FMCW laser radar real-time nonlinear correction device and method based on FPGA control

Abstract

The invention discloses an FMCW laser radar real-time nonlinear correction device and method based on FPGA control, and the method comprises the steps: taking a DFB laser as a light source, driving the DFB laser by an initial driving current signal, generating an optical signal through a modulation end of the DFB laser, and inputting the optical signal into an FMCW delay heterodyne measurement module; the FMCW delay heterodyne measurement module converts the optical signal into an FMCW beat frequency signal and inputs the FMCW beat frequency signal into the FPGA module; the FPGA module generates a triangular wave driving signal from the FMCW beat frequency signal through a secant iterative learning control algorithm; the laser driving module comprises a current stabilization module, the current stabilization module converts a triangular wave driving signal from the FPGA module into a driving current signal, the driving current signal is input into a DFB laser, and the driving current signal is corrected through a laser radar nonlinear correction loop composed of the DFB laser, the FMCW delay heterodyne measurement module, the FPGA module and the current stabilization module. And the non-linear correction of the current signal is completed.

Description

Technical Field

[0001] The present invention relates to the technical field of laser radar and laser ranging, and in particular to a real-time nonlinear correction device and method for an FMCW laser radar based on FPGA control. Background Art

[0002] Laser ranging and LiDAR technology has a wide range of applications, involving scientific research, industrial manufacturing, robotics and self-driving cars. Compared with the traditional pulse time-of-flight method, Frequency Modulated Continuous Wave (FMCW) technology can achieve high resolution without the need for fast electronic components or high optical power, and due to the use of coherent detection, FMCW technology is not affected by direct sunlight and other radar transmitters. In addition, it can detect the position and speed of the target simultaneously in one measurement through Doppler shift.

[0003] FMCW LiDAR uses frequency-scanning lasers and coherent detection. The reflected light from the target is combined with the local reference light in the photodetector to convert the round-trip distance into a beat frequency signal. Since most tunable lasers do not have an inherent linear relationship between the optical frequency and the tuning signal, the beat frequency of a stationary target varies in time. Residual nonlinearity will reduce the resolution and signal-to-noise ratio of LiDAR detection. Therefore, a linearization method is needed to achieve linear frequency scanning.

[0004] At present, there are two main methods to achieve linear frequency scanning, including post-processing of sampled data and linearized laser frequency scanning. Among them, the resampling method in post-processing of sampled data will blur the Doppler signal due to the unevenness of the time domain, so it is incompatible with speed detection; the use of an optical phase-locked loop in the linearized laser frequency scanning method to achieve real-time active frequency scanning linearization can obtain good frequency scanning linearity, but the optical phase-locked loop requires fast electronic components with short loop delays, which increases the complexity and cost of the system. Other methods for generating linear frequency scanning include using an external modulator for sideband modulation and stretching ultrafast optical pulses, but these methods usually have limited frequency offsets and require complex settings. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a real-time nonlinear correction device and method for an FMCW lidar based on FPGA control, which adopts a DFB laser as a light source, a laser driving module to provide a stable frequency sweeping current, and an FPGA module to perform real-time closed-loop nonlinear compensation.

[0006] To achieve the above technical objectives, the present invention adopts the following technical solutions: a real-time nonlinear correction device for FMCW laser radar based on FPGA control, comprising: a DFB laser, an FMCW delay heterodyne measurement module, an FPGA module and a laser driving module;

[0007] The DFB laser is driven by an initial driving current signal as a light source, and an optical signal is generated through a modulation end of the DFB laser and input into a FMCW delay heterodyne measurement module;

[0008] The FMCW delay heterodyne measurement module converts the optical signal into an FMCW beat frequency signal and inputs it into the FPGA module;

[0009] The FPGA module generates a triangular wave drive signal from the FMCW beat frequency signal through a secant iterative learning control algorithm;

[0010] The laser driving module includes a current stabilizing module, which converts a triangle wave driving signal from the FPGA module into a driving current signal, inputs the signal into the DFB laser, and corrects the driving current signal through a laser radar nonlinear correction loop composed of the DFB laser, the FMCW delay heterodyne measurement module, the FPGA module and the current stabilizing module until the driving current signal completes the nonlinear correction.

