FMCW laser radar ranging and correction system based on DFB laser and its method

Abstract

The present invention discloses a DFB laser-based FMCW laser radar ranging and correction system and method. The system includes a Mach-Zehnder interferometer ranging system and a nonlinear correction system. The frequency sweeping light source uses a DFB laser driven by current modulation. The signal acquisition, processing, and demodulation components utilize computer-programmed signal acquisition, analysis, processing, correction, and demodulation programs. Furthermore, an auxiliary reference arm based on the Mach-Zehnder interferometer is constructed to address frequency modulation nonlinearity. Software interpolation and resampling are used to measure changes in the laser tuning rate over the entire wavelength sweep range. This tuning rate change information is then used to resample the original beat frequency signal, converting the signal from equal time intervals to equal frequency intervals. This removes nonlinear factors contained in the time information, effectively preventing the impact of nonlinearity and reducing spectrum broadening to obtain correct beat frequency signal information. This improves the accuracy of beat frequency signal frequency extraction and, consequently, measurement accuracy.

Description

Technical Field

[0001] The present invention relates to the field of laser ranging technology, and in particular to a FMCW laser radar ranging and correction system based on a DFB laser and a method thereof. Background Art

[0002] Frequency modulation of a laser actually modulates its output wavelength. Since frequency is proportional to the inverse of wavelength, nonlinear variations are inevitable. Furthermore, some interference noise can also introduce nonlinearity. Either cause can lead to nonlinearity in frequency modulation, causing the actual output modulation waveform to deviate from the ideal modulation waveform. This causes the frequency of the difference frequency signal to vary over time rather than being constant, reducing or even inaccurate frequency extraction accuracy, ultimately leading to errors in measurement results. Summary of the Invention

[0003] The purpose of the present invention is to provide an FMCW lidar ranging and correction system and method based on a DFB laser, so as to solve the problem that the FMCW lidar ranging system is affected by nonlinear factors in the frequency extraction of the difference frequency signal, resulting in reduced accuracy or even errors, thereby reducing measurement accuracy.

[0004] The technical solution adopted in the present invention is:

[0005] The FMCW laser radar ranging and correction system based on a DFB laser includes a DFB laser modulation system. The modulated laser light emitted by the DFB laser modulation system is connected to a coupler CP1 via an optical isolator ISO. The first port of the coupler CP1 outputs a first measurement light as a measurement arm, and the second port of the coupler CP1 outputs a second measurement light as an auxiliary arm.

[0006] The first measuring light is connected to the measuring arm Mach-Zehnder interferometer, and the second measuring light is connected to the auxiliary arm Mach-Zehnder interferometer; the measuring arm Mach-Zehnder interferometer includes a coupler CP2, a circulator, a focusing system, a first optical attenuator VOA, a coupler CP3 and a photodetector PD1. The first measuring light is connected to the coupler CP2 and is divided into two signals, one signal is connected to the first port of the circulator via the first port of the coupler CP2, and the other signal is connected to the first optical attenuator VOA via the second port of the coupler CP2. The focusing system is connected to the second port of the circulator. The focusing system uses the measuring light passing through the circulator to detect target information to form a target signal, which is then output by the circulator. The third port of the circulator and the output end of the first optical attenuator VOA are combined into one signal through the coupler CP3 and then connected to the photodetector PD1; the other measuring light is attenuated by the first optical attenuator VOA as the original signal, which generates difference frequency interference with the target signal on the surface of the photodetector PD1 to obtain a difference frequency electrical signal; the difference frequency signal generated by the photodetector PD1 is synchronously collected and connected to the signal acquisition, processing and demodulation system as the measurement signal;

[0007] The auxiliary arm Mach-Zehnder interferometer includes a coupler CP4, a delay fiber, a second optical attenuator VOA, a coupler CP5 and a photodetector PD2; the second measurement light is connected to the coupler CP4 and divided into two signals, one of which is connected to one end of the delay fiber via the first port of the coupler CP4, and the other is connected to the second optical attenuator VOA via the second port of the coupler CP4; the other end of the delay fiber and the output end of the second optical attenuator VOA are combined into one signal through the coupler CP5 and then connected to the photodetector PD2; the difference frequency signal generated by the delay fiber is synchronously collected and then connected to the signal acquisition, processing and demodulation system as a correction signal;

[0008] The signal acquisition, processing and demodulation system collects and processes the difference frequency signals of the measuring arm Mach-Zehnder interferometer and the auxiliary arm Mach-Zehnder interferometer, and analyzes and calculates the corrected target information; at the same time, it forms frequency modulation information and sends it to the DFB laser modulation system for generating modulated laser.

[0009] Specifically, the modulated light emitted by the laser is divided into a measuring arm Mach-Zehnder interferometer and an auxiliary arm Mach-Zehnder interferometer through a coupler. The signal entering the measuring arm Mach-Zehnder interferometer is divided into an original signal path and a target signal path. The target signal is obtained by receiving target information from a circulator. The original signal and the target signal produce difference-frequency interference on the surface of the photodetector PD1 to obtain a difference-frequency electrical signal. The optical signal entering the auxiliary arm Mach-Zehnder interferometer is divided into two signals. One signal passes through a delay optical fiber with a fixed length difference, and then is combined with the other signal passing through the optical attenuator VOA through a coupler CP5 to form one signal.

[0010] Furthermore, the DFB laser modulation system includes a laser fixture and a DFB laser, a laser driver, and a current source respectively connected to the laser fixture. The signal acquisition, processing, and demodulation system are respectively connected to and control the current source and the laser driver. The laser driver uses a constant temperature drive module to make the DFB laser output a stable wavelength. The current source provides the working power required by the DFB laser. The output end of the DFB laser is connected to the optical isolator ISO.

[0011] Furthermore, the laser driver uses USB to connect to the host computer to achieve power supply and serial communication.

[0012] Furthermore, the current source adopts a digitally controlled constant current source to supply power through a triangular waveform current, and the current source supplies power within a specified range.

[0013] Further, the coupler CP1 is a 90:10 coupler, the first measurement light is 90% light, and the second measurement light is 10% light.

[0014] Furthermore, coupler CP2, coupler CP3, coupler CP4 and coupler CP5 are all 50:50 couplers.

[0015] Furthermore, the measuring arm Mach-Zehnder interferometer and the auxiliary arm Mach-Zehnder interferometer are respectively connected to the signal acquisition, processing and demodulation system.

[0016] Furthermore, the acquisition, processing and demodulation system includes a host computer and at least two acquisition cards connected to the host computer. The measuring arm Mach-Zehnder interferometer and the auxiliary arm Mach-Zehnder interferometer are each connected to the host computer through an acquisition card, that is, the photodetector PD1 is connected to one acquisition card, and the photodetector PD2 is connected to another acquisition card.

