A frequency-modulated continuous wave laser radar velocity and distance measuring device and method

Abstract

The application discloses a frequency-modulated continuous wave laser radar velocity and distance measuring device and method, and relates to the technical field of laser radar. The velocity and distance measuring device comprises a single-frequency seed laser, a modulation frequency sweeping module located on the outgoing direction of the single-frequency seed laser, a laser beam splitter used for splitting the frequency sweeping laser into two beams, an acousto-optic frequency shifting module used for irradiating a target after frequency shifting of the first beam of frequency sweeping laser or used for frequency shifting of the second beam of frequency sweeping laser, a laser beam combiner used for combining the second beam of frequency sweeping laser and the echo laser reflected by the target, and a data acquisition and analysis module used for collecting the combined laser to output the velocity and / or distance of the target. Since the modulation frequency sweeping module is used to modulate the laser into triangular wave type frequency sweeping laser, and then the acousto-optic frequency shifting module is used to frequency shift the first beam of frequency sweeping laser or the second beam of frequency sweeping laser, the problem of frequency aliasing caused by the fact that the Doppler frequency shift of the velocity measuring target is greater than the target distance does not exist, and therefore the accuracy of velocity measurement and distance measurement is higher.

Description

Technical Field

[0001] This invention relates to the field of radar speed and distance measurement technology, and in particular to a frequency-modulated continuous wave lidar speed and distance measurement device and method. Background Technology

[0002] With the advent of the era of autonomous driving, long-range, high-precision LiDAR has become a research hotspot. Frequency Modulated Continuous Wave (FMCW) and Time-of-Flight (TOF) are the two mainstream technologies in LiDAR. Among them, FMCW technology is widely regarded as the ultimate solution for vehicle-mounted LiDAR due to its high ranging resolution and real-time speed measurement capabilities.

[0003] The main working principle of FMCW technology is as follows: A frequency-sweeping light source is generated using external or internal modulation. The instantaneous laser has a narrow linewidth, and the frequency sweep is a triangular wave. The weak frequency-sweeping laser is amplified by a laser power amplifier, and then split into two beams: one as the local oscillator laser and the other as the probe laser. The probe laser passes through a circulator and a beam expander before entering the air and illuminating the target. The laser echo signal reflected from the target passes through a beam expander and a circulator, then enters a beam combiner and is optically mixed with the local oscillator laser. Finally, a photoelectric balanced detector detects the beat frequency signal to extract the target's range and velocity information. For stationary targets, only a range-delay-related frequency shift is introduced into the beat frequency signal, while for moving targets, a Doppler frequency shift is superimposed on the beat frequency signal, resulting in two frequencies during the upper and lower sweeps of the triangular wave. These two frequencies are the sum and minus the Doppler frequency shift based on the distance delay frequency shift. Therefore, when the Doppler frequency shift is greater than the distance delay frequency shift, frequency aliasing will occur, leading to misjudgment of speed and distance.

[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a frequency-modulated continuous wave lidar speed and distance measurement device and method to address the above-mentioned deficiencies of the prior art, aiming to solve the problem of inaccurate speed and distance measurement caused by frequency aliasing due to Doppler frequency shift in the prior art.

[0006] The technical solution adopted by this invention to solve the technical problem is as follows:

[0007] A frequency-modulated continuous wave lidar velocity and ranging device, comprising:

[0008] Single-frequency seed laser;

[0009] The modulation sweep module is located in the emission direction of the single-frequency seed laser;

[0010] A laser beam splitter is located in the emission direction of the modulation sweep module and is used to split the sweep laser into two beams.

[0011] An acousto-optic frequency shifting module is located in the emission direction of the first swept laser beam and is used to shift the frequency of the first swept laser beam to illuminate the target, or it is located in the emission direction of the second swept laser beam and is used to shift the frequency of the second swept laser beam.

[0012] A laser beam combiner is used to combine a second frequency-sweeping laser beam and an echo laser beam reflected from the target.

[0013] The data acquisition and analysis module is used to acquire the combined laser beam to output the target's velocity and / or distance;

[0014] The modulation and sweeping module modulates and sweeps the laser emitted by the single-frequency seed laser into a triangular wave sweeping laser.

[0015] The target is in a moving state relative to the single-frequency seed laser.

