Laser radar ranging system and method for multi-direction echo phase parallel mediation

Abstract

The invention relates to the technical field of laser radars, in particular to a laser radar ranging system and method for multi-direction echo phase parallel modulation. According to the system, a laser emitter emits a laser beam, and the laser beam is divided into a local oscillator beam and a detection beam through a beam splitter; the signal generator controls the phase modulator to generate a phase modulation signal, and performs phase modulation on the detection light beam; the optical frequency comb generation unit enables the detection light beam to generate a light wave signal of an optical frequency comb, inputs the light wave signal to an optical circulator, then transmits the light wave signal to the dispersion unit, and receives an echo light beam reflected from a target to be subjected to distance measurement; the optical fiber coupler performs frequency mixing on the local oscillation light beam and the echo light beam, converts the mixed light beam into an electric signal through a photoelectric detector, inputs the electric signal into a filtering unit, filters a specific-frequency-band wave signal and shields other-frequency-band wave signals; and carrying out data processing and analysis on the reserved frequency band wave signal through a digital signal processing unit, and calculating to obtain distance information between the system and the target to be subjected to distance measurement. The method has the advantage of improving the system detection speed.

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 for parallel modulation of multi-directional echo phases. Background Art

[0002] In order to address the limitations of the phase modulated continuous wave (PhMCW) coherent ranging method in point cloud imaging, especially the lack of frame rate and imaging speed, researchers and engineers are exploring the technology of multi-directional parallel detection. Although the existing PhMCW lidar ranging system can accurately measure the distance of a single angle (direction), in order to achieve three-dimensional imaging, multiple detection angles must be scanned one by one. This process is time-consuming, because the ranging of each direction may take 10 microseconds, and a complete 3D point cloud image may require measuring tens of thousands of different directions. In this way, the time to generate a frame of point cloud image will reach hundreds of milliseconds, which is far more than the 50 milliseconds (i.e. 20 frames per second) required for real-time 3D imaging. An intuitive solution is to replicate the PhMCW laser ranging system in multiple sets, with each system fixed at a specific detection angle, so as to achieve simultaneous distance measurement in multiple directions. This method can theoretically increase the imaging speed by N times, where N is the number of replicated systems. However, this approach has obvious disadvantages. It not only increases the complexity of the system and makes operation more difficult, but also leads to a significant increase in system volume, cost, weight and power consumption, because each set requires its own laser and detector. This increase is unacceptable for practical distance measurement applications.

[0003] Although this parallel system method can speed up the acquisition of 3D point cloud images, it is not easy to implement in practical applications due to the above problems, especially in situations that require compactness, cost-effectiveness, and low energy consumption. Therefore, although PhMCW technology performs well in distance measurement, in order to meet the requirements of real-time 3D imaging, it is still urgent to develop more efficient multi-directional parallel detection technology. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a laser radar ranging system and method for parallel modulation of multi-directional echo phases.

[0005] The first object of the present invention is to provide a laser radar ranging system with multi-directional echo phase parallel modulation, comprising a laser transmitter, a beam splitter, a phase modulator, a signal generator, 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;

[0006] The laser emitter is used to emit a laser beam;

[0007] The beam splitter is used to split the laser beam into a local oscillator beam and a detection beam;

[0008] The phase modulator is used to perform phase modulation on the detection beam so that the phase of the laser signal changes regularly;

[0009] The signal generator is used to control the phase modulator to generate a phase modulation signal and output a preset phase;

[0010] The optical frequency comb generating unit is used to generate a light wave signal of an optical frequency comb from the detection light beam modulated by the phase modulator, and input the light wave signal into the optical circulator;

[0011] The optical circulator is used to transmit the optical wave signal to the dispersion unit and receive the echo light beam reflected from the target to be measured;

[0012] 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;

[0013] The optical fiber coupler is used to mix the local oscillator light beam with the echo light beam to obtain an intermediate frequency signal;

[0014] The photoelectric detector is used to convert the intermediate frequency signal into an electrical signal and input it into the filtering unit;

[0015] The filtering unit includes N independent filters for filtering wave signals of a specific frequency band and shielding wave signals of other frequency bands;

[0016] 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 echo phase parallel modulation and the target to be measured.

