CN110780310A - Polarization diversity dual-channel speed measuring and distance measuring coherent laser radar measuring method and device - Google Patents

Polarization diversity dual-channel speed measuring and distance measuring coherent laser radar measuring method and device Download PDF

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CN110780310A
CN110780310A CN201911410110.4A CN201911410110A CN110780310A CN 110780310 A CN110780310 A CN 110780310A CN 201911410110 A CN201911410110 A CN 201911410110A CN 110780310 A CN110780310 A CN 110780310A
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polarization
speed
light beam
ranging
beam splitter
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CN110780310B (en
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职亚楠
孙建锋
潘卫清
田克汉
戴恩文
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Sun Jianfeng
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Hangzhou Erae Technology 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
    • 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
    • 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

Abstract

The invention discloses a polarization diversity dual-channel speed measurement and distance measurement coherent laser radar measuring method and a device, wherein a laser light source output light beam is divided into a speed measurement light beam and a distance measurement light beam which are orthogonally polarized by a first polarization beam splitter; the speed measurement light beam adopts orthogonal demodulation coherent homodyne Doppler laser to measure speed; the ranging light beam adopts pseudo-random code high-speed phase modulation laser ranging; the invention realizes high-precision synchronous measurement of the speed and the distance of a long-distance target through polarization diversity. The invention can synchronously measure the speed and the distance of the target, has very excellent accuracy of measuring the speed and the distance, and has the advantages of miniaturization of the whole system, easy operation and good development prospect.

Description

Polarization diversity dual-channel speed measuring and distance measuring coherent laser radar measuring method and device
Technical Field
The invention relates to the technical field of laser ranging and speed measurement, in particular to a polarization diversity dual-channel speed measurement and ranging coherent laser radar measurement method and device 。
Background
The environment sensing technology is an important component of the autonomous driving platform, and is used for sensing the surrounding environment by using sensors such as a laser radar and a millimeter wave radar and providing decision basis for the autonomous driving platform. The laser radar technology, one of the key core technologies, can effectively provide information required by a decision and control system of an autonomous driving platform, and has become an indispensable sensor for autonomous driving environment perception at present. The distance and the speed of the target are important information for judging the external environment by the autonomous driving platform, and are indispensable parts for realizing intelligent driving in a complex dynamic environment. The laser radar is used for realizing synchronous measurement of the target distance and the target speed, has high real-time performance and measurement precision, is an urgent need for autonomous driving environment perception, and has important significance for improving the perception capability of an autonomous driving platform to the surrounding environment and enhancing the intelligent decision-making capability.
The current commercialized laser radar generally adopts a single pulse laser Time of Flight (Time of Flight) ranging method, has the advantages of simple structure and mature technology, has the defects that only the distance information of a target can be provided, and the speed is obtained by differential calculation according to the change of distance measurement data. The conventional speed measurement method cannot obtain correct speed information due to the discontinuity of distance, and the obtained speed data has a very large error and lacks real-time performance.
One of the prior arts (see zhou yan, wang chong, liu yanping, xia hai yun, coherent wind lidar research progress and application, progress in laser and optoelectronics, 2019, vol. 56, number 2, 020001) a coherent wind doppler lidar emits a laser pulse with a certain width, a pulse window covers one period of a doppler signal, and doppler signal frequencies at different distances are obtained through fourier transform, so as to analyze the speed of a target.
The chirp frequency modulation continuous wave laser radar performs linear modulation on the frequency of transmitted laser, coherent reception is performed on echo signals and local oscillation signals, distance measurement of a target is achieved by acquiring heterodyne frequency, and Doppler velocity measurement is achieved by waveform modulation. This is the most widely used laser radar system for synchronous speed and distance measurement at present, and is typically the doppler laser radar in the aloat project of NASA in the united states (see f, Amzajerdian, d, Pierrottet, l, petway, et al, Lidar systems for precision navigation and safety networking systems, NASA, 2011.) and can realize high-precision spatial target synchronous distance and speed measurement by adopting optical coherence technology, isosceles triangle wave linear frequency modulation technology, and fiber optics technology.
In order to further improve the accuracy of ranging and velocity measurement, the Langley Research Center of NASA improves the modulation waveform into symmetrical isosceles trapezoid chirp (see f. Amzajerdian, d. Pierrottet, l. petway, et al. Lidar sensors for autonomous and halyard amplitude, aiaa Space Conference Proceedings, 2013.) including up-conversion, fixed frequency and down-conversion, doppler velocity can be obtained in the fixed frequency stage, the data loss caused by the fact that the frequency obtained in the up-conversion and down-conversion stages is very close to zero can be solved, and the measurement ambiguity in some cases can be reduced. However, the chirp frequency modulation continuous wave laser radar usually adopts an external cavity tunable laser to generate linear frequency modulation laser pulse, and is limited by the hardware condition of the laser, so that the cost is very high; the Pulse Repetition Frequency (PRF) is severely limited given the large tuning range available to achieve high range resolution; the frequency modulation nonlinearity brought by large-range frequency sweep is still an unsolved problem, and the accuracy of speed measurement and distance measurement is seriously influenced.
Wu army et al propose a dual-frequency dual-modulation dual-local-oscillator symmetric triangular chirp coherent ranging and speed measuring laser radar system, which expands the range of the symmetric triangular chirp ranging and speed measuring system and has high detection repetition frequency (in the fourth of the prior art, Wu army, Hongguang, He Zhi Ping, Shurong, a large-ranging dynamic range high-repetition frequency coherent ranging and speed measuring laser radar (I) system and performance, infrared and millimeter wave academic report, 2014, Vol.33, No.6, 680-. But greatly increases the complexity of the system and influences the application prospect.
Chirp amplitude modulation continuous wave lidar makes linear frequency modulation on the amplitude of transmitted laser, mixes the delayed chirp modulated on the echo intensity with the initial chirp during transmission to obtain a difference frequency proportional to the echo delay, and can realize synchronous detection of the distance and speed of the target through coherent reception (five in the prior art, howling, surging, rong, and shurong, and zero difference detection of distance and speed by chirp amplitude modulation lidar, optics report, 2011, vol.31, No.6, 0606002). Because the chirp signal is modulated on the laser intensity instead of being directly modulated on the laser frequency, the technical difficulty is low, the realization is easy, and the linearity can be better; the distance information of the target is reflected on the amplitude of the laser echo, the speed information is reflected on the frequency domain of the laser echo, and the interference of the two kinds of information is avoided optically. But limits the furthest detectable range of chirped amplitude modulated lidar due to attenuation of the transmitted laser energy caused by modulation in amplitude. Moreover, the pulse repetition frequency of the chirped amplitude modulation continuous wave lidar is still limited, and the range ambiguity caused by high repetition frequency cannot be eliminated.
The Complex optical field coherent laser radar adopts an electro-optic in-phase-quadrature modulator at a transmitting end to realize Complex optical field modulation of carrier suppression, can obtain flexible frequency band modulation, measures speed through a continuous wave without modulation, and measures distance through linear frequency modulation, thereby realizing high-precision target speed and distance synchronous measurement (sixth of the prior art, Shuang Gao, MaguriceO' Sullivan, and Rongqin Hui, Complex-optical-field Lidar system for ranging and vector velocity measurement, Optics Express, 2012, Vol.20, No.23, 25867 and 25875.). The modulation can be regarded as an improvement of the chirped frequency modulation continuous wave laser radar, the requirement on laser source hardware is reduced, but the modulation scheme is complex, the realization difficulty is high, and the application prospect is limited.
