A frequency correction method and system based on an FMCW laser output signal

Abstract

The application discloses a kind of based on FMCW laser output signal frequency correction method and correction system, by using the method for error compensation to carry out the correction of FMCW light source output signal frequency.Laser is regarded as system function, signal source is regarded as excitation, the linear fitting data of output signal frequency is obtained by linear regression equation, then the error between original output signal frequency and linear fitting data is calculated, the error is loaded to linear fitting data, the correction data opposite to the change trend of original output signal frequency is obtained as signal source, finally signal source is input into system function, and the corrected signal is obtained by the action of laser.This method converts nonlinear frequency modulation into linear frequency modulation, improves spectral resolution and distance, velocity calculation accuracy.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optoelectronics, and particularly relates to a frequency correction method and a correction system based on an output signal of an FMCW laser. BACKGROUND

[0002] In the prior art, the FMCW laser radar can realize the ranging and speed measurement of a target object, because the FMCW light source in the core component has the characteristic of linear frequency modulation. In order to realize the decoupling of distance and speed, the triangular wave frequency modulation mode is usually adopted, so that the frequency has two trends of up-sweep frequency and down-sweep frequency. When the target moves, the Doppler effect will cause the distance frequency of the echo light to shift, the distance frequency in the up-sweep frequency band decreases, and the distance frequency in the down-sweep frequency band increases, and the shift amounts of the two are the same, both being the Doppler shift. The frequency values in the up-sweep frequency band and the down-sweep frequency band are extracted, and then the average of the sum of the two frequencies can offset the influence of the Doppler effect and be used to measure the distance, and the average of the difference between the two frequencies can measure the speed of the target.

[0003] In order to obtain accurate distance and speed information, the FMCW laser needs to have the characteristic of strict linear frequency modulation. However, due to the nonlinear relationship between the laser wavelength and the injected current, the current affects the temperature of the gain medium and causes the wavelength to fluctuate and other influences, so the frequency modulation of the laser cannot be completely linear. This causes the distance and speed spectrum calculated by the difference frequency signal to be widened, resulting in a decrease in frequency resolution and a large calculation error.

[0004] Therefore, it is necessary to correct the output signal frequency of the laser to reduce or eliminate the adverse effects of nonlinear frequency modulation on distance and speed measurement. SUMMARY

[0005] The purpose of the application is to provide a frequency correction method for the output signal of an FMCW laser, which solves the technical problem of large calculation error caused by nonlinear frequency modulation of the laser in the prior art.

[0006] The application also provides a correction system for implementing the frequency correction method for the output signal of an FMCW laser.

[0007] The technical solution of the application to solve the technical problem is as follows:

[0008] A frequency correction method for the output signal of an FMCW laser, the up-sweep frequency part and the down-sweep frequency part of the original output signal are processed in the same way but not synchronously, and the method specifically comprises the following steps:

[0009] S1: obtaining a linear regression equation of the up-sweep frequency part and the down-sweep frequency part of the original output signal according to the original output signal;

[0010] S2: obtaining standard data according to the linear regression equation of the frequency sweep part of the original output signal;

[0011] S3: obtaining error data by subtracting the standard data from the original output signal frequency sweep part data, and obtaining correction data according to the error data;

[0012] S4: inputting the correction data into the system function to obtain a corrected output signal, and judging whether the correlation coefficient between the corrected output signal frequency sweep part and the standard data is greater than 0.999, if yes, outputting the corrected output signal, if no, entering step S5;

[0013] S5: taking the corrected output signal as the original output signal, and repeating steps S1-S4.

[0014] The correction data has an opposite change trend with the frequency of the original output signal.

[0015] The original output signal is a triangular wave frequency modulation signal with nonlinear frequency modulation characteristics.

[0016] The correction data is a modulation signal source.

[0017] The system function is an FMCW laser.

[0018] A correction system for implementing an FMCW laser output signal frequency correction method, comprising: an FMCW laser for generating a frequency-modulated continuous laser light source;

[0019] A signal source for modulating the signal of the FMCW laser to generate a continuous light source with a symmetric triangular wave modulation frequency;

[0020] A tunable laser for adjusting its laser wavelength to be consistent with the wavelength of the FMCW laser to generate a beat frequency signal;

[0021] A spectrometer for observing whether the wavelengths of the tunable laser and the FMCW laser are consistent;

[0022] A coupler for coupling the output light source signals of the FMCW laser and the tunable laser to generate a difference frequency signal;

[0023] A detector for detecting and receiving the difference frequency signal and converting the optical signal into an electrical signal;

[0024] An oscilloscope for observing the waveform of the difference frequency signal and storing the current signal;

[0025] A computer for controlling the output wavelength of the tunable laser and running Matlab software to perform time-frequency analysis on the output signal;

[0026] The coupler is connected with the FMCW laser, the spectrometer, the detector and the tunable laser through optical fibers respectively; the FMCW laser is electrically connected with the signal source; the detector is electrically connected with the power supply and the oscilloscope respectively; and the tunable laser is electrically connected with the computer.

