Laser radar ranging system and method with parallel modulation of multi-directional intermediate frequency pulses

Abstract

The present invention relates to the field of laser radar technology, and in particular to a laser radar ranging system and method with parallel modulation of multi-directional intermediate frequency pulses. The system includes: a laser transmitter emits a laser beam, which is modulated by a phase modulator and incident on a beam splitter and is divided into a local oscillator beam and a detection beam; an optical frequency comb generating unit generates a light wave signal of an optical frequency comb from the detection beam, and inputs the light wave signal into an optical circulator, which is then transmitted to a dispersion unit, and receives an echo beam reflected from a target to be measured; an optical fiber coupler mixes the local oscillator beam with the echo beam, converts the mixed signal into an electrical signal through a photoelectric detector, and inputs the mixed signal into a filtering unit, filters a specific frequency band wave signal, and shields other frequency band wave signals; a digital signal processing unit processes and analyzes the reserved frequency band wave signal, and calculates the distance between the system and the target to be measured. The advantages are: parallel detection is achieved without increasing the volume and cost of the system, thereby improving the detection speed of the system.

Description

Technical Field

[0001] The present invention relates to the field of laser radar technology, and in particular to a laser radar ranging system and method with parallel modulation of multi-directional intermediate frequency pulses. Background Art

[0002] Traditional LiDAR ranging methods include the following three:

[0003] (1) Triangulation distance measurement: The principle is that a laser transmitter emits a laser, which is reflected by the target object and then captured by a receiving lens (CMOS) (an image sensor). The distance between the target object and the laser transmitter can be calculated based on the position information of the capture point on the CMOS.

[0004] (2) Time of flight (ToF) ranging: It can be divided into direct time of flight (dToF) ranging and indirect time of flight (iToF) ranging. Direct time of flight ranging uses the principle of light speed ranging. The laser transmitter emits a short laser pulse, and the timer records the emission time. The laser is reflected by the target object and then received by the receiver. The timer records the reception time. The time difference is multiplied by the speed of light to calculate twice the distance between the laser transmitter and the target object. Indirect time of flight ranging is a method of indirectly obtaining the laser flight time by measuring the phase difference between the emitted light wave and the received light wave and converting it into a time difference.

[0005] (3) FMCW method: a laser coherent detection technology. The principle is that after linear modulation, the laser transmitter emits a continuous wave signal with changing frequency within the sweep period. The echo signal reflected by the target object is received by the photodetector. Due to the linear modulation, there is a fixed frequency difference between the echo signal and the local oscillator signal (i.e., the transmitting signal) after a period of time. This frequency difference can be obtained through mixing or coherent beat frequency, thereby obtaining the distance information between the target object and the laser transmitter.

[0006] However, the above three ranging methods have the following problems: (1) In triangulation ranging, when the distance between the target object and the laser emitter is far, the point captured on the COMS after reflection will be very small, which requires the CMOS to have a higher detection accuracy; in addition, the farther the distance between the target and the laser emitter, the less obvious the position change of the captured point on the COMS will be, which greatly reduces the measurement accuracy of the laser radar and limits the measurement range. Therefore, the triangulation ranging principle is only applicable to short-range target ranging environments; (2) Time of flight ranging is not limited by the distance measurement range and has high measurement accuracy. , but the cost is relatively high. In order to keep the received pulse signal from being distorted, the laser transmitter needs to emit high-quality pulsed light. In addition, since the speed of light is too fast, direct time-of-flight ranging has high requirements on the accuracy of the timer recording the round-trip time of the laser. Indirect time-of-flight ranging has poor anti-interference ability. If the detection distance is too far, the received waveform will have problems such as reduced signal-to-noise ratio and phase ambiguity. (3) Frequency modulated continuous wave (FMCW) ranging has extremely high requirements on the coherence of the laser and requires a laser with a narrow linewidth and high frequency modulation bandwidth, which increases the technical difficulty and is accompanied by high costs.

[0007] To solve the above problems, a phase modulated continuous wave (PhMCW) ranging method is proposed in the prior art. However, the PhMCW system consists of a laser transmitter and a photodetector, but the laser radar ranging system can only measure distance at one angle (direction). To achieve 3D imaging, it is necessary to scan the detection angle and measure the distance point by point at each angle. Because each direction requires a period of time to measure the distance, for example, 10μs, and a 3D point cloud image needs to measure tens of thousands of directions, the time required for a frame of point cloud image is hundreds of milliseconds, which is much higher than the 50ms (20 frames / second) required for real-time 3D imaging. A simple solution is to copy the above PhMCW laser ranging system to N sets, and each set of the system is fixed to one angle for distance measurement, so that N directions can be measured at the same time, and the imaging speed is increased by N times. However, this not only increases the complexity of the system and makes the operation of the system more difficult, but also greatly increases the volume, cost, weight, and power consumption (requiring N lasers and N detectors), making it difficult to implement in actual distance measurement work.

