical signal with the adjusted polarization state is used as a first transmitted optical signal, the first transmitted optical signal and a second transmitted optical signal with the orthogonal polarization state are combined by a polarization beam combiner and amplified to 500mW by laser, the polarization extinction ratio is ensured to be larger than 25dB, the first transmitted optical signal is transmitted to a target by a polarization diversity optical circulator through an optical scanner (such as a MEMS scanner) and a transmitting/receiving optical telescope, and a first target echo signal returned from the target is time delay tau S1 The optical field is denoted as:
wherein ,ES1 Is the amplitude phi of the first echo optical signal N1_OA Is the noise phase of the first transmitted light signal due to the optical amplifier; phi (phi) NS1 Is the first echo light signal due to the targetNoise phase caused by factors such as speckle, atmospheric turbulence, vibration of an optical machine structure and the like;
time delay τ of first echo signal S1 Time delay τ with first local oscillator optical signal L1 Expressed as:wherein c is the speed of light, R is the target distance, and V is the radial speed of relative movement of the radar platform and the target;
as shown in fig. 3, the second modulated optical signal uses a second optical bandpass filter to filter the residual carrier and sidebands, the second optical bandpass filter uses a thermally tuned fiber bragg grating filter in reflection mode, and the center frequency is set to be such that the 3dB passband bandwidth of the filter is about 5GHz and the side-to-side rejection ratio is greater than 25dB. Therefore, the negative second-order modulation sideband can be obtained, the frequency modulation bandwidth is 1.2GHz, the frequency modulation period is 10 mu s, the repetition frequency is 100kHz, the sawtooth wave linear modulation is adopted, the frequency of a modulation signal changes into sawtooth with time, and the negative frequency modulation is realized in one period. The second optical bandpass filter passes the-k order single sideband optical signal (as shown in fig. 5), denoted as:
wherein ,E2 Is the second modulated optical signal amplitude, denoted E 2 ＝J k (β)E 0_PM ，E 0_PM Is the amplitude of the modulated laser signal output by the optical phase modulator, J k (β) is a first class Bessel function representing the k-th order, -k is the second bandpass filtered single sideband order, and β is the phase modulation factor of the optical phase modulator; t is time; f (f) 0 Is the carrier frequency of the laser light source;is the frequency modulation rate; t is a frequency modulation period; b is the frequency modulation bandwidth; phi (phi) N_SR (t) is the noise phase introduced by the linewidth of the laser source; phi (phi) N_PM (t) is the phase of noise introduced by the optical phase modulator; phi (phi) N_RF (t) is the noise phase introduced by the rf drive circuit;/>exp is an exponential function based on a natural constant e; />
With phi N2 (t) represents the noise phase of the second modulated optical signal:
φ N2 (t)＝φ N_SR (t)+φ N_PM (t)-kφ N_RF (t)；
the filtered second modulated optical signal is divided into a second transmitted optical signal and a second local oscillation optical signal by a second polarization controller and a third optical beam splitter (1/99), wherein a small part of energy is used as the second local oscillation optical signal, and the second local oscillation optical signal is time delay tau L2 The optical field is denoted as:
wherein ,ELO2 Is the first local oscillator optical signal amplitude;
the majority of the energy of the second modulated optical signal with the adjusted polarization state is taken as a second emitted optical signal, the second modulated optical signal and the first emitted optical signal with the orthogonal polarization state are combined through a polarization beam combiner (as shown in a spectrum measuring result shown in fig. 6), the polarization extinction ratio is ensured to be larger than 25dB after the laser is amplified to 500mW, the second modulated optical signal is transmitted to a target through an optical scanner (MEMS scanner) and a transmitting/receiving optical telescope after the polarization extinction ratio is ensured to be larger than 25dB through a polarization diversity optical circulator (as shown in fig. 7, a Mach-Zehnder structure polarization diversity optical circulator is adopted), and a second target echo signal returned from the target is time delay tau S2 The optical field is denoted as:
wherein ,ES2 Is the amplitude phi of the second echo optical signal N2_OA (t) is the noise phase of the second transmitted optical signal introduced by the optical amplifier; phi (phi) NS2 Is the second echo light signal due to the target dispersionNoise phase caused by factors such as specks, atmospheric turbulence, vibration of an optical machine structure and the like;
time delay τ of second echo optical signal S2 Time delay τ with second local oscillator optical signal L2 Expressed as:
since the first and second transmitted optical signals are transmitted and received coaxially, i.e. τ S1 ＝τ S2 ，τ L1 ＝τ L2 ThenThe first and second transmitted optical signals pass through the same optical amplifier and the introduced phase noise is the same, i.e. N_OA ＝φ N1_OA ＝φ N2_OA The method comprises the steps of carrying out a first treatment on the surface of the The two echo optical signals are affected by the target speckle, the atmospheric turbulence and the vibration of the optical-mechanical structure approximately the same, namely phi NS ＝φ NS1 ＝φ NS2 。
After the first echo signal and the second echo signal are obtained, coherent mixing is carried out, and first combined light obtained by combining the first echo signal and the first local oscillator light signal is expressed as:
the 4 paths of output of the first combined light after being mixed by the first optical bridge are respectively:
；
wherein ,representing Doppler shift caused by relative motion of the radar platform and the target;
then the first photoelectric balance detector (bandwidth 500MHz, alternating current coupling) receives, and after band-pass filtering (passband is 10MHz-500 MHz), a first orthogonal beat signal is obtained:
wherein ,σin_1 The response of the first photodetector, σ, being the I-channel qu_1 The response rate of the first photodetector, which is the Q channel;
and the second combined beam light obtained by combining the second echo signal and the second local oscillation optical signal is expressed as:
the 4 paths of output of the second combined light after being mixed by the second optical bridge are respectively:
wherein ,representing Doppler shift caused by relative motion of the radar platform and the target;
the second photoelectric balance detector (bandwidth 500MHz, alternating current coupling) receives, and after band-pass filtering (passband is 10MHz-500 MHz), the second orthogonal beat frequency signal is obtained as follows:
/>
wherein ,σin_2 The response of the second photodetector, σ, being the I-channel qu_2 The response rate of the second photodetector, which is the Q channel;
due to polarization diversity, crosstalk isolation is achieved between the first modulated optical signal and the second modulated optical signal by polarization, even though for some same polarization components, such as the first channel crosstalk signal into the second channel, can be expressed as:
the crosstalk signal is crosstalk isolated; and the coherently received output signal necessarily contains a frequency of 2kf RF_B If the fundamental frequency difference of the two modulated optical signals is far greater than Doppler frequency shift, the fundamental frequency difference is eliminated through low-pass filtering, so that crosstalk suppression is realized.
The four paths of beat frequency signals after the steps are sent into an analog signal processing unit for analog signal processing, and the steps are as follows:
first, the four-channel beat signal performs analog multiplication operation in pairs, expressed as:
let sigma in_1 σ in_2 ＝σ qu_1 σ qu_2 ＝σ in_1 σ qu_2 ＝σ qu_1 σ in_2 =Λ, and then performing a two-by-two analog addition and subtraction operation to obtain three analog channel output signals:
in the above, I a1 (t) is an amount including the target distance, I a2(t) and Ia3 (t) is the amount containing target Doppler information;
at I a1 In (t), the noise phase introduced by the linewidth of the laser light source, the noise phase introduced by the optical phase modulator, the noise phase output by the radio frequency amplifier and the target speckle noise are completely eliminated through symmetrical double-sideband modulation differential processingAnd atmospheric turbulence noise; and the noise phase introduced by the radio frequency mixer is suppressed by optimizing the radio frequency device.
After the output 3 paths of analog signals are subjected to analog-to-digital conversion, a digital signal processing unit (field programmable gate array (FPGA)) is used for carrying out Fast Fourier Transform (FFT) processing on the obtained samples, so that the parallel synchronous measurement of the distance and the speed of a remote scattering target can be realized, specifically:
performing fast Fourier transform on the beat frequency signal of the first analog channel, and extracting the position of a frequency spectrum peak value by a gravity center method to obtain an intermediate frequency f IF1 ；
The second analog channel and the third analog channel are obtained by multiplexing:
the complex beat frequency signal is subjected to fast Fourier transformation, and the position of a frequency spectrum peak value is extracted through a gravity center method to obtain an intermediate frequency f IF2 ；
The two intermediate frequencies are respectively expressed as:
the magnitude and direction of the radial velocity of the relative motion of the radar platform and the target are obtained by the method, and are expressed as follows:wherein positive values represent the radar platform moving towards the target and negative values represent the radar platform moving away from the target;
the distance between the laser radar and the target point is also obtained by the following steps:
while ranging resolution is expressed as:
the speed measurement resolution is expressed as:
in this embodiment, an external trigger circuit is used to synchronously trigger the frequency modulation signal and the fundamental frequency signal, so as to realize modulation phase synchronization.