[0011] Furthermore, the FMCW delay heterodyne measurement module includes: an adjustable optical attenuator VOA, a Mach-Zehnder interferometer MZI and a balanced detector BPD, the adjustable optical attenuator VOA is used for adjusting the optical power of the optical signal, the Mach-Zehnder interferometer MZI generates a beat frequency signal from the optical signal with adjusted optical power, and the balanced detector BPD converts the beat frequency signal into an FMCW beat frequency signal.

[0012] Furthermore, the Mach-Zehnder interferometer MZI divides the optical signal with optical power adjustment into two optical signals through a 50:50 1×2 coupler. After one optical signal passes through a 50:50 2×2 coupler, it is coupled with the other optical signal passing through a fixed-length differential delay optical fiber to obtain a beat frequency signal.

[0013] Furthermore, the FPGA module includes: an analog-to-digital converter ADC, a second low-pass filter LPF2, a delayer, an inverse tangent module Atan2, a phase unwrapping module, a differential module, a third low-pass filter LPF3 and a secant iterative learning control algorithm module. The FMCW beat frequency signal is obtained by the analog-to-digital converter ADC to obtain a digital signal, which is transmitted to the second low-pass filter LPF2 to generate a filtered output signal. The filtered output signal is passed through a delayer to obtain a phase-delayed filtered output signal. The filtered output signal and the phase-delayed filtered output signal are converted into an instantaneous phase signal through the inverse tangent module Atan2. The instantaneous phase signal is converted into a phase unwrapping signal through the phase unwrapping module. The phase unwrapping signal is input into the differential module for differential conversion to obtain an instantaneous frequency signal. The instantaneous frequency signal is input into the third low-pass filter LPF3 for filtering processing to obtain a real frequency signal. The difference between the real frequency signal and the expected frequency signal is calculated to obtain a frequency error signal. The frequency error signal is input into the secant iterative learning control algorithm module to generate a triangular wave drive signal.

[0014] Furthermore, the current stabilization module includes: a second digital-to-analog converter DAC2, a gain amplifier circuit, a first low-pass filter LPF1 and a current source. The second digital-to-analog converter DAC2 converts the triangular wave drive signal into a current signal, and converts the current signal into a voltage signal through the gain amplifier circuit, filters out high-order harmonics from the voltage signal through the first low-pass filter LPF1, and converts the filtered voltage signal into a drive current signal for driving the DFB laser through the current source.

[0015] Furthermore, the laser driving module also includes a TEC temperature control module, which includes: a first digital-to-analog converter DAC1 and a TEC temperature control circuit, which converts the triangular wave driving signal into a voltage control signal for temperature setting through the first digital-to-analog converter DAC1 and inputs it into the TEC temperature control circuit, and the TEC temperature control circuit converts the voltage control signal into a bidirectional current to achieve temperature control.

[0016] Furthermore, the present invention also provides a FMCW laser radar real-time nonlinear correction method of the FMCW laser radar real-time nonlinear correction device based on FPGA control, which specifically includes the following steps:

[0017] Step S1: The DFB laser is driven by an initial driving current signal;

[0018] Step S2: driving the current signal to generate an optical signal through the modulation end of the DFB laser, converting the optical signal into an FMCW beat frequency signal through the FMCW delay heterodyne measurement module, and inputting the signal into the FPGA module to generate a triangular wave driving signal through the secant iterative learning control algorithm;

[0019] Step S3: converting the triangular wave driving signal input into a driving current signal by the current stabilization module, and performing driving current signal correction through the laser radar nonlinear correction loop composed of the DFB laser, the FMCW delay heterodyne measurement module, the FPGA module and the current stabilization module;

[0020] Step S4: Repeat steps S2-S3 until the maximum number of iterations is reached, and the drive current signal correction is completed.