[0008] Although PhMCW can measure distance very well, it has problems of low frame rate and slow imaging speed in point cloud imaging. Therefore, there is an urgent need for a multi-directional parallel detection method to improve the imaging speed. Summary of the invention

[0009] In order to solve the above problems, the present invention provides a laser radar ranging system and method with parallel modulation of multi-directional intermediate frequency pulses.

[0010] The first object of the present invention is to provide a laser radar ranging system with parallel modulation of multi-directional intermediate frequency pulses, including a laser transmitter, a phase modulator, a signal generator, a beam splitter, an optical frequency comb generating unit, an optical circulator, a dispersion unit, an optical fiber coupler, a photodetector, a filtering unit and a digital signal processing unit;

[0011] The laser emitter is used to emit a laser beam;

[0012] The phase modulator is used to perform phase modulation on the laser beam so that the phase of the laser signal changes regularly;

[0013] The signal generator is used to control the phase modulator to generate a phase modulation signal and output a preset phase;

[0014] The beam splitter is used to split the light beam modulated by the phase modulator into a local oscillator light beam and a detection light beam;

[0015] The optical frequency comb generating unit is used to make the detection light beam generate a light wave signal of an optical frequency comb, and input the light wave signal into the optical circulator;

[0016] The optical circulator is used to transmit the optical wave signal modulated by the optical frequency comb generating unit to the dispersion unit, and receive the echo light beam reflected from the target to be measured;

[0017] The dispersion unit is used to split the optical wave signal, which is incident on the target to be measured and then reflected to become the echo light beam, and then returns to the optical circulator;

[0018] The optical fiber coupler is used to mix the local oscillator light beam with the echo light beam to obtain an intermediate frequency signal;

[0019] The photoelectric detector is used to convert the intermediate frequency signal into an electrical signal and input it into the filtering unit;

[0020] The filtering unit includes N independent filters for filtering wave signals of a specific frequency band and shielding wave signals of other frequency bands;

[0021] The digital signal processing unit is used to perform data processing and analysis on the reserved frequency band wave signal passing through the filtering unit, and calculate the distance information between the laser radar ranging system with multi-directional intermediate frequency pulse parallel modulation and the target to be measured.

[0022] Preferably, the filter is a bandpass filter or a low-pass filter.

[0023] Preferably, the optical frequency comb generating unit is any one of a silicon nitride micro-ring optical comb, a phase modulation optical comb, or a cyclic frequency shift optical comb including an acousto-optic modulator and a gain medium.

[0024] Preferably, the optical frequency comb generating unit comprises an acousto-optic modulator, a gain medium and two couplers; the gain medium is an optical fiber amplifier; the light passing through the acousto-optic modulator generates a frequency shift of A coupler couples part of the energy into the fiber amplifier for optical power amplification, and couples it back to the AOM through another coupler, generating a frequency shift of 2 light; repeated modulation, the final frequency shift is , 2 , 3 ,……,n The light wave signal of the optical frequency comb.

[0025] Preferably, the light field expression of the light wave signal of the optical frequency comb is:

[0026] ;

[0027] In the formula, is the electric field amplitude of the emitted light wave at the nth angle, is the angular frequency of light, The acousto-optic modulator produces a specific frequency output, t is the time, is the phase of the emitted light wave at the nth angle.

[0028] Preferably, the local oscillator light beam and the echo light beam generate a local oscillator signal LO and an echo signal R respectively;

[0029] The light field expression of the local oscillator signal LO is:

[0030] ;

[0031] The light field expression of the echo signal R is:

[0032] ;

[0033] In the formula, is the initial amplitude, is the initial frequency, is the phase of the local oscillator light wave, is the electric field amplitude of the echo light wave at the nth angle, The acousto-optic modulator generates a specific frequency output, t is the transmission time of the light wave signal, is the time interval flight time of the light wave at the nth angle, is the phase of the emitted light wave at the nth angle, The phase of the emitted light wave at the nth angle when there is a time interval is the change with time, and n is the emitted light wave at the nth angle.

[0034] Preferably, the light field expression of the intermediate frequency signal is:

[0035] IF= ;

[0036] In the formula, is the amplitude of the nth intermediate frequency signal, Produce a specific frequency output for the AOM, The phase of the emitted light wave at the nth angle when there is a time interval Changes over time, is the phase of the local oscillator light wave.

[0037] Preferably, the method further comprises a collimator disposed between the optical circulator and the dispersion unit, for collimating the optical wave signal and the echo light beam.