Through experiments, the laser radar system of the embodiment has the ranging resolution of 12.5cm and the speed measuring resolution of 0.155m/s.
In summary, the method of unified modulation and symmetric order filtering is adopted in the invention, positive and negative double-chirp orthogonal polarization laser signals modulated by symmetric sidebands are synchronously generated, then orthogonal beat signals are respectively generated through respective coherent reception, and analog signal processing is carried out on the double-orthogonal beat signals, so that the effect is that the noise phase introduced by the line width of a laser light source, the noise phase introduced by an optical phase modulator, the noise phase output by a radio frequency amplifier, target speckle noise, atmospheric turbulence noise and vibration noise of an optical machine structure can be completely eliminated through differential processing, the ranging precision can be improved, the ranging sensitivity can be improved, the ranging range can be improved, the emission repetition frequency can be improved, and the parallel synchronous ranging and speed measurement can be realized. Therefore, the invention has the advantages of high ranging precision, good sensitivity and strong anti-interference capability, can realize the high-precision ranging of a long-distance scattering target, and has the function of speed measurement. Has good development prospect in the fields of airborne and spaceborne surveying and mapping radars and the like.

Claims (8)

1. The symmetrical double-sideband modulated differential frequency modulation continuous wave laser radar method is characterized in that: at the transmitting end of the radar platform, an optical signal generated by a single-frequency continuous laser source firstly passes through an optical phase modulator, a frequency modulation signal is mixed with a fundamental frequency signal to obtain a radio frequency mixing signal, and the radio frequency mixing signal is used as a driving signal of the optical phase modulator to carry out phase modulation on the optical signal to generate a modulated laser signal; the modulated laser signals are divided into a first modulated optical signal and a second modulated optical signal through a first optical beam splitter, the first modulated optical signal and the second modulated optical signal are respectively subjected to optical bandpass filtering and then respectively synchronously generate positive and negative double-chirp laser signals modulated by symmetrical sidebands, and the positive and negative double-chirp laser signals respectively generate two modulated lights in orthogonal polarization states through a polarization controller; the two modulated light beams are respectively split to respectively obtain a first transmitting light signal and a first local oscillator light signal and a second transmitting light signal and a second local oscillator light signal; the first emission optical signal and the second emission optical signal enter a laser amplifier after polarization beam combination, and the two amplified emission optical signals are emitted to a target through a common optical device and two echo beams are received; at the receiving end of the radar platform, the returned two paths of echo light beams are respectively subjected to coherent mixing with the corresponding first local oscillator optical signals and second local oscillator optical signals after passing through the polarization diversity circulator, then the four-channel photoelectric balance detector is respectively used for receiving and obtaining orthogonal beat frequency signals containing target distance and vector speed information, the two paths of orthogonal beat frequency signals are subjected to analog signal processing to realize differential elimination of phase noise, and then the parallel synchronous measurement of the distance and the vector speed between the radar platform and the target is realized through ADC sampling and digital signal processing.
2. The symmetric double sideband modulated differential frequency modulated continuous wave laser radar method of claim 1 wherein: the single frequency continuous laser source generates an unmodulated laser signal, represented as:
E 0 (t)＝E 0 exp[j2πf 0 t+jφ N_SR (t)+jφ 0 ]；
in the formula ,f0 Is the carrier frequency of the laser light source; phi (phi) N_SR (t) is the noise phase of the laser source; phi (phi) 0 Initial phase for the output beam; e (E) 0 Is the output beam amplitude, t is the time,exp is an exponential function based on a natural constant e.