[0016] The frequency-modulated continuous wave lidar velocity and ranging device, wherein the modulation and frequency sweeping module includes:

[0017] A carrier-suppressed single-sideband modulator is located in the emission direction of the single-frequency seed laser;

[0018] The frequency sweep source is connected to the carrier-suppressed single-sideband modulator.

[0019] In the frequency-modulated continuous wave lidar velocity and ranging device, the carrier-suppressed single-sideband modulator is either a lithium niobate modulator or a silicon photonic modulator.

[0020] The sweep frequency source is one of DDS, DAC or phase-locked feedback voltage-controlled oscillator, and the sweep frequency bandwidth of the sweep frequency source is greater than or equal to 500MHz.

[0021] The frequency-modulated continuous wave lidar velocity and ranging device, wherein the acousto-optic frequency shifting module includes:

[0022] An acousto-optic modulator is located in the emission direction of the first swept laser beam of the laser beam splitter, or in the emission direction of the second swept laser beam.

[0023] The driving source is connected to the acousto-optic modulator.

[0024] The frequency-modulated continuous wave lidar velocity and distance measuring device, wherein the acousto-optic modulator is one of fiber optic coupling or free space modulator, and the acousto-optic modulator is used to detect the frequency shift of light;

[0025] The output frequency of the driving source is a radio frequency signal ranging from 30MHz to 500MHz.

[0026] The frequency-modulated continuous wave lidar velocity and distance measuring device, wherein the single-frequency seed laser is a 1.5μm or 1.3μm laser with a linewidth of less than or equal to 500kHz;

[0027] The single-frequency seed laser is one of a semiconductor laser, a fiber laser, or a solid-state gain medium laser.

[0028] The laser beam splitter is one of the following: fiber coupler, lens coated with a beam splitter film, or spatial polarization beam splitter. The power ratio of the first swept laser beam to the second swept laser beam is greater than 8:1.

[0029] The laser beam combiner is either an optical fiber beam combiner or a free-space beam combiner.

[0030] In the frequency-modulated continuous wave lidar velocity and ranging device, a laser power amplifier is provided between the modulation sweep module and the laser beam splitter to amplify the power of the sweep laser.

[0031] A laser circulator and a laser beam expander are provided between the acousto-optic frequency shifting module and the target. The laser circulator is used to separate the first frequency-sweeping laser beam from the echo laser reflected by the target, and the laser beam expander is used to compress the divergence angle of the first frequency-sweeping laser beam and irradiate it onto the target.

[0032] In the frequency-modulated continuous wave lidar velocity and ranging device, the laser power amplifier is one of EDFAEYDFA and semiconductor laser amplifier;

[0033] The laser circulator is either a fiber optic circulator or a space laser circulator.

[0034] The laser beam expander is either a transmission beam expander or a reflection beam expander.

[0035] The frequency-modulated continuous wave lidar velocity and ranging device, wherein the data acquisition and analysis module includes:

[0036] A photoelectric balance detector is used to convert combined laser beams into electrical signals;

[0037] The data acquisition module is used to acquire electrical signals;

[0038] The data processing module is used to process the acquired electrical signals to output the target's speed and / or distance.

[0039] In the frequency-modulated continuous wave lidar velocity and ranging device, the photoelectric balance detector is either a PIN balance detector or an APD balance detector.

[0040] The data acquisition module is an ADC analog-to-digital converter;

[0041] The data processing module is an FPGA or DSP module.

[0042] A frequency-modulated continuous wave lidar method for velocity and ranging measurement, comprising the following steps:

[0043] The laser emitted by the single-frequency seed laser is modulated and frequency-sweeped, and then split into a first frequency-sweeping laser and a second frequency-sweeping laser; wherein, the first frequency-sweeping laser and the second frequency-sweeping laser are both triangular wave frequency-sweeping lasers.

[0044] The first frequency-sweeping laser beam is frequency-shifted before irradiating the target; wherein the target is in a moving state relative to the single-frequency seed laser;

[0045] The second frequency-sweeping laser beam and the echo laser beam reflected from the target are combined;

[0046] The velocity and / or distance of the target are obtained from the combined laser beam.

[0047] The frequency-modulated continuous wave lidar velocity and distance measurement method, wherein obtaining the target's velocity and / or distance based on the combined laser beam includes:

[0048] The combined laser beam is acquired to obtain a beat frequency signal of one triangular wave period, and the slope of the swept triangular wave and / or the frequency of the combined laser beam are determined.