[0038] Preferably, the beam splitter is any one of a beam splitter, a silicon photonic chip or a 90:10 optical fiber beam splitter; the phase modulator is a lithium niobate electro-optic phase modulator or a silicon waveguide thermo-optic phase modulator; and the dispersion unit is a beam splitter grating or a prism.

[0039] The second object of the present invention is to provide a laser radar ranging method with parallel modulation of multi-directional intermediate frequency pulses, which uses a laser radar ranging system with parallel modulation of multi-directional intermediate frequency pulses for measurement, comprising the following steps:

[0040] S1. The laser transmitter emits a laser beam, and the phase modulator performs phase modulation on the laser beam so that the phase of the laser signal changes regularly;

[0041] S2. The laser beam modulated by the phase modulator is incident on the beam splitter and is divided into a local oscillator beam and a detection beam;

[0042] S3. The detection beam is modulated by the optical frequency comb generating unit to generate a light wave signal of the optical frequency comb, and the light wave signal is input to port 1 of the optical circulator;

[0043] S4. The light wave signal is output from the second port of the optical circulator and split by the dispersion unit, then incident on the target to be measured and reflected to become an echo beam, and then input from the second port of the optical circulator;

[0044] S5. The echo beam is output from port three of the optical circulator and mixed with the local oscillator beam in the fiber coupler to obtain an intermediate frequency signal;

[0045] S6. The intermediate frequency signal is converted into an electrical signal by a photodetector and input into the filtering unit;

[0046] S7. Filter the specific frequency band wave signal and shield other frequency band wave signals through N independent filters in the filtering unit, and transmit the reserved frequency band wave signal to the digital signal processing unit;

[0047] S8. The digital signal processing unit performs data processing and analysis on the reserved frequency band wave signal to calculate the time interval ; Then solve to obtain the distance d between the target object to be measured in each direction and the laser radar ranging system with multi-directional intermediate frequency pulse parallel modulation n ; The solution formula is as follows:

[0048] ;

[0049] In the formula, is the time interval and c is the speed of light.

[0050] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0051] The multi-directional intermediate frequency pulse parallel modulation laser radar ranging system proposed in the present invention uses only one laser and one detector, and can perform multi-angle simultaneous (parallel) measurement. It only adds the structure of generating optical frequency comb (OFC), dispersion unit and digital signal processing unit, and realizes parallel detection without significantly increasing the volume, cost, weight and power consumption of the system, making the system more concise and easy to operate, and will not increase the cost too much, which is conducive to a wider range of applications. Based on PhMCW, the proposed parallel detection scheme improves the frame rate (or detection speed), overcomes the technical defects of the prior art that N points need to be measured N times and the detection speed is slow. The present invention can achieve the beneficial effect of measuring N points once. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a structural schematic diagram of a laser radar ranging system with parallel modulation of multi-directional intermediate frequency pulses according to the present invention.

[0053] Figure 2 It is a structural schematic diagram of a laser radar ranging system with multi-directional intermediate frequency pulse parallel modulation provided according to an embodiment of the present invention.

[0054] Figure 3 Schematic diagram of the spectrum and bandpass filter of the intermediate frequency signal IF provided according to an embodiment of the present invention.

[0055] Figure 4 It is a structural schematic diagram of a laser radar ranging system with multi-directional intermediate frequency pulse parallel modulation provided according to an embodiment of the present invention.

[0056] Figure 5 Schematic diagram of the spectrum and low-pass filter of the multiplier output signal provided according to an embodiment of the present invention.

[0057] Reference numerals:

[0058] 1. Laser transmitter;

[0059] 2. Phase modulator;

[0060] 3. Signal generator;

[0061] 4. Beam splitter;

[0062] 5. Optical frequency comb generation unit;

[0063] 501, coupler; 502, acousto-optic modulator; 503, erbium-doped fiber amplifier;

[0064] 6. Optical circulator;

[0065] 7. Spectral grating;

[0066] 8. Fiber optic coupler;

[0067] 9. Photoelectric detector;

[0068] 10. Filter unit;

[0069] 1001, N-channel low-pass filter; 1002, phase-locked loop;

[0070] 11. Digital signal processing unit;

[0071] 12. Collimator. DETAILED DESCRIPTION

[0072] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same modules are represented by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, the detailed description thereof will not be repeated.