Maureson and the like insert a periodic code into a pseudo-random code to form a modulation code, the amplitude of a laser radar transmitting signal is modulated by using the modulation code, and a receiving end measures a target distance by calculating a correlation function of a target echo signal and a local modulation code on one hand, and analyzes the speed of a Doppler frequency measurement target by sampling a heterodyne signal of a periodic code time slot on the other hand, thereby realizing synchronous measurement of the target distance and the speed (seven in the prior art, Xuesong Mao, Daisuke Inoue, HiroyukiMatsubara, and Manabu Kagami, demodulation of in-car Doppler laser radar 1.55 μm for range and speed measurement, IEEE Transactions on Intelligent transport Systems, 2013, VOL. 14, number 2, 599-. However, the modulation code is formed by inserting a pseudo random code into a periodic code, which reduces the correlation of the pseudo random code on the one hand and has a limited range for speed measurement on the other hand. In order to improve the correlation of modulation codes and expand the range of velocity measurement, Mao Xuezong and the like propose to perform amplitude correction on Doppler signals and then use a non-equidistant sampling Fourier spectrum analysis method to obtain Doppler frequency. However, the signal-to-noise ratio of the algorithm is high, the head position of the doppler signal needs to be determined through the distance calculation process to ensure that the sampling sequence is the doppler signal mixed with noise instead of pure noise, the process is complex, the calculation amount is large, and the speed measurement accuracy is limited.
In conclusion, the existing laser radar technology has the problems of low distance resolution and limited speed measurement precision, and the whole system is complex and has high operation difficulty, so that the application prospect is limited.
Disclosure of Invention
The invention aims to provide a method and a device for measuring a polarization diversity dual-channel speed measurement and distance measurement coherent laser radar. The invention can synchronously measure the speed and the distance of the target, has high precision and good stability, has miniaturized whole system, easy operation and good development prospect, and in addition, the invention also utilizes the speed measurement result to feed back and control the frequency shift quantity, overcomes the influence of Doppler frequency shift generated by the relative motion of the target and the laser radar in the distance measurement process, and greatly improves the accuracy of the distance measurement.
The technical scheme of the invention is as follows: a coherent laser radar measuring method for measuring speed and distance of dual channels of polarization diversity comprises the steps that a laser light source outputs a beam, and the beam is divided into a speed measuring beam and a distance measuring beam in orthogonal polarization states by a first polarization beam splitter;
dividing a speed measurement light beam into a speed measurement local oscillator light beam and a speed measurement emission light beam with the same polarization through a first polarization beam splitter, enabling an echo light beam emitted by the speed measurement emission light beam to a target to obtain an echo speed measurement light beam with the same polarization through a third polarization beam splitter, enabling the speed measurement local oscillator light beam and the echo speed measurement light beam to enter a first optical bridge for orthogonal coherent reception to obtain an in-phase signal and an orthogonal signal with orthogonal characteristics, performing Fourier transform on the in-phase signal and the orthogonal signal to obtain a Doppler frequency spectrum, performing cross-spectrum processing to obtain an imaginary part, extracting the position and the positive and negative of a peak value in the Doppler frequency spectrum by using a gravity center method, and analyzing the position and the positive and negative of the Doppler peak value to obtain the size;
dividing the ranging light beam into a ranging local oscillator light beam and a ranging emission light beam with the same polarization through a second polarization-maintaining beam splitter, carrying out phase modulation on the ranging emission light beam through a pseudo-random code signal generated by a waveform generator, then obtaining an echo ranging light beam with the same polarization through a third polarization beam splitter by an echo light beam emitted to a target, and enabling the ranging local oscillator light beam and the echo ranging light beam to enter a second optical bridge for coherent reception to obtain a coherent reception signal; pseudo-random code signals and coherent receiving signals generated by a waveform generator are synchronously received by a data collector, and two paths of synchronously received signals are subjected to correlation processing in a main control computer to obtain target distance information;
the second polarization-maintaining beam splitter is connected with a frequency shifter, the frequency shifter is connected with the second optical bridge, and the frequency shifter is connected with a main control computer through a radio frequency driver; the main control computer obtains Doppler frequency shift generated by relative motion of the laser radar and the target by using the position and the positive and negative of the obtained Doppler frequency spectrum peak value, and then drives the frequency shifter to adjust the frequency shift amount of the ranging local oscillator light beam according to the information of the Doppler frequency shift, so that the influence of the Doppler frequency shift generated by the relative motion between the laser radar and the target is eliminated, and the ranging precision is improved.
In the above polarization diversity dual-channel speed measurement and distance measurement coherent laser radar measurement method, the speed measurement local oscillator light beam and the echo speed measurement light beam enter the first optical bridge for orthogonal coherent reception, and the light field is expressed as:
Figure DEST_PATH_IMAGE002
；
wherein is the target distance, is the laser carrier frequency, is the doppler shift caused by the target velocity,
Figure DEST_PATH_IMAGE010
it is the speed of light that is, the phase of the echo speed measurement light beam is the noise phase of the speed measurement local oscillator light beam; (ii) a Is the time; is the echo velocimetry light beam amplitude; measuring the amplitude of the local oscillator light beam;
the four outputs after the frequency mixing by the first optical bridge are respectively:
，
wherein
Figure DEST_PATH_IMAGE026
Is a mixing noise phase;
Figure DEST_PATH_IMAGE028
is the direct current quantity related to the echo speed measuring light beam;
Figure DEST_PATH_IMAGE030
the direct current quantity related to the speed measurement local oscillator light beam;
the in-phase signal and the orthogonal signal with the orthogonal characteristic are received by the low-speed photoelectric balanced detector, and the in-phase signal and the orthogonal signal output are respectively as follows:
Figure DEST_PATH_IMAGE032
；
wherein Is the photo-balanced detector responsivity of the in-phase signal,
Figure DEST_PATH_IMAGE036
is the photoelectric balance detector responsivity of the quadrature signal,
Figure DEST_PATH_IMAGE038
and
Figure DEST_PATH_IMAGE040
the noise phase of the in-phase signal and the quadrature signal, respectively.
According to the polarization diversity dual-channel speed measurement and ranging coherent laser radar measuring method, the in-phase signal and the orthogonal signal are output and enter a main control computer after being subjected to analog-to-digital conversion, the in-phase signal and the orthogonal signal are subjected to fast Fourier transform respectively, and the Fourier transform of the in-phase signal is expressed as follows:
Figure DEST_PATH_IMAGE042
；
the orthogonal signal fourier transform is represented as:
；
after Fourier transform, the frequency spectrum information only contains target Doppler information;
performing cross-spectrum processing on the two channels:
；
finally, only the imaginary part is taken to obtain
Figure DEST_PATH_IMAGE048
；
The Doppler shift is proportional to the velocity of the target motion, denoted as
Wherein the content of the first and second substances, is the target radial velocity of the beam of light,
Figure DEST_PATH_IMAGE054
is the light source emission wavelength;
and finally obtaining the size and the direction of the radial velocity of the target by analyzing the position, the positive and the negative of the peak value of the Doppler frequency spectrum, thereby realizing the velocity measurement of the target.