[0021] Furthermore, the specific process of the drive current signal correction in step S4 is:

[0022] Step S41, the FMCW beat frequency signal is converted into a digital signal by an analog-to-digital converter ADC, and the digital signal is transmitted to the second low-pass filter LPF2 to generate a filter output signal, and the filter output signal is passed through a delay device to obtain a phase-delay filter output signal, and the filter output signal and the phase-delay filter output signal are converted into an instantaneous phase signal by an inverse tangent module Atan2, and the instantaneous phase signal is converted into a phase-unwrapped signal by a phase-unwrapped module, and the phase-unwrapped signal is input into a differential module for differential conversion to obtain an instantaneous frequency signal, and the instantaneous frequency signal is input into a third low-pass filter LPF3 for filtering to obtain a real frequency signal, and the difference between the real frequency signal and the expected frequency signal is calculated to obtain a frequency error signal e(t)=v(t)-v d (t), where v(t) represents the real frequency signal, v d (t) represents the desired frequency signal;

[0023] Step S42: The frequency error signal e k (t) is input into the secant iterative learning control algorithm with the triangular wave drive signal at the last iteration k-1, and the triangular wave drive signal u at the kth iteration is predicted. k (t):

[0024] u k (t) = u k-1 (t)+p·e k (t)

[0025] Wherein, p represents a constant coefficient; when k=1, u0(t) is the triangle wave driving signal set for initialization;

[0026] Step S43, convert the predicted triangle wave signal into a driving current signal through the current stabilization module, generate an FMCW beat frequency signal through the DFB laser and the FMCW delay heterodyne measurement module, repeat steps S41-S42 until the maximum number of iterations is reached, and complete the nonlinear correction of the driving current signal.

[0027] Compared with the prior art, the present invention has the following beneficial effects: the current stabilization module of the real-time nonlinear correction device of the FMCW laser radar controlled by FPGA in the present invention ensures the accuracy of the generation of the driving current under the control of the FPGA module, thereby ensuring that the DFB laser provides a stable scanning current and wavelength stability, and improving the ranging accuracy; at the same time, the nonlinear correction device of the FMCW laser radar of the present invention adopts the FPGA module as the main control unit, which has the advantages of parallel processing, low latency, flexibility and high efficiency, making it suitable for high-performance and real-time application scenarios; and, the secant iterative learning control algorithm is used in the FPGA module to generate a triangular wave driving signal, which does not require complex feedback control or post-processing, and can be easily implemented on any type of tunable laser, and is suitable for the laser frequency scanning linearization of the FMCW laser radar and a high-performance, low-cost and simple-to-setup system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of the nonlinear correction device of FMCW laser radar based on FPGA control of the present invention;

[0029] Figure 2 It is a flow chart of the real-time nonlinear correction method of FMCW laser radar based on FPGA control of the present invention;

[0030] Figure 3 It is a frequency diagram of the instantaneous frequency of the electrical signal of the FPGA main control unit in the present invention before it is iterated by the nonlinear iterative correction algorithm;

[0031] Figure 4 It is a frequency diagram of the instantaneous frequency of the electric signal of the FPGA main control unit in the present invention after iterating through the nonlinear iterative correction algorithm. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further explained below in conjunction with the accompanying drawings.

[0033] like Figure 1The present invention is a structural schematic diagram of an FMCW laser radar nonlinear correction device based on FPGA control, the FMCW laser radar nonlinear correction device comprises: a DFB laser, an FMCW delay heterodyne measurement module, an FPGA module and a laser driving module; the DFB laser is driven by an initial driving current signal as a light source, and generates an optical signal through the modulation end of the DFB laser, which is input into the FMCW delay heterodyne measurement module; the FMCW delay heterodyne measurement module converts the optical signal into an FMCW beat frequency signal, which is input into the FPGA module; the FPGA module generates a triangular wave driving signal from the FMCW beat frequency signal through a secant iterative learning control algorithm; the laser driving module comprises a current stabilizing module, the current stabilizing module converts the triangular wave driving signal from the FPGA module into a driving current signal, which is input into the DFB laser, and the driving current signal is corrected through a laser radar nonlinear correction loop composed of the DFB laser, the FMCW delay heterodyne measurement module, the FPGA module and the current stabilizing module until the driving current signal correction is completed. The current stabilization module of the FMCW laser radar real-time nonlinear correction device based on FPGA control of the present invention ensures the accuracy of driving current generation under the control of the FPGA module, thereby ensuring that the DFB laser provides a stable scanning current and wavelength stability, thereby improving the ranging accuracy.