[0073] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0074] The present invention provides a laser radar ranging system with parallel modulation of multi-directional intermediate frequency pulses ( Figure 1 ),include:

[0075] A laser transmitter 1, used for transmitting a laser beam;

[0076] Phase modulator 2 is used to phase modulate the laser beam so that the phase of the emitted laser signal changes regularly. The emitted signal passes through phase modulator 2 to phase modulate the emitted signal. The modulated waveform is a square wave with a certain duty cycle. The initial optical phase is , the modulation depth is , the period is T;

[0077] Furthermore, the square wave is specifically a square wave with a duty cycle of 50% and a period of 10 μs; the material and structure of the phase modulator 2 are not limited, such as a lithium niobate electro-optic phase modulator, a silicon waveguide thermo-optic phase modulator, etc.;

[0078] A signal generator 3 is used to control the phase modulator 2 to generate a phase modulation signal and output a preset phase;

[0079] The beam splitter 4 is used to split the modulated laser beam into two paths, one of which is used as a local oscillator beam (generating a local oscillator signal LO), and the other detection beam is modulated and emitted into space for distance detection (hereinafter referred to as "emission signal"); the type and splitting ratio of the beam splitter are not limited and can be selected according to system requirements. For example, a 90:10 optical fiber beam splitter can be used, and a beam splitter, a silicon photonic chip, etc. can also be used for beam splitting;

[0080] The phase of the local oscillator signal LO for:

[0081] ;

[0082] Assume the initial amplitude is , the initial frequency is , the modulation phase is , then the light field expression of the local oscillator signal LO is:

[0083] ;

[0084] In the formula, is the initial amplitude, is the initial frequency, t is the transmission time of the light wave signal, is the phase of the local oscillator light wave;

[0085] An optical frequency comb generating unit 5, used to generate equally spaced discrete spectra in the frequency domain, so that the detection beam generates a light wave signal of the optical frequency comb, and inputs the light wave signal to the optical circulator 6;

[0086] An optical circulator 6, used for transmitting the optical wave signal modulated by the optical frequency comb generating unit to the dispersion unit, and receiving the echo light beam reflected from the target to be measured;

[0087] A dispersion unit, used to split the light wave signal, which is incident on the target to be measured and then reflected to become the echo light beam, and then returns to the optical circulator 6; the type of dispersion unit is not limited, including but not limited to a splitter grating, a prism, etc.;

[0088] The local oscillator beam is incident on the optical fiber coupler 8, and the detection beam is incident on the target to be measured and then reflected to become an echo beam. The echo beam is also incident on the optical fiber coupler 8, and the optical fiber coupler 8 mixes the local oscillator beam (local oscillator signal LO) and the echo beam (echo signal R);

[0089] The photodetector 9 is used to convert the intermediate frequency signal obtained by mixing into an electrical signal;

[0090] The filter unit 10 is used to filter a specific frequency band and shield the wave signals of other frequency bands;

[0091] The digital signal processing unit 11 is used to process and analyze the reserved frequency band wave signal, and then calculate the distance information between the laser radar ranging system with multi-directional intermediate frequency pulse parallel modulation and the target object to be measured.

[0092] Part of the structure in the laser radar ranging system with multi-directional intermediate frequency pulse parallel modulation of the present invention can be replaced by other structural methods, for example:

[0093] (1) The principle of phase modulation is not limited. It can be thermo-optical modulation (heating the waveguide, changing the temperature, changing the waveguide refractive index, and changing the light phase) or electro-optical modulation (doping the waveguide with P-type and N-type, adjusting the PN junction voltage, adjusting the number of carriers in the waveguide, adjusting the refractive index, and adjusting the phase).

[0094] (2) There is no limit to the method of generating optical frequency combs, including silicon nitride micro-ring optical combs, cyclic frequency-shifted optical combs containing an acousto-optic modulator and a gain medium, and phase-modulated optical combs. In the cyclic frequency-shifted optical combs of an acousto-optic modulator + a gain medium, there is no limit to the type of gain medium, including semiconductor optical amplifiers, erbium-doped fiber amplifiers, etc.

[0095] (3) Types and calculations of digital signal processing units There is no restriction on the method, for example: use TDC (time-to-digital converter, a chip that can measure pulse width) to directly time; or use ADC (analog-to-digital converter, oscilloscope, collect pulse waveform and then analyze) to collect phase modulated signal and IF signal for counting / timing; or use ADC to sample phase modulated signal and IF signal, calculate the correlation coefficient between the two, and find the time delay with the largest correlation coefficient; all of the above methods can achieve data analysis and obtain That's it.

[0096] Furthermore, the system further comprises: a collimator 12 disposed between the optical circulator 6 and the beam splitter grating 7 for collimating the detection beam and the echo beam.

[0097] Furthermore, the optical frequency comb generation unit (OFC) includes a frequency shift loop composed of an acousto-optic modulator (AOM), an erbium-doped fiber amplifier (EDFA) and a coupler; its working principle is as follows: the light passing through the AOM generates a certain frequency shift , the coupler couples part of the energy into the EDFA, and the remaining energy is transmitted to the optical circulator 6 port 1; the frequency shift is The light is amplified by an erbium-doped fiber amplifier to compensate for the energy loss caused by the coupler and transmission loss, and then coupled to the echo optical modulator again through the coupler to produce a frequency shift of 2 Repeat the above process, the optical frequency comb generation unit will generate light with a frequency shift of , 2 , 3 Equal frequency comb.