[0049] The processed beat frequency signal is obtained by performing an FFT calculation on the beat frequency signal of one triangular wave cycle.

[0050] The processed beat frequency signal is denoised, and the two peak values ​​of the processed beat frequency signal are determined.

[0051] The distance to the target is calculated based on the two peaks and the slope of the swept triangular wave; and / or, the velocity of the target is calculated based on the two peaks and the frequency of the combined laser beam.

[0052] In the frequency-modulated continuous wave lidar velocity and ranging method described above, the distance to the target is:

[0053]

[0054] Where D represents the distance to the target, f1 represents the frequency component of the beat frequency signal of the combined laser sweeping on the triangular wave, f2 represents the frequency component of the beat frequency signal of the combined laser sweeping under the triangular wave, α represents the slope of the triangular wave of the combined laser sweeping, and c represents the speed of light.

[0055] The speed of the target is:

[0056]

[0057]

[0058] Where υ represents the velocity of the target, λ represents the frequency of the combined laser beam, and f AOM f represents the frequency shift of the first swept laser beam. doppler This indicates the Doppler shift caused by velocity.

[0059] Beneficial effects: Since the present invention uses a modulation sweep frequency module to modulate the laser into a triangular wave sweep frequency laser, and then uses an acousto-optic frequency shift module to shift the frequency of the first or second sweep frequency laser, there will be no frequency aliasing problem caused by the Doppler frequency shift of the velocity measurement target being greater than the target distance, thus the accuracy of velocity and distance measurement is higher. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of the frequency-modulated continuous wave lidar velocity and distance measuring device in this invention.

[0061] Figure 2 This is a schematic diagram of time, laser frequency, and beat frequency signals in this invention.

[0062] Figure 3 This is a flowchart of the frequency-modulated continuous wave lidar velocity and distance measurement method in this invention.

[0063] Explanation of reference numerals in the attached figures:

[0064] 101. Single-frequency seed laser; 102. Carrier-suppressed single-sideband modulator; 103. Frequency sweep source; 104. Laser power amplifier; 105. Laser beam splitter; 106. Acousto-optic modulator; 107. Driver source; 108. Laser circulator; 1. First port; 2. Second port; 3. Third port; 109. Laser beam expander; 110. Laser beam combiner; 111. Photoelectric balance detector; 112. Data acquisition module; 113. Data processing module. Detailed Implementation

[0065] To make the objectives, technical solutions, and advantages of this invention clearer and more explicit, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0066] Please also refer to Figures 1-3 This invention provides some embodiments of a frequency-modulated continuous wave lidar velocity and distance measuring device.

[0067] The frequency-modulated continuous wave (FM-CW) lidar speed and distance measuring device of this invention is applied to vehicle-mounted lidar. The device is mounted on a vehicle and measures the speed and distance to targets around the vehicle. These targets can be moving or stationary, and the vehicle can be stationary or moving. Of course, there will be relative movement between the vehicle and the target (at least one of them is moving, and their speeds are not the same). In other words, the target is moving relative to the FM-CW lidar speed and distance measuring device.

[0068] like Figures 1-2 As shown, a frequency-modulated continuous wave lidar velocity and ranging device of the present invention includes:

[0069] Single-frequency seed laser 101;

[0070] The modulation sweep module is located in the emission direction of the single-frequency seed laser 101;

[0071] The laser beam splitter 105 is located in the emission direction of the modulation sweep module and is used to split the sweep laser into two beams.

[0072] An acousto-optic frequency shifting module is located in the emission direction of the first swept laser beam and is used to shift the frequency of the first swept laser beam to illuminate the target, or it is located in the emission direction of the second swept laser beam and is used to shift the frequency of the second swept laser beam.

[0073] Laser beam combiner 110 is used to combine the second frequency-sweeping laser beam and the echo laser reflected from the target.

[0074] The data acquisition and analysis module is used to acquire the combined laser beam to output the target's velocity and / or distance;

[0075] The modulation sweeping module modulates and sweeps the laser emitted by the single-frequency seed laser 101 into a triangular wave sweeping laser.

[0076] The target is in a moving state relative to the single-frequency seed laser 101.