[0034] The FMCW delay heterodyne measurement module of the present invention comprises: an adjustable optical attenuator VOA, a Mach-Zehnder interferometer MZI and a balanced detector BPD. The adjustable optical attenuator VOA is used for adjusting the optical power of an optical signal. When the driving current signal is 200-300 mA, the optical power output by the DFB laser is less than 15 dBm. The adjustable optical attenuator VOA can be used to ensure that the optical power entering the balanced detector BPD is approximately -19 dBm, thereby preventing the balanced detector BPD from being damaged due to excessive input optical power. The Mach-Zehnder interferometer MZI generates a beat frequency signal from the optical signal with optical power adjustment. Specifically, the Mach-Zehnder interferometer MZI generates a beat frequency signal from the optical signal with optical power adjustment. The Zehnder interferometer MZI divides the optical signal with optical power adjustment into two optical signals through a 50:50 1×2 coupler. After one optical signal passes through a 50:50 2×2 coupler, it is coupled with the other optical signal passing through a fixed-length differential delay optical fiber to obtain a beat signal. In the present invention, the intermediate frequency of the beat signal should be less than 10 MHz, and the optical wavelength is about 1550 nm. The balanced detector BPD converts the beat signal into an FMCW beat signal. The bandwidth of the balanced detector BPD used in the present invention is 200 MHz, and the input optical wavelength range is 800-1700 nm, which can cover the signal range input to the balanced detector BPD.

[0035] The FPGA module in the present invention includes: an analog-to-digital converter ADC, a second low-pass filter LPF2, a delayer, an inverse tangent module Atan2, a phase unwrapping module, a differential module, a third low-pass filter LPF3 and a secant iterative learning control algorithm module. The FMCW beat frequency signal is obtained by the analog-to-digital converter ADC to obtain a digital signal, which is transmitted to the second low-pass filter LPF2 to generate a filter output signal. The filter output signal is passed through the delayer to obtain a phase-delayed filter output signal. The filter output signal and the phase-delayed filter output signal are converted into an instantaneous phase signal through the inverse tangent module Atan2. The instantaneous phase signal is converted into a phase unwrapping signal through the phase unwrapping module. The phase unwrapping signal is input into the differential module for differential conversion to obtain an instantaneous frequency signal. The instantaneous frequency signal is input into the third low-pass filter LPF3 for filtering processing to obtain a real frequency signal. The difference between the real frequency signal and the expected frequency signal is calculated to obtain a frequency error signal. The frequency error signal is input into the secant iterative learning control algorithm module to generate a triangular wave drive signal. The present invention adopts FPGA module as the main control unit, which has the advantages of parallel processing, low latency, flexibility and efficiency, making it suitable for high-performance and real-time application scenarios; and, the FPGA module adopts the secant iterative learning control algorithm to generate a triangular wave drive signal, which does not require complex feedback control or post-processing, and can be easily implemented on any type of tunable laser, and is suitable for laser frequency scanning linearization of FMCW lidar and high-performance, low-cost and simple to set up systems.

[0036] The current stabilization module in the present invention includes: a second digital-to-analog converter DAC2, a gain amplifier circuit, a first low-pass filter LPF1 and a current source. The second digital-to-analog converter DAC2 converts a triangular wave driving signal into a current signal. Since the second digital-to-analog converter DAC2 used in the present invention is a current-type DAC, and the amplitude of the output current signal is limited, it is necessary to convert the current signal into a voltage signal through a gain amplifier circuit, and adjust the peak value of the voltage signal to a required range, and filter out high-order harmonics from the voltage signal through the first low-pass filter LPF1, and convert the filtered voltage signal into a driving current signal for driving a DFB laser through a current source. The current source used in the present invention is a high-precision voltage-controlled current source, which is linearly controlled. When an AC voltage signal of 2 to 3V is input, an AC current signal of 200 to 300mA is generated at the output end accordingly, thereby generating a driving current signal and transmitting it to the modulation end LD+ of the DFB laser.