[0017] Preferably, the filter is a bandpass filter or a low-pass filter.

[0018] 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.

[0019] Preferably, the optical frequency comb generating unit comprises an acousto-optic modulator, a gain medium and two couplers; the gain medium is a fiber amplifier; the light passing through the acousto-optic modulator generates light with a frequency shift of Δω, a coupler couples a part of the energy into the fiber amplifier for optical power amplification, and couples it back to the acousto-optic modulator again through another coupler to generate light with a frequency shift of 2Δω; the modulation is repeated to finally generate a light wave signal of an optical frequency comb with a frequency shift of Δω, 2Δω, 3Δω, ..., nΔω.

[0020] Preferably, the light field expression of the light wave signal of the optical frequency comb is:

[0021]

[0022] In the formula, A n is the amplitude of each beam of the amplified light wave signal, ω0 is the initial frequency, Δω is the specific frequency output generated by the acousto-optic modulator, t is the transmission time of the light wave signal, is the function of the modulation phase changing with time (i.e., the phase of the nth wavelength changing with time), A n and are all known constants.

[0023] Preferably, the local oscillator light beam and the echo light beam generate a local oscillator signal LO and an echo signal R respectively;

[0024] The light field expression of the local oscillator signal LO is:

[0025]

[0026] The light field expression of the echo signal R is:

[0027]

[0028] In the formula, B n is the amplitude of each beam of the echo signal, ω0 is the initial frequency, is the initial phase, Δω is the specific frequency output generated by the AOM, t is the transmission time of the light wave signal, τ n is the time interval, The light wave signal of the nth wavelength exists with the time interval τ n The changing phase of n is the light wave signal with the nth wavelength.

[0029] Preferably, the light field expression of the intermediate frequency signal is:

[0030]

[0031] Where Δω is the specific frequency output generated by the AOM, t is the transmission time of the light wave signal, and τ n is the time interval, The light wave signal of the nth wavelength exists with the time interval τ n The changing phase of n is the light wave signal with the nth wavelength.

[0032] 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.

[0033] Preferably, the beam splitter is any one of a beam splitter, a silicon photonic chip or a fiber beam splitter with a splitting ratio of 90:10; 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.

[0034] The second object of the present invention is to provide a laser radar ranging method with multi-directional echo phase parallel modulation, which uses a laser radar ranging system with multi-directional echo phase parallel modulation for measurement, and includes the following steps:

[0035] S1. The laser transmitter emits a laser beam, which is divided into a local oscillator beam and a detection beam after passing through a beam splitter;

[0036] S2. The phase modulator performs phase modulation on the detection beam so that the phase of the laser signal changes regularly;

[0037] S3. The detection beam modulated by the phase modulator generates a light wave signal of an optical frequency comb after passing through an optical frequency comb generating unit, and inputs the light wave signal to port 1 of the optical circulator;

[0038] 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;

[0039] 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;

[0040] S6. The intermediate frequency signal is converted into an electrical signal by a photodetector and input into the filtering unit;

[0041] 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;

[0042] S8. The digital signal processing unit performs data processing and analysis on the reserved frequency band wave signal to calculate the time interval τ n ; 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:

[0043]

[0044] In the formula, τ n is the time interval and c is the speed of light.

[0045] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0046] The present invention proposes a laser radar ranging system that uses only one laser and one detector for multi-directional echo phase parallel modulation, which can perform multi-angle simultaneous (parallel) measurement. It only adds a structure for generating an optical frequency comb (OFC), a dispersion unit, and a digital signal processing unit. Parallel detection is achieved 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), and changes the defect of measuring N points in the prior art that N points need to be measured N times. The present invention can achieve the beneficial effect of measuring N points once. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a structural schematic diagram of a laser radar ranging system with multi-directional echo phase parallel modulation according to the present invention.

[0048] Figure 2 It is a structural schematic diagram of a laser radar ranging system with multi-directional echo phase parallel modulation provided according to an embodiment of the present invention.