[0098] The optical signal E entering port 1 of optical circulator 6 T The light field expression is:

[0099] ;

[0100] In the formula, is the electric field amplitude of the emitted light wave at the nth angle, is the angular frequency of light, The acousto-optic modulator produces a specific frequency output, t is the time, is the phase of the emitted light wave at the nth angle, in which n are equal, the same as the square wave modulation signal waveform.

[0101] Light wave signal E T Enters into the port 1 of the optical circulator 6 and exits from the port 2 of the optical circulator 6, is collimated by the collimator 12, and then is incident on the dispersion unit;

[0102] Different frequencies mean that the wavelengths of the light waves are different. After being reflected by the dispersion unit, they are emitted at different diffraction angles, so that the light beams are dispersed and hit the measured object in different directions. After the light waves encounter the measured object, they are reflected. Due to the reversible principle of the optical path, the echo signals R reflected in each direction are returned to the optical circulator 6 again after passing through the dispersion unit and the collimator. Then, using the characteristics of the optical circulator 6 (the light entering from Port 2 will be emitted from Port 3), the echo signal R is transmitted to the optical fiber coupler through the optical circulator 6. The local oscillator signal LO (that is, the laser beam emitted by the laser transmitter) is used as a reference signal to mix with the echo signal R to obtain the intermediate frequency signal IF. The echo signal R has a flight time interval. , and a delay is generated relative to the local oscillator signal LO. The light field expressions of the echo signal R and the intermediate frequency signal IF are:

[0103] ;

[0104] ;

[0105] In the formula, is the electric field amplitude of the echo light wave at the nth angle, The acousto-optic modulator generates a specific frequency output, t is the transmission time of the light wave signal, is the flight time interval of the light wave at the nth angle, is the phase of the emitted light wave at the nth angle, The phase of the emitted light wave at the nth angle when there is a time interval The change with time, n is the emitted light wave at the nth angle; due to , The two terms are constants, which are useless for distance measurement and do not carry information. For the convenience of writing, they are discarded hereafter; so they are expressed as:

[0106] .

[0107] Specifically, the light wave signal T passes through the optical circulator 6, is collimated and hits the dispersion unit (grating). Since the light wave contains a series of light beams with different and increasing frequencies, according to the relationship between the wavelength and frequency of the light wave , c is the speed of light, it can be seen that the wavelength of light is inversely proportional to the frequency, then the light wave signal T is emitted at different diffraction angles after being reflected by the grating, each beam of light waves encounters each target object in different directions and is reflected back, and enters the optical circulator 6 again after being reflected by the grating, and outputs the echo signal R from Port 3. The echo signal R has a flight time interval , and a delay is generated relative to the local oscillator signal LO, and its light field expression is:

[0108] ;

[0109] In the formula, is the electric field amplitude of the echo light wave at the nth angle, is the initial frequency, The acousto-optic modulator generates a specific frequency output, t is the transmission time of the light wave signal, is the time interval flight time of the light wave at the nth angle, is the phase of the emitted light wave at the nth angle, The phase of the emitted light wave at the nth angle when there is a time interval The change with time, n is the emitted light wave at the nth angle;

[0110] The echo signal R is transmitted to the fiber coupler through the optical circulator 6. The local oscillator signal LO (i.e., the laser beam modulated by the phase modulator 2) is used as a reference signal to mix with the echo signal R to obtain the intermediate frequency signal IF. The local oscillator signal LO and the echo signal R are coherently superimposed to generate a new light field. The light field expression is:

[0111] ;

[0112] Since the light intensity is proportional to the square of the light field, and the light intensity is proportional to the power, then the power ,symbol It means taking the average over time, then the power P is:

[0113] ;

[0114] because and is the DC component of the local oscillator signal LO and the echo signal R that can be detected by the photodetector. It contains no information and has no effect on the ranging and can be ignored. It can be simplified to:

[0115] ;

[0116] Define the intermediate frequency signal IF:

[0117] ;

[0118] In the formula, is the electric field amplitude of the local oscillator light wave, is the electric field amplitude of the echo light wave at the nth angle, is the angular frequency of light, The acousto-optic modulator produces a specific frequency output, t is the time, The phase of the emitted light wave at the nth angle when there is a time interval Changes over time, is the phase of the local oscillator light wave, is the time interval (flight time) of the light wave at the nth angle. , is a constant, which is useless for distance measurement and does not carry any information. For the convenience of writing, it is discarded hereafter; it is expressed as:

[0119] .