In the foregoing method for measuring a polarization diversity dual-channel speed and distance measuring coherent lidar, the pseudo-random code signal is:
Figure DEST_PATH_IMAGE056
；
wherein the content of the first and second substances, is the pseudo random code sequence symbol width of the pseudo random code signal,
Figure DEST_PATH_IMAGE060
is the number of the code element,
Figure DEST_PATH_IMAGE062
is the total number of symbols,
Figure DEST_PATH_IMAGE064
is a pseudo random number, and takes the value of 0 or 1;
the main characteristics of a pseudorandom code signal are its autocorrelation function:
Figure DEST_PATH_IMAGE066
；
the autocorrelation function of the pseudo-random code is a sharp pulse sequence, and the smaller the pulse width is, the sharper the waveform is;
the cross-correlation properties of the pseudo-random code signals are:
Figure DEST_PATH_IMAGE068
；
wherein, P 1And P 2Two independent pseudo-random code sequences;
the echo ranging light beam is as follows:
Figure DEST_PATH_IMAGE070
；
wherein is the target distance, is the laser carrier frequency, is the doppler shift caused by the target velocity, it is the speed of light that is, is the noise phase of the echo ranging beam; (ii) a
Figure DEST_PATH_IMAGE083
Is the time; ranging the amplitude of the beam for the echo;
the ranging local oscillator beam is
Figure DEST_PATH_IMAGE087
；
Figure DEST_PATH_IMAGE089
Is the noise phase of the ranging local oscillator beam,
Figure DEST_PATH_IMAGE091
is the amount of frequency shift;
Figure DEST_PATH_IMAGE093
measuring the amplitude of the local oscillator light beam;
the two paths of outputs after the ranging local oscillator light beam and the echo ranging light beam enter the second optical bridge for frequency mixing are respectively as follows:
，
Figure DEST_PATH_IMAGE096
the noise phase after frequency mixing is direct current quantity related to the echo ranging beam and is direct current quantity related to the ranging local oscillator beam;
the two paths of output are received and output by a high-speed photoelectric balance detector, and the output is as follows:
；
Figure DEST_PATH_IMAGE104
is the responsivity of a high-speed photoelectric balance detector, is the noise phase output by the high-speed photoelectric balance detector;
order to
Figure DEST_PATH_IMAGE108
The following can be obtained:
；
wherein
Figure DEST_PATH_IMAGE112
Is the amplitude;
due to the fact that The coherent receiving signal is obtained by simplifying the above formula according to the characteristics of cosine signals, wherein the sequence is a series of sequences of 0 and pi, namely the cosine signals have random change of phase pi:
Figure DEST_PATH_IMAGE116
；
wherein
Figure DEST_PATH_IMAGE118
，
Figure DEST_PATH_IMAGE119
Is a pseudo random number and takes a value of 1 or-1.
In the method for measuring the polarization diversity dual-channel speed measurement and distance measurement coherent laser radar, the pseudo-random code signal and the coherent receiving signal are subjected to analog-to-digital conversion and then enter a main control computer for correlation processing: in which the pseudo-random code signals are shifted in sequence
Figure DEST_PATH_IMAGE121
And multiplied by the coherent received signal to obtain:
Figure DEST_PATH_IMAGE123
；
during the duration of the pulse signal The internal integration can be obtained as follows:
；
as can be seen from the nature of the sinc function,
Figure DEST_PATH_IMAGE129
the higher the value of (A), the lower the height of the peak of the correlation function, at When n is an integer, the peak value of the correlation function is zero; in the same way
Figure DEST_PATH_IMAGE133
In this case, the longer the duration of the phase encoding pulse, the greater the influence of the doppler shift on the correlation result;
get
Figure DEST_PATH_IMAGE135
Fast Fourier transform of the compensated correlation functionThe Fourier transform spectrum has no obvious peak when the time of the code element of the shift delay is not related to the time delay caused by the target motion; when the symbol time of the shift delay coincides with the amount of delay caused by the target motion, the fourier transform spectrum has a significant peak at the intermediate frequency; thereby, the number of delay symbols corresponding to the maximum peak value of the Fourier transform spectrum
Figure DEST_PATH_IMAGE137
Obtaining target distance information:
the target distance is:
Figure DEST_PATH_IMAGE139
thereby improving the precision of distance measurement;
since the high-speed pseudo-random code modulation is performed in a wide pulse, so that the range resolution of the system does not depend on the pulse width but on the modulation symbol width, i.e., on the modulation rate, high-speed modulation is employed to obtain high-resolution ranging:
the ranging resolution is as follows:
Figure DEST_PATH_IMAGE141
。
in the method for measuring the polarization diversity dual-channel speed measurement and distance measurement coherent laser radar, the echo speed measurement light beam is transmitted to the second polarization beam splitter for polarization-maintaining coupling, then enters the polarization diversity optical circulator for polarization diversity, passes through the optical scanner, is transmitted by the optical telescope and receives the echo light beam, and the echo light beam obtains the echo speed measurement light beam through the third polarization beam splitter;
the echo ranging beam is transmitted to the second polarization beam splitter for polarization-maintaining coupling after the ranging emission beam is subjected to phase modulation, then enters the polarization diversity optical circulator for polarization diversity, passes through the optical scanner, is emitted by the optical telescope and receives the echo beam, and the echo beam is subjected to the third polarization beam splitter to obtain the echo ranging beam.
The device for realizing the polarization diversity dual-channel speed measurement and ranging coherent laser radar measuring method comprises a laser light source, wherein the laser light source is connected with a first polarization-preserving beam splitter and a second polarization-preserving beam splitter through a first polarization beam splitter;
the output end of the first polarization-preserving beam splitter is sequentially connected with a second polarization beam splitter, a polarization diversity optical circulator, an optical scanner and an optical telescope; the polarization diversity optical circulator is connected with a third polarization beam splitter, the first polarization beam splitter and the third polarization beam splitter are jointly connected with a first optical bridge, and the first optical bridge is connected with a low-speed analog-to-digital converter through a low-speed photoelectric balance detector; the low-speed analog-to-digital converter is connected with a main control computer through a low-speed data acquisition unit;
the output end of the second polarization-maintaining beam splitter is sequentially connected with a second polarization beam splitter, a polarization diversity optical circulator, an optical scanner and an optical telescope through an electro-optic phase modulator; the second polarization-maintaining beam splitter and the third polarization beam splitter are jointly connected with a second optical bridge, the second optical bridge is connected with a data acquisition unit through a high-speed photoelectric balance detector and a first high-speed analog-to-digital converter, and the data acquisition unit is connected with a main control computer; the data acquisition unit is also connected with a waveform generator, and the waveform generator is connected with the electro-optic phase modulator; a frequency shifter is also arranged between the second polarization-maintaining beam splitter and the second optical bridge; the main control computer is also connected with a radio frequency driver, and the radio frequency driver is connected with the frequency shifter; the radio frequency driver utilizes the speed measurement result to feed back and control the frequency shift quantity of the frequency shifter, overcomes Doppler broadening in the distance measurement process, and improves the distance measurement precision.
According to the device for the polarization diversity dual-channel speed measurement and ranging coherent laser radar measuring method, a polarizer is further arranged between the laser light source and the first polarization beam splitter; a first laser amplifier is further arranged on a speed measuring emission beam transmission line between the first polarization beam splitter and the second polarization beam splitter; a second laser amplifier is also arranged between the second polarization-maintaining beam splitter and the second polarization beam splitter; the main control computer is connected with an external trigger circuit, and the external trigger circuit is arranged between the waveform generator and the data collector; the data acquisition unit is also connected with a second high-speed analog-to-digital converter, and the second high-speed analog-to-digital converter is connected with the waveform generator.
According to the device for the coherent laser radar measuring method of polarization diversity dual-channel speed measurement and distance measurement, the polarization diversity optical circulator comprises a first polarization beam splitter prism, and the first polarization beam splitter prism is connected with a first Faraday optical rotator and a first half-wave plate through a first total reflector; the first polarization beam splitter prism is also connected with a second half-wave plate and a second holophote through a second Faraday optical rotator; the first half-wave plate and the second total reflector are connected with a second polarization beam splitter prism together; the first Faraday optical rotator and the second Faraday optical rotator respectively rotate the polarization states of vertically polarized light and horizontally polarized light by 45 degrees, and the slow axes of the first half-wave plate and the second half-wave plate form 22.5 degrees with the incident polarization state.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention divides the laser light source output beam into a speed measuring beam and a distance measuring beam through a first polarization beam splitter;
during speed measurement, an in-phase signal and an orthogonal signal with orthogonal characteristics are obtained through orthogonal coherent reception of a speed measurement local oscillator light beam and an echo speed measurement light beam, and the magnitude and the direction of the radial speed of a target are obtained through computer processing. The speed resolution of the invention can reach 1cm/s magnitude, the speed measuring range can reach 100km/h magnitude, and the precision and the range of speed measurement are greatly improved.