[0049] 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.

[0050] Figure 4 It is a structural schematic diagram of a laser radar ranging system with multi-directional echo phase parallel modulation provided according to an embodiment of the present invention.

[0051] 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.

[0052] Reference numerals:

[0053] 1. Laser transmitter;

[0054] 2. Beam splitter;

[0055] 3. Phase modulator;

[0056] 4. Signal generator;

[0057] 5. Optical frequency comb generation unit;

[0058] 501, coupler; 502, acousto-optic modulator; 503, erbium-doped fiber amplifier;

[0059] 6. Optical circulator;

[0060] 7. Spectral grating;

[0061] 8. Fiber optic coupler;

[0062] 9. Photoelectric detector;

[0063] 10. Filter unit;

[0064] 1001, N-channel low-pass filter; 1002, phase-locked loop;

[0065] 11. Digital signal processing unit;

[0066] 12. Collimator. DETAILED DESCRIPTION

[0067] 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.

[0068] 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.

[0069] The present invention provides a laser radar ranging system with multi-directional echo phase parallel modulation, comprising:

[0070] A laser transmitter, used for emitting a laser beam;

[0071] A beam splitter is used to split the 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 the "transmitted signal"); the type and splitting ratio of the beam splitter are not limited and can be selected according to system requirements. For example, a fiber beam splitter with a splitting ratio of 90:10 can be used, or a beam splitter, a silicon photonic chip, etc. can be used for beam splitting;

[0072] The local oscillator signal LO, assuming the initial frequency is ω0, the initial phase is Then the light field expression of the local oscillator signal LO is:

[0073]

[0074] Where ω0 is the initial frequency, is the initial phase.

[0075] The phase modulator is used to phase modulate the laser beam so that the phase of the emitted laser signal changes regularly. The emitted signal passes through the phase modulator to phase modulate the emitted signal. The modulation waveform is a square wave with a certain duty cycle, and its modulation period is T. m ;

[0076] 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 are not limited, such as a lithium niobate electro-optic phase modulator, a silicon waveguide thermo-optic phase modulator, etc.;

[0077] A signal generator, used for controlling the phase modulator to generate a phase modulation signal and output a preset phase;

[0078] The local oscillator signal LO is modulated and amplified by the phase modulator and the acousto-optic modulator to obtain the light wave signal T. At this time, the light field expression of the light wave signal T is:

[0079]

[0080] In the formula, A n is the amplitude of each beam of the amplified light wave signal, ω0 is the initial frequency, Δω is the specific frequency output generated by the acousto-optic modulator, t is the transmission time of the light wave signal, is the function of the modulation phase changing with time (i.e., the phase of the nth wavelength changing with time), A n and are all known constants;

[0081] An optical frequency comb generating unit, used for generating equally spaced discrete spectra in the frequency domain, so that the detection light beam modulated by the phase modulator generates a light wave signal of the optical frequency comb, and inputs the light wave signal into the optical circulator;

[0082] An optical circulator, used for transmitting the modulated laser signal to the dispersion unit and receiving the echo beam reflected from the target to be measured;

[0083] A dispersion unit, used to split composite light containing different wavelengths; the type of dispersion unit is not limited, including but not limited to a splitter grating, a prism, etc.;

[0084] Fiber coupler, 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 also incident on the fiber coupler, and the fiber coupler mixes the local oscillator beam (local oscillator signal LO) and the echo beam (echo signal R);

[0085] A photodetector, used to convert the intermediate frequency signal obtained by mixing into an electrical signal;

[0086] A filter unit is used to filter a specific frequency band and shield the wave signals of other frequency bands;

[0087] The digital signal processing unit 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 echo phase parallel adjustment and the target object to be measured.

[0088] Part of the structure in the laser radar ranging system with multi-directional echo phase parallel modulation of the present invention can be replaced by other structural methods, for example:

[0089] (1) The principle of phase modulation is not limited. It can be thermo-optic modulation (heating the waveguide, changing the temperature, changing the waveguide refractive index, and changing the light phase) or electro-optic 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).