[0027] The detector is a balanced detector.

[0028] The present application has the advantages that: the FMCW light source output signal frequency is corrected by using the error compensation method. The laser is regarded as a system function, the signal source is regarded as an excitation, the linear fitting data of the output signal frequency is obtained through the linear regression equation, the error between the original output signal frequency and the linear fitting data is calculated, the error is loaded on the linear fitting data, the correction data opposite to the change trend of the original output signal frequency is obtained as the signal source, and finally the signal source is input into the system function, and the corrected signal is obtained through the laser. This method converts the nonlinear frequency modulation into linear frequency modulation, reduces the calculation error, and improves the calculation accuracy. In addition, the correction method is simple, and only linear regression calculation, error calculation between the output signal waveform and the linear regression standard data, and error loading are performed in each cycle process, the time complexity of the algorithm is low, and the calculation of massive data under the condition of high sampling rate can be adapted. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a flowchart of the correction method of the present application;

[0030] Figure 2 It is the original output signal time-frequency diagram of the present application;

[0031] Figure 3 It is the corrected output signal time-frequency diagram of the present application;

[0032] Figure 4 It is the experimental optical path connection diagram of the correction system of the present application. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application.

[0034] As shown in the drawings, Figure 1 A FMCW laser output signal frequency correction method based on the present application, the processing method of the up-sweeping frequency part and the down-sweeping frequency part of the original output signal is the same, and the processing time is not synchronized, and specifically includes the following steps:

[0035] S1: obtaining a linear regression equation of the original output signal sweeping part according to the original output signal; the original output signal is a triangular wave frequency modulation signal with nonlinear frequency modulation characteristics, and the linear regression equation is a one-dimensional linear regression fitting equation.

[0036] S2: obtaining standard data according to the linear regression equation of the frequency sweep part of the original output signal; the standard data is obtained by fitting the equation by one-dimensional linear regression.

[0037] S3: obtaining error data by subtracting the standard data from the original output signal frequency sweep part data, and obtaining correction data according to the error data; wherein, in the initial correction process, the correction data is equal to the difference between the standard data and the error data; in the subsequent cyclic correction process, the correction data is equal to the difference between the last correction data and the error data.

[0038] S4: inputting the correction data into the system function to obtain the corrected output signal, and judging whether the correlation coefficient between the corrected output signal frequency sweep part and the standard data is greater than 0.999, if yes, outputting the corrected output signal, if no, entering step S5; the correction data has an opposite trend with the original output signal frequency, and the correction data is a modulation signal source; the system function is an FMCW laser.

[0039] S5: taking the corrected output signal as the original output signal, and repeating steps S1-S4.

[0040] As shown in Figure 2 , Figure 3 , compared with the original output signal, the corrected output signal well eliminates the nonlinear component of the original output signal frequency, and corrects the up-sweep and down-sweep parts of the modulation frequency to an approximate straight line. The correlation coefficient between the corrected output signal and the standard data of linear regression is close to 1. This method can well solve the calculation error caused by the nonlinearity in the FMCW light source. This method needs several algorithm cycles for nonlinear correction, and each cycle only performs linear regression calculation, error calculation between the output signal waveform and the linear regression standard data, and error loading. The time complexity of the algorithm is low, and it can adapt to the calculation of massive data under high sampling rate conditions.

[0041] As shown in Figure 4 , a correction system for implementing an FMCW laser output signal frequency correction method, comprising: an FMCW laser for generating a frequency-modulated continuous laser light source;

[0042] a signal source for modulating the signal of the FMCW laser to generate a continuous light source with a symmetric triangular wave modulation frequency;

[0043] a tunable laser for adjusting its laser wavelength to be consistent with the wavelength of the FMCW laser to generate a beat signal;

[0044] a spectrometer for observing whether the wavelengths of the tunable laser and the FMCW laser are consistent;

[0045] a coupler, for coupling the FMCW laser with the output light source signal of the tunable laser to generate a beat signal;

[0046] a detector, for detecting and receiving the beat signal and converting the optical signal into an electrical signal; the detector adopts a balanced detector.