[0077] Specifically, since the present invention uses a modulation sweep frequency module to modulate the laser into a triangular wave sweep frequency laser, and then uses an acousto-optic frequency shift module to shift the frequency of the first or second sweep frequency laser, there will be no frequency aliasing problem caused by the Doppler frequency shift of the velocity measurement target being greater than the target distance, thus the accuracy of velocity and distance measurement is higher.

[0078] The modulation sweep module modulates the laser into a triangular wave sweep laser with a slope of α. When the acousto-optic frequency shift module shifts the frequency of the first or second sweep laser beam, the shift is f. AOM The size can be set as needed. The relationship between the time of the second swept laser beam and the echo laser reflected from the target and the laser frequency is as follows: Figure 2 As shown, the relationship between the timing of the second sweeping laser beam and the echo laser reflected from the target and the beat frequency signal is as follows: Figure 2 As shown, the beat frequency signal is acquired by the data acquisition and analysis module. The following relationship can be obtained:

[0079] f1 = f AOM +α*τ+f doppler

[0080] f2=f AOM -α*τ+f doppler

[0081] Where f1 represents the frequency component of the combined laser beat frequency signal sweeping on the triangular wave, f2 represents the frequency component of the combined laser beat frequency signal sweeping under the triangular wave, α represents the slope of the swept triangular wave of the combined laser, c represents the speed of light, τ represents the time delay due to distance, and f doppler This represents the Doppler frequency shift caused by velocity. From this, we can calculate:

[0082]

[0083]

[0084] Then the distance D to the target can be further calculated as follows:

[0085]

[0086] The target's velocity υ is:

[0087]

[0088] Where λ represents the frequency of the combined laser beam.

[0089] It is understandable that f AOMWhen the values ​​are appropriate, f1 and f2 will not have frequencies less than 0, thus avoiding frequency aliasing. The frequency-modulated continuous wave (FMCW) lidar speed and distance measurement device of this invention avoids the frequency aliasing problem caused by excessive Doppler frequency shift. Compared with previous methods using complex algorithms and receiving structures, it is simple and practical, which is beneficial for the application of FMCW technology in vehicle-mounted lidar.

[0090] In a preferred implementation of this invention, such as Figures 1-2 As shown, the modulation sweep module includes: a carrier-suppressed single-sideband modulator 102, located in the emission direction of the single-frequency seed laser 101;

[0091] The frequency sweep source 103 is connected to the carrier-suppressed single-sideband modulator 102.

[0092] Specifically, the laser frequency is swept in a triangular wave manner after the seed laser carrier-suppressed single-sideband modulator 102 and the sweep frequency source 103 module.

[0093] In a preferred implementation of this invention, such as Figures 1-2 As shown, the single-frequency seed laser 101 is a 1.5μm laser with a linewidth of less than or equal to 200kHz.

[0094] Specifically, the single-frequency seed laser 101 is a narrow-linewidth laser with a linewidth of 1.5 μm, a linewidth of less than 200 kHz, and an output power greater than 10 dBm.

[0095] In a preferred implementation of this invention, such as Figures 1-2 As shown, the single-frequency seed laser 101 is one of a semiconductor laser, a fiber laser, or a solid-state gain medium laser.

[0096] Specifically, different types of single-frequency seed lasers 101 can be used as needed.

[0097] In a preferred implementation of this invention, such as Figures 1-2 As shown, the carrier-suppressed single-sideband modulator 102 is either a lithium niobate modulator or a silicon photonics modulator, and the carrier suppression ratio of the carrier-suppressed single-sideband modulator 102 is greater than 10dB.

[0098] Specifically, a carrier-suppressed single-sideband modulator 102 made of different materials can be used as needed.

[0099] In a preferred implementation of this invention, such as Figures 1-2As shown, the sweep frequency source 103 is one of a DDS, DAC, or phase-locked feedback voltage-controlled oscillator, and the sweep frequency bandwidth of the sweep frequency source 103 is greater than or equal to 1 GHz. The carrier-suppressed single-sideband modulator 102 can be an in-phase quadrature (IQ) modulator.