[0017] Furthermore, the signal acquisition, processing and demodulation system uses a programming tool to write a program to analyze and process the correction signal. The peak and valley positions of the obtained correction signal are used as a resampling sequence, and the resampling sequence is used to interpolate and resample the measurement signal; the signal acquisition, processing and demodulation system uses the DFB laser parameters and calculation formulas to demodulate the resampled measurement signal and calculate the corrected target information.

[0018] The method for ranging and frequency modulation nonlinear correction of an FMCW laser radar ranging and correction system based on a DFB laser comprises the following steps:

[0019] Step 1: drive the DFB laser to emit a frequency-modulated signal, which is divided into a first measurement light and a second measurement light through a coupler CP1, and enters the measuring arm Mach-Zehnder interferometer and the auxiliary arm Mach-Zehnder interferometer respectively; further, step 1 is specifically as follows:

[0020] Step 1.1: Laser driving: A constant temperature driving module is used to maintain the laser temperature at a set temperature so as to stabilize the output wavelength; further, the set temperature is 25°C.

[0021] Step 1.2: Provide a triangular wave frequency-modulated current through a digitally controlled constant current source. By converting the current coefficient corresponding to the wavelength, the center current corresponds to the center wavelength of the modulation signal, and the triangular current fluctuation value corresponds to the signal bandwidth. The DFB laser is modulated to output a triangular wave optical signal with the target center wavelength.

[0022] Furthermore, the target central wavelength is 1550 nm.

[0023] Furthermore, the signal frequency of the triangular wave optical signal changes linearly with time, and the rise time is the same as the fall time. The sweep period T of the triangular waveform optical signal satisfies And the speed of light signal The frequency sweep slope γ of the triangular waveform optical signal should satisfy The center frequency f of the triangular waveform optical signal c satisfy Among them L max is the maximum value of the measured target distance, c is the speed of light in vacuum, n is the refractive index of the medium, B is the sweep bandwidth, and λ is the signal wavelength.

[0024] At this time, the optical frequency increases linearly with time. If the initial emission frequency of the laser is f0, the instantaneous frequency of the laser at time t is expressed as:

[0025] f(t)=f0+γt (1-1)

[0026] Step 2: The first measurement light entering the measuring arm Mach-Zehnder interferometer is attenuated by the first optical attenuator VOA and used as the original signal; the target information is received by the circulator to obtain the target signal, and the original signal and the target signal generate difference frequency interference on the surface of the photodetector PD1 to obtain a difference frequency electrical signal;

[0027] Specifically, the original signal and the target signal interfere with each other to produce a frequency difference Δf. From the time-frequency perspective of the signal, the frequency difference is the frequency variation f introduced by the distance delay τ. R The frequency difference is generated at the rising and falling edges of the frequency. The value of the frequency difference and its mathematical relationship with the distance can be obtained through mathematical geometric relationships.

[0028] The instantaneous frequency obtained after the target signal and the original signal are interfered and mixed by the photoelectric detector is:

[0029] f(t)=f0+γt (2-1)

[0030] The obtained difference frequency electrical signal can be simplified as:

[0031]

[0032] Among them, A0 is the amplitude of the difference frequency signal, Δf is the frequency of the difference frequency signal after interference mixing by the photoelectric detector, is the initial phase of the difference frequency signal;

[0033] At this time, Δf is mainly caused by the difference frequency f introduced by the distance R The mathematical relationship between the laser sweep slope γ and the distance delay τ is:

[0034] Δf=f R =γτ (2-3)

[0035] The physical formula of distance delay τ and its difference frequency f introduced by distance R The mathematical relationship between γ and the laser sweep slope γ is:

[0036]

[0037] The physical formula of distance L and its difference frequency f introduced by distance R The mathematical relationship between γ and the laser sweep slope γ is:

[0038]

[0039] Among them, f R Indicates the frequency difference introduced by distance, Δf=f R =γτ; γ represents the laser sweep slope; τ represents the distance delay; v represents the speed of the optical signal, c is the speed of light in vacuum, n is the refractive index of the medium, B is the sweep bandwidth, and T is the optical signal sweep period.

[0040] Step 3: The signal acquisition processing and demodulation system synchronously acquires the difference frequency signal output by the measuring arm Mach-Zehnder interferometer as a measurement signal; and optimizes the measurement signal by adopting a suitable filter and denoising algorithm according to the data characteristics of the measurement signal to obtain an optimized measurement signal;

[0041] Furthermore, the specific steps of step 3 include:

[0042] Step 3-1: The difference frequency electrical signal is received by the signal acquisition card, converted into an analog signal / digital signal (A / D), and connected to the host computer as a measurement signal; the measurement signal is collected in real time; the corresponding driver for the signal acquisition card is installed, and the data receiving program is written using an appropriate programming tool. The data transmission channel is established, and the corresponding resource name, channel information, scanning information, collection method, and time limit are set to collect the measurement signal in real time;

[0043] Step 3-2: Use programming tools to write a program to analyze and process the measurement signal, and optimize it by using appropriate filters and denoising algorithms based on the data characteristics;

[0044] Step 3-3: Demodulate the processed measurement signal according to the DFB laser parameters and through Fourier transform to calculate the measured target information.

[0045] Step 4: The second measurement light entering the auxiliary arm Mach-Zehnder interferometer generates a difference frequency signal through the delay fiber;

[0046] In step 5, the signal acquisition, processing, and demodulation system synchronously acquires the difference frequency signal of the auxiliary arm Mach-Zehnder interferometer as a correction signal; the signal acquisition, processing, and demodulation system analyzes and processes the correction signal to obtain a resampling sequence based on the peak and valley positions of the correction signal; further, the specific steps in step 5 are:

[0047] Step 5-1: The difference frequency signal of the auxiliary arm Mach-Zehnder interferometer is received by the photodetector PD2 and converted into an electrical signal. The signal is then received by the signal acquisition card for A / D conversion and connected to the host computer as a correction signal to achieve synchronous acquisition of the correction signal.

[0048] Install the corresponding driver of the signal acquisition card, write the data receiving program through the applicable programming tool, establish the data transmission channel, set the corresponding resource name, channel information, scanning information, acquisition method, and limit time, and synchronously acquire the correction signal.

[0049] Step 5-2: After using programming tools to perform necessary analysis and processing on the correction signal, write a signal correction program based on the signal characteristics. The specific steps include: locating the peak and valley corresponding moments of the correction signal, and using the peak and valley positions of the correction signal as the resampling sequence.