[0090] (2) There is no limit to the method of generating the optical frequency comb, including silicon nitride micro-ring optical comb, circular frequency shift optical comb including acousto-optic modulator and gain medium, phase modulation optical comb, etc.; in the circular frequency shift optical comb of acousto-optic modulator + gain medium, there is no limit to the type of gain medium, including semiconductor optical amplifier, erbium-doped fiber amplifier, etc.

[0091] (3) Types of digital signal processing units and calculation of τ n There is no restriction on the method, for example: using TDC (time-to-digital converter, a chip that can measure pulse width) to directly time; or using ADC (analog-to-digital converter, oscilloscope, collecting pulse waveform and then analyzing) to collect phase modulation signal and IF signal for counting / timing; or using ADC to sample phase modulation signal and IF signal, calculate the mutual correlation coefficient between the two, and find the time delay with the largest correlation coefficient; all of the above methods can realize the analysis of data to obtain τ n That's it.

[0092] Furthermore, the system also includes: a collimator arranged between the optical circulator and the beam splitter grating, for collimating the detection light beam and the echo light beam.

[0093] Furthermore, the optical frequency comb generation unit (OFC) includes an acousto-optic modulator (AOM), an erbium-doped fiber amplifier (EDFA) and a frequency shift loop composed of a coupler; its working principle is as follows: the light passing through the AOM generates a certain frequency shift Δω, the coupler couples part of the energy into the EDFA, and the remaining energy is transmitted to port one of the optical circulator; the light with a frequency shift of Δω is amplified by the erbium-doped fiber amplifier to compensate for the energy loss caused by the coupler and transmission loss, and is coupled back to the acousto-optic modulator through the coupler to generate light with a frequency shift of 2Δω; repeating the above process, the optical frequency comb generation unit will generate frequency combs with frequency shifts of Δω, 2Δω, 3Δω, etc.

[0094] The light wave signal E entering the optical circulator port 1 T The light field expression is:

[0095]

[0096] In the formula, Indicates the phase of the nth wavelength changing with time. are equal, the same as the square wave modulation signal waveform.

[0097] Light wave signal E T Enters into the optical circulator port 1 and exits from the optical circulator port 2, is collimated by the collimator, and then is incident on the dispersion unit;

[0098] 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 beam is dispersed and hits the object to be measured in different directions. After the light wave encounters the object to be measured, it is reflected. Due to the reversible principle of the optical path, the echo signal R reflected in each direction returns to the optical circulator again after passing through the dispersion unit and the collimator. Then, using the characteristics of the optical circulator (the light entering from Port2 will be emitted from Port3), the echo signal R is transmitted to the fiber coupler through the optical circulator. 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 τ. n , 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:

[0099]

[0100]

[0101] In the formula, B n is the amplitude of each beam of the echo signal, ω0 is the initial frequency, is the initial phase, Δω is the specific frequency output generated by the AOM, t is the transmission time of the light wave signal, τ n is (time interval), is the light wave signal of the nth wavelength with the time interval τ n The phase change), n is (the light wave signal of the nth wavelength); due to ω0τ n , nΔωτ n and The three 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:

[0102]

[0103] The intermediate frequency signal is the sum of a series of cosine terms; note that Δω is usually in the order of tens of MHz. The bandwidth is only a few MHz, which can be obtained by expanding the Bessel function: The term is a narrowband signal with a center frequency of nΔω and a bandwidth of several MHz. The IF signal is the sum of a series of narrowband signals with a center frequency of nΔω and a bandwidth of several MHz. These narrowband signals have no frequency band overlap (such as Figure 3 As shown), each narrowband signal corresponds to one direction.

[0104] Therefore, by inputting the IF signal into bandpass filters of different frequency bands, the IF signals in all directions can be filtered out, that is, each item is After finding arccos, we get Subtracting the term nΔωt, we get That is, the flight time τ in each direction n The phase expression of the delay. Through the analysis and calculation of the digital signal processing unit, the original phase modulation signal and We can analyze τ n or use TDC (time-to-digital converter) to phase modulate the signal and The time interval τ can be directly measured by n (The time required for the light wave to be emitted to the obstacle and scattered back to the radar). 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.