3. The symmetric double sideband modulated differential frequency modulated continuous wave laser radar method of claim 2 wherein: the frequency modulation signal generated by the frequency modulation signal generator, the fundamental frequency signal generated by the fundamental frequency signal generator, the frequency modulation signal and the fundamental frequency signal are mixed to obtain a radio frequency mixed signal, and the radio frequency mixed signal is expressed as:
wherein M is the amplification factor of the radio frequency circuit, V RF_M Is the amplitude of the frequency modulated signal, V RF_B Is the amplitude of the fundamental frequency signal,is the frequency modulation rate of the frequency modulated signal, denoted +.>f RF_B Is the frequency of the fundamental frequency signal, f RF_H Is the high frequency cut-off frequency of the frequency modulated signal, f RF_L Is the low frequency cut-off frequency of the frequency-modulated signal, T is the period of the frequency-modulated signal, B is the frequency-modulated bandwidth, phi N_RF (t) is the noise phase of the mixed signal; t is time;
The radio frequency mixed signal after radio frequency amplification is used as a radio frequency driving signal of an optical phase modulator to carry out phase modulation on an incident laser signal, and the generated modulated laser signal is:
wherein ,E0_PM Is the amplitude of the modulated laser signal output by the optical phase modulator; f (f) 0 Is the carrier frequency of the laser source; phi (phi) N_SR (t) is the noise phase introduced by the linewidth of the laser source; phi (phi) 0 Is the initial phase of the laser source output;is the frequency modulation rate of the frequency modulated signal; phi (phi) N_PM (t) is the phase of noise introduced by the optical phase modulator; phi (phi) N_RF (t) is the phase of noise introduced by the rf driver; beta is the phase modulation factor of the optical phase modulator, denoted +.> wherein Vπ Is the half-wave voltage of the optical phase modulator; t is time, < >>exp is an exponential function based on a natural constant e;
the above equation is developed by the Bessel function:
wherein ,Jn Is a first class of n-order bessel functions, n=0, 1,2 …; wherein J 0 Representing the optical carrier, the rest J n The term then represents a modulated sideband optical signal comprising a positive sideband and a negative sideband; the power of a single frequency continuous laser source is spread over n modulation sidebands whose amplitudes are controlled by the respective orders of the Bessel function of the first type with parameter beta, and carrier suppression is achieved by varying the amplitudes of the frequency modulated signal and the fundamental frequency signal.
4. The symmetric double sideband modulated differential frequency modulated continuous wave laser radar method of claim 1 wherein: the modulated laser signal is divided into a first modulated optical signal and a second modulated optical signal through a first optical beam splitter;
the first modulated optical signal filters the residual carrier and the sidebands by using a first optical bandpass filter, so that +k-order sideband optical signals pass through, and the method is expressed as follows:
wherein ,E1 Is the first modulated optical signal amplitude, denoted E 1 ＝J k (β)E 0_PM ，E 0_PM Is the amplitude of the modulated laser signal output by the optical phase modulator, J k (beta) is a Bessel function of the first class representing the k-order, +k is the first bandpass filtered single sideband orderBeta is the phase modulation factor of the optical phase modulator; t is time; f (f) 0 Is the carrier frequency of the laser light source;is the frequency modulation rate; t is a frequency modulation period; b is the frequency modulation bandwidth; phi (phi) N_SR (t) is the noise phase introduced by the linewidth of the laser source; phi (phi) N_PM (t) is the phase of noise introduced by the optical phase modulator; phi (phi) N_RF (t) is the noise phase introduced by the rf drive circuit; />exp is an exponential function based on a natural constant e;
with phi N1 (t) represents the noise phase of the first modulated optical signal:
φ N1 (t)＝φ N_SR (t)+φ N_PM (t)+kφ N_RF (t)；
the first modulated optical signal after optical filtering is divided into a first transmitted optical signal and a first local oscillation optical signal by a first polarization controller and a second optical beam splitter, wherein a small part of energy is used as the first local oscillation optical signal, and the first local oscillation optical signal is time delay tau L1 The optical field is denoted as:
wherein ,ELO1 Is the first local oscillator optical signal amplitude;
the majority of energy of the first modulated optical signal with the adjusted polarization state is used as a first transmitted optical signal, the first modulated optical signal and a second transmitted optical signal with the orthogonal polarization state are combined and amplified by a polarization beam combiner, and then transmitted to a target through an optical scanner and a transmitting/receiving optical telescope by a polarization diversity optical circulator, and a first target echo signal returned from the target is time delay tau S1 The optical field is denoted as:
wherein ,ES1 Is the amplitude phi of the first echo optical signal N1_OA Is the noise phase of the first transmitted light signal due to the optical amplifier; phi (phi) NS1 Is the noise phase of the first echo optical signal caused by target speckle, atmospheric turbulence and optical-mechanical structure vibration factors;