[0050] Specifically, the time-frequency characteristic curve of the FM signal is a stable straight line under ideal conditions. The FM slope is fixed at the rising and falling edges and the error is very small. At this time, the output light frequency increases linearly with time. The instantaneous frequency of the laser is shown in formula (1-1). Taking one and a half cycles as an example, the ideal linear frequency can be changed to:

[0051]

[0052] However, in practice, due to the existence of nonlinear factors, the frequency modulation curve is a curve whose slope changes with time. Let the nonlinear term of the modulation frequency be f nl (t), then the instantaneous frequency of the laser at time t is:

[0053]

[0054] Then the target signal and the original signal are mixed by the photoelectric detector to obtain the difference frequency electrical signal:

[0055]

[0056] From formula (3-3), we can see that With the existence of , the frequency modulation slope changes from γ which does not change with time to γ ​​which is affected by time This causes the slope to be nonlinear, causing the signal frequency to change over time;

[0057] Formula (3-3) can be further modified as follows:

[0058]

[0059] As shown in formula (3-4), is a constant term, 2πτγt is the ideal linear frequency modulation difference signal, and the frequency is Δf=γτ=f R , 2πτf nl (t) is the time-related nonlinear term caused by the nonlinearity of the frequency modulation slope;

[0060] As shown in the following formula (3-4), compared with the electrical signal in the ideal frequency modulation case, due to the nonlinear term, the beat frequency at time t is Because f nl (t) is a value that changes with time and is not constant, which causes the frequency information to contain nonlinear factors. From the perspective of the spectrum, it will cause the spectrum to be broadened, resulting in frequency extraction errors;

[0061] The correction signal and the measurement signal are of the same source, that is, the initial phase and frequency of the optical path are consistent, so different beat frequency signals are generated on the photodetector only because of the different distance delays. The distance delay is only related to the length of the delay fiber. Let the delay fiber length of the correction signal be L r , the refractive index of the delay fiber is n r , then the distance delay of the correction signal is:

[0062]

[0063] The corresponding correction signal is:

[0064]

[0065] The signal correction program is used to find the peaks and valleys of the correction signal. To prevent errors caused by interference with the correction signal and sudden changes in values ​​that may occur in some cases, the present invention does not simply use direct differentiation to find maximum and minimum values, but instead uses numerical statistical analysis.

[0066] Furthermore, in step 5-2, a numerical statistical analysis method is used to solve the peak value of the correction signal. The specific steps are as follows: Step 5-2-1: Filter and denoise the correction signal;

[0067] Step 5-2-2: Find the maximum value of the correction signal and record the corresponding serial number;

[0068] Step 5-2-3: Set the maximum amplitude threshold according to the overall signal situation;

[0069] Step 5-2-4: Traverse the maximum value of the correction signal and determine whether it is greater than or equal to the set maximum amplitude threshold; if so, record it as the peak value; otherwise, discard the corresponding maximum value;

[0070] Step 5-2-5: Record the determined peak position and integrate the resampling sequence;

[0071] Furthermore, a numerical statistical analysis method is used to solve the valley value of the correction signal. The specific steps are as follows:

[0072] Step 5-2-11: Filter and denoise the correction signal;

[0073] Step 5-2-12: Find the minimum value of the correction signal and record the corresponding serial number;

[0074] Step 5-2-13: Set the minimum amplitude threshold according to the overall signal situation;

[0075] Step 5-2-14: Traverse the minimum value of the correction signal and determine whether it is less than or equal to the set minimum amplitude threshold; if so, record it as a valley value; otherwise, abandon the corresponding minimum value;

[0076] Step 5-2-15: Record the determined valley positions and integrate the resampling sequence.

[0077] Step 6, using the resampling sequence of the processed correction signal to resample the measurement signal using a software interpolation resampling method;

[0078] Specifically, the measurement signal is resampled to correct nonlinear factors in the measurement signal, and according to the Nyquist theorem, the delay optical fiber length of the auxiliary arm Mach-Zehnder interferometer is made at least greater than twice the target maximum distance.

[0079] Specifically, from a mathematical perspective, finding the peak and valley positions of the correction signal can be viewed as taking the derivative of the correction signal formula. The correction signal formula is:

[0080]

[0081] When taking U′ r (t)=0, then:

[0082]

[0083] Further changing the formula, we can get the instantaneous optical frequency at time t:

[0084]

[0085] The correction signal and the measurement signal are of the same source, so the instantaneous optical frequency can be substituted into the difference frequency electrical signal formula (2-2) to obtain:

[0086]

[0087] From formula (3-8), we can see the specific mathematical results of software interpolation resampling. When resampling is performed using the correction signal frequency, the time information of the signal has been removed from the mathematical formula, and the result becomes a correlation equation with the ordinal number m as the variable. Therefore, the formula can be changed to:

[0088]

[0089] At this point, from formula (3-9), we can see that the resampled measurement signal changes from equal time intervals to equal frequency intervals, removing the time information;

[0090] Step 7: Demodulate the resampled measurement signal using the laser parameters and calculation formula to calculate the corrected target distance information. Furthermore, perform Fourier transform on the resampled information, and then calculate the corrected target distance L from the frequency difference Δf using coherent demodulation. The corresponding calculation formula is:

[0091]

[0092] Where Δf r is the frequency of the resampled signal, L r is the delay fiber length of the correction signal, n r is the refractive index of the delay fiber;

[0093] Furthermore, the ratio of the medium refractive index to the refractive index of the delayed fiber in formula (3-9) is Can be regarded as a constant, L r For a fixed delay fiber length, the resampled signal frequency is only related to the target distance L, so the formula can be rewritten as:

[0094]

[0095] in, is the frequency of the resampled signal;

[0096] The calculation formula of the measured target distance after resampling is as follows:

[0097]

[0098] In summary, after resampling, the signal is converted from being related to time information to being related to the frequency change of the correction signal, the time correlation is weakened, the nonlinear factors contained in the time information are eliminated from the level of mathematical formula, and the influence of nonlinearity is effectively prevented.

[0099] The present invention adopts the above technical solution, which includes a Mach-Zehnder interferometer ranging system and a nonlinear correction system. The swept frequency light source adopts a DFB laser driven by current modulation. The signal acquisition, processing and demodulation parts adopt computer-written signal acquisition, analysis, processing, correction and demodulation programs. The overall design structure is simple and compact, the frequency modulation method is simple, the frequency modulation speed is fast, the required power consumption is low, the cost-effectiveness is high, the calculation time is fast, and the measurement accuracy is high. It is an ideal solution for realizing high-precision ranging of lidar.