[0105] Specifically, the light wave signal T passes through the optical circulator, is collimated by the collimator and then hits the dispersion unit. Since the light wave contains a series of light beams with different and increasing frequencies, from the relationship between the wavelength of the light wave and the frequency c=υλ, c is the speed of light, it can be known that the wavelength of the light wave is inversely proportional to the frequency. Then, after the light wave signal T is reflected by the dispersion unit, it is emitted at different diffraction angles. After encountering each target object to be measured in different directions, each light wave is reflected back, and enters the optical circulator again after being reflected by the dispersion unit, and outputs the echo signal R from Port 3; the echo signal R has a flight time interval τ n , and a delay is generated relative to the local oscillator signal LO, and its light field expression is:

[0106]

[0107] The echo signal R is transmitted to the fiber coupler through the optical circulator. The local oscillator signal LO (i.e., 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 local oscillator signal LO and the echo signal R are coherently superimposed to generate a new light field. The light field expression is:

[0108]

[0109] 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 P∝It =E 2 (t) t ,symbol t It means taking the average over time, then the power P is:

[0110]

[0111] because and I R It 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, so it can be ignored. So it can be simplified to

[0112]

[0113] Define the intermediate frequency signal IF:

[0114]

[0115] Where ω0 is the initial frequency, is the initial phase, Δω is the specific frequency output generated by the AOM, Bn, n and τ n is a constant term, which does not carry information and has no effect on distance measurement. To simplify the formula, ω0τ is ignored. n , nΔωτ n and Three items, so it can be expressed as:

[0116]

[0117] Example 1

[0118] like Figure 1-Figure 3 As shown, this embodiment provides a laser radar ranging system with multi-directional echo phase parallel modulation, including:

[0119] A laser transmitter 1, used for transmitting a laser beam;

[0120] The beam splitter 2 is used to split the laser beam into two paths, one of which is used as a local oscillator beam (generating a local oscillator signal LO), and the other is used as a detection beam, which is modulated and emitted into space for distance detection (hereinafter referred to as a "transmitted signal");

[0121] The phase modulator 3 is used to perform phase modulation on the laser beam so that the phase of the emitted laser signal changes regularly;

[0122] A signal generator 4 is used to control the phase modulator to generate a phase modulation signal and output a preset phase;

[0123] The optical frequency comb generating unit 5 includes 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;

[0124] An optical circulator 6, used for transmitting the modulated laser signal to the grating and receiving the echo signal;

[0125] A collimator 12, used for collimating the detection beam and the echo beam;

[0126] The beam splitter grating 7 is used to split the composite light containing different wavelengths;

[0127] 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;

[0128] The photodetector 9 is used to convert the intermediate frequency signal obtained by mixing into an electrical signal;

[0129] The filter unit 10 is used to filter a specific frequency band and shield the wave signals of other frequency bands;

[0130] 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;

[0131] The intermediate frequency signal IF is the sum of a series of cosine terms; note that Δω is usually in the order of tens of megahertz (MHz). The bandwidth is only a few megahertz (MHz), which can be obtained by expanding the Bessel function: The term is a narrowband signal with a center frequency of nΔω and a bandwidth of several megahertz (MHz). The intermediate frequency signal IF is the sum of a series of narrowband signals with a center frequency of nΔω and a bandwidth of several megahertz (MHz). These narrowband signals have no frequency band overlap (such as Figure 3 As shown), each narrowband signal corresponds to one direction.

[0132] Therefore, by inputting the intermediate frequency signal IF into the bandpass filters of different frequency bands, the IF signals in all directions can be filtered out, that is, each item is The inverse trigonometric function is calculated by the digital processing unit, and arccos is obtained. Subtracting the term nΔωt, we get That is, the flight time τ in each direction n Phase expression for the delay.