[0100] Specifically, Direct Digital Frequency Synthesizers (DDS) employ an all-digital architecture, offering advantages such as wide relative bandwidth of the synthesized signal, short frequency conversion time, high frequency resolution, and phase connectivity of the synthesized signal. Digital-to-Analog Converters (DACs)

[0101] In a preferred implementation of this invention, such as Figures 1-2 As shown, the acousto-optic frequency shifting module includes:

[0102] The acousto-optic modulator 106 is located in the emission direction of the first swept laser beam of the laser beam splitter 105, or in the emission direction of the second swept laser beam.

[0103] The driving source 107 is connected to the acousto-optic modulator 106.

[0104] Specifically, the acousto-optic modulator 106 can frequency shift one of the first and second swept laser beams.

[0105] In a preferred implementation of this invention, such as Figures 1-2 As shown, the acousto-optic modulator 106 is either an optical fiber coupler or a free-space modulator, and is used to detect the frequency shift of light; the output frequency of the driver source 107 is a radio frequency signal from 30MHz to 500MHz. Specifically, the frequency of the driver source 107 is set as needed, and the frequency of the driver source 107 needs to be large enough to prevent frequency aliasing. It should be noted that the magnitude of the acousto-optic frequency shift needs to satisfy the frequency shift f. AOM greater than the sum of the Doppler frequency shift caused by velocity and the frequency shift caused by distance, f Doppler +α*τ can effectively avoid frequency aliasing of the beat frequency signal, i.e., f AOM >f Doppler +α*τ, that is

[0106] In a preferred implementation of this invention, such as Figures 1-2 As shown, the laser beam splitter 105 is one of an optical fiber coupler, a lens coated with a beam splitter film, or a spatial polarization beam splitter, and the power ratio of the first swept laser beam to the second swept laser beam is greater than 9:1.

[0107] Specifically, the power ratio of the first swept laser beam and the second swept laser beam is greater than 9:1. For example, the power ratio of the first swept laser beam and the second swept laser beam can be 99:1. 99% of the swept laser beam enters the acousto-optic frequency shifting module for frequency shifting, and 1% of the swept laser beam enters the laser beam combiner 110 as the local oscillator laser.

[0108] In a preferred implementation of this invention, such as Figures 1-2 As shown, the laser beam combiner 110 is one of an optical fiber or a free space beam combiner, and the power ratio of the combined beam is 1:1. Specifically, the power ratio of the combined beam can be set as needed.

[0109] In a preferred implementation of this invention, such as Figures 1-2 As shown, a laser power amplifier 104 is disposed between the modulation sweep module and the laser beam splitter 105 to amplify the power of the sweep laser. Specifically, the laser power amplifier 104 amplifies the power of a weak sweep laser.

[0110] In a preferred implementation of this invention, such as Figures 1-2 As shown, a laser circulator 108 and a laser beam expander 109 are disposed between the acousto-optic frequency shifting module and the target. The laser circulator 108 is used to separate the first swept laser beam and the echo laser reflected by the target. The laser beam expander 109 is used to compress the divergence angle of the first swept laser beam and irradiate it onto the target. Specifically, the first swept laser beam is incident on the air after passing through the first port 1 of the laser circulator 108, the second port 2 of the laser circulator 108, and the laser beam expander 109, and irradiates the target. The laser is reflected on the surface of the target, and the reflected echo laser passes through the laser beam expander 109 and reaches the second port 2 of the laser circulator 108. The laser circulator 108 propagates the reflected echo laser from the third port 3 of the laser circulator 108 to the laser beam combiner 110.

[0111] In a preferred implementation of this invention, such as Figures 1-2 As shown, the laser power amplifier 104 is one of EDFA and EYDFA semiconductor laser amplifiers (SOA). The input power of the laser power amplifier 104 is -50dBm to 10dBm, and the output power is 0dBm to 30dBm.

[0112] Specifically, an erbium-doped fiber amplifier (EDFA) is a type of optical fiber in which erbium (Er), a rare-earth element, is injected into the fiber core, allowing it to directly amplify optical signals of a specific wavelength under the action of a pump light source. An erbium-yterbium-doped fiber amplifier (EYDFA) is also a type of optical fiber in which both erbium (Er) and yttrium (Y), two rare-earth elements, are injected into the fiber core.

[0113] In a preferred implementation of this invention, such as Figures 1-2 As shown, the laser circulator 108 is either an optical fiber circulator or a space laser circulator 108.