During ranging, ranging light beams are transmitted to a target after being modulated by pseudo-random code phases, echo ranging light beams are received, the echo ranging light beams and ranging local oscillator light beams enter an optical bridge for coherent reception, coherent receiving signals are obtained, synchronous receiving and acquisition of random code signals and the coherent receiving signals are achieved, two paths of signals acquired synchronously are subjected to correlation processing, distance information of the target is obtained, and accuracy of distance measurement is greatly improved. Therefore, the invention can realize synchronous speed and distance measurement for the target, and the invention adopts an original structure, so that the measurement result has excellent stability and precision.
2. The speed measuring light beam and the distance measuring light beam are independent, the speed measuring light beam is not influenced by the length of the pulse sequence of the distance measuring light beam, therefore, the length of a proper pseudo-random code sequence is selected under a certain modulation rate, the repetition frequency of the system can reach the MHz magnitude, and the speed measuring light beam and the distance measuring light beam have relative independence, and even if one function is damaged, the other function can still work.
3. The invention realizes polarization diversity by the second polarization beam splitter, the polarization diversity optical circulator and the third polarization beam splitter, realizes coaxial receiving and transmitting by the optical scanner and the optical telescope, is beneficial to integration miniaturization, reduces the complexity of the system, optimizes the speed and distance measurement processing algorithm, further improves the stability and precision of the measurement result and has good development prospect.
4. The invention utilizes the obtained radial speed and direction of the target to carry out frequency shift control on the ranging local oscillator light beam, is used for eliminating the influence of Doppler frequency shift generated by relative motion between the laser radar and the target and improves the ranging precision. Specifically, an external trigger circuit controlled by a main control computer is adopted to provide a trigger signal for a waveform generator, the waveform generator generates a pseudo-random code signal and sends the pseudo-random code signal to an electro-optical phase modulator, and a ranging emission beam is subjected to phase modulation by the pseudo-random code signal generated by the waveform generator to obtain an echo ranging emission beam which is accompanied and modulated by the pseudo-random code. And simultaneously, the main control computer controls the external trigger circuit to trigger the waveform generator to generate a second path of pseudo-random code signal and transmit the second path of pseudo-random code signal to the data acquisition unit, and the pseudo-random code signal and a coherent receiving signal which is subjected to pseudo-random code concomitant modulation are synchronously acquired in the data acquisition unit and then are subjected to correlation processing, so that the distance information of the target is finally obtained. The invention also uses the speed measuring result obtained from the main control computer to control the radio frequency driver to drive the frequency shifter to adjust the frequency shift amount, namely, the frequency shift amount of the ranging local oscillator light beam is fed back and controlled by the speed measuring result of the speed measuring light beam, which is used for overcoming (or eliminating) Doppler broadening in the ranging process, thereby improving the ranging precision, the modulation rate can reach GHz level, the distance resolution can reach 10cm level, the ranging precision reaches 1cm level, and the invention also has very high sensitivity, especially the precision of remote detection.
Drawings
Fig. 1 is a schematic diagram of the principle of the present invention.
FIG. 2 is a schematic diagram of a polarization diversity optical circulator of the present invention.
FIG. 3 is a schematic diagram of a first optical bridge according to the present invention.
FIG. 4 is a schematic diagram of a second optical bridge according to the present invention.
Reference numerals
1. A laser light source; 2. a polarizer; 3. a first polarizing beam splitter; 4. a first polarization maintaining beam splitter; 5. a second polarization maintaining beam splitter; 6. a frequency shifter; 7. a radio frequency driver; 8. an electro-optic phase modulator; 9. a waveform generator; 10. a first laser amplifier; 11. a second laser amplifier; 12. a second polarizing beam splitter; 13. a polarization diversity optical circulator; 14. an optical scanner; 15. an optical telescope; 16. a third polarization beam splitter; 17. a first optical bridge; 18. a second optical bridge; 19. a low-speed photoelectric balance detector; 20. a high-speed photoelectric balance detector; 21. a low speed analog to digital converter; 22. a first high-speed analog-to-digital converter; 23. a low-speed data collector; 24. a data acquisition unit; 25. an external trigger circuit; 26. a main control computer; 27. a second high-speed analog-to-digital converter; 131. a first polarization beam splitter prism; 132. a first total reflection mirror; 133. a first Faraday rotator; 134. a first half wave plate; 135. a second Faraday rotator; 136. a second half-wave plate; 137. a second total reflection mirror; 138. a second polarization beam splitter prism; 171. a third polarization beam splitter prism; 172. a third total reflection mirror; 173. a third half-wave plate; 174. a fourth half-wave plate; 175. a fifth half-wave plate; 176. a quarter wave plate; 177. a first polarization beam splitting combination prism; 178. a second polarization beam splitting combination prism; 181. a fourth polarization beam splitter prism; 182. a fourth total reflection mirror; 183. a sixth half-wave plate; 184. a seventh half wave plate; 185. and a third polarization beam splitting and combining prism.
Detailed Description
The invention is further illustrated by the following figures and examples, which are not to be construed as limiting the invention.
Example (b): a polarization diversity dual-channel speed and distance measuring coherent laser radar measuring device is shown in figure 1 and comprises a laser source 1, a 1550nm single-mode narrow-line-width continuous optical fiber laser safe to human eyes is adopted, the line width of the laser is 10kHz, the output power is 20mW, the optical fiber output is isolated and protected, the laser source 1 is polarized by a polarizer 2, the polarization extinction ratio is ensured to be larger than 25dB, and the polarization direction can be controlled to rotate; the output light beam of the laser light source 1 after polarization is divided into a vertical polarization light beam and a horizontal polarization light beam through a first polarization beam splitter 3; the light intensity of the vertically polarized light beam and the horizontally polarized light beam is 50: 50;
taking the vertical polarized light beam as a speed measuring light beam and taking the horizontal polarized light beam as a distance measuring light beam; the speed measuring light beam is split into a speed measuring local oscillator light beam and a speed measuring emission light beam by a first polarization-preserving beam splitter 4, and the beam splitting ratio of the speed measuring local oscillator light beam to the speed measuring emission light beam is 10: 90; the distance measuring light beam is split into a distance measuring local oscillator light beam and a distance measuring emission light beam by a second polarization-preserving beam splitter 5, and the beam splitting ratio of the distance measuring local oscillator light beam to the distance measuring emission light beam is 10: 90; the output end of the first polarization-preserving beam splitter 4 is sequentially connected with a second polarization beam splitter 12, a polarization diversity optical circulator 13, an optical scanner 14 and an optical telescope 15 through a first laser amplifier 10; the polarization diversity optical circulator 13 is connected with a third polarization beam splitter 16, the first polarization beam splitter 4 and the third polarization beam splitter 16 are connected with a first optical bridge 17 together, and the first optical bridge 17 is connected with a low-speed analog-to-digital converter 21 through a low-speed photoelectric balance detector 19; the low-speed analog-to-digital converter 21 is connected with a main control computer 26 through a low-speed data acquisition unit 23;
the output end of the second polarization-maintaining beam splitter 5 is sequentially connected with a second polarization beam splitter 12, a polarization diversity optical circulator 13, an optical scanner 14 and an optical telescope 15 through an electro-optic phase modulator 8; an electro-optic phase modulator 8 and a second laser amplifier 11 are further arranged on a distance measuring emission beam transmission line between the second polarization-maintaining beam splitter 5 and the second polarization beam splitter 12; the second polarization-maintaining beam splitter 5 and the third polarization beam splitter 16 are connected with a second optical bridge 18 together, the second optical bridge 18 is connected with a data acquisition unit 24 through a high-speed photoelectric balanced detector 20 and a first high-speed analog-to-digital converter 22, and the data acquisition unit 24 is connected with a main control computer 26; the data acquisition unit 24 is also connected with a waveform generator 9, and the waveform generator 9 is connected with the electro-optic phase modulator 8; a frequency shifter 6 is arranged between the second polarization-maintaining beam splitter 5 and the second optical bridge 18; the main control computer 26 is also connected with a radio frequency driver 7, and the radio frequency driver 7 is connected with the frequency shifter 6;
the main control computer 26 is also connected with an external trigger circuit 25, and the external trigger circuit 25 is respectively connected with the waveform generator 9 and the data acquisition unit 24 and is used for realizing synchronous acquisition of pseudo-random code signals and coherent receiving signals; the main control computer 26 is further connected with a radio frequency driver 7, the radio frequency driver 7 is connected with the frequency shifter 6, and is used for providing heterodyne intermediate frequency signals, and feeding back and controlling the frequency shift amount of the frequency shifter 6 through data acquired by a speed measurement channel so as to compensate Doppler broadening introduced by target speed.