[0037] The laser driving module also includes a TEC temperature control module, which includes: a first digital-to-analog converter DAC1 and a TEC temperature control circuit. The triangular wave driving signal is converted into a voltage control signal for temperature setting through the first digital-to-analog converter DAC1 and input into the TEC temperature control circuit. The TEC temperature control circuit converts the voltage control signal into a bidirectional current to achieve temperature control.

[0038] like Figure 2 The present invention also provides a FMCW laser radar real-time nonlinear correction method based on an FMCW laser radar real-time nonlinear correction device controlled by FPGA, which specifically includes the following steps:

[0039] Step S1: The DFB laser is driven by an initial driving current signal. Before generating the initial driving current signal, the temperature, DC bias signal and triangle wave periodic signal need to be initialized. Specifically, the process of initializing the temperature is as follows: the first digital-to-analog converter DAC1 is a low-speed 12-bit multi-channel DAC, which receives and processes the initial temperature setting instruction sent by the host computer, generates a voltage control signal for setting the temperature and transmits it to the TEC temperature control circuit. The TEC temperature control circuit converts the voltage control signal into a bidirectional current to realize laser temperature control of the laser, thereby ensuring the stability of the laser wavelength output. The process of initializing the DC bias signal and the triangular wave periodic signal is as follows: the digital potentiometer adopts a three-wire serial SPI communication, receives and processes the initialization DC bias signal instruction sent by the host computer, and can flexibly adjust the DC bias size of the drive current signal so that the waveform of the drive current signal moves to a suitable current range; the triangular wave periodic signal is stored in the RAM of the FPGA main control unit in the form of a mif file, so that the second digital-to-analog converter DAC2 generates an initial drive current signal for frequency modulation, wherein the second digital-to-analog converter DAC2 adopts a current-type high-speed 16-bit parallel DAC, which has the advantages of low latency, high conversion speed and strong anti-interference.

[0040] Step S2: driving the current signal to generate an optical signal through the modulation end of the DFB laser, converting the optical signal into an FMCW beat frequency signal through the FMCW delay heterodyne measurement module, and inputting the signal into the FPGA module to generate a triangular wave driving signal through the secant iterative learning control algorithm;

[0041] Step S3: converting the triangular wave driving signal input into a driving current signal by the current stabilization module, and performing driving current signal correction through the laser radar nonlinear correction loop composed of the DFB laser, the FMCW delay heterodyne measurement module, the FPGA module and the current stabilization module;

[0042] Step S4: repeat steps S2-S3 until the maximum number of iterations is reached, and the drive current signal correction is completed; specifically,

[0043] Step S41, the FMCW beat frequency signal is converted into a digital signal by an analog-to-digital converter ADC, and the digital signal is transmitted to the second low-pass filter LPF2 to generate a filter output signal, and the filter output signal is passed through a delay device to obtain a phase-delay filter output signal, and the filter output signal and the phase-delay filter output signal are converted into an instantaneous phase signal by an inverse tangent module Atan2, and the instantaneous phase signal is converted into a phase-unwrapped signal by a phase-unwrapped module, and the phase-unwrapped signal is input into a differential module for differential conversion to obtain an instantaneous frequency signal, and the instantaneous frequency signal is input into a third low-pass filter LPF3 for filtering to obtain a real frequency signal, and the difference between the real frequency signal and the expected frequency signal is calculated to obtain a frequency error signal e(t)=v(t)-v d (t), where v(t) represents the real frequency signal, v d (t) represents the desired frequency signal;

[0044] Step S42: The frequency error signal e k (t) is input into the secant iterative learning control algorithm with the triangular wave drive signal at the last iteration k-1, and the triangular wave drive signal u at the kth iteration is predicted. k (t):

[0045] u k (t) = u k-1 (t)+p·e k (t)

[0046] Wherein, p represents a constant coefficient; when k=1, u0(t) is the triangle wave driving signal set for initialization;

[0047] Step S43, convert the predicted triangle wave signal into a driving current signal through the current stabilization module, generate an FMCW beat frequency signal through the DFB laser and the FMCW delay heterodyne measurement module, repeat steps S41-S42 until the maximum number of iterations is reached, and complete the nonlinear correction of the driving current signal.