[0120] Example 1

[0121] like Figure 2-Figure 3 As shown, this embodiment provides a laser radar ranging system with parallel modulation of multi-directional intermediate frequency pulses, including:

[0122] A laser transmitter 1, used for transmitting a laser beam;

[0123] Phase modulator 2, used to perform phase modulation on the laser beam so that the phase of the laser signal changes regularly;

[0124] A signal generator 3, used to control the phase modulator 2 to generate a phase modulation signal and output a preset phase;

[0125] A beam splitter 4 is used to split the light beam modulated by the phase modulator 2 into a local oscillator beam (generating a local oscillator signal LO) and a detection beam, and the detection beam is emitted into space for distance detection;

[0126] An optical frequency comb generating unit, comprising a coupler 501, an acousto-optic modulator 502 (AOM), an erbium-doped fiber amplifier 503 (EDFA) and a frequency shift loop formed by the coupler 501;

[0127] An optical circulator 6, used for transmitting the modulated laser signal to the grating and receiving the echo signal;

[0128] A collimator 12, used for collimating the detection beam and the echo beam;

[0129] The beam splitter grating 7 is used to split the composite light containing different wavelengths;

[0130] The fiber coupler 8, the local oscillator beam is incident on the fiber coupler, the detection beam is incident on the target to be measured and then reflected to become an echo beam, the echo beam is incident on the fiber coupler, and the fiber coupler mixes the local oscillator signal LO and the echo signal R;

[0131] The photodetector 9 is used to convert the intermediate frequency signal obtained by mixing into an electrical signal;

[0132] The filter unit 10 is used to filter a specific frequency band and shield the wave signals of other frequency bands;

[0133] The filtering unit 10 includes N bandpass filters; since the intermediate frequency signal is the sum of a series of non-overlapping narrowband signals in the frequency domain, the bandpass filter directly filters out each narrowband signal, so a filter with a high Q value is required;

[0134] The intermediate frequency signal IF is the sum of a series of cosine terms; in the time domain, The signal is a series of pulses with a pulse width equal to The intermediate frequency signal IF itself contains the flight time information, and the flight time can be directly obtained by measuring the pulse width. ; However, in the frequency domain, due to Usually in the order of tens of megahertz (MHz), The bandwidth of is equal to that of the square wave modulation signal, which is only a few MHz. By expanding the Bessel function, we can get: The term is a central frequency , narrowband signals with a bandwidth of several MHz.

[0135] The intermediate frequency signal IF is a series of center frequencies. , the sum of narrowband signals with bandwidths of several MHz, which have no frequency overlap (such as Figure 3 As shown in the figure, each narrowband signal corresponds to one direction. Therefore, by inputting the intermediate frequency signal IF into the bandpass filters of different frequency bands, the intermediate frequency signal IF in each direction can be filtered out, that is, each item , the waveform has a frequency of A pulse stream is superimposed on the cosine signal, and the pulse width is equal to .

[0136] The digital signal processing unit 11 is used to process and analyze the reserved frequency band wave signal, and then calculate the distance information between the laser radar ranging system with multi-directional intermediate frequency pulse parallel modulation and the target object to be measured; after digital sampling, the time length from the rising edge to the falling edge of the pulse is obtained through the analysis and calculation processing of the digital signal processing unit 11, or the pulse width is directly measured by TDC (time-to-digital converter) to obtain the time interval According to the formula (c is the speed of light) the distance information between the target object and the laser radar in each direction can be obtained.

[0137] Example 2

[0138] like Figure 4-Figure 5 As shown, this embodiment provides a laser radar ranging system with parallel modulation of multi-directional intermediate frequency pulses, including:

[0139] A laser transmitter 1, used for transmitting a laser beam;

[0140] Phase modulator 2, used to perform phase modulation on the laser beam so that the phase of the laser signal changes regularly;

[0141] A signal generator 3, used to control the phase modulator 2 to generate a phase modulation signal and output a preset phase;

[0142] A beam splitter 4 is used to split the light beam modulated by the phase modulator 2 into a local oscillator beam (generating a local oscillator signal LO) and a detection beam, and the detection beam is emitted into space for distance detection;

[0143] An optical frequency comb generating unit, comprising a coupler 501, an acousto-optic modulator 502 (AOM), an erbium-doped fiber amplifier 503 (EDFA) and a frequency shift loop formed by the coupler 501;

[0144] An optical circulator 6, used for transmitting the modulated laser signal to the grating and receiving the echo signal;

[0145] A collimator 12, used for collimating the detection beam and the echo beam;

[0146] The beam splitter grating 7 is used to split the composite light containing different wavelengths;