The polarization diversity optical circulator 13, the optical scanner 14 and the optical telescope 15 on the transmission route of the speed measuring emission beam and the distance measuring emission beam are used for emitting the speed measuring emission beam and the distance measuring emission beam and receiving the echo beam; the polarization diversity optical circulator 13 includes a first polarization beam splitter 131, a first total reflector 132, a first faraday rotator 133, a first half-wave plate 134, a second faraday rotator 135, a second half-wave plate 136, a second total reflector 137, and a second polarization beam splitter 138, and is configured to rotate the polarization state of the speed measurement emission beam or the distance measurement emission beam by 90 degrees, while the polarization state of the echo beam remains unchanged.
The third polarization beam splitter 16 connected to the polarization diversity optical circulator 13 splits the echo beam into an echo speed measurement beam and an echo distance measurement beam;
the velocity measurement local oscillator light beam and the echo velocity measurement light beam are input to the first optical bridge 17 to realize orthogonal coherent reception, the schematic structural diagram of the first optical bridge 17 is shown in fig. 3, and the optical bridge with a free space structure of 2 × 490 degrees is adopted and is composed of a third polarization beam splitter prism 171, a third total reflector 172, a third half-wave plate 173, a fourth half-wave plate 174, a fifth half-wave plate 175, a quarter-wave plate 176, a first polarization beam splitter combined prism 177 and a second polarization beam splitter combined prism 178, where a light field of the first optical bridge 17 can be expressed as:
Figure DEST_PATH_IMAGE142
；
wherein is the target distance, is the laser carrier frequency, is the doppler shift caused by the target velocity,
Figure DEST_PATH_IMAGE010A
it is the speed of light that is,
Figure DEST_PATH_IMAGE012A
the phase of the echo speed measurement light beam is the noise phase of the speed measurement local oscillator light beam; (ii) a Is the time; is the echo velocimetry light beam amplitude; measuring the amplitude of the local oscillator light beam;
the four outputs after the frequency mixing by the first optical bridge are respectively:
Figure DEST_PATH_IMAGE146
；
wherein
Figure DEST_PATH_IMAGE147
Is a mixing noise phase;
Figure DEST_PATH_IMAGE148
is the direct current quantity related to the echo speed measuring light beam;
Figure DEST_PATH_IMAGE030A
the direct current quantity related to the speed measurement local oscillator light beam;
obtaining an in-phase signal and an orthogonal signal with orthogonal characteristics, and receiving the in-phase signal and the orthogonal signal by a low-speed photoelectric balance detector 19, wherein the bandwidth is 100MHz, and the direct current coupling is realized; the in-phase signal and the quadrature signal output are respectively:
Figure DEST_PATH_IMAGE149
；
wherein
Figure DEST_PATH_IMAGE150
Is the photo-balanced detector responsivity of the in-phase signal,
Figure DEST_PATH_IMAGE036A
is the photoelectric balance detector responsivity of the quadrature signal,
Figure DEST_PATH_IMAGE151
and
Figure DEST_PATH_IMAGE152
noise phases of the in-phase signal and the quadrature signal, respectively; the output of the low-speed photoelectric balance detector 19 is subjected to analog-to-digital conversion by a low-speed analog-to-digital converter 21, and finally collected by a low-speed data collector 23, wherein the sampling rate is 500 MHz; the collected in-phase signal and quadrature signal are input into the main control computer 26 for processing, the in-phase signal and the quadrature signal are respectively subjected to Fast Fourier Transform (FFT), the fourier transform of the in-phase signal is expressed as:
Figure DEST_PATH_IMAGE153
；
the orthogonal signal fourier transform is represented as:
Figure DEST_PATH_IMAGE154
after Fourier transform, the frequency spectrum information only contains target Doppler information;
performing cross-spectrum processing on the two channels:
Figure DEST_PATH_IMAGE155
；
finally, only the imaginary part is taken to obtain
Figure DEST_PATH_IMAGE048A
The Doppler shift is proportional to the velocity of the target motion and can be expressed as
Figure DEST_PATH_IMAGE050A
Wherein the content of the first and second substances,
Figure 68147DEST_PATH_IMAGE052
is the target radial velocity of the beam of light,
Figure 664345DEST_PATH_IMAGE054
is the light source emission wavelength;
and finally obtaining the size and the direction of the radial velocity of the target by analyzing the position, the positive and the negative of the peak value of the Doppler frequency spectrum. The peak position of the Doppler frequency spectrum is extracted by adopting cross-spectrum processing and a gravity center method, the speed measurement precision of the Doppler frequency spectrum peak position measuring device can reach 1cm/s, and the maximum speed measurement range can reach 279 km/h.
Wherein the ranging local oscillator beam and the echo ranging beam are sequentially input into the second optical bridge 18 and the high-speed photoelectric balanced detector 20 for coherent reception. The structural schematic diagram of the second optical bridge 18 is shown in fig. 4, and the optical bridge with a free space structure of 2 × 2180 ° is composed of a fourth polarization beam splitting prism 181, a fourth total reflection mirror 182, a sixth half-wave plate 183, a seventh half-wave plate 184, and a third polarization beam splitting combination prism 185.