[0133] 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 echo phase parallel modulation and the measured target object; specifically, through the analysis and calculation processing of the digital signal processing unit 11, the original phase modulation signal and the phase expression after the flight time delay in each direction are sampled by a high-speed sampling oscilloscope. We can analyze τ n or use TDC (time-to-digital converter) to phase modulate the signal and The time interval τ can be directly measured by n 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.

[0134] Example 2

[0135] like Figure 4-Figure 5 As shown, this embodiment provides a laser radar ranging system with multi-directional echo phase parallel modulation, including:

[0136] A laser transmitter 1, used for transmitting a laser beam;

[0137] The beam splitter 2 is used to split the laser beam into two paths, one of which is used as a local oscillator beam (generating a local oscillator signal LO), and the other is used as a detection beam, which is modulated and emitted into space for distance detection (hereinafter referred to as a "transmitted signal");

[0138] The phase modulator 3 is used to perform phase modulation on the laser beam so that the phase of the emitted laser signal changes regularly;

[0139] A signal generator 4 is used to control the phase modulator to generate a phase modulation signal and output a preset phase;

[0140] 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;

[0141] An optical circulator 6, used for transmitting the modulated laser signal to the grating and receiving the echo signal;

[0142] A collimator 12, used for collimating the detection beam and the echo beam;

[0143] The beam splitter grating 7 is used to split the composite light containing different wavelengths;

[0144] 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;

[0145] The photodetector 9 is used to convert the intermediate frequency signal obtained by mixing into an electrical signal;

[0146] 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.

[0147] The intermediate frequency signal IF converts the light wave signal into an electrical signal output through a photodetector. At this time, the signal generator drives the acousto-optic modulator with a signal with a frequency of Δω. At the same time, the signal with a frequency of Δω also acts on the phase-locked loop, so that the phase-locked loop generates a series of signals with integer multiples of Δω, and the intermediate frequency signal IF is multiplied with this series of signals. Taking the signal with a frequency of Δω as an example, the intermediate frequency signal IF is multiplied with it, and the result of the operation is the multiplication output signal:

[0148]

[0149] The multiplication output signal is the sum of a series of cosine terms; Δω is usually in the order of tens of MHz. The bandwidth is only a few MHz, which can be obtained by expanding the Bessel function: The term is a low-frequency narrowband signal with a bandwidth of several MHz. The term is a high-frequency narrowband signal with a center frequency of nΔω and a bandwidth of several MHz (as shown in the figure below). Therefore, the mixing signal is the sum of a low-frequency signal with a bandwidth of several MHz and a series of narrowband signals with a center frequency of nΔω and a bandwidth of several MHz. These narrowband signals have no frequency band overlap (such as Figure 5 As shown). The cutoff frequency of the low-pass filter is set to a value much smaller than Δω. When the above mixed signal passes through the low-pass filter 1001, the first term The signal will be filtered out, and after calculating arccos, we get Similarly, the intermediate frequency signal IF is multiplied by a series of absolute Δω integer multiple signals, and the mixed signals are passed through N low-pass filters to obtain That is, the flight time τ in each direction n Phase expression for the delay.

[0150] 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 echo phase parallel modulation and the measured target object; specifically, through the analysis and calculation processing of the digital signal processing unit 11, the original phase modulation signal and We can analyze τ n or use TDC (time-to-digital converter) to phase modulate the signal and The time interval τ can be directly measured by n 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.

[0151] Example 3

[0152] A laser radar ranging method with multi-directional echo phase parallel modulation includes the following steps:

[0153] S1. The laser transmitter emits a laser beam, which is divided into a local oscillator beam and a detection beam after passing through a beam splitter;

[0154] S2. The phase modulator performs phase modulation on the detection beam so that the phase of the laser signal changes regularly;

[0155] S3. The detection beam modulated by the phase modulator generates a light wave signal of an optical frequency comb after passing through the optical frequency comb generating unit, and the light wave signal is input to port 1 of the optical circulator;

[0156] 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;

[0157] S5. The echo beam is output from port 3 of the optical circulator and mixed with the local oscillator beam in the fiber coupler to obtain an intermediate frequency signal;

[0158] S6. The intermediate frequency signal is converted into an electrical signal through a photodetector and input into a filtering unit;

[0159] 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;

[0160] S8. The digital signal processing unit performs data processing and analysis on the reserved frequency band wave signal and calculates the time interval τ n ; 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:

[0161]

[0162] In the formula, τ n is the time interval and c is the speed of light.

