Target distance and velocity measurement system and method based on radio frequency modulation direct detection lidar

Abstract

The application discloses a target distance and speed measurement system and method based on radio frequency modulation direct detection laser radar, and belongs to the technical field of target distance and speed measurement.The application solves the problem that the existing direct detection laser radar based on radio frequency phase modulation technology cannot measure the distance information of a target.The application introduces radio frequency technology into the direct detection laser radar by means of laser radio frequency modulation and demodulation technology, and utilizes a beam splitter and an optical chopper to process the echo signals of a reference target and a detection target, so that the detection performance of the target distance and speed can be improved, and the problem that the existing method cannot measure the distance information of the target is solved.Further, the measurement method of the application utilizes the frequency information of the radio frequency signal, and avoids information waste.The method of the application can be applied to the technical field of target distance and speed measurement.

Description

Target Range and Velocity Measurement System and Method Based on Radio Frequency Modulation Direct Probe LiDAR Technical Field

[0001] This invention belongs to the field of target distance and velocity measurement technology, and specifically relates to a target distance and velocity measurement system and method. Background Technology

[0002] Direct-probe lidar based on Fabry-Poret interferometer edge technology has garnered significant attention since its inception due to its ability to measure clear-sky atmospheric wind speed using the Doppler frequency shift of atmospheric molecular echo signal light. It also boasts advantages such as relatively relaxed requirements for light sources and optical components, and ease of implementation. However, its detector output signal is a baseband signal, resulting in a large system bandwidth (and consequently, significant noise entering the system), and the lack of physical mechanisms for noise suppression, leading to lower measurement accuracy. For this reason, phase-modulated direct-probe lidar was proposed. It retains the advantages of direct-probe methods—relaxed requirements for optical systems and lasers and ease of engineering implementation—while also offering high measurement accuracy. However, its relatively low Doppler frequency shift measurement dynamic range makes it difficult to meet practical measurement needs. Therefore, methods such as parametric synthesis and star-track vector mapping have been proposed to improve the dynamic range of Doppler frequency shift measurements. However, this type of direct-probe lidar based on radio frequency phase modulation technology has a low modulation frequency. It only utilizes the amplitude and phase information of the modulated radio frequency signal for Doppler frequency shift measurement, without utilizing the frequency information of the radio frequency signal, which greatly wastes information. In addition, this type of radio frequency modulation direct-probe lidar cannot measure the distance information of the target, which also greatly limits its application range. Summary of the Invention

[0003] The purpose of this invention is to solve the problem that existing direct detection lidar based on radio frequency phase modulation technology cannot measure the distance information of targets, and to propose a target distance and velocity measurement system and method based on radio frequency modulation direct detection lidar.

[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0005] A target distance and velocity measurement system based on radio frequency modulation direct detection lidar, the system comprising two parts: an optical path and a circuit.

[0006] The optical path includes a frequency-stabilized continuous fiber laser, a fiber phase modulator, an erbium-doped fiber amplifier, a fiber circulator, an optical antenna, a beam splitter, a first optical chopper, a second optical chopper, a fiber Fabry-Perot interferometer, and a square-law photodetector; wherein:

[0007] The output end of the frequency-stabilized continuous fiber laser is connected to the first input end of the fiber phase modulator.

[0008] The output of the fiber phase modulator is connected to the input of the erbium-doped fiber amplifier.

[0009] The output end of the erbium-doped fiber amplifier is connected to the In end of the fiber optic circulator;

[0010] The Out terminal of the fiber optic circulator is connected to the first input / output terminal of the optical antenna.

[0011] The second input / output terminal of the optical antenna is connected to the first input / output terminal of the beam splitter;

[0012] The second input / output terminal of the beam splitter is connected to the first input / output terminal of the first optical chopper; the signal output from the second input / output terminal of the first optical chopper illuminates the reference target;

[0013] The third input / output terminal of the beam splitter is connected to the first input / output terminal of the second optical chopper; the signal output from the second input / output terminal of the second optical chopper illuminates the detection target;

[0014] The Re terminal of the fiber optic circulator is connected to the input terminal of the fiber optic Fabry-Perot interferometer;

[0015] The output of the fiber optic Fabry-Perot interferometer is connected to the input of the square law photodetector.

[0016] The circuitry includes a computer and software-defined radio;

[0017] The software-defined radio includes an interface controller, a transmit controller, a first digital up-converter, a second digital up-converter, a first digital-to-analog converter, a second digital-to-analog converter, a first low-pass filter, a second low-pass filter, a first local oscillator, a first power amplifier, a second power amplifier, a second local oscillator, a third low-pass filter, a fourth low-pass filter, a first analog-to-digital converter, a second analog-to-digital converter, a first digital down-converter, a second digital down-converter, a receive controller, a first mixer, a second mixer, a third mixer, and a fourth mixer; wherein:

[0018] The computer's input / output terminals are connected to the input / output terminals of the interface controller;

[0019] The output of the interface controller is connected to the input of the transmitter controller;

[0020] The first output terminal of the transmitter controller is connected to the input terminal of the first digital up-converter; the second output terminal of the transmitter controller is connected to the input terminal of the second digital up-converter.

[0021] The output of the first digital-to-digital converter is connected to the input of the first digital-to-analog converter; the output of the second digital-to-digital converter is connected to the input of the second digital-to-analog converter.

[0022] The output of the first digital-to-analog converter is connected to the input of the first low-pass filter; the output of the second digital-to-analog converter is connected to the input of the second low-pass filter.

[0023] The first output terminal of the first local oscillator is connected to the first input terminal of the first mixer; the second output terminal of the first local oscillator is connected to the first input terminal of the second mixer.

[0024] The output terminal of the first low-pass filter is connected to the second input terminal of the first mixer; the output terminal of the second low-pass filter is connected to the second input terminal of the second mixer.

[0025] The output terminals of the first mixer and the second mixer are connected to the input terminal of the first power amplifier;

[0026] The output of the first power amplifier is connected to the second input of the fiber optic phase modulator.

[0027] The output terminal of the square law photodetector is connected to the input terminal of the second power amplifier;

[0028] The output terminal of the second power amplifier is connected to the first input terminal of the third mixer and the first input terminal of the fourth mixer, respectively.

[0029] The first output terminal of the second local oscillator is connected to the second input terminal of the third mixer; the second output terminal of the second local oscillator is connected to the second input terminal of the fourth mixer.

[0030] The output of the third mixer is connected to the input of the third low-pass filter; the output of the fourth mixer is connected to the input of the fourth low-pass filter.

[0031] The output of the third low-pass filter is connected to the input of the first analog-to-digital converter; the output of the first analog-to-digital converter is connected to the input of the first digital down-converter.

[0032] The output of the fourth low-pass filter is connected to the input of the second analog-to-digital converter; the output of the second analog-to-digital converter is connected to the input of the second digital down-converter.

[0033] The output of the first digital down-converter is connected to the first input of the receiver controller; the output of the second digital down-converter is connected to the second input of the receiver controller.

[0034] The output of the receiver controller is connected to the input of the interface controller.

[0035] A method for measuring target distance and velocity based on radio frequency modulation direct detection lidar, the method specifically includes the following steps:

[0036] Two orthogonal digital intermediate frequency (IF) signals generated by the computer are sequentially passed through an interface controller and a transmitter controller. One IF signal is output from the transmitter controller and then sequentially passes through a first digital up-converter, a first digital-to-analog converter, and a first low-pass filter. The other IF signal is output from the transmitter controller and then sequentially passes through a second digital up-converter, a second digital-to-analog converter, and a second low-pass filter. The first and second low-pass filters are used to output two orthogonal analog IF signals.

[0037] Two sinusoidal radio frequency local oscillator signals with the same frequency and orthogonality are generated by the first local oscillator. After the simulated intermediate frequency signal is mixed with the sinusoidal radio frequency local oscillator signal, two mixed radio frequency signals are obtained. The two mixed radio frequency signals are then combined into one radio frequency signal. The combined radio frequency signal is then amplified by the first power amplifier. The amplified signal is then used to perform phase modulation on the fiber optic phase modulator.

[0038] The optical signal generated by the frequency-stabilized continuous fiber laser is transmitted to the fiber phase modulator. The optical signal output by the fiber phase modulator is amplified by the erbium-doped fiber amplifier and then input into the fiber circulator.

[0039] The optical signal is transmitted to the optical antenna through the Out end of the fiber optic circulator; the optical signal output by the optical antenna is split into two parts by a beam splitter. One part of the optical signal is converted into periodic signal light after passing through the first optical chopper. The periodic signal light output by the first optical chopper illuminates the stationary reference target. The other part of the optical signal is converted into periodic signal light after passing through the second optical chopper. The periodic signal light output by the second optical chopper illuminates the detection target.

[0040] The echo signal light from the reference target and the detection target is then collected by the optical antenna. The echo signal light passes through the Out end and Re end of the fiber optic circulator in sequence, and then passes through the fiber optic Fabry-Perot interferometer and is incident on the square law photodetector 10.

[0041] Two sinusoidal local oscillator radio frequency signals with the same frequency and orthogonal are generated by the second ground oscillator. The radio frequency signal generated by the square law photodetector is amplified by the second power amplifier. The signal after amplification by the second power amplifier is divided into two parts.