[0047] an oscilloscope, for observing the waveform of the beat signal and storing the current signal;

[0048] a computer, for controlling the output wavelength of the tunable laser and performing time-frequency analysis on the output signal by running Matlab software.

[0049] The coupler is connected with the FMCW laser, the spectrometer, the detector, the tunable laser through optical fibers respectively; the FMCW laser is electrically connected with the signal source; the detector is electrically connected with the power supply and the oscilloscope respectively; the power supply supplies power for the detector; and the tunable laser is electrically connected with the computer.

[0050] The specific correction process of the correction method of the correction system is as follows:

[0051] Connect and power on the experimental equipment including the FMCW laser, the signal source, the tunable laser, the spectrometer, the coupler, the detector, the oscilloscope, the power supply, the computer and the U disk; at this time, the signal source outputs an ideal linear symmetrical triangular wave modulation signal; the wavelength of the tunable laser is adjusted by the computer, and the wavelength of the tunable laser is adjusted to be consistent with the wavelength of the FMCW laser according to the wavelength data of the spectrometer; then the oscilloscope is observed, and when the beat signal waveform is generated, the signal waveform is saved in the U disk; the signal saved in the U disk is analyzed by the Matlab software in the computer to obtain the time-frequency analysis diagram of the signal; the output signal is nonlinearly corrected by using the output signal frequency correction method based on the FMCW laser; the corrected correction data is uploaded to the signal source, and is transmitted to the FMCW laser as a new modulation signal. The signal is corrected for multiple times, and after multiple cycles of operation, the waveform in the oscilloscope is saved in the U disk, and the time-frequency characteristics are analyzed by the Matlab software. At this time, if the correlation coefficients of the up-sweeping frequency and the down-sweeping frequency of the output signal with the linear regression fitting straight line are greater than 0.999, it is indicated that the correction is completed. The correction data at this time is the final signal source.

[0052] All other embodiments obtained by the person skilled in the art without making creative labor on the basis of the embodiments in the present application belong to the protection scope of the present application.

Claims

1. A method for frequency correction of output signal from an FMCW laser, characterized in that, The up-sweep and down-sweep portions of the original output signal are processed using the same method, but at different times. Specifically, the process includes the following steps: S1: Obtain the linear regression equation for the frequency sweep portion of the original output signal based on the original output signal; S2: Obtain the standard data based on the linear regression equation of the frequency sweep section of the original output signal; S3: Obtain error data by subtracting the frequency sweep data and standard data of the original output signal, and obtain correction data based on the error data; S4: Input the calibration data into the system function to obtain the calibration output signal, and determine whether the correlation coefficient between the frequency sweep part of the calibration output signal and the standard data is greater than 0.

999. If yes, output the calibration output signal; otherwise, proceed to step S5. S5: Use the corrected output signal as the original output signal and repeat steps S1-S4; The standard data is obtained by fitting a univariate linear regression equation. In the initial calibration process, the calibration data is equal to the difference between the standard data and the error data. In subsequent cyclic calibration processes, the calibration data is equal to the difference between the previous calibration data and the error data. The calibration data and the original output signal frequency have opposite trends. The calibration data is a modulation signal source. The system function is an FMCW laser.

2. The method for frequency correction of FMCW laser output signal according to claim 1, characterized in that: The original output signal is a triangular wave frequency-modulated signal with nonlinear frequency modulation characteristics.

3. A correction system for implementing the FMCW laser output signal frequency correction method according to any one of claims 1-2, characterized in that, include: FMCW lasers are used to generate frequency-modulated continuous laser sources. The signal source is used to modulate the signal for the FMCW laser, generating a continuous light source with a frequency modulated by a symmetrical triangular wave. A tunable laser is used to adjust its laser wavelength to match that of an FMCW laser to generate a beat frequency signal. A spectrometer is used to observe whether the wavelengths of a tunable laser and an FMCW laser are consistent. A coupler is used to couple the output light source signal of an FMCW laser to that of a tunable laser to generate a difference frequency signal. A detector is used to detect and receive difference frequency signals and convert optical signals into electrical signals. An oscilloscope is used to observe the waveform of a difference frequency signal and store the current signal. A computer is used to control the output wavelength of the tunable laser and run Matlab software to perform time-frequency analysis on the output signal. The coupler is connected to the FMCW laser, spectrometer, detector, and tunable laser via optical fibers; the FMCW laser is electrically connected to the signal source; the detector is electrically connected to the power supply and oscilloscope; and the tunable laser is electrically connected to the computer.

4. The correction system for implementing the FMCW laser output signal frequency correction method according to claim 3, characterized in that: The detector is a balanced detector.

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