time delay τ of first echo signal S1 Time delay τ with first local oscillator optical signal L1 Expressed as:
wherein c is the speed of light, R is the target distance, and V is the radial speed of relative movement of the radar platform and the target;
the second modulated optical signal filters the residual carrier and sidebands using a second optical bandpass filter to pass the-k order sideband optical signal, expressed as:
wherein ,E2 Is the second modulated optical signal amplitude, denoted E 2 ＝J k (β)E 0_PM ，E 0_PM Is the amplitude of the modulated laser signal output by the optical phase modulator, J k (β) is a first class Bessel function representing the k-th order, -k is the second bandpass filtered single sideband order, and β is the phase modulation factor of the optical phase modulator; t is time; f (f) 0 Is the carrier frequency of the laser light source;is the frequency modulation rate; t is a frequency modulation period; b is the frequency modulation bandwidth; phi (phi) N_SR (t) is the noise phase introduced by the linewidth of the laser source; phi (phi) N_PM (t) is the phase of noise introduced by the optical phase modulator; phi (phi) N_RF (t) is radio frequency driven electricityNoise phase introduced by the road; />exp is an exponential function based on a natural constant e;
with phi N2 (t) represents the noise phase of the second modulated optical signal:
φ N2 (t)＝φ N_SR (t)+φ N_PM (t)-kφ N_RF (t)；
the second modulated optical signal after optical filtering is divided into a second transmitted optical signal and a second local oscillation optical signal by a second polarization controller and a third optical beam splitter, wherein a small part of energy is used as the second local oscillation optical signal, and the second local oscillation optical signal is time delay tau L2 The optical field is denoted as:
wherein ,ELO2 Is the first local oscillator optical signal amplitude;
the majority of energy of the second modulated optical signal with the adjusted polarization state is used as a second transmitted optical signal, the second transmitted optical signal with the orthogonal polarization state and the first transmitted optical signal are combined and amplified by a polarization beam combiner, and then transmitted to a target through an optical scanner and a transmitting/receiving optical telescope by a polarization diversity optical circulator, and a second target echo signal returned from the target is time delay tau S2 The optical field is denoted as:
wherein ,ES2 Is the amplitude phi of the second echo optical signal N2_OA (t) is the noise phase of the second transmitted optical signal introduced by the optical amplifier; phi (phi) NS2 Is the noise phase of the second echo optical signal caused by target speckle, atmospheric turbulence and optical-mechanical structure vibration factors;
second oneTime delay τ of a return wave optical signal S2 Time delay τ with second local oscillator optical signal L2 Expressed as:
since the first and second transmitted optical signals are transmitted and received coaxially, i.e. τ S1 ＝τ S2 ，τ L1 ＝τ L2 Then
The first and second transmitted optical signals pass through the same optical amplifier and the introduced phase noise is the same, i.e. N_OA ＝φ N1_OA ＝φ N2_OA The method comprises the steps of carrying out a first treatment on the surface of the The two echo optical signals are affected by target speckle, atmospheric turbulence, optical-mechanical structure vibration and other factors approximately the same, namely phi NS ＝φ NS1 ＝φ NS2 。
5. The symmetric double sideband modulated differential frequency modulated continuous wave laser radar method of claim 1 wherein: the coherent mixing is that a first combined beam light obtained by combining the first echo optical signal and the first local oscillation optical signal is expressed as follows:
the 4 paths of output of the first combined light after being mixed by the first optical bridge are respectively:
wherein ,indicating lightningAchieving Doppler shift caused by relative motion between the platform and the target;
Then the first photoelectric balance detector receives the signal, and after band-pass filtering, a first orthogonal beat frequency signal is obtained:
wherein ,σin_1 The response of the first photodetector, σ, being the I-channel qu_1 The response rate of the first photodetector, which is the Q channel;
and the second combined beam light obtained by combining the second echo signal and the second local oscillation optical signal is expressed as:
the 4 paths of output of the second combined light after being mixed by the second optical bridge are respectively:
wherein ,representing Doppler shift caused by relative motion of the radar platform and the target;
the second photoelectric balance detector receives the second orthogonal beat signal, and the second orthogonal beat signal is obtained after band-pass filtering:
wherein ,σin_2 The response of the second photodetector, σ, being the I-channel qu_2 The response rate of the second photodetector, which is the Q channel;
due to polarization diversity, crosstalk isolation is realized between the first modulated optical signal and the second modulated optical signal through polarization, and if the fundamental frequency difference of the two modulated optical signals is far greater than Doppler frequency shift, crosstalk suppression is realized through low-pass filtering.