[0042] One part of the signal is mixed with a sinusoidal local oscillator radio frequency signal generated by the second ground oscillator. After mixing, the signal passes through a third low-pass filter, a first analog-to-digital converter, and a first digital down-converter in sequence. The other part is mixed with another sinusoidal local oscillator radio frequency signal generated by the second ground oscillator. After mixing, the signal passes through a fourth low-pass filter, a second analog-to-digital converter, and a second digital down-converter in sequence.

[0043] The digital intermediate frequency (IF) signals output from the first and second digital down-converters are sent to the computer for processing after passing through the receiver controller and interface controller. The computer then outputs the distance and velocity measurement results of the detected target.

[0044] The beneficial effects of this invention are:

[0045] This invention utilizes laser radio frequency modulation and demodulation technology to introduce radio frequency technology into direct detection lidar. By using a beam splitter and optical chopper to process the echo signals from the reference target and the detected target, it improves the detection performance for target distance and velocity, solving the problem that existing methods cannot measure target distance information. Furthermore, the measurement method of this invention utilizes the frequency information of the radio frequency signal, avoiding information waste. Attached Figure Description

[0046] Figure 1 is a schematic diagram of a radio frequency modulation direct detection lidar.

[0047] Figure 2(a) shows the time-domain signal of radio frequency crosstalk when there is no target echo signal;

[0048] Figure 2(b) shows the FFT amplitude spectrum corresponding to Figure 2(a);

[0049] Figure 2(c) is a magnified view of the spectrum of Figure 2(b) near 800kHz;

[0050] Figure 2(d) is a magnified view of the spectrum of Figure 2(b) near 1.6MHz;

[0051] Figure 3(a) shows the time-domain signals of radio frequency crosstalk and reference target echo;

[0052] Figure 3(b) shows the FFT amplitude spectrum corresponding to Figure 3(a);

[0053] Figure 3(c) is a magnified view of the spectrum of Figure 3(b) near 800 kHz;

[0054] Figure 3(d) is a magnified view of the spectrum of Figure 3(b) near 1.6MHz;

[0055] Figure 4(a) shows the time-domain signals of radio frequency crosstalk and the echo of the detected target;

[0056] Figure 4(b) shows the FFT amplitude spectrum corresponding to Figure 4(a);

[0057] Figure 4(c) is a magnified view of the spectrum of Figure 4(b) near 800 kHz;

[0058] Figure 4(d) is a magnified view of the spectrum of Figure 4(b) near 1.6MHz;

[0059] Figure 5(a) shows the time-domain signals of radio frequency crosstalk, reference and detection target echoes;

[0060] Figure 5(b) shows the FFT amplitude spectrum corresponding to Figure 5(a);

[0061] Figure 5(c) is a magnified view of the spectrum of Figure 5(b) near 800 kHz;

[0062] Figure 5(d) is a magnified view of the spectrum of Figure 5(b) near 1.6MHz;

[0063] Figure 6 shows the results of distance measurement for a stationary target.

[0064] Figure 7(a) shows the mid-frequency time-domain signal of the rotating fan blades as the detection target;

[0065] Figure 7(b) shows the amplitude spectrum of the FFT corresponding to Figure 7(a);

[0066] Figure 7(c) is a magnified view of the spectrum of Figure 7(b) near 800 kHz;

[0067] Figure 7(d) is a magnified view of the spectrum of Figure 7(b) near 2.4MHz;

[0068] Figure 8(a) is a magnified view of the amplitude spectrum of the intermediate frequency time domain signal near 800kHz when the rotational speed of the fan blades is changed.

[0069] Figure 8(b) is a magnified view of the amplitude spectrum of the intermediate frequency time domain signal near 1.6MHz when the rotational speed of the fan blades is changed;

[0070] Figure 9(a) shows the mid-frequency time-domain signal caused by the simultaneous reference and rotating detection target;

[0071] Figure 9(b) shows the FFT amplitude spectrum corresponding to Figure 9(a);

[0072] Figure 9(c) is a magnified view of the spectrum of Figure 9(b) near 800 kHz;

[0073] Figure 9(d) is a magnified view of the spectrum of Figure 9(b) near 2.4MHz;

[0074] Figure 10(a) shows the mean and standard deviation of the target distance measurement at different speeds;

[0075] Figure 10(b) shows the mean and standard deviation of the target velocity measurement at different speeds. Detailed Implementation

[0076] Specific Implementation Method 1: This implementation method is illustrated in conjunction with Figure 1. The target distance and velocity measurement system based on radio frequency modulation direct detection lidar described in this implementation method includes two parts: an optical path and a circuit.

[0077] The optical path includes a frequency-stabilized continuous wave fiber laser (CWFL) 1, a fiber phase modulator (FPM) 2, an erbium-doped fiber amplifier (EDFA) 3, a fiber optical circulator (FOC) 4, an optical antenna (OA) 5, beam splitters (BS) 6, a first optical chopper (OC) 7, a second optical chopper 8, a fiber Fabry-Perot interferometer (FFPI) 9, and a square rate photodetector (PD) 10; wherein:

[0078] The output end of the frequency-stabilized continuous fiber laser 1 is connected to the input end 2A of the fiber phase modulator 2.

[0079] The output end of the fiber phase modulator 2 is connected to the input end of the erbium-doped fiber amplifier 3;

[0080] The output end of the erbium-doped fiber amplifier 3 is connected to the In end of the fiber optic circulator 4;

[0081] The Out terminal of the fiber optic circulator 4 is connected to the first input / output terminal 5A of the optical antenna 5;

[0082] The second input / output terminal 5B of the optical antenna 5 is connected to the first input / output terminal 6A of the beam splitter 6;

[0083] The second input / output terminal 6B of the beam splitter 6 is connected to the first input / output terminal 7A of the first optical chopper 7; the signal output from the second input / output terminal 7B of the first optical chopper 7 illuminates a stationary reference target (RT);

[0084] The third input / output terminal 6C of the beam splitter 6 is connected to the first input / output terminal 8A of the second optical chopper 8; the signal output from the second input / output terminal 8B of the second optical chopper 8 illuminates the detection target (RT);

[0085] The Re terminal of the fiber optic circulator 4 is connected to the input terminal of the fiber optic Fabry-Perot interferometer 9.

[0086] The output of the fiber optic Fabry-Perot interferometer 9 is connected to the input of the square law photodetector 10;

[0087] The circuitry includes a computer 11 and a software-defined radio (SDR);

[0088] The software-defined radio includes an interface controller 12, a transmit controller 13, a first digital upconverter (DUC) 14, a second digital upconverter 15, a first digital-to-analog converter (DAC) 16, a second DAC 17, a first low-pass filter (LPF) 18, a second low-pass filter 19, a first local oscillator (LO) 20, a first power amplifier 21, a second power amplifier 22, a second local oscillator 23, a third low-pass filter 24, a fourth low-pass filter 25, a first analog-to-digital converter (ADC) 26, a second analog-to-digital converter 27, a first digital downconverter (DDC) 28, a second digital downconverter 29, a receive controller 30, a first mixer 31, a second mixer 32, a third mixer 33, and a fourth mixer 34; wherein:

[0089] The input / output terminal 11A of the computer 11 is connected to the input / output terminal 12A of the interface controller 12;

[0090] The output terminal of the interface controller 12 is connected to the input terminal of the transmitter controller 13;

[0091] The first output terminal 13A of the transmitter controller 13 is connected to the input terminal of the first digital up-converter 14; the second output terminal 13B of the transmitter controller 13 is connected to the input terminal of the second digital up-converter 15.

[0092] The output terminal of the first digital-to-digital converter 14 is connected to the input terminal of the first digital-to-analog converter 16; the output terminal of the second digital-to-digital converter 15 is connected to the input terminal of the second digital-to-analog converter 17.

[0093] The output terminal of the first digital-to-analog converter 16 is connected to the input terminal of the first low-pass filter 18; the output terminal of the second digital-to-analog converter 17 is connected to the input terminal of the second low-pass filter 19.

[0094] The first output terminal 20A of the first local oscillator 20 is connected to the first input terminal 31A of the first mixer 31; the second output terminal 20B of the first local oscillator 20 is connected to the first input terminal 32A of the second mixer 32.

[0095] The output terminal of the first low-pass filter 18 is connected to the second input terminal 31B of the first mixer 31; the output terminal of the second low-pass filter 19 is connected to the second input terminal 32B of the second mixer 32.

[0096] The output terminals of the first mixer 31 and the second mixer 32 are connected to the input terminal of the first power amplifier 21.

[0097] The output terminal of the first power amplifier 21 is connected to the second input terminal 2B of the fiber optic phase modulator 2;

[0098] The output terminal of the square law photodetector 10 is connected to the input terminal of the second power amplifier 22;

[0099] The output terminal of the second power amplifier 22 is connected to the first input terminal 33A of the third mixer 33 and the first input terminal 34A of the fourth mixer 34, respectively.

[0100] The first output terminal 23A of the second local oscillator 23 is connected to the second input terminal 33B of the third mixer 33; the second output terminal 23B of the second local oscillator 23 is connected to the second input terminal 34B of the fourth mixer 34.

[0101] The output of the third mixer 33 is connected to the input of the third low-pass filter 24; the output of the fourth mixer 34 is connected to the input of the fourth low-pass filter 25.

[0102] The output of the third low-pass filter 24 is connected to the input of the first analog-to-digital converter 26; the output of the first analog-to-digital converter 26 is connected to the input of the first digital down-converter 28.