[0114] In a preferred implementation of this invention, such as Figures 1-2 As shown, the laser beam expander 109 is either a transmission beam expander or a reflection beam expander, and the diameter of the emitted laser spot of the laser beam expander 109 is greater than 2 mm. Specifically, after the laser beam expander 109 expands the beam, the laser diameter becomes larger, which is beneficial for irradiating the target.

[0115] In a preferred implementation of this invention, such as Figures 1-2 As shown, the data acquisition and analysis module includes:

[0116] The photoelectric balance detector 111 is used to convert the combined laser beam into an electrical signal;

[0117] Data acquisition module 112 is used to acquire electrical signals;

[0118] The data processing module 113 is used to process the acquired electrical signals to output the speed and / or distance of the target.

[0119] Specifically, the beat frequency signal of the combined laser beam is detected by the photoelectric balance detector 111, and the speed and / or distance of the target are obtained through acquisition and processing.

[0120] In a preferred implementation of this invention, such as Figures 1-2 As shown, the photoelectric balance detector 111 is either a PIN balance detector or an APD balance detector;

[0121] The data acquisition module 112 is an ADC analog-to-digital converter;

[0122] The data processing module 113 is an FPGA or DSP module.

[0123] Specifically, a PIN balanced detector refers to a photodetector with an intrinsic layer added between the P-type and N-type regions. An APD balanced detector utilizes the avalanche effect of photogenerated carriers in a high electric field region to obtain photocurrent gain, offering advantages such as high sensitivity and fast response. It is commonly used in laser ranging, lidar, and low-light detection (nonlinearity). An ADC (Analog-to-Digital Converter) converts analog signals to digital signals. An FPGA (Field-Programmable Gate Array) module is a field-programmable gate array. The data processing module 113 performs Fourier transform on the acquired signal and analyzes the target's velocity and distance information carried in the signal. A DSP (Digital Signal Processing) module performs digital signal processing.

[0124] The present invention also provides a preferred embodiment of a frequency-modulated continuous wave lidar method for velocity and ranging:

[0125] like Figure 3 As shown, the frequency-modulated continuous wave lidar velocity and ranging method of this invention includes the following steps:

[0126] Step S100: After modulating and sweeping the laser emitted by the single-frequency seed laser, it is split into a first swept laser beam and a second swept laser beam; wherein, the first swept laser beam and the second swept laser beam are both triangular wave swept laser beams.

[0127] Specifically, the laser emitted by the single-frequency seed laser is modulated and swept into a triangular wave swept laser by the modulation sweep module, and the triangular wave swept laser is split into two beams by the laser beam splitter, namely the first swept laser beam and the second swept laser beam.

[0128] Step S200: The first frequency-sweeping laser beam is frequency-shifted and then used to irradiate the target; wherein the target is in a moving state relative to the single-frequency seed laser.

[0129] Specifically, the first sweeping laser beam is frequency-shifted using an acousto-optic frequency-shifting module and then used to illuminate the target. Alternatively, the first sweeping laser beam can be frequency-shifted without shifting its frequency, and the target can be illuminated directly. Then, the second sweeping laser beam can be frequency-shifted using the acousto-optic frequency-shifting module.

[0130] Step S300: Combine the second frequency-sweeping laser beam and the echo laser beam reflected from the target.

[0131] Specifically, the first frequency-sweeping laser beam is reflected after illuminating the target to form an echo laser. The second frequency-sweeping laser beam and the echo laser reflected by the target are combined by a laser beam combiner.

[0132] Step S400: Obtain the target's velocity and / or distance based on the combined laser beam.

[0133] Specifically, the target's velocity and / or distance are obtained from the combined laser beam through the data acquisition and analysis module.

[0134] Compared to traditional FMCW lidar velocity measurement algorithms, which require performing Fourier transforms (FFTs) on the upper and lower frequency sweeps of the triangular wave separately, extracting the peak values, and then calculating the difference between them to obtain the target's velocity and direction, this implementation only requires performing a single Fourier transform on the signal for one triangular wave cycle to obtain the target's velocity and direction information, avoiding multiple calculations. The specific processing steps are as follows:

[0135] Step S400 includes:

[0136] Step S410: Acquire the combined laser beam to obtain a beat frequency signal of one triangular wave period, and determine the slope and frequency of the swept triangular wave.