[0147] The fiber coupler 8, the local oscillator beam is incident on the fiber coupler, the detection beam is incident on the target to be measured and then reflected to become an echo beam, the echo beam is incident on the fiber coupler, and the fiber coupler mixes the local oscillator signal LO and the echo signal R;

[0148] The photodetector 9 is used to convert the intermediate frequency signal obtained by mixing into an electrical signal;

[0149] The filtering unit 10 includes a multiplier and N low-pass filters 1001; specifically, the multiplier is a phase-locked loop 1002; since the intermediate frequency signal is the sum of a series of non-overlapping narrowband signals in the frequency domain, the multiplier moves a narrowband signal to the baseband, and then uses a low-pass filter to filter out other signals, making it easier to manufacture a low-pass filter with a high Q value;

[0150] The driving frequency of the AOM 502 is This frequency is also applied to the phase-locked loop 1002, causing the phase-locked loop 1002 to generate a series of absolute Integer frequency multiple signals are used to multiply the IF signal by this series of signals. As an example, the IF signal is multiplied with it, and the result of the operation is the multiplication output signal: ;

[0151] The multiplication output signal is the sum of a series of cosine terms; note that In the time domain, it is a series of pulses with a pulse width equal to , which contains the flight time information, and can be directly obtained by measuring the pulse width , but the multiplier output also contains other cosine terms, which need to be further filtered out; in the frequency domain, due to Usually tens of MHz. The bandwidth is only a few MHz, so the Bessel function expansion can be obtained: The term is a low-frequency narrowband signal with a bandwidth of several MHz, and The term is the center frequency Therefore, the output of the multiplier is the sum of a low-frequency narrowband signal with a bandwidth of several MHz and a series of high-frequency narrowband signals with a center frequency of n∆ω and a bandwidth of several MHz. These narrowband signals have no frequency band overlap (such as Figure 5 The cutoff frequency of the low-pass filter is set to be much smaller than When the multiplier output signal passes through a low-pass filter, the first term The signal will be filtered out. This item is a series of pulses in the time domain, and the pulse width is equal to the flight time. Various methods can be used to measure the pulse width to complete the distance measurement, that is, to obtain the distance in the first direction. Similarly, the IF signal is matched with the output of the phase-locked loop 1002 (a series of absolute Integer multiple frequency signals) are multiplied respectively, and then passed through N low-pass filters respectively, and the By measuring the pulse width of these items, the flight time in each direction can be obtained. .

[0152] The digital signal processing unit 11 is used to process and analyze the reserved frequency band wave signal, and then calculate the distance information between the laser radar ranging system with multi-directional intermediate frequency pulse parallel modulation and the target object to be measured; specifically, after digital sampling, the time length from the rising edge to the falling edge of the pulse is obtained through the analysis and calculation processing of the digital signal processing unit 11, or the pulse width is directly measured using a TDC (time-to-digital converter) to obtain the time interval According to the formula (c is the speed of light) the distance information between the target object and the laser radar in each direction can be obtained.

[0153] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the disclosure of the present invention can be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution disclosed in the present invention can be achieved, and this document does not limit this.

[0154] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A laser radar ranging system with parallel modulation of multi-directional intermediate frequency pulses, characterized by: It includes a laser transmitter, a phase modulator, a signal generator, a beam splitter, an optical frequency comb generation unit, an optical circulator, a dispersion unit, an optical fiber coupler, a photodetector, a filtering unit and a digital signal processing unit; The laser emitter is used to emit a laser beam; The phase modulator is used to perform phase modulation on the laser beam so that the phase of the laser signal changes regularly; The signal generator is used to control the phase modulator to generate a phase modulation signal and output a preset phase; The beam splitter is used to split the light beam modulated by the phase modulator into a local oscillator light beam and a detection light beam; The optical frequency comb generating unit is used to make the detection beam generate a light wave signal of an optical frequency comb, and input the light wave signal into the optical circulator; the optical frequency comb generating unit includes an acousto-optic modulator, a gain medium and two couplers; the gain medium is an optical fiber amplifier; the light passing through the acousto-optic modulator generates a frequency shift of A coupler couples part of the energy into the fiber amplifier for optical power amplification, and couples it back to the AOM through another coupler, generating a frequency shift of 2 of light; Repeated modulation eventually produces a frequency shift of , 2 , 3 ,……,n The light wave signal of the optical frequency comb; The optical circulator is used to transmit the optical wave signal modulated by the optical frequency comb generating unit to the dispersion unit, and receive the echo light beam reflected from the target to be measured; The dispersion unit is used to split the optical wave signal, which is incident on the target to be measured and then reflected to become the echo light beam, and then returns to the optical circulator; A collimator is arranged between the optical circulator and the dispersion unit, and the collimator is used to collimate the optical wave signal and the echo light beam; The optical fiber coupler is used to mix the local oscillator light beam with the echo light beam to obtain an intermediate frequency signal; The photoelectric detector is used to convert the intermediate frequency signal into an electrical signal and input it into the filtering unit; The filtering unit includes N independent filters for filtering wave signals of a specific frequency band and shielding wave signals of other frequency bands; The digital signal processing unit is used to perform data processing and analysis on the reserved frequency band wave signal passing through the filtering unit, and calculate the distance information between the laser radar ranging system with multi-directional intermediate frequency pulse parallel modulation and the target to be measured.