[0103] The output of the fourth low-pass filter 25 is connected to the input of the second analog-to-digital converter 27; the output of the second analog-to-digital converter 27 is connected to the input of the second digital down-converter 29.

[0104] The output terminal of the first digital down-converter 28 is connected to the first input terminal 30A of the receiver controller 30; the output terminal of the second digital down-converter 29 is connected to the second input terminal 30B of the receiver controller 30.

[0105] The output terminal of the receiving controller 30 is connected to the input terminal of the interface controller 12.

[0106] Specific Implementation Method Two: A measurement method for a target distance and velocity measurement system based on a radio frequency modulation direct detection lidar as described in Implementation Method One, wherein the method specifically comprises:

[0107] The two orthogonal digital intermediate frequency (IF) signals generated by the computer 11 are sequentially passed through the interface controller 12 and the transmitter controller 13. One of the digital IF signals is output by the transmitter controller 13 and then sequentially passes through the first digital up-converter 14, the first digital-to-analog converter 16, and the first low-pass filter 18. The other digital IF signal is output by the transmitter controller 13 and then sequentially passes through the second digital up-converter 15, the second digital-to-analog converter 17, and the second low-pass filter 19. The first low-pass filter 18 and the second low-pass filter 19 are used to output two orthogonal analog IF signals.

[0108] Two sinusoidal radio frequency local oscillator signals with the same frequency and orthogonal are generated by the first local oscillator 20. After the simulated intermediate frequency signal is mixed with the sinusoidal radio frequency local oscillator signal, two mixed radio frequency signals are obtained. The two mixed radio frequency signals are then combined into one radio frequency signal. The combined radio frequency signal is then amplified by the first power amplifier 21. The amplified signal is then used to perform phase modulation on the fiber optic phase modulator 2.

[0109] The optical signal generated by the frequency-stabilized continuous fiber laser 1 is transmitted to the fiber phase modulator 2. The optical signal output by the fiber phase modulator 2 is amplified by the erbium-doped fiber amplifier 3 and then input to the fiber circulator 4.

[0110] The optical signal is transmitted to the optical antenna 5 through the Out end of the fiber optic circulator 4; the optical signal output by the optical antenna 5 is split into two parts by the beam splitter 6. The part of the optical signal with lower power is converted into periodic signal light after passing through the first optical chopper 7. The periodic signal light output by the first optical chopper 7 illuminates the stationary reference target. The other part of the optical signal with higher power is converted into periodic signal light after passing through the second optical chopper 8. The periodic signal light output by the second optical chopper 8 illuminates the detection target.

[0111] The optical antenna 5 is then used to collect the echo signal light from the reference target and the detection target. The echo signal light passes through the Out end and Re end of the fiber optic circulator 4 in sequence, and then passes through the fiber optic Fabry-Perot interferometer 9 and is incident on the square law photodetector 10.

[0112] Two sinusoidal local oscillator radio frequency signals with the same frequency and orthogonal are generated by the second ground oscillator 23. The radio frequency signal generated by the square law photodetector 10 enters the second power amplifier 22 for amplification. The signal amplified by the second power amplifier 22 is divided into two parts.

[0113] One portion of the signal is mixed with a sinusoidal local oscillator radio frequency signal generated by the second ground oscillator 23. After mixing, the signal passes through the third low-pass filter 24, the first analog-to-digital converter 26, and the first digital down-converter 28 in sequence. The other portion is mixed with another sinusoidal local oscillator radio frequency signal generated by the second ground oscillator 23. After mixing, the signal passes through the fourth low-pass filter 25, the second analog-to-digital converter 27, and the second digital down-converter 29 in sequence.

[0114] The digital intermediate frequency signal output by the first digital down-converter 28 and the digital intermediate frequency signal output by the second digital down-converter 29 are sent to the computer 11 for processing after passing through the receiver controller 30 and the interface controller 12. After processing by the computer 11, the distance and velocity measurement results of the detected target are output.

[0115] This invention utilizes a beam splitter (BS) to address the problem that phase delay contains random quantities and cannot be directly used for measuring target distance R. When the target DT is stationary, the target radio frequency signal i corresponds to frequencies f1 and f2. f D1 and i fWithout a Doppler shift at D2, the spectra of the reference and probe target RF signals will overlap, making it impossible to accurately obtain their respective phase values ​​using Fourier transform. Furthermore, inevitably, some RF signals will crosstalk directly from the TX end of the software radio to the RX end, and their spectrum will also overlap with the spectral lines of the stationary probe and reference target RF signals. This invention utilizes an optical chopper to convert the continuous echo signal light from the reference and probe targets into periodic signal light. This discretizes the spectra of their generated RF signals with frequency intervals equal to the reciprocal of the period, and then indirectly calculates the required phase value using these non-overlapping discrete spectra.

[0116] Specific Implementation Method 3: This implementation method further defines Specific Implementation Method 2, wherein the frequency-stabilized continuous fiber laser 1 emits a single-frequency signal light E. T Specifically, it is as follows:

[0117] E T =E0exp(jωt+φ0)

[0118] Where E0 is the single-frequency signal light E T The amplitude, j is the imaginary unit, and ω is the single-frequency signal light E. T The angular frequency, t is time, and φ0 is the single-frequency signal light E. T The initial phase.

[0119] The other steps and parameters are the same as in Specific Implementation Method Two.

[0120] Specific Implementation Method Four: This implementation method further defines Specific Implementation Method Three. The radio frequency signal U output by the first power amplifier 21 in the circuit section is:

[0121] U = sin(2πf1t) + sin(2πf2t)

[0122] Where sin(2πf1t) is the radio frequency signal with frequency f1, sin(2πf2t) is the radio frequency signal with frequency f2, and t is time.

[0123] The first digital-to-analog converter (DAC) simultaneously generates f. 01 and f 02 The sinusoidal intermediate frequency signal of frequency f is also generated by the second digital-to-analog converter (DAC). 01 and f 02 The two sinusoidal intermediate frequency (IF) signals are orthogonal and intersect with a frequency of f. OL The sinusoidal RF local oscillator signal is mixed and up-converted to obtain two orthogonal sinusoidal RF signals, each of which includes a frequency of f1 = f 01 +f OLThe radio frequency signal portion and frequency are f2 = f 02 +f OL The radio frequency signal section.

[0124] The other steps and parameters are the same as in Specific Implementation Method 3.

[0125] Specific Implementation Method Five: This implementation method further defines Specific Implementation Method Four. The echo signal light from the reference target, after passing through the fiber optic Fabry-Perot interferometer 9, generates a period of T at the square-law photodetector 10. R radio frequency signals With a period of T R radio frequency signals The echo signal light from the target being detected passes through the fiber optic Fabry-Perot interferometer 9 and then generates a period of T at the square law photodetector 10. D radio frequency signals With a period of T D radio frequency signals And T R ≠T D ;

[0126] The frequency generated by the second local oscillator 23 is f OL The sinusoidal local oscillator radio frequency signal is mixed to obtain a period of T. R intermediate frequency signal The frequency generated by the second local oscillator 23 is f OL The sinusoidal local oscillator radio frequency signal is mixed to obtain a period of T. R intermediate frequency signal

[0127] The frequency generated by the second local oscillator 23 is f OL The sinusoidal local oscillator radio frequency signal is mixed to obtain a period of T. D intermediate frequency signal The frequency generated by the second local oscillator 23 is f OL The sinusoidal local oscillator radio frequency signal is mixed to obtain a period of T. D intermediate frequency signal

[0128] The intermediate frequency signal and After low-pass filtering, analog-to-digital conversion, and digital down-conversion, the data is sent to a computer for processing.

[0129] The method for measuring the distance and velocity of the detected target is as follows:

[0130] intermediate frequency signal The fundamental frequency and the frequency values ​​of each harmonic component are expressed as follows: intermediate frequency signal The fundamental frequency and the frequency values ​​of each harmonic component are expressed as follows: intermediate frequency signal The fundamental frequency and the frequency values ​​of each harmonic component are expressed as follows: intermediate frequency signal The fundamental frequency and the frequency values ​​of each harmonic component are expressed as follows: but:

[0131]

[0132] Where k is an integer, k = 0 represents the fundamental frequency component, k ≠ 0 represents the kth harmonic component, and f1 R This represents the continuous radio frequency signal of the reference target that has not been periodized by the first optical chopper. Frequency value, f2 R This represents the continuous radio frequency signal of the reference target that has not been periodized by the first optical chopper. Frequency value, f1 D This indicates the continuous radio frequency signal of the detected target that has not been periodized by the second optical chopper. Frequency value, f2 D This indicates the continuous radio frequency signal of the detected target that has not been periodized by the second optical chopper. Frequency value, f1 R f2 R f1 D and f2 D It can be obtained through Fourier transform;

[0133] Will The corresponding phase value is expressed as Will The corresponding phase value is expressed as Will The corresponding phase value is expressed as Will The corresponding phase value is expressed as

[0134] When the target is stationary, the periodic intermediate frequency signal and The spectral lines of the k = ±1 harmonic components remain separate and do not coincide with the spectral lines of the fundamental frequency component. The phase values ​​of these k = ±1 harmonic components can be measured using Fourier transform. and and and as well as and

[0135] For intermediate frequency signals Perform Fourier transform to obtain and For intermediate frequency signals Perform Fourier transform to obtain and For intermediate frequency signals Perform Fourier transform to obtain and For intermediate frequency signals Perform Fourier transform to obtain and Recalculate and

[0136]

[0137] The frequency value of the fundamental frequency component and The difference and phase value and The difference is:

[0138]

[0139] Then according to and Calculate the relative distance R between the reference target and the detection target, and calculate the distance of the detection target based on the distance to the stationary reference target and the relative distance R;

[0140] The relative velocity ν between the stationary reference target and the detection target is calculated based on Δf1 and Δf2, thus obtaining the velocity of the detection target.