[0100] The present invention builds an auxiliary reference arm based on a Mach-Zehnder interferometer to target frequency modulation nonlinearity. It uses a software interpolation resampling method to measure the change in laser tuning rate within the entire wavelength scanning range, and uses the tuning rate change information to resample from the original beat frequency signal, converting the signal from equal time intervals to equal frequency intervals, removing the nonlinear factors contained in the time information, effectively preventing the influence of nonlinearity, reducing the broadening of the spectrum to obtain correct difference frequency signal information, thereby improving the accuracy of difference frequency signal frequency extraction, and thus improving the accuracy of measurement. At the same time, compared to taking the near-zero point as the sampling point, the present invention uses the method of numerical statistical analysis to resample with peak and valley values ​​as sampling points, resulting in smaller errors and further improving the accuracy of measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0101] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments;

[0102] Figure 1 Schematic diagram of the structure of the FMCW laser radar ranging and correction system and method based on DFB laser of the present invention;

[0103] Figure 2 Schematic diagram of the FMCW lidar ranging and correction system based on DFB laser of the present invention;

[0104] Figure 3 Schematic diagram of the specific connection relationship of the laser modulation part of the present invention;

[0105] Figure 4 Schematic diagram of the relationship between the current of the laser modulation part and time variation;

[0106] Figure 5 Schematic diagram of the frequency sweep signal model of the present invention;

[0107] Figure 6 Schematic diagram of the signal interference measurement process of the present invention. DETAILED DESCRIPTION

[0108] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0109] like Figures 1 to 6 As shown in FIG1 , the present invention discloses a FMCW laser radar ranging and correction system based on a DFB laser, which includes a DFB laser modulation system. The modulated laser emitted by the DFB laser modulation system is connected to a coupler CP1 via an optical isolator ISO. The first port of the coupler CP1 outputs a first measurement light as a measurement arm, and the second port of the coupler CP1 outputs a second measurement light as an auxiliary arm.

[0110] The first measuring light is connected to the measuring arm Mach-Zehnder interferometer, and the second measuring light is connected to the auxiliary arm Mach-Zehnder interferometer; the measuring arm Mach-Zehnder interferometer includes a coupler CP2, a circulator, a focusing system, a first optical attenuator VOA, a coupler CP3 and a photodetector PD1. The first measuring light is connected to the coupler CP2 and is divided into two signals, one signal is connected to the first port of the circulator via the first port of the coupler CP2, and the other signal is connected to the first optical attenuator VOA via the second port of the coupler CP2. The focusing system is connected to the second port of the circulator. The focusing system uses the measuring light passing through the circulator to detect target information to form a target signal, which is then output by the circulator. The third port of the circulator and the output end of the first optical attenuator VOA are combined into one signal through the coupler CP3 and then connected to the photodetector PD1; the other measuring light is attenuated by the first optical attenuator VOA as the original signal, which generates difference frequency interference with the target signal on the surface of the photodetector PD1 to obtain a difference frequency electrical signal; the difference frequency signal generated by the photodetector PD1 is synchronously collected and connected to the signal acquisition, processing and demodulation system as the measurement signal;

[0111] The auxiliary arm Mach-Zehnder interferometer includes a coupler CP4, a delay fiber, a second optical attenuator VOA, a coupler CP5 and a photodetector PD2; the second measurement light is connected to the coupler CP4 and divided into two signals, one of which is connected to one end of the delay fiber via the first port of the coupler CP4, and the other is connected to the second optical attenuator VOA via the second port of the coupler CP4; the other end of the delay fiber and the output end of the second optical attenuator VOA are combined into one signal through the coupler CP5 and then connected to the photodetector PD2; the difference frequency signal generated by the delay fiber is synchronously collected and then connected to the signal acquisition, processing and demodulation system as a correction signal;

[0112] The signal acquisition, processing and demodulation system collects and processes the difference frequency signals of the measuring arm Mach-Zehnder interferometer and the auxiliary arm Mach-Zehnder interferometer, and analyzes and calculates the corrected target information; at the same time, it forms frequency modulation information and sends it to the DFB laser modulation system for generating modulated laser.

[0113] Specifically, the modulated light emitted by the laser is divided into a measuring arm Mach-Zehnder interferometer and an auxiliary arm Mach-Zehnder interferometer through a coupler. The signal entering the measuring arm Mach-Zehnder interferometer is divided into an original signal path and a target signal path. The target signal is obtained by receiving target information from a circulator. The original signal and the target signal produce difference-frequency interference on the surface of the photodetector PD1 to obtain a difference-frequency electrical signal. The optical signal entering the auxiliary arm Mach-Zehnder interferometer is divided into two signals. One signal passes through a delay optical fiber with a fixed length difference, and then is combined with the other signal passing through the optical attenuator VOA through a coupler CP5 to form one signal.

[0114] Furthermore, the DFB laser modulation system includes a laser fixture and a DFB laser, a laser driver, and a current source respectively connected to the laser fixture. The signal acquisition, processing, and demodulation system are respectively connected to and control the current source and the laser driver. The laser driver uses a constant temperature drive module to make the DFB laser output a stable wavelength. The current source provides the working power required by the DFB laser. The output end of the DFB laser is connected to the optical isolator ISO.

[0115] Furthermore, the laser driver uses USB to connect to the host computer to achieve power supply and serial communication.

[0116] Furthermore, the current source adopts a digitally controlled constant current source to supply power through a triangular waveform current, and the current source supplies power within a specified range.

[0117] Further, the coupler CP1 is a 90:10 coupler, the first measurement light is 90% light, and the second measurement light is 10% light.

[0118] Furthermore, coupler CP2, coupler CP3, coupler CP4 and coupler CP5 are all 50:50 couplers.

[0119] Furthermore, the measuring arm Mach-Zehnder interferometer and the auxiliary arm Mach-Zehnder interferometer are respectively connected to the signal acquisition, processing and demodulation system.

[0120] Furthermore, the acquisition, processing and demodulation system includes a host computer and at least two acquisition cards connected to the host computer. The measuring arm Mach-Zehnder interferometer and the auxiliary arm Mach-Zehnder interferometer are each connected to the host computer through an acquisition card, that is, the photodetector PD1 is connected to one acquisition card, and the photodetector PD2 is connected to another acquisition card.

[0121] Furthermore, the signal acquisition, processing and demodulation system uses a programming tool to write a program to analyze and process the correction signal. The peak and valley positions of the obtained correction signal are used as a resampling sequence, and the resampling sequence is used to interpolate and resample the measurement signal; the signal acquisition, processing and demodulation system uses the DFB laser parameters and calculation formulas to demodulate the resampled measurement signal and calculate the corrected target information.

[0122] The method for ranging and frequency modulation nonlinear correction of an FMCW laser radar ranging and correction system based on a DFB laser comprises the following steps:

[0123] Step 1: drive the DFB laser to emit a frequency-modulated signal, which is divided into a first measurement light and a second measurement light through a coupler CP1, and enters the measuring arm Mach-Zehnder interferometer and the auxiliary arm Mach-Zehnder interferometer respectively; further, step 1 is specifically as follows:

[0124] Step 1.1: Laser driving: A constant temperature driving module is used to maintain the laser temperature at a set temperature so as to stabilize the output wavelength; further, the set temperature is 25°C.