[0163] 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.

[0164] 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 echo phases, characterized by: It includes a laser transmitter, a beam splitter, a phase modulator, a signal generator, 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 beam splitter is used to split the laser beam into a local oscillator beam and a detection beam; The phase modulator is used to perform phase modulation on the detection 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 optical frequency comb generating unit is used to generate a light wave signal of an optical frequency comb from the detection light beam modulated by the phase modulator, and input the light wave signal into the optical circulator; The optical circulator is used to transmit the optical wave signal 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; 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 echo phase parallel modulation and the target to be measured.

2. The laser radar ranging system with multi-directional echo phase parallel adjustment 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 echo phase parallel adjustment 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 echo phase parallel adjustment according to claim 3 is characterized in that: The optical frequency comb generating unit comprises an acousto-optic modulator, a gain medium and two couplers; the gain medium is a fiber amplifier; the light passing through the acousto-optic modulator generates light with a frequency shift of Δω, a coupler couples a part of the energy into the fiber amplifier for optical power amplification, and couples it back to the acousto-optic modulator through another coupler to generate light with a frequency shift of 2Δω; Repeating the modulation eventually generates a light wave signal of an optical frequency comb with a frequency shift of Δω, 2Δω, 3Δω, ..., nΔω.

5. The laser radar ranging system with multi-directional echo phase parallel adjustment according to claim 4 is characterized in that: The optical field expression of the optical wave signal of the optical frequency comb is: In the formula, A n is the amplitude of each beam of the amplified light wave signal, ω0 is the initial frequency, Δω is the specific frequency output generated by the acousto-optic modulator, t is the transmission time of the light wave signal, is the function of the modulation phase changing with time (i.e., the phase of the nth wavelength changing with time), A n and are all known constants.

6. The laser radar ranging system with multi-directional echo phase parallel adjustment according to claim 5, 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, B n is the amplitude of each beam of the echo signal, ω0 is the initial frequency, is the initial phase, Δω is the specific frequency output generated by the AOM, t is the transmission time of the light wave signal, τ n is the time interval, The light wave signal of the nth wavelength exists with the time interval τ n The changing phase of n is the light wave signal with the nth wavelength.

7. The laser radar ranging system with multi-directional echo phase parallel adjustment according to claim 6, characterized in that: The light field expression of the intermediate frequency signal is: Where Δω is the specific frequency output generated by the AOM, t is the transmission time of the light wave signal, and τ n is the time interval, The light wave signal of the nth wavelength exists with the time interval τ n The changing phase of n is the light wave signal with the nth wavelength.

8. The laser radar ranging system with multi-directional echo phase parallel adjustment according to any one of claims 1 to 7, characterized in that: It also includes a collimator arranged between the optical circulator and the dispersion unit, which is used to collimate the light wave signal and the echo light beam.

9. The laser radar ranging system with multi-directional intermediate frequency pulse parallel modulation according to claim 8, characterized in that: The beam splitter is any one of a beam splitter, a silicon photonic chip or a fiber beam splitter with a splitting ratio of 90:10; 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.

10. A laser radar ranging method with multi-directional echo phase parallel adjustment, using the laser radar ranging system with multi-directional echo phase parallel adjustment as claimed in any one of claims 1 to 9 for measurement, characterized in that: The steps include: S1. The laser transmitter emits a laser beam, which is divided into a local oscillator beam and a detection beam after passing through a beam splitter; S2. The phase modulator performs phase modulation on the detection beam so that the phase of the laser signal changes regularly; S3. The detection beam modulated by the phase modulator generates a light wave signal of an optical frequency comb after passing through an optical frequency comb generating unit, and inputs the light wave signal 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 τ n ; 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, τ n is the time interval and c is the speed of light.

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