[0141] The other steps and parameters are the same as in Specific Implementation Method Four.

[0142] Specific Implementation Method Six: This implementation method is a further limitation of Specific Implementation Method Five, wherein the method is based on... and The specific process for calculating the relative distance R between the reference target and the detection target is as follows:

[0143]

[0144] Where c is the speed of light.

[0145] The other steps and parameters are the same as in Specific Implementation Method 5.

[0146] Specific Implementation Method Seven: This implementation method further defines Specific Implementation Method Six. The specific process for calculating the relative velocity ν between the reference target and the detection target based on Δf1 and Δf2 is as follows:

[0147]

[0148] The other steps and parameters are the same as in Specific Implementation Method Six.

[0149] Implementation Method Eight: This implementation method further defines Implementation Method Six. Specifically, the calculation of the distance to the detected target based on the distance to the reference target and the relative distance R is as follows:

[0150] R = R1 - R0

[0151] Where R0 is the reference target distance and R1 is the detection target distance.

[0152] The other steps and parameters are the same as in Specific Implementation Method Six.

[0153] Theoretical basis

[0154] The single-frequency signal light emitted by a continuous-wave fiber laser (CWFL) is E T =E0exp(jωt+φ0), after being phase-modulated by the RF signal U=U0sinΩt generated by software-defined radio, can be expressed as:

[0155] E T =E0exp[j(ωt+κU0sinΩt+φ0)] (1)

[0156] Where E0, ω, and φ0 are the amplitude, angular frequency, and initial phase of the emitted signal light, respectively; j is the imaginary unit; κ is the modulation coefficient of the phase modulator; and Ω and U0 are the angular frequency and amplitude of the radio frequency signal, respectively.

[0157] Define β=κU0 as the phase modulation depth, and assume β≤0.9. Using Bessel functions, equation (1) can be expanded into a superposition of three frequency components (the carrier at frequency ω and the ±1st order sidebands at frequencies ω±Ω), i.e.:

[0158] E T ≈E0J1exp{j[(ω+Ω)t+φ0]}+E0J0exp[j(ωt+φ0)]-E0J1exp{j[(ω-Ω)t+φ0]} (2)

[0159] Here, J0 and J1 are the first-order and second-order Bessel functions of the first kind, respectively, and their magnitudes are related to the phase modulation depth β. Since β is a constant here, J0 and J1 can be considered as constants.

[0160] After the emitted signal light is reflected back by a target with radial distances and velocities of R and ν, respectively, all three frequency components of the emitted signal light undergo Doppler shift and phase delay. Ignoring factors such as amplitude attenuation, the optical field intensity E of the echo signal light... R It can be approximated as:

[0161]

[0162] Among them, E 01 =E0J1,E 00 =E0J0, where c is the speed of light.

[0163] Because the ±1st order sidebands are symmetrical with respect to the carrier, when this echo signal light is directly incident on a square-law detector, the radio frequency signals (equal in frequency and phase, but opposite in amplitude) generated by the +1st order sideband beating the carrier and the -1st order sideband beating the carrier, respectively, completely cancel each other out, resulting in no radio frequency signal output. However, if the echo signal light passes through an FFPI (Focus-Focus Intensity Pipeline), the edge of its field strength transmission curve disrupts the symmetry of the amplitude and phase of the ±1st order sidebands, causing the detector to output a radio frequency signal. Assuming the field strength transmission coefficient of the FFPI is T (a function of the signal light frequency), the field strength of the echo signal light after passing through the FFPI becomes:

[0164]

[0165] in,

[0166] Equation (4) represents the echo signal light incident on the square-law detector after passing through the FFPI. The output current i of the square-law detector is proportional to the optical field E. R The square of the modulus, that is |E R | 2 It contains 9 product terms. The sum of 3 of these product terms corresponds to the DC signal. The sum of the four product terms corresponds to an RF signal with a modulation frequency Ω of 1. The sum of the two product terms corresponds to a radio frequency signal of 2Ω at twice the modulation frequency. That is i=i d +i Ω +i 2Ω DC signal i d and radio frequency signal i 2Ω This signal will be filtered out by the software-defined radio module and will not be acquired or processed. Here, we only care about the radio frequency signal i at 1 times the modulation frequency Ω. Ω The values ​​of each product term it contains are as follows:

[0167]

[0168] Combine equation (5) and item, and If the term is given, then we can obtain:

[0169]

[0170] Let complex number The modulus and complex angle are respectively Combining the two terms in equation (6), we get the radio frequency signal i with a modulation angular frequency of 1 times Ω. Ω It can be represented as:

[0171]

[0172] Analysis of formula (7) shows that, relative to the radio frequency signal output from the software radio TX terminal... RF signal i output by PD to the software radio RX terminal Ω The angular frequency of (ν,R) changed The magnitude of the Doppler frequency shift can be directly used to measure the target velocity ν, as the phase changes. The delay in size, due to its inclusion of a random quantity φ (according to complex numbers) As can be seen from the definition, its complex angle φ is related to factors such as the target velocity ν and the laser angular frequency ω. In actual work, its magnitude will change randomly, and it cannot be directly used to measure the target distance R.

[0173] To solve this problem, we use a beam splitter (BS) to split the emitted laser in the structure shown in Figure 1 into two beams. One beam illuminates a stationary reference target RT at a constant distance R0, and the other beam illuminates a detection target DT at a distance of R1 and a velocity of ν, respectively. The distance difference between the detection target DT and the reference target RT is R = R1 - R0. According to formula (7), the echo signals from the reference target and the detection target will generate radio frequency (RF) signals, and the detector output RF signal will contain two components:

[0174]

[0175] in,

[0176] This refers to the radio frequency signal generated by the RT echo signal light from the reference target. This refers to the radio frequency signal generated by the DT echo signal light of the detected target.

[0177] In formula (8), Ω is used.R =Ω and They represent Frequency and phase; using and They represent The frequency and phase. If the radio frequency signal generated by the reference target RT echo signal light... For reference, the radio frequency signal generated by the DT echo signal light of the detection target. The frequency occurred The magnitude of the Doppler frequency shift can also be used to measure velocity ν, and the phase changes. The size delay, since it does not contain a random quantity φ, can be used to obtain information about the relative distance R of the measured target.

[0178] At the transmitting end, a radio frequency (RF) signal is loaded onto the emitted signal light. The speed and distance of the reference and detection targets cause changes in the frequency and phase of the signal light, which in turn inevitably leads to changes in the frequency and phase of the RF signal loaded onto it. At the receiving end, the RF signal is demodulated from the echo signal light, and the echo RF signal from the detection target is used to... With reference echo radio frequency signal Frequency difference The difference between the phase and the phase It can obtain the relative speed and distance information of the target being detected, which is the differential detection principle of radio frequency modulation direct detection lidar.

[0179] This invention retains the advantages of lidar in terms of spatial resolution, while seamlessly integrating the theoretical, methodological, and technological advantages of radio frequency (RF) radar signal processing into lidar, thereby enhancing its detection capabilities. Because the RF modulation direct detection lidar proposed in this invention uses software-definable radio waves as its RF components, it can generate, measure, and process different RF signals through software programming. Therefore, different RF radar ranging and velocity measurement methods can be implemented using software algorithms without changing the hardware.

[0180] A radio frequency signal U = sin(2πf1t) + sin(2πf2t) containing both frequency components f1 and f2 is generated using software radio. The emitted signal light is then phase-modulated. According to formula (7), the echo signals from both the reference and detection targets will contain these two frequency components. Therefore, the final output radio frequency signal from the detector will contain four components:

[0181]

[0182] in,

[0183] and These are the radio frequency signals generated by the reference and detection targets respectively in response to the transmitted radio frequency signal at frequency f1. and These are the radio frequency signals generated by the reference and measurement targets respectively when they transmit radio frequency signals at frequency f2.

[0184] According to differential detection theory, in order to obtain the relative distance R and distance velocity ν of the target, it is necessary to measure the DT radio frequency signal of the target. Relative to the reference target RT radio frequency signal frequency change and phase delay And detect the target DT radio frequency signal Relative to the reference target RT radio frequency signal frequency change and phase delay

[0185] As the relative distance R increases, the phase... and They will all change periodically between -π and +π, that is... and These are multivalued functions of the relative distance R, so only a certain range within 2π can be selected. and The measured values ​​are used to calculate the relative distance to the target. and Furthermore, since the values ​​of f1 and f2 are very high (approximately 10), 9 (on the order of Hz), in the range of 2π and The change in the relative distance R will correspond to a very small measurement range (10). -1 (On the order of m), which cannot meet the requirements of radar detection, therefore it cannot be used alone. and The relative distance R of the measured target can be directly calculated from the measured value. However, the difference between two phase measurements can be used. Using formula

[0186]

[0187] Calculate the relative distance R to the detected target. Since f2-f1 can be very small, when it is 10... 3 At the Hz level, in the 2π range The change in distance R corresponds to a change of 10. 2 The speed is on the order of km, which can meet the measurement requirements of lidar.