[0125] Step 1.2: Provide a triangular wave frequency-modulated current through a digitally controlled constant current source. By converting the current coefficient corresponding to the wavelength, the center current corresponds to the center wavelength of the modulation signal, and the triangular current fluctuation value corresponds to the signal bandwidth. The DFB laser is modulated to output a triangular wave optical signal with the target center wavelength.

[0126] Furthermore, the target central wavelength is 1550 nm.

[0127] Furthermore, the signal frequency of the triangular wave optical signal changes linearly with time, and the rise time is the same as the fall time. The sweep period T of the triangular waveform optical signal satisfies And the speed of light signal The frequency sweep slope γ of the triangular waveform optical signal should satisfy The center frequency f of the triangular waveform optical signal c satisfy Among them L max is the maximum value of the measured target distance, c is the speed of light in vacuum, n is the refractive index of the medium, B is the sweep bandwidth, and λ is the signal wavelength.

[0128] At this time, the optical frequency increases linearly with time. If the initial emission frequency of the laser is f0, the instantaneous frequency of the laser at time t is expressed as:

[0129] f(t)=f0+γt (1-1)

[0130] Step 2: The first measurement light entering the measuring arm Mach-Zehnder interferometer is attenuated by the first optical attenuator VOA and used as the original signal; the target information is received by the circulator to obtain the target signal, and the original signal and the target signal generate difference frequency interference on the surface of the photodetector PD1 to obtain a difference frequency electrical signal;

[0131] Specifically, the original signal and the target signal interfere with each other to produce a frequency difference Δf. From the time-frequency perspective of the signal, the frequency difference is the frequency variation f introduced by the distance delay τ. R The frequency difference is generated at the rising and falling edges of the frequency. The value of the frequency difference and its mathematical relationship with the distance can be obtained through mathematical geometric relationships.

[0132] The instantaneous frequency obtained after the target signal and the original signal are interfered and mixed by the photoelectric detector is:

[0133] f(t)=f0+γt (2-1)

[0134] The obtained difference frequency electrical signal can be simplified as:

[0135]

[0136] Among them, A0 is the amplitude of the difference frequency signal, Δf is the frequency of the difference frequency signal after interference mixing by the photoelectric detector, is the initial phase of the difference frequency signal;

[0137] At this time, Δf is mainly caused by the difference frequency f introduced by the distance R The mathematical relationship between the laser sweep slope γ and the distance delay τ is:

[0138] Δf=f R =γτ (2-3)

[0139] The physical formula of distance delay τ and its difference frequency f introduced by distance R The mathematical relationship between γ and the laser sweep slope γ is:

[0140]

[0141] The physical formula of distance L and its difference frequency f introduced by distance R The mathematical relationship between γ and the laser sweep slope γ is:

[0142]

[0143] Among them, f R Indicates the frequency difference introduced by distance, Δf=f R =γτ; γ represents the laser sweep slope; τ represents the distance delay; v represents the speed of the optical signal, c is the speed of light in vacuum, n is the refractive index of the medium, B is the sweep bandwidth, and T is the optical signal sweep period.

[0144] Step 3: The signal acquisition processing and demodulation system synchronously acquires the difference frequency signal output by the measuring arm Mach-Zehnder interferometer as a measurement signal; and optimizes the measurement signal by adopting a suitable filter and denoising algorithm according to the data characteristics of the measurement signal to obtain an optimized measurement signal;

[0145] Furthermore, the specific steps of step 3 include:

[0146] Step 3-1: The difference frequency electrical signal is received by the signal acquisition card, converted into an analog signal / digital signal (A / D), and connected to the host computer as a measurement signal; the measurement signal is collected in real time; the corresponding driver for the signal acquisition card is installed, and the data receiving program is written using an appropriate programming tool. The data transmission channel is established, and the corresponding resource name, channel information, scanning information, collection method, and time limit are set to collect the measurement signal in real time;

[0147] Step 3-2: Use programming tools to write a program to analyze and process the measurement signal, and optimize it by using appropriate filters and denoising algorithms based on the data characteristics;

[0148] Step 3-3: Demodulate the processed measurement signal according to the DFB laser parameters and through Fourier transform to calculate the measured target information.

[0149] Step 4: The second measurement light entering the auxiliary arm Mach-Zehnder interferometer generates a difference frequency signal through the delay fiber;

[0150] In step 5, the signal acquisition, processing, and demodulation system synchronously acquires the difference frequency signal of the auxiliary arm Mach-Zehnder interferometer as a correction signal; the signal acquisition, processing, and demodulation system analyzes and processes the correction signal to obtain a resampling sequence based on the peak and valley positions of the correction signal; further, the specific steps in step 5 are:

[0151] Step 5-1: The difference frequency signal of the auxiliary arm Mach-Zehnder interferometer is received by the photodetector PD2 and converted into an electrical signal. The signal is then received by the signal acquisition card for A / D conversion and connected to the host computer as a correction signal to achieve synchronous acquisition of the correction signal.

[0152] Install the corresponding driver of the signal acquisition card, write the data receiving program through the applicable programming tool, establish the data transmission channel, set the corresponding resource name, channel information, scanning information, acquisition method, and limit time, and synchronously acquire the correction signal.

[0153] Step 5-2: After using programming tools to perform necessary analysis and processing on the correction signal, write a signal correction program based on the signal characteristics. The specific steps include: locating the peak and valley corresponding moments of the correction signal, and using the peak and valley positions of the correction signal as the resampling sequence.

[0154] Specifically, the time-frequency characteristic curve of the FM signal is a stable straight line under ideal conditions. The FM slope is fixed at the rising and falling edges and the error is very small. At this time, the output light frequency increases linearly with time. The instantaneous frequency of the laser is shown in formula (1-1). Taking one and a half cycles as an example, the ideal linear frequency can be changed to:

[0155]

[0156] However, in practice, due to the existence of nonlinear factors, the frequency modulation curve is a curve whose slope changes with time. Let the nonlinear term of the modulation frequency be f nl (t), then the instantaneous frequency of the laser at time t is:

[0157]

[0158] Then the target signal and the original signal are mixed by the photoelectric detector to obtain the difference frequency electrical signal:

[0159]

[0160] From formula (3-3), we can see that With the existence of , the frequency modulation slope changes from γ which does not change with time to γ ​​which is affected by time This causes the slope to be nonlinear, causing the signal frequency to change over time;

[0161] Formula (3-3) can be further modified as follows:

[0162]

[0163] As shown in formula (3-4), is a constant term, 2πτγt is the ideal linear frequency modulation difference signal, and the frequency is Δf=γτ=f R , 2πτf nl (t) is the time-related nonlinear term caused by the nonlinearity of the frequency modulation slope;