The pseudo-random code signal is:
;
wherein the content of the first and second substances,
Figure DEST_PATH_IMAGE157
is the pseudo random code sequence symbol width of the pseudo random code signal,
Figure DEST_PATH_IMAGE060A
is the number of the code element,
Figure DEST_PATH_IMAGE158
is the total number of symbols,
Figure DEST_PATH_IMAGE159
is a pseudo random number, and takes the value of 0 or 1;
the main characteristics of a pseudorandom code signal are its autocorrelation function:
Figure DEST_PATH_IMAGE160
；
the autocorrelation function of the pseudo-random code is a sharp pulse sequence, and the smaller the pulse width is, the sharper the waveform is;
the cross-correlation property of the pseudo-random code signal is
Wherein, P 1And P 2Two independent pseudo-random code sequences;
the echo ranging beam is represented as:
Figure DEST_PATH_IMAGE162
；
wherein is the target distance, is the laser carrier frequency, is the doppler shift caused by the target velocity, it is the speed of light that is,
Figure DEST_PATH_IMAGE079A
is the noise phase of the echo ranging beam; (ii) a
Figure DEST_PATH_IMAGE083A
Is the time; ranging the amplitude of the beam for the echo;
the ranging local oscillator beam is
；
Figure DEST_PATH_IMAGE089A
Is the noise phase of the ranging local oscillator beam, is the amount of frequency shift; measuring the amplitude of the local oscillator light beam;
the two outputs after the ranging local oscillator beam and the echo ranging beam enter the second optical bridge 18 for frequency mixing are respectively:
Figure DEST_PATH_IMAGE169
，
Figure DEST_PATH_IMAGE096A
the noise phase after frequency mixing is direct current quantity related to the echo ranging beam and is direct current quantity related to the ranging local oscillator beam;
the two outputs are received and output by the high-speed photoelectric balance detector 20, and the outputs are:
Figure DEST_PATH_IMAGE170
；
Figure 376616DEST_PATH_IMAGE104
is the responsivity of a high-speed photoelectric balance detector, is the noise phase output by the high-speed photoelectric balance detector;
order to
Figure 835596DEST_PATH_IMAGE108
The following can be obtained:
Figure DEST_PATH_IMAGE171
；
wherein
Figure DEST_PATH_IMAGE172
Is the amplitude;
due to the fact that
Figure DEST_PATH_IMAGE173
The coherent receiving signal is obtained by simplifying the above formula according to the characteristics of cosine signals, wherein the sequence is a series of sequences of 0 and pi, namely the cosine signals have random change of phase pi:
Figure DEST_PATH_IMAGE174
；
wherein
Figure DEST_PATH_IMAGE175
， Is a pseudo random number and takes a value of 1 or-1.
Coherent receiving signals of the ranging emission beam and the echo ranging beam are converted by a first high-speed analog-to-digital converter 22, and are finally collected by a data collector 24, data are input into a main control computer 26, and the data collector 24 simultaneously collects and converts pseudo-random code signals generated by a waveform generator 9 by a second high-speed analog-to-digital converter 27, wherein the modulation rate is 1 GHz/s; in order to ensure the synchronism, an external trigger circuit 25 is adopted to simultaneously provide trigger signals for the data acquisition unit 24 and the waveform generator 9, the pseudo-random code sequence and the coherent receiving signals are synchronized, and the sampling rate of each channel of the data acquisition unit 24 is 5 GHz; the two paths of signals acquired synchronously are processed in a main control computer: sequential shifting of pseudo-random code signals And multiplied by the coherent received signal to obtainTo
Figure DEST_PATH_IMAGE177
During the duration of the pulse signal The internal integration can be obtained as follows:
Figure DEST_PATH_IMAGE179
，
as can be seen from the nature of the sinc function,
Figure DEST_PATH_IMAGE129A
the higher the value of (A), the lower the height of the peak of the correlation function, at
Figure DEST_PATH_IMAGE180
When n is an integer, the peak value of the correlation function is zero; in the same way
Figure DEST_PATH_IMAGE133A
In this case, the longer the duration of the phase encoding pulse, the greater the influence of the doppler shift on the correlation result; thus compensating for the doppler shift.
Herein take
Figure 580305DEST_PATH_IMAGE135
Performing fast Fourier transform on the compensated correlation function, wherein when the symbol time of the shift delay is not correlated with the delay caused by the target motion, the Fourier transform frequency spectrum has no obvious peak value; when the symbol time of the shift delay coincides with the amount of delay caused by the object motion, the fourier transform spectrum has a significant peak at the intermediate frequency. Therefore, the number of delay symbols corresponding to the occurrence of the maximum peak in the Fourier transform spectrum can be determined
Figure 605899DEST_PATH_IMAGE137
And obtaining target distance information.
The target distance is:
Figure DEST_PATH_IMAGE181
since the high-speed pseudo random code modulation is performed in the wide pulse, so that the range resolution of the system does not depend on the pulse width but depends on the modulation symbol width, i.e., on the modulation rate, high-speed modulation can be employed to obtain high-resolution ranging.
The ranging resolution is as follows:
。
the invention utilizes the speed measurement result obtained from the main control computer to control the radio frequency driver to drive the frequency shifter to adjust the frequency shift quantity, namely, the frequency shift quantity of the distance measurement light beam is controlled through the feedback of the speed measurement quantity, thereby realizing heterodyne intermediate frequency
Figure DEST_PATH_IMAGE182
The Doppler frequency shift is a stable value, the influence of Doppler frequency shift is effectively inhibited, the ranging precision is improved, and the precision of remote detection is particularly improved.
The invention adopts a gravity center method to extract the position of a frequency spectrum peak value, and obtains the ranging resolution of 15cm and the ranging precision of 1cm under the conditions that the length of a pseudorandom sequence is 1000 and the repetition frequency is 1 MHz.
In conclusion, in the field of speed measurement, the speed resolution can reach 1cm/s magnitude, the speed measurement range can reach 100km/h magnitude, and the accuracy and the range of speed measurement are greatly improved. In the ranging field, the modulation rate of the invention can reach GHz level, the ranging resolution can reach 10cm level, and the ranging precision can reach 1cm level. Therefore, the invention can synchronously measure the speed and the distance of the target, has very excellent precision of measuring the speed and the distance, and has the advantages of miniaturization of the whole system, easy operation and good development prospect.

Claims (9)

1. The polarization diversity double-channel speed measurement and ranging coherent laser radar measuring method is characterized by comprising the following steps of: the laser light source outputs a light beam which is divided into a speed measuring light beam and a distance measuring light beam in orthogonal polarization states by a first polarization beam splitter;
dividing a speed measurement light beam into a speed measurement local oscillator light beam and a speed measurement emission light beam with the same polarization through a first polarization beam splitter, enabling an echo light beam emitted by the speed measurement emission light beam to a target to obtain an echo speed measurement light beam with the same polarization through a third polarization beam splitter, enabling the speed measurement local oscillator light beam and the echo speed measurement light beam to enter a first optical bridge for orthogonal coherent reception to obtain an in-phase signal and an orthogonal signal with orthogonal characteristics, performing Fourier transform on the in-phase signal and the orthogonal signal to obtain a Doppler frequency spectrum, performing cross-spectrum processing to obtain an imaginary part, extracting the position and the positive and negative of a peak value in the Doppler frequency spectrum by using a gravity center method, and analyzing the position and the positive and negative of the Doppler peak value to obtain the size;
dividing the ranging light beam into a ranging local oscillator light beam and a ranging emission light beam with the same polarization through a second polarization-maintaining beam splitter, carrying out phase modulation on the ranging emission light beam through a pseudo-random code signal generated by a waveform generator, then obtaining an echo ranging light beam with the same polarization through a third polarization beam splitter by an echo light beam emitted to a target, and enabling the ranging local oscillator light beam and the echo ranging light beam to enter a second optical bridge for coherent reception to obtain a coherent reception signal; pseudo-random code signals and coherent receiving signals generated by a waveform generator are synchronously received by a data collector, and two paths of synchronously received signals are subjected to correlation processing in a main control computer to obtain target distance information;
the second polarization-maintaining beam splitter is connected with a frequency shifter, the frequency shifter is connected with the second optical bridge, and the frequency shifter is connected with a main control computer through a radio frequency driver; the main control computer obtains Doppler frequency shift generated by relative motion of the laser radar and the target by using the position and the positive and negative of the obtained Doppler frequency spectrum peak value, and then drives the frequency shifter to adjust the frequency shift amount of the ranging local oscillator light beam according to the information of the Doppler frequency shift, so that the influence of the Doppler frequency shift generated by the relative motion between the laser radar and the target is eliminated, and the ranging precision is improved.