[0188] The velocity of the target can be calculated using the measured values ​​of Δf1 and Δf2 respectively. and Theoretically, they are equal (ν1 = ν2) and can each be used individually as a measurement of the target velocity. In practice, we can average them, that is:

[0189]

[0190] In actual measurements, the four radio frequency components can be obtained by performing a Fourier transform on the radio frequency signal output by the detector. and Frequency value f1 R f1 D f2 R and f2 D and phase value and Therefore, the differential phase delay of the two radio frequency signals at frequencies f1 and f2 can be calculated respectively. and And differential Doppler frequency shift Δf1=f1 D -f1 R and Δf2=f2 D -f2 R Then, by using formulas (10) and (11), the relative distance R and relative velocity v of the target DT can be calculated.

[0191] However, when the target DT is stationary, the target radio frequency signals corresponding to frequencies f1 and f2 are... and No Doppler shift occurred, i.e., f1 D =f1 R =f1 and f2 D =f2 R =f2, the spectra of the reference and probe target RF signals will overlap, making it impossible to accurately obtain their respective phase values ​​using Fourier transform. Furthermore, inevitably, some RF signals will crosstalk directly from the TX end of the software radio to the RX end, and their spectrum will also overlap with the spectral lines of the stationary probe and reference target RF signals. Therefore, when the spectra of the crosstalk RF signal, the reference, and the probe target RF signals overlap, the phase values ​​of the four RF signals cannot be directly obtained using Fourier transform. and Therefore, it is impossible to calculate. and The relative distance information of the target was obtained by using a dual-frequency distance-velocity measurement method.

[0192] To address the aforementioned problems, this invention utilizes a first optical chopper and a second optical chopper to transform the continuous echo signal light from the reference and detection targets into periodic signal light. This discretizes the spectrum of their generated radio frequency signals at frequency intervals equal to the reciprocal of the period. The required phase value is then indirectly calculated using these non-overlapping discrete spectra. Let the period of the reference target echo signal light be T. R The period of the target echo signal light is T. D And T R ≠T D .use and This indicates that the spectrum of the periodized reference target radio frequency signal will be 1 / T R The frequency interval is discretized into a superposition of the fundamental frequency component and each harmonic component; using and This indicates that the frequency spectrum of the periodized target radio frequency signal will change by 1 / T. D The frequency interval is discretized into a superposition of the fundamental frequency component and each harmonic component. The frequencies of these discrete fundamental and harmonic components are expressed as follows:

[0193]

[0194] f1 R (k) and f2 R (k) represent the reference target periodic radio frequency signal, respectively. and The frequency values ​​of the fundamental frequency and harmonic components, and their corresponding phase values ​​are used. and f1 indicates. D (k) and f2 D (k) represent the periodic radio frequency signals of the detection target. and The frequency values ​​of the fundamental frequency and harmonic components, and their corresponding phase values ​​are used. and The symbol represents the fundamental frequency component. k is an integer, k = 0 represents the fundamental frequency component, and k ≠ 0 corresponds to the kth harmonic component.

[0195] According to signal processing theory, the phase of the k = ±1 harmonic components of a periodic signal is oddly symmetric about the phase of the fundamental frequency component, that is:

[0196]

[0197] Furthermore, as can be seen from formula (12), due to the periodic radio frequency signal and The frequency value of the fundamental frequency component is equal to that of the continuous radio frequency signal. and The frequency value, i.e., f1 R (0)=f1 R f2 R (0)=f2 R f1 D (0)=f1 D and f2 D (0)=f2 D Therefore, the phase value of the fundamental frequency component of a periodic radio frequency signal can be used to replace the phase of a continuous radio frequency signal, i.e. and Used to obtain the relative distance R of the target being detected.

[0198] Although, due to radio frequency crosstalk and the stationary nature of the detection target, continuous echo radio frequency signals and Their spectra overlap, thus causing their phases to... and They cannot be directly obtained using Fourier transform, but they can be transformed into periodic radio frequency signals. and Then, the frequencies f1 of their respective k=±1 harmonics. R (-1) and f1 R (+1), f2 R (-1) and f2 R (+1), f1 D (-1) and f1 D (+1) and f2 D (-1) and f2 D (+1) are not equal to each other, and are related to the frequency f1 of their fundamental frequency components. R (0), f2 R (0), f1 D (0) and f2 D (0) are also not equal, and their corresponding spectral lines are separated from each other in the spectrum, so the phase of the k = ±1 harmonic is... and and and as well as and The phase of the fundamental frequency component can be obtained directly through Fourier transform, and then indirectly calculated using formula (13). and This allows us to calculate the differential phase delay of the radio frequency signals at frequencies f1 and f2. and Finally, the relative distance R of the target can be calculated using formula (10).

[0199] Signal processing methods for periodic intermediate frequency signals

[0200] As shown in Figure 1, the software radio module simultaneously generates f through a digital-to-analog converter (DAC). 01 and f 02 A sinusoidal intermediate frequency signal with frequency f, and a frequency of f OL The sinusoidal radio frequency local oscillator signal is mixed and then up-converted to produce f1 = f 01 +f OL and f2 = f 02 +f OL A sinusoidal radio frequency signal of frequency T is output to an optical fiber phase modulator via the TX pin of a software-defined radio, where the output signal light undergoes dual-frequency phase modulation. R The reference target echo signal light, after passing through the FFPI, generates a photodetector with a period of T. R radio frequency signals and Entering the software wireless RX end and f OL The radio frequency local oscillator signal is mixed and down-converted to a frequency with a period of T. R intermediate frequency signal and The period is T D The target echo signal light, after passing through the FFPI, generates a photodetector with a period of T. D Radio frequency signals and Entering the software wireless RX end and f OL The radio frequency local oscillator signal is mixed and down-converted to a frequency with a period of T. D intermediate frequency signal and These four intermediate frequency signals also contain the fundamental frequency and each harmonic component, and the corresponding frequency values ​​can be expressed by formula (12) after frequency down-conversion:

[0201]

[0202] and These represent the intermediate frequency signals of the reference target, respectively. and The frequency values ​​of the fundamental frequency and harmonic components, and their corresponding phase values ​​are used. and express; and They represent the intermediate frequency signals of the detected target, respectively. and The frequency values ​​of the fundamental frequency and harmonic components, and their corresponding phase values ​​are used. and k is an integer, k = 0 represents the fundamental frequency component, and k ≠ 0 represents the kth harmonic component. fOL The phase of the sinusoidal local oscillator radio frequency signal.

[0203] Because of T R ≠T D When the target is stationary, the periodic intermediate frequency signal and The spectral lines of the k = ±1 harmonic components remain separate and do not coincide with the spectral lines of the fundamental frequency component. The phase values ​​of these k = ±1 harmonic components can be measured using Fourier transform. and and and as well as and The phase of the fundamental frequency component of the periodic intermediate frequency signal can still be calculated based on the phase relationship between the harmonic component and the fundamental frequency component in formula (13). and

[0204] Periodic intermediate frequency signal and The frequency value of the fundamental frequency component and Difference and phase values and The difference satisfies:

[0205]

[0206] The frequency difference value of the fundamental frequency component of the periodic intermediate frequency signal can be used. and The frequency difference Δf = f1 replaces the continuous radio frequency signal D -f1 R and Δf2=f2 D -f2 R The relative velocity ν of the target can be calculated using formula (11); the phase difference value of the fundamental frequency component of the periodic intermediate frequency signal can be used. and Phase difference replacing continuous radio frequency signals and The relative distance R of the target can be calculated using formula (10).

[0207] Experimental Section

[0208] To experimentally verify the principle of radio frequency modulation direct detection lidar, this invention constructed the experimental device shown in Figure 1. The optical path of this device uses an ORION fiber laser module from RIO Corporation, producing a single-frequency continuous laser with an output power of approximately 10mW, a wavelength of approximately 1550nm, and a linewidth ≤15kHz. The fiber phase modulator is an MPZ-LN-10 type manufactured by iXblue Corporation, with a maximum modulation bandwidth of 12GHz. The optical signal output from the fiber phase modulator is amplified by an EFDFA-MC-CW-30-S type continuous fiber amplifier module manufactured by OPEAK Corporation, producing a continuous laser with a maximum output power of approximately 1W. The laser light is then output through the In and Out ends of a fiber circulator to a TC25APC-1550 type fiber expander collimator from Thorlab Corporation, where it is converted into parallel light before being output to illuminate the target. A target with a reflective strip on its surface reflects the signal light backward. This reflected light is then collected again by a beam expander and collimator, enters the Out end of a fiber optic circulator, and is output from the Re end to a Micron Optics FFP-TF2 fiber FFPI to disrupt the symmetry of the phase-modulated signal spectrum. The light is then detected by a Newport 1414 photodetector, which outputs an RF signal. The circuitry uses an ETTUS USRP B200min software-defined radio module, which has one RF transmitter (TX) and one RF receiver (RX). The RF signal generated by the transmitter is modulated by a phase modulator and applied to the emitted laser. The receiver receives the RF signal output from the photodetector. The module's RF signal frequency range is 70MHz to 6GHz, with an instantaneous bandwidth of 56MHz. The module connects to a PC via a high-speed USB 3.0 interface for data stream transmission and power supply. The generation, reception, and processing of the RF signal by this software-defined radio module are all controlled by a user program on the PC.