[0164] As shown in the following formula (3-4), compared with the electrical signal in the ideal frequency modulation case, due to the nonlinear term, the beat frequency at time t is Because f nl (t) is a value that changes with time and is not constant, which causes the frequency information to contain nonlinear factors. From the perspective of the spectrum, it will cause the spectrum to be broadened, resulting in frequency extraction errors;

[0165] The correction signal and the measurement signal are of the same source, that is, the initial phase and frequency of the optical path are consistent, so different beat frequency signals are generated on the photodetector only because of the different distance delays. The distance delay is only related to the length of the delay fiber. Let the delay fiber length of the correction signal be L r , the refractive index of the delay fiber is n r , then the distance delay of the correction signal is:

[0166]

[0167] The corresponding correction signal is:

[0168]

[0169] The signal correction program is used to find the peaks and valleys of the correction signal. To prevent errors caused by interference with the correction signal and sudden changes in values ​​that may occur in some cases, the present invention does not simply use direct differentiation to find maximum and minimum values, but instead uses numerical statistical analysis.

[0170] Furthermore, in step 5-2, a numerical statistical analysis method is used to solve the peak value of the correction signal. The specific steps are as follows: Step 5-2-1: Filter and denoise the correction signal;

[0171] Step 5-2-2: Find the maximum value of the correction signal and record the corresponding serial number;

[0172] Step 5-2-3: Set the maximum amplitude threshold according to the overall signal situation;

[0173] Step 5-2-4: Traverse the maximum value of the correction signal and determine whether it is greater than or equal to the set maximum amplitude threshold; if so, record it as the peak value; otherwise, discard the corresponding maximum value;

[0174] Step 5-2-5: Record the determined peak position and integrate the resampling sequence;

[0175] Furthermore, a numerical statistical analysis method is used to solve the valley value of the correction signal. The specific steps are as follows:

[0176] Step 5-2-11: Filter and denoise the correction signal;

[0177] Step 5-2-12: Find the minimum value of the correction signal and record the corresponding serial number;

[0178] Step 5-2-13: Set the minimum amplitude threshold according to the overall signal situation;

[0179] Step 5-2-14: Traverse the minimum value of the correction signal and determine whether it is less than or equal to the set minimum amplitude threshold; if so, record it as a valley value; otherwise, abandon the corresponding minimum value;

[0180] Step 5-2-15: Record the determined valley positions and integrate the resampling sequence.

[0181] Step 6, using the resampling sequence of the processed correction signal to resample the measurement signal using a software interpolation resampling method;

[0182] Specifically, the measurement signal is resampled to correct nonlinear factors in the measurement signal, and according to the Nyquist theorem, the delay optical fiber length of the auxiliary arm Mach-Zehnder interferometer is made at least greater than twice the target maximum distance.

[0183] Specifically, from a mathematical perspective, finding the peak and valley positions of the correction signal can be viewed as taking the derivative of the correction signal formula. The correction signal formula is:

[0184]

[0185] When taking U′ r (t)=0, then:

[0186]

[0187] Further changing the formula, we can get the instantaneous optical frequency at time t:

[0188]

[0189] The correction signal and the measurement signal are of the same source, so the instantaneous optical frequency can be substituted into the difference frequency electrical signal formula (2-2) to obtain:

[0190]

[0191] From formula (3-8), we can see the specific mathematical results of software interpolation resampling. When resampling is performed using the correction signal frequency, the time information of the signal has been removed from the mathematical formula, and the result becomes a correlation equation with the ordinal number m as the variable. Therefore, the formula can be changed to:

[0192]

[0193] At this point, from formula (3-9), we can see that the resampled measurement signal changes from equal time intervals to equal frequency intervals, removing the time information;

[0194] Step 7: Demodulate the resampled measurement signal using the laser parameters and calculation formula to calculate the corrected target distance information. Furthermore, perform Fourier transform on the resampled information, and then calculate the corrected target distance L from the frequency difference Δf using coherent demodulation. The corresponding calculation formula is:

[0195]

[0196] Where Δf r is the frequency of the resampled signal, L r is the delay fiber length of the correction signal, n r is the refractive index of the delay fiber;

[0197] Furthermore, the ratio of the medium refractive index to the refractive index of the delayed fiber in formula (3-9) is Can be regarded as a constant, L r For a fixed delay fiber length, the resampled signal frequency is only related to the target distance L, so the formula can be rewritten as:

[0198]

[0199] in, is the frequency of the resampled signal;

[0200] The calculation formula of the measured target distance after resampling is as follows:

[0201]

[0202] In summary, after resampling, the signal is converted from being related to time information to being related to the frequency change of the correction signal, the time correlation is weakened, the nonlinear factors contained in the time information are eliminated from the level of mathematical formula, and the influence of nonlinearity is effectively prevented.

[0203] The specific principle of the present invention is described in detail below:

[0204] Attachment Figure 1This is a flow chart of the main steps of the present invention. First, a driving current is obtained to drive a DFB laser to obtain a modulated swept-frequency beam. Second, the laser is divided into a measurement signal optical path and a correction signal optical path. The measurement signal optical path obtains a difference frequency signal between the target signal and the original signal through a Mach-Zehnder interferometer, which is received by a signal acquisition and processing system as a measurement signal. The correction signal optical path obtains a difference frequency signal between the delayed optical fiber and the original signal through a Mach-Zehnder interferometer, which is received by a signal acquisition and processing system as a correction signal. Then, a program is written using a programming tool to analyze and process the measurement signal, and an appropriate filter and denoising algorithm are adopted for optimization based on the data characteristics. A correction program is written to create a maximum and minimum traversal sequence of the correction signal. After conditional judgment, the maximum and minimum values ​​that meet the conditions are determined to be peaks and valleys, and the corresponding positions are recorded as a resampling sequence. Next, the processed measurement signal is interpolated and resampled according to the resampling sequence of the correction signal. Finally, the resampled signal is Fourier transformed, and the accurate target distance is calculated through mathematical relationships.