2. The polarization diversity dual-channel speed and range coherent lidar measurement method of claim 1, wherein: the speed measuring local oscillator light beam and the echo speed measuring light beam enter the first optical bridge for orthogonal coherent reception, and the light field is expressed as:
Figure 876949DEST_PATH_IMAGE001
；
wherein
Figure 374183DEST_PATH_IMAGE002
Is the distance to the target, and is,
Figure 622762DEST_PATH_IMAGE003
is the carrier frequency of the laser light,
Figure 611447DEST_PATH_IMAGE004
is the doppler shift caused by the velocity of the target,
Figure 894660DEST_PATH_IMAGE005
it is the speed of light that is,
Figure 61331DEST_PATH_IMAGE006
is the noise phase of the echo velocimetry beam,
Figure 797206DEST_PATH_IMAGE007
is the noise phase of the local oscillator beam;
Figure 589581DEST_PATH_IMAGE008
；
Figure 727301DEST_PATH_IMAGE009
is the time;
Figure 563408DEST_PATH_IMAGE010
is the echo velocimetry light beam amplitude;
Figure 786579DEST_PATH_IMAGE011
measuring the amplitude of the local oscillator light beam;
the four outputs after the frequency mixing by the first optical bridge are respectively:
Figure 851487DEST_PATH_IMAGE012
，
wherein
Figure 109293DEST_PATH_IMAGE013
Is a mixing noise phase;
Figure 883345DEST_PATH_IMAGE014
is the direct current quantity related to the echo speed measuring light beam;
Figure 593812DEST_PATH_IMAGE015
the direct current quantity related to the speed measurement local oscillator light beam;
the in-phase signal and the orthogonal signal with the orthogonal characteristic are received by the low-speed photoelectric balanced detector, and the in-phase signal and the orthogonal signal output are respectively as follows:
Figure 727990DEST_PATH_IMAGE016
；
wherein
Figure 840303DEST_PATH_IMAGE017
Is the photo-balanced detector responsivity of the in-phase signal,
Figure 32860DEST_PATH_IMAGE018
is the photoelectric balance detector responsivity of the quadrature signal,
Figure 230624DEST_PATH_IMAGE019
and
Figure 902913DEST_PATH_IMAGE020
are respectively in-phase signalsAnd the noise phase of the quadrature signal.
3. The polarization diversity dual-channel speed and range coherent lidar measurement method of claim 2, wherein: the in-phase signal and the orthogonal signal are output to a main control computer after being subjected to analog-to-digital conversion, and the in-phase signal and the orthogonal signal are subjected to fast Fourier transform respectively, wherein the Fourier transform of the in-phase signal is expressed as follows:
；
the orthogonal signal fourier transform is represented as:
；
after Fourier transform, the frequency spectrum information only contains target Doppler information;
performing cross-spectrum processing on the two channels:
Figure 670646DEST_PATH_IMAGE023
；
finally, only the imaginary part is taken to obtain
Figure 21993DEST_PATH_IMAGE024
；
The Doppler shift is proportional to the velocity of the target motion, denoted as
Wherein the content of the first and second substances,
Figure 379342DEST_PATH_IMAGE026
is the target radial velocity of the beam of light,
Figure 925599DEST_PATH_IMAGE027
is the light source emission wavelength;
and finally obtaining the size and the direction of the radial velocity of the target by analyzing the position, the positive and the negative of the peak value of the Doppler frequency spectrum, thereby realizing the velocity measurement of the target.
4. The polarization diversity dual-channel speed and range coherent lidar measurement method according to any of claims 1-3, characterized by: the pseudo-random code signal is:
；
wherein the content of the first and second substances,
Figure 881103DEST_PATH_IMAGE029
is the pseudo random code sequence symbol width of the pseudo random code signal,
Figure 463394DEST_PATH_IMAGE030
is the number of the code element,
Figure 123045DEST_PATH_IMAGE031
is the total number of symbols,
Figure 691561DEST_PATH_IMAGE032
is a pseudo random number, and takes the value of 0 or 1;
the main characteristics of a pseudorandom code signal are its autocorrelation function:
Figure 221899DEST_PATH_IMAGE033
；
the autocorrelation function of the pseudo-random code is a sharp pulse sequence, and the smaller the pulse width is, the sharper the waveform is;
the cross-correlation properties of the pseudo-random code signals are:
Figure 99725DEST_PATH_IMAGE034
；
wherein, P 1And P 2Two independent pseudo-random code sequences;
the echo ranging light beam is as follows:
；
wherein
Figure 120344DEST_PATH_IMAGE036
Is the distance to the target, and is,
Figure 770769DEST_PATH_IMAGE037
is the carrier frequency of the laser light,
Figure 553917DEST_PATH_IMAGE038
is the doppler shift caused by the velocity of the target,
Figure 188160DEST_PATH_IMAGE039
it is the speed of light that is,
Figure 223113DEST_PATH_IMAGE040
is the noise phase of the echo ranging beam;
Figure 868989DEST_PATH_IMAGE041
；
Figure 698404DEST_PATH_IMAGE042
is the time;
Figure 678999DEST_PATH_IMAGE043
ranging the amplitude of the beam for the echo;
the ranging local oscillator beam is
；
Figure 516560DEST_PATH_IMAGE045
Is the noise phase of the ranging local oscillator beam,
Figure 782456DEST_PATH_IMAGE046
is the amount of frequency shift;
Figure 984767DEST_PATH_IMAGE047
measuring the amplitude of the local oscillator light beam;
the two paths of outputs after the ranging local oscillator light beam and the echo ranging light beam enter the second optical bridge for frequency mixing are respectively as follows:
Figure 627101DEST_PATH_IMAGE048
，
Figure 372203DEST_PATH_IMAGE049
is the noise phase after the mixing of the frequencies,
Figure 684367DEST_PATH_IMAGE050
is a direct current quantity related to the echo ranging beam,
Figure 249340DEST_PATH_IMAGE051
is the direct current quantity related to the ranging local oscillator beam;
the two paths of output are received and output by a high-speed photoelectric balance detector, and the output is as follows:
Figure 554420DEST_PATH_IMAGE052
；
Figure 154028DEST_PATH_IMAGE053
is the responsivity of a high-speed photoelectric balance detector,
Figure 138558DEST_PATH_IMAGE054
is the noise phase output by the high-speed photoelectric balance detector;
order to
Figure 190828DEST_PATH_IMAGE055
The following can be obtained:
Figure 34019DEST_PATH_IMAGE056
；
wherein Is the amplitude;
due to the fact that
Figure 532313DEST_PATH_IMAGE058
The coherent receiving signal is obtained by simplifying the above formula according to the characteristics of cosine signals, wherein the sequence is a series of sequences of 0 and pi, namely the cosine signals have random change of phase pi:
Figure 947245DEST_PATH_IMAGE059
；
wherein
Figure 469494DEST_PATH_IMAGE060
，
Figure 902749DEST_PATH_IMAGE061
Is a pseudo random number and takes a value of 1 or-1.