[0209] The software-defined radio module simultaneously generates frequencies f at a sampling rate of 6.4MHz via a digital-to-analog converter (DAC). 01 =800kHz and f 02 A 2.4MHz intermediate frequency sinusoidal signal, with a frequency of f OL The 5GHz radio frequency local oscillator signal is mixed and up-converted to generate frequencies f1 = f 01 +f OL =5.0008GHz and f2=f 02 +f OLA sinusoidal radio frequency (RF) signal of 5.0024 GHz is used. The frequency difference between the two RF signals is f2 - f1 = 1.6 MHz (a relative phase delay of 2π allows for ranging of the relative distance R of a target within a range <93.75 m). The signal is output to an optical fiber phase modulator via the TX port of a software-defined radio, where the output signal light undergoes dual-frequency phase modulation. The periodic echo signal light from the reference and target passes through an FFPI sensor and generates a periodic RF signal in the photodetector. and Entering the software wireless RX end and f OL =5GHz RF local oscillator signal is mixed and down-converted into a periodic intermediate frequency signal. and The signal is converted into a digital intermediate frequency signal by an analog-to-digital converter (ADC) at a sampling rate of 6.4 MHz and then enters the PC. The sampling time is approximately 0.23 seconds.

[0210] Experimental Results and Analysis

[0211] The reference target and the detection target were removed from the lidar shown in Figure 1, ensuring that no target echo signal light entered the lidar's photodetector (PD). Then, the software-defined radio's ADC performed intermediate frequency (IF) signal acquisition. The acquired time-domain IF signal and the amplitude spectrum of the Fast Fourier Transform (FFT) are shown in Figures 2(a) and 2(b), respectively. As can be seen from the figures, even without target echo signal light (i.e., no RF signal output from the detector to the software-defined radio's RX terminal), the software-defined radio ADC can still measure the signal at f... 01 =800kHz and f 02 An intermediate frequency signal exists at a frequency of 1.6 MHz. The amplified spectra of these two frequencies are shown in Figures 2(c) and 2(d), respectively. This experimental result shows that in the lidar structure proposed in this invention, a portion of the radio frequency signal directly crosstalks from the TX end of the software radio to the RX end, which affects the measurement of the radio frequency signals of the stationary reference and the detected target.

[0212] When only the reference target RT is placed into the lidar shown in Figure 1 and the first optical chopper is activated, the intermediate frequency signal measured by the software radio is shown in Figure 3(a). By observation, it can be found that due to the effect of the optical chopper, the intermediate frequency signal generated by the reference target has become a periodic square wave. Waveform measurements show that its period is approximately T. R ≈7.19ms(1 / T R ≈139Hz). Its FFT amplitude spectrum is shown in Figure 3(b), and it can be seen that in and A signal exists at the frequency location, and this signal is more pronounced than in the case of only radio frequency crosstalk shown in Figure 2(b), indicating that a new echo signal generated by the reference target is superimposed on top of the radio frequency crosstalk. and The frequency spectrum is magnified and shown in Figures 3(c) and 3(d), respectively. Observation of Figure 3(c) reveals that... Two new spectral lines appeared on either side of the original spectral line, because they are related to... The interval is also approximately 139Hz (equal to the reciprocal of the period of a periodic square wave, 1 / T). R ≈139Hz), indicating that they are periodic reference target echo signals. The k = ±1st harmonic, i.e. and and Spectral lines are derived from the fundamental frequency of the target echo signal. Spectral lines and radio frequency crosstalk f 01 The spectral lines are superimposed. Similarly, as can be observed in Figure 3(d), in... Two new spectral lines also appeared on either side of the original spectral line, because they are related to... The intervals are also approximately 139Hz, indicating that they are periodic reference target echo signals. Second harmonic, i.e. and and Spectral lines are derived from the fundamental frequency of the target echo signal. Spectral lines and radio frequency crosstalk f 02 It is formed by the superposition of spectral lines.

[0213] By simply placing the target into the device shown in Figure 1 and activating the second optical chopper, the intermediate frequency (IF) signal measured by the software radio is shown in Figure 4(a). Observation reveals that, due to the chopper, the IF signal generated by the target has been transformed into a periodic square wave. Measurements show that its period is approximately T. D ≈12.20ms(1 / T D ≈82Hz). Its FFT transform amplitude spectrum is shown in Figure 4(b), and it can be seen that in and A signal exists at the frequency location, and this signal is more pronounced than in the case of only radio frequency crosstalk shown in Figure 2(b), indicating that a new echo signal generated by the detected target is superimposed on top of the radio frequency crosstalk. and The frequency spectrum is magnified and shown in Figures 4(c) and 4(d), respectively. Observation of Figure 4(c) reveals that... Two new spectral lines appeared on either side of the original spectral line, because they are related to... The interval is also approximately 82Hz (equal to the reciprocal of the period of a periodic square wave, 1 / T). D ≈82Hz), indicating that they are periodic target echo signals. The k = ±1st harmonic, i.e. and and Spectral lines are periodic detection target echo signals Fundamental frequency component Spectral lines and radio frequency crosstalk f 01 The superposition of spectral lines. Similarly, as can be observed in Figure 4(d), in... Two new spectral lines also appeared on either side of the original spectral line, because they are related to... The intervals are also approximately 82Hz, indicating that they are periodically detecting target echo signals. The k = ±1st harmonic, i.e. and And it is known Spectral lines are the fundamental frequency components of the periodic target echo signal. Spectral lines and radio frequency crosstalk f 02 Their spectral lines overlap.

[0214] Finally, the reference and detection targets are simultaneously placed into the structure shown in Figure 1, with the first and second optical choppers still operating at the same frequency (1 / T). R ≈139Hz and 1 / T D Operating at approximately 82Hz, Figure 5(a) shows the waveforms of the intermediate frequency signals of the reference and detected target echoes, which can be approximated as the superposition of the waveforms in Figures 3(b) and 4(b). The FFT amplitude spectrum is shown in Figure 5(b). and The magnified spectrum of the vicinity is shown in Figures 5(c) and 5(d), respectively. Observing Figure 5(c), it can be seen that... The spectral line at position is f 01 Radio frequency crosstalk signals, stationary reference targets Baseband signals and stationary detection targets The superposition of the three spectral lines of the fundamental frequency signal, with a spectral line approximately 82 Hz apart on either side. and It is the k=±1 harmonic of a stationary detection target; the spectral lines on both sides are approximately 139Hz apart. and It is the k = ±1 harmonic of the stationary reference target. Similarly, by observing Figure 5(d), we can see that... It is f 02 Radio frequency crosstalk signals, stationary reference targets Baseband signals and stationary detection targets The superposition of the three spectral lines of the fundamental frequency signal, with a spectral line approximately 82 Hz apart on either side. and It is the k=±1 harmonic of a stationary detection target; the spectral lines on both sides are approximately 139Hz apart. and It is the k=±1 harmonic of the stationary reference target. Four-cycle intermediate frequency signal. and The frequency of the k=±1st harmonic and Since they are not equal, the corresponding spectral lines are separated from each other, so their corresponding phase values... and Both can be measured using the phase spectrum of FFT, and the phase of the fundamental frequency component can be calculated using formula (13). Then use formula (15) to calculate and Finally, the relative distance R of the target is calculated using formula (10).

[0215] Stationary target distance measurement

[0216] Under otherwise unchanged conditions, the distance R of the detected target was increased sequentially in steps of 0.5m. The distance R was measured at each location using the method of this invention. Ten measurements were taken at each location, and the results were averaged and the standard deviation was calculated. The distance measurement results are shown in Figure 6. In Figure 6, the circles represent the average values ​​of the measurement results at different locations, and the length of the solid line segment represents the magnitude of the standard deviation. Observation shows that as the actual distance increases linearly, the distance measurement value also increases substantially linearly. These experimental results demonstrate that the radio frequency modulation direct detection lidar proposed in this invention can measure the distance to stationary targets.