[0048] In one embodiment of the present invention, the initial temperature of the TEC temperature control module of the laser driving module is set to 25°C, the second digital-to-analog converter DAC2 is set to output an initial triangular wave driving signal with an amplitude of 0-10mA and a frequency of 5kHz and is stored in the RAM of the FPGA main control unit in the form of a mif file, and the initial DC bias voltage of the host computer is 2.25V, and an initial driving current for laser modulation is generated, which is a triangular wave signal of 200-300mA. Under this condition, the intermediate frequency of the beat signal output by the laser is 2-3MHz, the bandwidth of the second low-pass filter LPF2 is set to 4MHz, the bandwidth of the third low-pass filter LPF3 is set to 0.5MHz, and the optical attenuator VOA is adjusted so that the optical power transmitted to the balanced detector BPD is -19dBm.

[0049] In this embodiment, the nonlinearity is calculated by gradually increasing the number of iterations until the optimal driving current waveform of the DFB laser is found. Figure 3 and Figure 4 The optical frequency curves in Figure 3 and Figure 4 In the optical frequency curve, 80% of the lower sweep frequency curve and 80% of the upper sweep frequency curve are used for nonlinearity calculation, and the nonlinearity before and after iteration is reduced from 1.59% and 1.47% to 0.032% and 0.027%, respectively; this indicates that the real-time nonlinear correction device and method for FMCW laser radar of the present invention can significantly suppress frequency modulation nonlinearity and improve the ranging accuracy of FMCW laser radar.

[0050] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A real-time nonlinear correction device for FMCW laser radar based on FPGA control, characterized in that: include: DFB laser, FMCW delay heterodyne measurement module, FPGA module and laser driver module; The DFB laser is driven by an initial driving current signal as a light source, and an optical signal is generated through a modulation end of the DFB laser and input into a FMCW delay heterodyne measurement module; The FMCW delay heterodyne measurement module converts the optical signal into an FMCW beat frequency signal and inputs it into the FPGA module; The FPGA module generates a triangular wave drive signal from the FMCW beat frequency signal through a secant iterative learning control algorithm; The laser driving module includes a current stabilizing module, which converts a triangle wave driving signal from the FPGA module into a driving current signal, inputs the signal into the DFB laser, and corrects the driving current signal through a laser radar nonlinear correction loop composed of the DFB laser, the FMCW delay heterodyne measurement module, the FPGA module and the current stabilizing module until the driving current signal completes the nonlinear correction.

2. According to the FPGA-controlled FMCW laser radar real-time nonlinear correction device of claim 1, it is characterized in that: The FMCW delay heterodyne measurement module comprises: an adjustable optical attenuator VOA, a Mach-Zehnder interferometer MZI and a balanced detector BPD, wherein the adjustable optical attenuator VOA is used for adjusting the optical power of an optical signal, the Mach-Zehnder interferometer MZI generates a beat frequency signal from the optical signal with optical power adjustment, and the balanced detector BPD converts the beat frequency signal into an FMCW beat frequency signal.

3. The real-time nonlinear correction device for FMCW laser radar based on FPGA control according to claim 2, characterized in that: The Mach-Zehnder interferometer MZI divides the optical signal with optical power adjustment into two optical signals through a 50:50 1×2 coupler. After passing through a 50:50 2×2 coupler, one optical signal is coupled with the other optical signal passing through a fixed-length differential delay optical fiber to obtain a beat frequency signal.

4. The real-time nonlinear correction device for FMCW laser radar based on FPGA control according to claim 2, characterized in that: The FPGA module includes: an analog-to-digital converter ADC, a second low-pass filter LPF2, a delayer, an inverse tangent module Atan2, a phase unwrapping module, a differential module, a third low-pass filter LPF3 and a secant iterative learning control algorithm module. The FMCW beat frequency signal is obtained by the analog-to-digital converter ADC to obtain a digital signal, which is transmitted to the second low-pass filter LPF2 to generate a filter output signal. The filter output signal is passed through the delayer to obtain a phase-delayed filter output signal. The filter output signal and the phase-delayed filter output signal are converted into an instantaneous phase signal through the inverse tangent module Atan2. The instantaneous phase signal is converted into a phase unwrapping signal through the phase unwrapping module. The phase unwrapping signal is input into the differential module for differential conversion to obtain an instantaneous frequency signal. The instantaneous frequency signal is input into the third low-pass filter LPF3 for filtering processing to obtain a real frequency signal. The difference between the real frequency signal and the expected frequency signal is calculated to obtain a frequency error signal. The frequency error signal is input into the secant iterative learning control algorithm module to generate a triangular wave drive signal.