5. The polarization diversity dual-channel speed and range coherent lidar measurement method of claim 4, wherein: the pseudo-random code signal and the coherent receiving signal enter a main control computer for correlation processing after analog-to-digital conversion: in which the pseudo-random code signals are shifted in sequence
Figure 117830DEST_PATH_IMAGE062
And multiplied by the coherent received signal to obtain:
Figure 253014DEST_PATH_IMAGE064
；
during the duration of the pulse signal
Figure 578953DEST_PATH_IMAGE065
The internal integration can be obtained as follows:
；
as can be seen from the nature of the sinc function,
Figure 987117DEST_PATH_IMAGE067
the higher the value of (A), the lower the height of the peak of the correlation function, at
Figure 766855DEST_PATH_IMAGE068
When n is an integer, the peak value of the correlation function is zero; in the same way
Figure 506272DEST_PATH_IMAGE069
In this case, the longer the duration of the phase encoding pulse, the greater the influence of the doppler shift on the correlation result;
get Performing fast Fourier transform on the compensated correlation function, wherein when the symbol time of the shift delay is not correlated with the delay caused by the target motion, the Fourier transform frequency spectrum has no obvious peak value; when the symbol time of the shift delay coincides with the amount of delay caused by the target motion, the fourier transform spectrum has a significant peak at the intermediate frequency; thereby, the number of delay symbols corresponding to the maximum peak value of the Fourier transform spectrum
Figure 471002DEST_PATH_IMAGE071
Obtaining target distance information:
the target distance is:
Figure 206877DEST_PATH_IMAGE072
thereby improving the precision of distance measurement;
since the high-speed pseudo-random code modulation is performed in a wide pulse, so that the range resolution of the system does not depend on the pulse width but on the modulation symbol width, i.e., on the modulation rate, high-speed modulation is employed to obtain high-resolution ranging:
the ranging resolution is as follows:
Figure DEST_PATH_IMAGE073
。
6. the polarization diversity dual-channel speed and range coherent lidar measurement method of claim 1, wherein: the echo speed measuring light beam is transmitted to a second polarization beam splitter for polarization-maintaining coupling through a speed measuring emission light beam, then enters a polarization diversity optical circulator for polarization diversity, passes through an optical scanner, is emitted by an optical telescope and receives the echo light beam, and the echo light beam obtains the echo speed measuring light beam through a third polarization beam splitter;
the echo ranging beam is transmitted to the second polarization beam splitter for polarization-maintaining coupling after the ranging emission beam is subjected to phase modulation, then enters the polarization diversity optical circulator for polarization diversity, passes through the optical scanner, is emitted by the optical telescope and receives the echo beam, and the echo beam is subjected to the third polarization beam splitter to obtain the echo ranging beam.
7. Device for implementing a polarization diversity dual-channel speed and range coherent lidar measurement method according to any of claims 1-6, characterized by: the polarization beam splitter comprises a laser light source (1), wherein the laser light source (1) is connected with a first polarization-preserving beam splitter (4) and a second polarization-preserving beam splitter (5) through a first polarization beam splitter (3);
the output end of the first polarization-preserving beam splitter (4) is sequentially connected with a second polarization beam splitter (12), a polarization diversity optical circulator (13), an optical scanner (14) and an optical telescope (15); the polarization diversity optical circulator (13) is connected with a third polarization beam splitter (16), the first polarization beam splitter (4) and the third polarization beam splitter (16) are connected with a first optical bridge (17) together, and the first optical bridge (17) is connected with a low-speed analog-to-digital converter (21) through a low-speed photoelectric balanced detector (19); the low-speed analog-to-digital converter (21) is connected with a main control computer (26) through a low-speed data acquisition unit (23);
the output end of the second polarization-maintaining beam splitter (5) is sequentially connected with a second polarization beam splitter (12), a polarization diversity optical circulator (13), an optical scanner (14) and an optical telescope (15) through an electro-optic phase modulator (8); the second polarization-maintaining beam splitter (5) and the third polarization beam splitter (16) are connected with a second optical bridge (18) together, the second optical bridge (18) is connected with a data acquisition unit (24) through a high-speed photoelectric balance detector (20) and a first high-speed analog-to-digital converter (22), and the data acquisition unit (24) is connected with a main control computer (26); the data acquisition unit (24) is also connected with a waveform generator (9), and the waveform generator (9) is connected with the electro-optic phase modulator (8); a frequency shifter (6) is arranged between the second polarization-maintaining beam splitter (5) and the second optical bridge (18); the main control computer (26) is also connected with a radio frequency driver (7), and the radio frequency driver (7) is connected with the frequency shifter (6); the radio frequency driver (7) utilizes the speed measurement result to feed back and control the frequency shift quantity of the frequency shifter (6), overcomes Doppler broadening in the distance measurement process, and improves the distance measurement precision.
8. The device of the polarization diversity dual-channel speed and range coherent lidar measurement method according to claim 7, wherein: a polarizer (2) is arranged between the laser light source (1) and the first polarization beam splitter (3); a first laser amplifier (10) is further arranged on a speed measuring emission light beam transmission line between the first polarization beam splitter (4) and the second polarization beam splitter (12); a second laser amplifier (11) is also arranged between the second polarization-maintaining beam splitter (5) and the second polarization beam splitter (12); the main control computer (26) is connected with an external trigger circuit (25), and the external trigger circuit (25) is arranged between the waveform generator (9) and the data collector (24); the data acquisition unit (24) is also connected with a second high-speed analog-to-digital converter (27), and the second high-speed analog-to-digital converter (27) is connected with the waveform generator (9).
9. The device of the polarization diversity dual-channel speed and range coherent lidar measurement method according to claim 7, wherein: the polarization diversity optical circulator (13) comprises a first polarization beam splitter prism (131), and the first polarization beam splitter prism (131) is connected with a first Faraday rotator (133) and a first half-wave plate (134) through a first total reflection mirror (132); the first polarization beam splitting prism (131) is also connected with a second half-wave plate (136) and a second total reflection mirror (137) through a second Faraday optical rotator (135); the first half-wave plate (134) and the second total reflection mirror (137) are connected with a second polarization beam splitting prism (138).
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CN111308488B (en) * 2020-03-16 2022-02-11 杭州爱莱达科技有限公司 Symmetrical pseudo-random code phase modulation all-optical focusing coherent laser radar method and device
CN111308489A (en) * 2020-03-16 2020-06-19 杭州爱莱达科技有限公司 Double-channel pseudo-random code phase modulation optical domain analysis focusing coherent laser method and device
CN111308489B (en) * 2020-03-16 2022-02-11 杭州爱莱达科技有限公司 Optical domain analysis focusing method and device of pseudo-random code phase modulation laser radar
CN111308488A (en) * 2020-03-16 2020-06-19 杭州爱莱达科技有限公司 Symmetrical pseudo-random code phase modulation all-optical focusing coherent laser method and device
CN111473856A (en) * 2020-04-01 2020-07-31 中国科学院微电子研究所 Bridge deck three-dimensional vibration detection device and method based on laser and storage medium
CN111337902A (en) * 2020-04-29 2020-06-26 杭州爱莱达科技有限公司 Multi-channel high-repetition-frequency large-dynamic-range distance and speed measuring laser radar method and device
CN113885042A (en) * 2021-08-17 2022-01-04 哈尔滨工业大学 1.55 mu m single photon coherent laser radar detection method and device
CN113885042B (en) * 2021-08-17 2022-06-03 哈尔滨工业大学 1.55 mu m single photon coherent laser radar detection method and device
WO2023065149A1 (en) * 2021-10-20 2023-04-27 深圳市速腾聚创科技有限公司 Laser radar and laser radar control method
WO2023072111A1 (en) * 2021-10-25 2023-05-04 瞬联软件科技（北京）有限公司 Autonomous-driving-oriented millimeter wave orthogonal waveform optimization method, and vehicle-borne radar system
CN115047475A (en) * 2022-04-14 2022-09-13 上海枢光科技有限公司 Synchronous measurement method and device for three-dimensional distance and speed of laser radar
CN114838803A (en) * 2022-04-29 2022-08-02 北京杏林睿光科技有限公司 Vibration measuring device and vibration measuring method
CN114838803B (en) * 2022-04-29 2023-11-10 北京杏林睿光科技有限公司 Vibration measuring device and vibration measuring method
CN114720997A (en) * 2022-06-07 2022-07-08 中国人民解放军国防科技大学 Large dynamic laser coherent detection device and method for high-speed moving target
CN115656983A (en) * 2022-12-08 2023-01-31 武汉聚合光子技术有限公司 Continuous laser for coherent laser radar

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