[0205] Attachment Figure 2 This is a schematic diagram of the system structure of the present invention, which includes a DFB laser, a laser driver connected to the DFB laser according to a circuit structure, and a laser modulation system consisting of a current source CS; an optical isolator ISO connected in sequence to the DFB laser, the output end of the optical isolator ISO connected to a 90:10 coupler CP1, the first port of the coupler serving as a measurement arm outputting 90% of the light, and a measurement interferometer connected in sequence to a 50:50 coupler CP2, a circulator, an optical attenuator VOA, a 50:50 coupler CP3, and a photodetector PD1; the measurement interferometer is sequentially connected to a signal acquisition, processing, and demodulation system;

[0206] The measuring interferometer is a Mach-Zehnder interferometer, specifically: circulator port 1 is connected to the first port of coupler CP2, optical attenuator VOA is connected to the second port of coupler CP2, circulator port 2 is connected to the focusing system, and circulator port 3 and the output end of optical attenuator VOA are combined into one channel through coupler CP3 and connected to photodetector PD1;

[0207] The second port of coupler CP1 serves as an auxiliary arm to output 10% of the light;

[0208] The second port of the coupler CP1 is connected in sequence to an auxiliary interferometer consisting of a 50:50 coupler CP4, a delay fiber, an optical attenuator VOA, a 50:50 coupler CP5, and a photodetector PD2, and the auxiliary interferometer is sequentially connected to a signal acquisition, processing, and demodulation system;

[0209] The auxiliary interferometer is a Mach-Zehnder interferometer, which splits the optical signal from one path into two paths through the coupler CP4. One path passes through a delay fiber with a fixed length difference, and is combined with the other path through the optical attenuator VOA through the coupler CP5 to form a single signal connected to the photodetector PD2.

[0210] Among them, the signal acquisition, processing and demodulation system includes a signal acquisition card and a host computer connected to the photoelectric detector in sequence. The signal acquisition and processing system will acquire, process and perform subsequent analysis and calculation on the difference frequency signals of the measuring interferometer and the auxiliary interferometer.

[0211] Attachment Figure 3 and 4 The following are the schematic diagrams of the laser driving part of the present invention and the relationship between the current and time. The laser modulation part includes a current source, a laser, a laser fixture, a laser driver and various serial ports. The specific connection mode of the laser modulation part is as follows: Figure 3 As shown, the DFB laser is connected to the fixture, and the fixture is connected to the laser driver. The laser output is stabilized by the constant temperature drive module. At the same time, the driver is connected to the PC via USB for power supply and serial communication. Finally, the power supply is connected to the specified range. The power supply is to be supplied by a digitally controlled constant current source through a triangular waveform current. The relationship between the current and time is as follows Figure 4 As shown, where A c is the center current, A' is the current fluctuation value, T is the current change period, and tan(θ) is the current linear change rate.

[0212] Attachment Figure 5 and 6 The schematic diagrams of the frequency sweep signal model and the measurement signal interference process of the present invention are respectively. The signal frequency of the triangular wave frequency modulation signal changes linearly with time, and the rise time and fall time are the same, wherein f c is the center frequency of the light source, B is the signal bandwidth, T is the signal sweep period, and tan(θ) is the sweep rate. The target signal interferes with the original signal to produce a frequency difference Δf, which is the frequency variation f introduced by the distance delay τ. R The frequency difference is generated at the rising and falling edges of the frequency. The value of the frequency difference and its mathematical relationship with the distance can be calculated through mathematical geometric relationships. Then, the target distance can be calculated from the frequency difference Δf through coherent demodulation.

[0213] The present invention adopts the above technical solution, which includes a Mach-Zehnder interferometer ranging system and a nonlinear correction system. The swept frequency light source adopts a DFB laser driven by current modulation. The signal acquisition, processing and demodulation parts adopt computer-written signal acquisition, analysis, processing, correction and demodulation programs. The overall design structure is simple and compact, the frequency modulation method is simple, the frequency modulation speed is fast, the required power consumption is low, the cost-effectiveness is high, the calculation time is fast, and the measurement accuracy is high. It is an ideal solution for realizing high-precision ranging of lidar.

[0214] The present invention builds an auxiliary reference arm based on a Mach-Zehnder interferometer to target frequency modulation nonlinearity. It uses a software interpolation resampling method to measure the change in laser tuning rate within the entire wavelength scanning range, and uses the tuning rate change information to resample from the original beat frequency signal, converting the signal from equal time intervals to equal frequency intervals, removing the nonlinear factors contained in the time information, effectively preventing the influence of nonlinearity, reducing the broadening of the spectrum to obtain correct difference frequency signal information, thereby improving the accuracy of difference frequency signal frequency extraction, and thus improving the accuracy of measurement. At the same time, compared to taking the near-zero point as the sampling point, the present invention uses the method of numerical statistical analysis to resample with peak and valley values ​​as sampling points, resulting in smaller errors and further improving the accuracy of measurement.

[0215] Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. In the absence of conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the present application is not intended to limit the scope of the application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

Claims

1. FMCW lidar ranging and correction system based on DFB laser, characterized by: It includes a DFB laser modulation system, wherein the modulated laser light emitted by the DFB laser modulation system is connected to a coupler CP1 via an optical isolator ISO; a first port of the coupler CP1 outputs a first measurement light as a measurement arm, and a second port of the coupler CP1 outputs a second measurement light as a secondary arm; The first measuring light is connected to the measuring arm Mach-Zehnder interferometer, and the second measuring light is connected to the auxiliary arm Mach-Zehnder interferometer; the measuring arm Mach-Zehnder interferometer includes a coupler CP2, a circulator, a focusing system, a first optical attenuator VOA, a coupler CP3 and a photodetector PD1. The first measuring light is connected to the coupler CP2 and is divided into two signals, one signal is connected to the first port of the circulator via the first port of the coupler CP2, and the other signal is connected to the first optical attenuator VOA via the second port of the coupler CP2. The focusing system is connected to the second port of the circulator. The focusing system uses the measuring light passing through the circulator to detect target information to form a target signal, which is then output by the circulator. The third port of the circulator and the output end of the first optical attenuator VOA are combined into one signal through the coupler CP3 and then connected to the photodetector PD1; the other first measuring light is attenuated by the first optical attenuator VOA as the original signal, generates difference frequency interference with the target signal on the surface of the photodetector PD1, and obtains a difference frequency electrical signal; The difference frequency signal generated by the photodetector PD1 is synchronously collected and then connected to the signal acquisition, processing and demodulation system as a measurement signal; The auxiliary arm Mach-Zehnder interferometer includes a coupler CP4, a delay fiber, a second optical attenuator VOA, a coupler CP5 and a photodetector PD2; the second measurement light is connected to the coupler CP4 and divided into two signals, one of which is connected to one end of the delay fiber via the first port of the coupler CP4, and the other is connected to the second optical attenuator VOA via the second port of the coupler CP4; the other end of the delay fiber and the output end of the second optical attenuator VOA are combined into one signal through the coupler CP5 and then connected to the photodetector PD2; the difference frequency signal generated by the delay fiber is synchronously collected and then connected to the signal acquisition, processing and demodulation system as a correction signal; The signal acquisition, processing, and demodulation system acquires and processes the difference frequency signals from the measuring arm Mach-Zehnder interferometer and the auxiliary arm Mach-Zehnder interferometer, and analyzes and calculates the corrected target information. The signal acquisition, processing, and demodulation system uses a programming tool to write a program to analyze and process the correction signal. The peak and valley positions of the obtained correction signal are used as a resampling sequence, and the resampling sequence is used to interpolate and resample the measurement signal. The signal acquisition, processing, and demodulation system uses DFB laser parameters and calculation formulas to demodulate the resampled measurement signal and calculate the corrected target information. The signal acquisition, processing and demodulation system simultaneously provides frequency modulation information and sends it to the DFB laser modulation system to generate modulated laser.