[0217] Distance and velocity measurement of moving targets

[0218] The reference target in the structure shown in Figure 1 is removed, and a fan is used instead of the second optical chopper and the stationary detection target. Figure 7(a) shows the intermediate frequency signal of the rotating fan blades as the detection target. Each moving fan blade generates an echo signal, and the continuously rotating fan blades repeatedly generate periodic waveforms with the same distance and velocity information. The period of this signal is approximately T. D ≈9.792ms (its reciprocal 1 / T) D≈102Hz), which is, to some extent, equivalent to using the second optical chopper in Figure 1 to convert the echo signal of the translational detection target into a periodic signal, and can be used to demonstrate the ability of this type of lidar to measure the distance and velocity of moving targets. Furthermore, by measuring the fan blades and the waveform in Figure 7(a), it can be seen that the distance change of the beam scanning one fan blade is approximately 8.0 cm, and the time is approximately 8.65 ms, thus calculating the fan blade velocity to be approximately -9.27 m / s. The amplitude spectrum of the FFT of the intermediate frequency signal of the rotating detection target in Figure 7(a) is shown in Figure 7(b). 01 =800kHz and f 02 Signals also exist at the 2.4MHz frequency position. These signals are more pronounced than those shown in Figure 2(b) with only radio frequency crosstalk, indicating that a new echo signal generated by a moving detection target is superimposed on top of the radio frequency crosstalk. (The last part, "f", appears to be a typo and can be omitted.) 01 =800kHz and f 02 The spectrum at the 2.4MHz frequency position is magnified and shown in Figures 7(c) and 7(d). Observing Figure 7(c), it can be seen that at f... 01 At approximately 308.8 Hz to the left of the 800 kHz radio frequency crosstalk line, a series of intervals approximately 102 Hz ≈ 1 / T appear. D The several spectral lines indicate that they are periodic with period T. D The fundamental frequency and harmonic component spectra of the fan blade echo signal with approximately 9.792 ms are shown, with the most amplitude spectral line being the fundamental frequency component. Its two sides are k = ±1 harmonics and Similarly, by observing Figure 7(d), we can see that in f 02 At approximately 308.8 Hz to the left of the 2.4 MHz radio frequency crosstalk line, a series of intervals approximately 102 Hz ≈ 1 / T appear. D The several spectral lines indicate that they are periodic with period T. D The fundamental frequency and harmonic component spectra of the fan blade echo signal with approximately 9.792 ms are shown, with the most amplitude spectral line being the fundamental frequency component. Its two sides are k = ±1 harmonics and

[0219] With other conditions remaining constant, changing the fan speed and rotation direction, the corresponding FFT amplitude spectrum of the intermediate frequency signal is given in Figures 8(a) and (b), represented by solid lines, dashed lines, and dotted lines, respectively. It can be seen that as the speed decreases from -9.26 m / s to -5.09 m / s, the fundamental frequency component of the intermediate frequency signal of the detected target changes from... and Move the position to the right and The position is closer to the radio frequency crosstalk spectral line, meaning the Doppler frequency shifts Δf1 and Δf2 are decreasing. When the fan reverse speed becomes a positive value of 6.26 m / s, the fundamental frequency component of the target intermediate frequency signal has moved to the right side of the radio frequency crosstalk spectral line. and The positions, namely Δf1 and Δf2, become positive. This experimental result demonstrates that the velocity of a target can be measured using the frequency variation of an optical radio frequency signal.

[0220] When a reference target is added to the lidar structure shown in Figure 1, the period of the first optical chopper corresponding to the reference target channel remains approximately 1 / T. R ≈139Hz, the fan cycle still meets 1 / T D ≈102Hz. The intermediate frequency signal waveform caused by the simultaneous reference and rotating detection target is shown in Figure 9(a), and its corresponding FFT amplitude spectrum is given in Figure 9(b). Similarly, for... and The frequency spectrum is magnified and shown in Figures 9(c) and 9(d), respectively. Observing Figure 9(c), it can be seen that the reciprocal of the chopper period is 1 / T. R ≈139Hz, so The appearance of spectral lines is f 01 Radio frequency crosstalk spectral lines and The superposition of the reference target's fundamental spectrum lines, with the reference target's k=±1 harmonic spectrum lines located at ±139Hz on both sides. Since the reciprocal of the fan cycle is 1 / T D ≈102Hz, at The 308.8 Hz position to the left of the spectral line is the fundamental frequency spectrum line of the target's intermediate frequency signal, and the 102 Hz positions on either side are the k=±1 harmonic spectral lines of the target's signal. As can be seen from Figure 9(d), f 02 Radio frequency crosstalk spectral lines and Superposition of reference target base spectrum lines The reference target k = ±1 harmonic spectral lines are located at positions ±139 Hz on both sides. exist The 308.8 Hz position to the left of the spectral line is the fundamental frequency spectrum line of the target's intermediate frequency signal, and the 102 Hz positions on either side are the k=±1 harmonic spectral lines of the target's signal.

[0221] As can be seen, in and The k=±1 harmonic components of the radio frequency signal in the reference target at the location are separated from each other and do not coincide with other spectral lines. The corresponding phase measurements are as follows: They can be used to calculate the fundamental frequency phase of the reference target. exist and If the fundamental frequency component of the target signal does not coincide with other spectral lines, the phase value can be measured directly. and The Doppler frequency shifts Δf1 and Δf2 of the two radio frequencies can be measured, and the velocity ν of the detected target can be calculated using formula (11). and The measured value can be calculated use and The measured value can be calculated Will and Substituting the measured value into formula (10) will allow you to detect the distance R of the target.

[0222] Under otherwise unchanged conditions, the distance to the target was increased in increments of 0.5m, and the target speed was changed at each distance. The distance and speed of the target were measured simultaneously at each different distance and speed. The average and standard deviation of the 10 measurements were calculated. The overall measurement results are shown in Figures 10(a) and 10(b). Figure 10(a) shows the mean and standard deviation of the distance measurements at different speeds. The dashed line represents the actual distance to the target, the circles represent the average distance measurement, and the solid line segment represents the standard deviation of the distance measurement. Observing Figure 10(a), it can be seen that the distance to the target can be measured relatively accurately at different speeds. Figure 10(b) shows the mean and standard deviation of the speed measurements at different distances. The dashed line represents the actual speed to the target, the circles represent the average speed measurement, and the solid line segment represents the standard deviation of the speed measurement. Observing Figure 10(b), it can be seen that the speed of the target can be measured relatively accurately at different distances.

[0223] The above examples of the present invention are merely illustrative of the computational model and process of the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is impossible to exhaustively list all possible implementations here. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A target range and velocity measurement system based on radio frequency modulation direct detection lidar, characterized in that, The system comprises two parts: an optical path and a circuit. The optical path includes a frequency-stabilized continuous fiber laser (1), a fiber phase modulator (2), an erbium-doped fiber amplifier (3), a fiber circulator (4), an optical antenna (5), a beam splitter (6), a first optical chopper (7), a second optical chopper (8), a fiber Fabry-Perot interferometer (9), and a square law photodetector (10). The output of the frequency-stabilized continuous fiber laser (1) is connected to the first input (2A) of the fiber phase modulator (2); the output of the fiber phase modulator (2) is connected to the input of the erbium-doped fiber amplifier (3); and the output of the erbium-doped fiber amplifier (3) is connected to the first input (2A) of the fiber circulator (4). The In end is connected; the Out end of the fiber optic circulator (4) is connected to the first input / output end (5A) of the optical antenna (5); the second input / output end (5B) of the optical antenna (5) is connected to the first input / output end (6A) of the beam splitter (6); the second input / output end (6B) of the beam splitter (6) is connected to the first input / output end (7A) of the first optical chopper (7); the signal output from the second input / output end (7B) of the first optical chopper (7) illuminates the reference target; the third input / output end (6C) of the beam splitter (6) is connected to the first input / output end (8A) of the second optical chopper (8); the second input / output end of the second optical chopper (8) is connected to the first input / output end (8A) of the second optical chopper (8). The signal output from the input / output terminal (8B) illuminates the target; the Re terminal of the fiber optic circulator (4) is connected to the input terminal of the fiber optic Fabry-Perot interferometer (9); the output terminal of the fiber optic Fabry-Perot interferometer (9) is connected to the input terminal of the square law photodetector (10); the circuit includes a computer (11) and a software-defined radio; the software-defined radio includes an interface controller (12), a transmit controller (13), a first digital up-converter (14), a second digital up-converter (15), a first digital-to-analog converter (16), a second digital-to-analog converter (17), a first low-pass filter (18), a second low-pass filter (19), and a first local oscillator (20). The computer (11) comprises a first power amplifier (21), a second power amplifier (22), a second local oscillator (23), a third low-pass filter (24), a fourth low-pass filter (25), a first analog-to-digital converter (26), a second analog-to-digital converter (27), a first digital down-converter (28), a second digital down-converter (29), a receiver controller (30), a first mixer (31), a second mixer (32), a third mixer (33), and a fourth mixer (34); wherein: the input / output terminal (11A) of the computer (11) is connected to the input / output terminal (12A) of the interface controller (12); the output terminal of the interface controller (12) is connected to the input terminal of the transmitter controller (13);The first output terminal (13A) of the transmitter controller (13) is connected to the input terminal of the first digital up-converter (14); the second output terminal (13B) of the transmitter controller (13) is connected to the input terminal of the second digital up-converter (15); the output terminal of the first digital up-converter (14) is connected to the input terminal of the first digital-to-analog converter (16); the output terminal of the second digital up-converter (15) is connected to the input terminal of the second digital-to-analog converter (17); the output terminal of the first digital-to-analog converter (16) is connected to the input terminal of the first low-pass filter (18); the output terminal of the second digital-to-analog converter (17) is connected to the input terminal of the second low-pass filter (19); the first output terminal of the first local oscillator (20) is connected to the input terminal of the first digital-to-analog converter (14); the second output terminal (13B) of the transmitter controller (13) is connected to the input terminal of the second digital-to-analog converter (15); the first output terminal (13A) of the first digital-to-analog converter (14) is connected to the input terminal of the first digital-to-analog converter (16); the second output terminal (13B) of the second digital-to-analog converter (15) is connected to the input terminal of the second digital-to-analog converter (17); the first output terminal (13B) of the first local oscillator (20) is connected to the input terminal of the first digital-to-analog converter (17); the second output terminal (13B) of the first digital-to-analog converter (16 ... The output terminal (20A) is connected to the first input terminal (31A) of the first mixer (31); the second output terminal (20B) of the first local oscillator (20) is connected to the first input terminal (32A) of the second mixer (32); the output terminal of the first low-pass filter (18) is connected to the second input terminal (31B) of the first mixer (31); the output terminal of the second low-pass filter (19) is connected to the second input terminal (32B) of the second mixer (32); the output terminals of the first mixer (31) and the second mixer (32) are connected to the input terminal of the first power amplifier (21); the output terminal of the first power amplifier (21) is connected to the second input terminal (2B) of the fiber optic phase modulator (2). Connections; the output of the square-rate photodetector (10) is connected to the input of the second power amplifier (22); the output of the second power amplifier (22) is connected to the first input (33A) of the third mixer (33) and the first input (34A) of the fourth mixer (34), respectively; the first output (23A) of the second local oscillator (23) is connected to the second input (33B) of the third mixer (33); the second output (23B) of the second local oscillator (23) is connected to the second input (34B) of the fourth mixer (34); the output of the third mixer (33) is connected to the input of the third low-pass filter (24); the output of the fourth mixer (34) is connected to the input of the third low-pass filter (24); the output of the fourth mixer (34) is connected to the input of the third low-pass filter (24). The output terminal of the third low-pass filter (24) is connected to the input terminal of the fourth low-pass filter (25); the output terminal of the third low-pass filter (24) is connected to the input terminal of the first analog-to-digital converter (26); the output terminal of the first analog-to-digital converter (26) is connected to the input terminal of the first digital down-converter (28); the output terminal of the fourth low-pass filter (25) is connected to the input terminal of the second analog-to-digital converter (27); the output terminal of the second analog-to-digital converter (27) is connected to the input terminal of the second digital down-converter (29); the output terminal of the first digital down-converter (28) is connected to the first input terminal (30A) of the receiver controller (30); the output terminal of the second digital down-converter (29) is connected to the second input terminal (30B) of the receiver controller (30).The output of the receiving controller (30) is connected to the input of the interface controller (12).