[0137] Specifically, the beat frequency signal of one triangular wave cycle is acquired through the data acquisition module. The size of the triangular wave cycle can be determined based on either the first or second sweep laser beam. The slope α and frequency λ of the sweep triangular wave can also be determined using the beat frequency signal of one triangular wave cycle.

[0138] Step S420: Perform an FFT calculation on the beat frequency signal of one triangular wave cycle to obtain the processed beat frequency signal.

[0139] Specifically, this application only needs to acquire the beat frequency signal of one triangular wave cycle and perform only one Fourier transform.

[0140] Step S430: Denoise the processed beat frequency signal and determine the two peaks of the processed beat frequency signal.

[0141] Specifically, a threshold algorithm is used to remove noise interference, and then a peak-finding algorithm is used within the range specified by the program to find the two largest peaks.

[0142] like Figure 2 As shown, due to the frequency shift f of the acousto-optic modulator AOM The frequency shift caused by the velocity exceeding the target velocity can be identified as follows: the higher peak value f2 represents the frequency component of the combined laser's beat frequency signal sweeping on a triangular wave, while the second peak value f1 represents the frequency component of the combined laser's beat frequency signal sweeping on a triangular wave. Furthermore, denoising processing can improve the accuracy of these two peak values.

[0143] Step S440: Calculate the target distance based on the two peaks and the slope of the swept triangular wave; and / or, calculate the target velocity based on the two peaks and the frequency of the combined laser beam.

[0144] The distance to the target is:

[0145]

[0146] Where D represents the distance to the target, f1 and f2 represent the two peak values ​​respectively, α represents the slope of the swept triangular wave of the combined laser beam, and c represents the speed of light;

[0147] The speed of the target is:

[0148]

[0149] Where υ represents the velocity of the target, λ represents the frequency of the combined laser beam, and f AOM This indicates the frequency shift of the first swept laser beam, specifically the frequency shift of the laser signal caused by the acousto-optic frequency shifting module.

[0150] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A frequency-modulated continuous wave lidar velocity and distance measuring device, characterized in that, include: Single-frequency seed laser; The modulation sweep module is located in the emission direction of the single-frequency seed laser; A laser beam splitter is located in the emission direction of the modulation sweep module and is used to split the sweep laser into two beams. An acousto-optic frequency shifting module is located in the emission direction of the first swept laser beam and is used to shift the frequency of the first swept laser beam to illuminate the target, or it is located in the emission direction of the second swept laser beam and is used to shift the frequency of the second swept laser beam; the frequency shifting of the acousto-optic frequency shifting module... The following relationship must be satisfied: > ,in, The frequency components representing the beat frequency signal of the combined laser beam swept across a triangular wave. The frequency components of the beat frequency signal of the combined laser beam, when swept under a triangular wave, are represented. and These are the two peak values ​​of the beat frequency signal. This indicates the Doppler frequency shift caused by velocity; A laser beam combiner is used to combine a second frequency-sweeping laser beam and an echo laser beam reflected from the target. The data acquisition and analysis module is used to acquire the combined laser beam to output the target's velocity and / or distance; The modulation and sweeping module modulates and sweeps the laser emitted by the single-frequency seed laser into a triangular wave sweeping laser. The target is in a moving state relative to the single-frequency seed laser; The acousto-optic frequency shifting module includes: An acousto-optic modulator is located in the emission direction of the first swept laser beam of the laser beam splitter, or in the emission direction of the second swept laser beam. The driving source is connected to the acousto-optic modulator; The speed of the target is: in, Indicates the speed of the target. This indicates the frequency of the combined laser beam.

2. The frequency-modulated continuous wave lidar velocity and ranging device according to claim 1, characterized in that, The modulation sweep module includes: A carrier-suppressed single-sideband modulator is located in the emission direction of the single-frequency seed laser; The frequency sweep source is connected to the carrier-suppressed single-sideband modulator.

3. The frequency-modulated continuous wave lidar velocity and ranging device according to claim 2, characterized in that, The carrier-suppressed single-sideband modulator is either a lithium niobate modulator or a silicon photonic modulator. The sweep frequency source is one of DDS, DAC or phase-locked feedback voltage-controlled oscillator, and the sweep frequency bandwidth of the sweep frequency source is greater than or equal to 500MHz.