2. The FMCW laser radar ranging and correction system based on DFB laser according to claim 1, characterized in that: The DFB laser modulation system includes a laser fixture and a DFB laser, laser driver, and current source connected to the laser fixture respectively. The signal acquisition, processing, and demodulation system are connected to and control the current source and laser driver respectively. The laser driver uses a constant temperature drive module to ensure that the DFB laser outputs a stable wavelength. The current source provides the working power required by the DFB laser. The output end of the DFB laser is connected to the optical isolator ISO.

3. The FMCW laser radar ranging and correction system based on DFB laser according to claim 1, characterized in that: The acquisition, processing and demodulation system includes a host computer and at least two acquisition cards connected to the host computer. The measuring arm Mach-Zehnder interferometer and the auxiliary arm Mach-Zehnder interferometer are each connected to the host computer through an acquisition card, that is, the photodetector PD1 is connected to one acquisition card, and the photodetector PD2 is connected to another acquisition card.

4. A method for FMCW laser radar ranging and frequency modulation nonlinear correction based on a DFB laser, employing the FMCW laser radar ranging and correction system based on a DFB laser according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: Step 1: Drive the DFB laser to emit a frequency-modulated signal. The frequency-modulated signal is divided into a first measurement light and a second measurement light through a coupler CP1, and enters the measurement arm Mach-Zehnder interferometer and the auxiliary arm Mach-Zehnder interferometer respectively. Step 2: The first measurement light entering the measuring arm Mach-Zehnder interferometer is attenuated by the first optical attenuator VOA and used as the original signal; the target information is received by the circulator to obtain the target signal, and the original signal and the target signal generate difference frequency interference on the surface of the photodetector PD1 to obtain a difference frequency electrical signal; Step 3: The signal acquisition processing and demodulation system synchronously acquires the difference frequency signal output by the measuring arm Mach-Zehnder interferometer as a measurement signal; and optimizes the measurement signal by adopting a suitable filter and denoising algorithm according to the data characteristics of the measurement signal to obtain an optimized measurement signal; Step 4: The second measurement light entering the auxiliary arm Mach-Zehnder interferometer generates a difference frequency signal through the delay fiber; Step 5: The signal acquisition, processing, and demodulation system synchronously acquires the difference frequency signal of the auxiliary arm Mach-Zehnder interferometer as a correction signal; the signal acquisition, processing, and demodulation system analyzes and processes the correction signal to obtain a resampling sequence based on the peak and valley positions of the correction signal; Step 6, using the resampling sequence of the processed correction signal to resample the measurement signal using a software interpolation resampling method; Step 7: Demodulate the resampled measurement signal using the laser parameters and calculation formula to calculate the corrected target distance information.

5. The method for ranging and frequency modulation nonlinear correction of FMCW laser radar based on DFB laser according to claim 4, characterized in that: Step 1 The specific steps are: Step 1.1: The laser is driven by using a constant temperature drive module to maintain the laser temperature at the set temperature in order to stabilize the output wavelength; Step 1.2: Provide a triangular wave frequency-modulated current through a digitally controlled constant current source. Through the corresponding wavelength-current coefficient conversion, the center current corresponds to the center wavelength of the modulation signal, and the triangular current fluctuation value corresponds to the signal bandwidth. The DFB laser is modulated to output a triangular wave optical signal with the target center wavelength.

6. The method for ranging and frequency modulation nonlinear correction of FMCW laser radar based on DFB laser according to claim 4, characterized in that: Step 3: The specific steps include: Step 3-1: The difference frequency electrical signal is received by the signal acquisition card, converted into an analog signal / digital signal and connected to the host computer as a measurement signal to realize real-time acquisition of the measurement signal; Step 3-2: Use programming tools to write a program to analyze and process the measurement signal, and optimize it by using appropriate filters and denoising algorithms based on the data characteristics; Step 3-3: Demodulate the processed measurement signal according to the DFB laser parameters and through Fourier transform to calculate the measured target information.

7. The method for FMCW laser radar ranging and frequency modulation nonlinear correction based on DFB laser according to claim 4, characterized in that The specific steps in step 5 are: Step 5-1: The difference frequency signal of the auxiliary arm Mach-Zehnder interferometer is received by the photodetector PD2 and converted into an electrical signal. The signal is then received by the signal acquisition card for A / D conversion and connected to the host computer as a correction signal to achieve synchronous acquisition of the correction signal. Step 5-2: Use a programming tool to write a program to analyze and process the correction signal, locate the corresponding moments of the peak and valley values ​​of the correction signal, and use the peak and valley value positions of the correction signal as the sampling sequence.

8. The method for ranging and frequency modulation nonlinear correction of FMCW laser radar based on DFB laser according to claim 7, characterized in that: In step 5-2, a numerical statistical analysis method is used to solve the peak value of the correction signal. The specific steps are as follows: Step 5-2-1: Filter and denoise the correction signal; Step 5-2-2: Find the maximum value of the correction signal and record the corresponding serial number; Step 5-2-3: Set the maximum amplitude threshold according to the overall signal situation; Step 5-2-4: Traverse the maximum value of the correction signal and determine whether it is greater than or equal to the set maximum amplitude threshold; if so, record it as the peak value; otherwise, discard the corresponding maximum value; Step 5-2-5: Record the determined peak position and integrate the resampling sequence; The numerical statistical analysis method is used to solve the valley value of the correction signal. The specific steps are as follows: Step 5-2-11: Filter and denoise the correction signal; Step 5-2-12: Find the minimum value of the correction signal and record the corresponding serial number; Step 5-2-13: Set the minimum amplitude threshold according to the overall signal situation; Step 5-2-14: Traverse the minimum value of the correction signal and determine whether it is less than or equal to the set minimum amplitude threshold; if so, record it as a valley value; otherwise, abandon the corresponding minimum value; Step 5-2-15: Record the determined valley positions and integrate the resampling sequence.

9. The method for ranging and frequency modulation nonlinear correction of FMCW laser radar based on DFB laser according to claim 4, characterized in that: In step 7, the resampled information is Fourier transformed, and then the corrected target distance L is calculated from the frequency difference Δf through coherent demodulation. The corresponding calculation formula is: Where Δf r is the frequency of the resampled signal, L r is the delay fiber length of the correction signal, n is the refractive index of the medium, n r is the refractive index of the delay fiber.

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