2. The measurement method for the target distance and velocity measurement system based on radio frequency modulation direct detection lidar as described in claim 1, characterized in that, The method is as follows: two orthogonal digital intermediate frequency signals generated by the computer (11) are sequentially passed through the interface controller (12) and the transmitter controller (13). One digital intermediate frequency signal is output by the transmitter controller (13) and then sequentially passes through the first digital up-converter (14), the first digital-to-analog converter (16), and the first low-pass filter (18). The other digital intermediate frequency signal is output by the transmitter controller (13) and then sequentially passes through the second digital up-converter (15), the second digital-to-analog converter (17), and the second low-pass filter (19). Two orthogonal analog intermediate frequency signals are output using the first low-pass filter (18) and the second low-pass filter (19). Two local oscillators (20) are used to generate two... Two mixed RF signals are obtained by mixing sinusoidal RF local oscillator signals of the same frequency and orthogonal frequency with the simulated intermediate frequency signal. The two mixed RF signals are then combined into one RF signal. The combined RF signal is then amplified by the first power amplifier (21) and the amplified signal is used to perform phase modulation on the fiber phase modulator (2). The optical signal generated by the frequency-stabilized continuous fiber laser (1) is transmitted to the fiber phase modulator (2). The optical signal output by the fiber phase modulator (2) is amplified by the erbium-doped fiber amplifier (3) and then input to the fiber circulator (4). The optical signal is transmitted to the optical antenna (5) through the Out end of the fiber circulator (4). (5) The output optical signal is split into two parts by the beam splitter (6). One part of the optical signal is converted into periodic signal light by the first optical chopper (7). The periodic signal light output by the first optical chopper (7) illuminates the stationary reference target. The other part of the optical signal is converted into periodic signal light by the second optical chopper (8). The periodic signal light output by the second optical chopper (8) illuminates the detection target. The optical antenna (5) is then used to collect the echo signal light from the reference target and the detection target. The echo signal light passes through the Out end and Re end of the fiber optic circulator (4) in sequence, and then passes through the fiber optic Fabry-Perot interferometer (9) and is incident on the square law photodetector (10). The second local oscillator (23) generates Two sinusoidal local oscillator radio frequency signals of the same frequency and orthogonal are generated. The radio frequency signal generated by the square law photodetector (10) enters the second power amplifier (22) for amplification. The signal after amplification by the second power amplifier (22) is divided into two parts. One part is mixed with a sinusoidal local oscillator radio frequency signal generated by the second local oscillator (23). After mixing, the signal passes through the third low-pass filter (24), the first analog-to-digital converter (26), and the first digital down-converter (28) in sequence. The other part is mixed with another sinusoidal local oscillator radio frequency signal generated by the second local oscillator (23). After mixing, the signal passes through the fourth low-pass filter (25), the second analog-to-digital converter (27), and the second digital down-converter (29) in sequence.The digital intermediate frequency (IF) signals output from the first digital down-converter (28) and the second digital down-converter (29) are sent to the computer (11) for processing after passing through the receiver controller (30) and the interface controller (12). The computer (11) then outputs the distance and velocity measurement results for the detected target.

3. The measurement method for the target distance and velocity measurement system based on radio frequency modulation direct detection lidar according to claim 2, characterized in that, The frequency-stabilized continuous fiber laser (1) emits a single-frequency signal light. Specifically, it is as follows: in, Single-frequency signal light The amplitude, The imaginary unit, Single-frequency signal light angular frequency, It is time. Single-frequency signal light The initial phase.

4. The measurement method for the target distance and velocity measurement system based on radio frequency modulation direct detection lidar according to claim 3, characterized in that, The radio frequency signal output by the first power amplifier (21) of the circuit section for: in, It is a frequency of radio frequency signals, It is a frequency of radio frequency signals, It's time.

5. The measurement method for the target distance and velocity measurement system based on radio frequency modulation direct detection lidar according to claim 4, characterized in that, The echo signal light from the reference target, after passing through a fiber optic Fabry-Perot interferometer (9), generates a period of [period missing] in a square-law photodetector (10). radio frequency signals and period is radio frequency signals The echo signal light from the target is transmitted through a fiber optic Fabry-Perot interferometer (9) and then generates a period of 1 in a square-law photodetector (10). radio frequency signals and period is radio frequency signals ;and ； The frequency generated by the second local oscillator 23 is The sinusoidal local oscillator radio frequency signal is mixed to obtain a period of intermediate frequency signal ， The frequency generated by the second local oscillator 23 is The sinusoidal local oscillator radio frequency signal is mixed to obtain a period of intermediate frequency signal ； The frequency generated by the second local oscillator 23 is The sinusoidal local oscillator radio frequency signal is mixed to obtain a period of intermediate frequency signal ， The frequency generated by the second local oscillator 23 is The sinusoidal local oscillator radio frequency signal is mixed to obtain a period of intermediate frequency signal The intermediate frequency signal 、 、 and After low-pass filtering, analog-to-digital conversion, and digital down-conversion, the signal is sent to a computer for processing; the method for measuring the distance and velocity of the detected target is as follows: the intermediate frequency signal... The fundamental frequency and the frequency values ​​of each harmonic component are expressed as follows: , intermediate frequency signal The fundamental frequency and the frequency values ​​of each harmonic component are expressed as follows: , intermediate frequency signal The fundamental frequency and the frequency values ​​of each harmonic component are expressed as follows: , intermediate frequency signal The fundamental frequency and the frequency values ​​of each harmonic component are expressed as follows: ,but: in, It is an integer. Indicates the fundamental frequency component. express Second harmonic components This represents the continuous radio frequency signal of the reference target that has not been periodized by the first optical chopper. The frequency value, This represents the continuous radio frequency signal of the reference target that has not been periodized by the first optical chopper. The frequency value, This indicates the continuous radio frequency signal of the detected target that has not been periodized by the second optical chopper. The frequency value, This indicates the continuous radio frequency signal of the detected target that has not been periodized by the second optical chopper. The frequency value; The corresponding phase value is expressed as ,Will The corresponding phase value is expressed as ,Will The corresponding phase value is expressed as ,Will The corresponding phase value is expressed as For intermediate frequency signals Perform Fourier transform to obtain and For intermediate frequency signals Perform Fourier transform to obtain and For intermediate frequency signals Perform Fourier transform to obtain and For intermediate frequency signals Perform Fourier transform to obtain and , then calculate 、 、 and ： The frequency value of the fundamental frequency component 、 、 and The difference and phase value 、 、 and The difference is: Then according to and Calculate the relative distance between the reference target and the detection target. Based on the distance to the reference target and the relative distance Calculate the distance to the target; based on and Calculate the relative velocity between the reference target and the detection target. That is, the speed at which the target is detected.

6. The measurement method for the target distance and velocity measurement system based on radio frequency modulation direct detection lidar according to claim 5, characterized in that, According to and Calculate the relative distance between the reference target and the detection target. The specific process is as follows: in, It is the speed of light.

7. The measurement method for the target distance and velocity measurement system based on radio frequency modulation direct detection lidar according to claim 6, characterized in that, According to and Calculate the relative velocity between the reference target and the detection target. The specific process is as follows: 。 8. The measurement method for the target distance and velocity measurement system based on radio frequency modulation direct detection lidar according to claim 7, characterized in that, The distance to the reference target and the relative distance are used as the basis. The distance to the target is calculated as follows: in, For reference target distance, To detect the distance to the target.

Images