2. The laser radar ranging system with multi-directional intermediate frequency pulse parallel modulation according to claim 1 is characterized in that: The filter is a bandpass filter or a lowpass filter.

3. The laser radar ranging system with multi-directional intermediate frequency pulse parallel modulation according to claim 2 is characterized in that: The optical frequency comb generating unit is any one of a silicon nitride micro-ring optical comb, a phase modulation optical comb or a cyclic frequency shift optical comb including an acousto-optic modulator and a gain medium.

4. The laser radar ranging system with multi-directional intermediate frequency pulse parallel modulation according to claim 3 is characterized in that: The optical field expression of the optical wave signal of the optical frequency comb is: ； In the formula, is the electric field amplitude of the emitted light wave at the nth angle, is the angular frequency of light, The acousto-optic modulator produces a specific frequency output, t is the time, is the phase of the emitted light wave at the nth angle.

5. The laser radar ranging system with multi-directional intermediate frequency pulse parallel modulation according to claim 4 is characterized in that: The local oscillator light beam and the echo light beam generate a local oscillator signal LO and an echo signal R respectively; The light field expression of the local oscillator signal LO is: ； The light field expression of the echo signal R is: ； In the formula, is the initial amplitude, is the initial frequency, is the phase of the local oscillator light wave, is the electric field amplitude of the echo light wave at the nth angle, The acousto-optic modulator generates a specific frequency output, t is the transmission time of the light wave signal, is the time interval of the light wave at the nth angle, is the phase of the emitted light wave at the nth angle, The phase of the emitted light wave at the nth angle when there is a time interval is the change with time, and n is the emitted light wave at the nth angle.

6. The laser radar ranging system with multi-directional intermediate frequency pulse parallel modulation according to claim 5 is characterized in that: The light field expression of the intermediate frequency signal is: ； In the formula, is the amplitude of the nth intermediate frequency signal, Produce a specific frequency output for the AOM, The phase of the emitted light wave at the nth angle when there is a time interval Changes over time, is the phase of the local oscillator light wave.

7. The laser radar ranging system with multi-directional intermediate frequency pulse parallel modulation according to claim 6 is characterized in that: The beam splitter is any one of a beam splitter, a silicon photonic chip or a 90:10 optical fiber beam splitter; the phase modulator is a lithium niobate electro-optic phase modulator or a silicon waveguide thermo-optic phase modulator; and the dispersion unit is a beam splitter grating or a prism.

8. A laser radar ranging method with parallel modulation of multi-directional intermediate frequency pulses, using the laser radar ranging system with parallel modulation of multi-directional intermediate frequency pulses as described in any one of claims 1 to 7 for measurement, characterized in that: The steps include: S1. The laser transmitter emits a laser beam, and the phase modulator performs phase modulation on the laser beam so that the phase of the laser signal changes regularly; S2. The laser beam modulated by the phase modulator is incident on the beam splitter and is divided into a local oscillator beam and a detection beam; S3. The detection beam is modulated by the optical frequency comb generating unit to generate a light wave signal of the optical frequency comb, and the light wave signal is input to port 1 of the optical circulator; S4. The light wave signal is output from the second port of the optical circulator and split by the dispersion unit, then incident on the target to be measured and reflected to become an echo beam, and then input from the second port of the optical circulator; S5. The echo beam is output from port three of the optical circulator and mixed with the local oscillator beam in the fiber coupler to obtain an intermediate frequency signal; S6. The intermediate frequency signal is converted into an electrical signal by a photodetector and input into the filtering unit; S7. Filter the specific frequency band wave signal and shield other frequency band wave signals through N independent filters in the filtering unit, and transmit the reserved frequency band wave signal to the digital signal processing unit; S8. The digital signal processing unit performs data processing and analysis on the reserved frequency band wave signal to calculate the time interval ; Then solve to obtain the distance d between the target object to be measured in each direction and the laser radar ranging system with multi-directional intermediate frequency pulse parallel modulation n ; The solution formula is as follows: ； In the formula, is the time interval and c is the speed of light.

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