5. The real-time nonlinear correction device for FMCW laser radar based on FPGA control according to claim 4, characterized in that: The current stabilization module includes: a second digital-to-analog converter DAC2, a gain amplifier circuit, a first low-pass filter LPF1 and a current source. The second digital-to-analog converter DAC2 converts a triangular wave driving signal into a current signal, and converts the current signal into a voltage signal through the gain amplifier circuit, and filters out high-order harmonics from the voltage signal through the first low-pass filter LPF1, and converts the filtered voltage signal into a driving current signal for driving the DFB laser through the current source.

6. The real-time nonlinear correction device for FMCW laser radar based on FPGA control according to claim 1, characterized in that: The laser driving module also includes a TEC temperature control module, which includes: a first digital-to-analog converter DAC1 and a TEC temperature control circuit, which converts the triangular wave driving signal into a voltage control signal for temperature setting through the first digital-to-analog converter DAC1 and inputs the signal into the TEC temperature control circuit, and the TEC temperature control circuit converts the voltage control signal into a bidirectional current to achieve temperature control.

7. A FMCW laser radar real-time nonlinear correction method according to claim 5, characterized in that: The specific steps include: Step S1: The DFB laser is driven by an initial driving current signal; Step S2: driving the current signal to generate an optical signal through the modulation end of the DFB laser, converting the optical signal into an FMCW beat frequency signal through the FMCW delay heterodyne measurement module, and inputting the signal into the FPGA module to generate a triangular wave driving signal through the secant iterative learning control algorithm; Step S3: converting the triangular wave driving signal input into a driving current signal by the current stabilization module, and performing driving current signal correction through the laser radar nonlinear correction loop composed of the DFB laser, the FMCW delay heterodyne measurement module, the FPGA module and the current stabilization module; Step S4: Repeat steps S2-S3 until the maximum number of iterations is reached, and the drive current signal correction is completed.

8. The FMCW laser radar real-time nonlinear correction method according to the FMCW laser radar real-time nonlinear correction device based on FPGA control according to claim 7, characterized in that: The specific process of driving current signal correction in step S4 is as follows: Step S41, the FMCW beat frequency signal is converted into a digital signal by an analog-to-digital converter ADC, and the digital signal is transmitted to the second low-pass filter LPF2 to generate a filter output signal, and the filter output signal is passed through a delay device to obtain a phase-delay filter output signal, and the filter output signal and the phase-delay filter output signal are converted into an instantaneous phase signal by an inverse tangent module Atan2, and the instantaneous phase signal is converted into a phase-unwrapped signal by a phase-unwrapped module, and the phase-unwrapped signal is input into a differential module for differential conversion to obtain an instantaneous frequency signal, and the instantaneous frequency signal is input into a third low-pass filter LPF3 for filtering to obtain a real frequency signal, and the difference between the real frequency signal and the expected frequency signal is calculated to obtain a frequency error signal e(t)=v(t)-v d (t), where v(t) represents the real frequency signal, v d (t) represents the desired frequency signal; Step S42: The frequency error signal e k (t) is input into the secant iterative learning control algorithm with the triangular wave drive signal at the last iteration k-1, and the triangular wave drive signal u at the kth iteration is predicted. k (t): u k (t)=u k-1 (t)+p·e k (t) Wherein, p represents a constant coefficient; when k=1, u0(t) is the triangle wave driving signal set for initialization; Step S43, convert the predicted triangle wave signal into a driving current signal through the current stabilization module, generate an FMCW beat frequency signal through the DFB laser and the FMCW delay heterodyne measurement module, repeat steps S41-S42 until the maximum number of iterations is reached, and complete the nonlinear correction of the driving current signal.

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