6. The symmetric double sideband modulated differential frequency modulated continuous wave laser radar method of claim 5 wherein: the analog signal processing steps are as follows:
First, the four-channel beat signal performs analog multiplication operation in pairs, expressed as:
let sigma in_1 σ in_2 ＝σ qu_1 σ qu_2 ＝σ in_1 σ qu_2 ＝σ qu_1 σ in_2 =Λ, and then performing a two-by-two analog addition and subtraction operation to obtain three analog channel output signals:
in the above, I a1 (t) is an amount including the target distance, I a2(t) and Ia3 (t) is the amount containing target Doppler information;
at I a1 In (t), through symmetrical double-sideband modulation differential processing, the noise phase introduced by the linewidth of the laser light source, the noise phase introduced by the optical phase modulator, the noise phase output by the radio frequency amplifier, the target speckle noise, the atmospheric turbulence noise and the vibration noise of the optical machine structure are completely eliminated; the remaining noise phase introduced by the rf driver circuit is suppressed by optimizing the rf device.
7. The symmetric double sideband modulated differential frequency modulated continuous wave laser radar method of claim 6 wherein: the parallel synchronous measurement of the distance and the vector speed between the radar platform and the target is as follows:
performing fast Fourier transform on the beat frequency signal of the first analog channel, and extracting the position of a frequency spectrum peak value by a gravity center method to obtain an intermediate frequency f IF1 ；
The second analog channel and the third analog channel are obtained by multiplexing:
the complex beat frequency signal is subjected to fast Fourier transformation, and the position of a frequency spectrum peak value is extracted through a gravity center method to obtain an intermediate frequency f IF2 ；
The two intermediate frequencies are respectively expressed as:
the magnitude and direction of the radial velocity of the relative motion of the radar platform and the target are obtained by the method, and are expressed as follows:
wherein positive values represent the radar platform moving towards the target and negative values represent the radar platform moving away from the target;
the distance between the laser radar and the target point is also obtained by the following steps:
while ranging resolution is expressed as:
the speed measurement resolution is expressed as:
8. an apparatus for implementing the symmetric double-sideband modulated differential frequency modulated continuous wave laser radar method of any one of claims 1-7, characterized in that: comprises a single-frequency connection laser light source (1), wherein the single-frequency connection laser light source (1) is connected with an optical phase modulator (2); the optical phase modulator (2) is respectively connected with a first optical beam splitter (3) and a radio frequency amplifier (4); the radio frequency amplifier (4) is connected with a radio frequency mixer (5), and the radio frequency mixer (5) is connected with a frequency modulation signal generator (6) and a fundamental frequency signal generator (7); the first optical beam splitter (3) is respectively connected with a first optical band-pass filter (8) and a second optical band-pass filter (9); the first optical band-pass filter (8) is connected with a second optical beam splitter (11) through a first polarization controller (10); the second optical band-pass filter (9) is connected with a third optical beam splitter (13) through a second polarization controller (12); the second optical beam splitter (11) and the third optical beam splitter (13) are connected with a polarization beam combiner (14), the polarization beam combiner (14) is connected with a polarization diversity optical circulator (16) through a laser amplifier (15), and the polarization diversity optical circulator (16) is connected with a transmitting and receiving telescope (18) through an optical scanner (17); the second optical beam splitter (11) and the polarization diversity optical circulator (16) are connected with a first optical bridge (19), and the first optical bridge (19) is connected with a first band-pass filter (21) through a first photoelectric balance detector (20); the third optical beam splitter (13) and the polarization diversity optical circulator (16) are connected with a second optical bridge (22), and the second optical bridge (22) is connected with a second band-pass filter (24) through a second photoelectric balance detector (23); the first band-pass filter (21) and the second band-pass filter (24) are connected with an analog signal processing unit (25) together, the analog signal processing unit (25) is connected with three analog-to-digital converters (26), the three analog-to-digital converters (26) are connected with a digital signal processing unit (27) together, and the digital signal processing unit (27) is connected with an upper computer (28); the digital signal processing unit (27) is connected with an external trigger circuit (29), and the external trigger circuit (29) is respectively connected with the frequency modulation signal generator (6) and the fundamental frequency signal generator (7); the digital signal processing unit (27) is also connected to the optical scanner (17).
CN202310044822.9A 2023-01-30 2023-01-30 Symmetrical double-sideband modulation differential frequency modulation continuous wave laser radar method and device Pending CN116819546A (en)

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