4. The frequency-modulated continuous wave lidar velocity and ranging device according to claim 1, characterized in that, The acousto-optic modulator is one of an optical fiber coupler or a free-space modulator, and the acousto-optic modulator is used to detect the frequency shift of light; The output frequency of the driving source is a radio frequency signal ranging from 30MHz to 500MHz.

5. The frequency-modulated continuous wave lidar velocity and ranging device according to claim 1, characterized in that, The single-frequency seed laser is a 1.5μm or 1.3μm laser with a linewidth of less than or equal to 500 kHz; The single-frequency seed laser is one of a semiconductor laser, a fiber laser, or a solid-state gain medium laser. The laser beam splitter is one of the following: fiber coupler, lens coated with a beam splitter film, or spatial polarization beam splitter. The power ratio of the first swept laser beam to the second swept laser beam is greater than 8:

1. The laser beam combiner is either an optical fiber beam combiner or a free-space beam combiner.

6. The frequency-modulated continuous wave lidar velocity and distance measuring device according to any one of claims 1-5, characterized in that, A laser power amplifier is provided between the modulation sweep module and the laser beam splitter to amplify the power of the sweep laser. A laser circulator and a laser beam expander are provided between the acousto-optic frequency shifting module and the target. The laser circulator is used to separate the first frequency-sweeping laser beam from the echo laser reflected by the target, and the laser beam expander is used to compress the divergence angle of the first frequency-sweeping laser beam and irradiate it onto the target.

7. The frequency-modulated continuous wave lidar velocity and ranging device according to claim 6, characterized in that, The laser power amplifier is one of EDFA, EYDFA, and semiconductor laser amplifier; The laser circulator is either a fiber optic circulator or a space laser circulator. The laser beam expander is either a transmission beam expander or a reflection beam expander.

8. The frequency-modulated continuous wave lidar velocity and distance measuring device according to any one of claims 1-5, characterized in that, The data acquisition and analysis module includes: A photoelectric balance detector is used to convert combined laser beams into electrical signals; The data acquisition module is used to acquire electrical signals; The data processing module is used to process the acquired electrical signals to output the target's speed and / or distance.

9. The frequency-modulated continuous wave lidar velocity and ranging device according to claim 8, characterized in that, The photoelectric balance detector is either a PIN balance detector or an APD balance detector; The data acquisition module is an ADC analog-to-digital converter; The data processing module is an FPGA or DSP module.

10. A method for velocity and distance measurement using a frequency-modulated continuous wave lidar, characterized in that, Including the following steps: The laser emitted by the single-frequency seed laser is modulated and frequency-sweeped, and then split into a first frequency-sweeping laser and a second frequency-sweeping laser; wherein, the first frequency-sweeping laser and the second frequency-sweeping laser are both triangular wave frequency-sweeping lasers. The first frequency-sweeping laser beam is frequency-shifted before irradiating the target; wherein the target is in a moving state relative to the single-frequency seed laser; The second frequency-sweeping laser beam and the echo laser beam reflected from the target are combined; The velocity and / or distance of the target are obtained from the combined laser beam; The speed of the target is: > in, Indicates the speed of the target. Indicates the frequency of the combined laser beam. This indicates the frequency shift of the first swept laser beam. This indicates the Doppler frequency shift caused by velocity. , These represent two peak values.

11. The frequency-modulated continuous wave lidar velocity and ranging method according to claim 10, characterized in that, The determination of the target's velocity and / or distance based on the combined laser beam includes: The combined laser beam is acquired to obtain a beat frequency signal of one triangular wave period, and the slope of the swept triangular wave and / or the frequency of the combined laser beam are determined. The processed beat frequency signal is obtained by performing an FFT calculation on the beat frequency signal of one triangular wave cycle. The processed beat frequency signal is denoised, and the two peak values ​​of the processed beat frequency signal are determined. The distance to the target is calculated based on the two peaks and the slope of the swept triangular wave; and / or, the velocity of the target is calculated based on the two peaks and the frequency of the combined laser beam.

12. The frequency-modulated continuous wave lidar velocity and ranging method according to claim 11, characterized in that, The distance to the target is: in, Indicates the distance to the target. , These represent two peak values. The slope of the swept triangular wave representing the combined laser beam. Represents the speed of light; The speed of the target is: > in, Indicates the speed of the target. Indicates the frequency of the combined laser beam. This indicates the frequency shift of the first swept laser beam. This indicates the Doppler shift caused by velocity.

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