CN-122017808-A - Linear frequency modulation DFB laser smooth predistortion iteration nonlinear correction method

CN122017808ACN 122017808 ACN122017808 ACN 122017808ACN-122017808-A

Abstract

The invention discloses a linear frequency modulation DFB laser smooth predistortion iteration nonlinear correction method, which relates to the technical field of photoelectrons and laser radars and comprises the following steps of generating an initial ideal triangular wave driving voltage signal by using an FPGA, driving a laser after a digital-to-analog converter, coupling an optical signal output by the laser into an unbalanced interferometer, obtaining a beat frequency signal by a balanced photoelectric detector, acquiring the beat frequency signal back to the FPGA after analog-to-digital conversion of an analog-to-digital converter, performing Hilbert transformation on the acquired beat frequency signal, and demodulating to obtain the actual instantaneous frequency of the laser Constructing an ideal frequency curve Calculating the frequency error between the actual instantaneous frequency and the smoothed ideal frequency, converting the frequency error into a voltage error, updating the driving voltage waveform of the next iteration according to the voltage error, and repeating the steps until the nonlinearity reaches a preset threshold value. By introducing a smooth ideal frequency model, the error mutation at the inflection point is eliminated, and the high-precision and fast-convergence linear frequency sweep is realized.

Inventors

ZHANG YUNSHAN
MA WENXUAN
Zhou mengxi
CHEN YIBING
ZOU HUI

Assignees

南京邮电大学

Dates

Publication Date: 20260512
Application Date: 20260224

Claims (8)

1. A linear frequency modulation DFB laser smooth predistortion iteration nonlinear correction method is characterized by comprising the following steps: s1, generating an initial ideal triangular wave driving voltage signal through an FPGA, and driving a DFB laser through a digital-to-analog converter (DAC); S2, coupling an optical signal output by a laser into an unbalanced Mach-Zehnder interferometer (MZI), obtaining a beat frequency signal through a Balanced Photoelectric Detector (BPD), and acquiring the beat frequency signal back to the FPGA through analog-digital conversion of an analog-digital converter; S3, performing Hilbert transformation on the acquired beat frequency signals, and demodulating to obtain the actual instantaneous frequency of the laser ; S4, constructing an ideal frequency curve The ideal frequency curve is directly calculated based on bandwidth and period in the middle linear region of the sweep period, and is processed by adopting a smoothing function in the inflection point region of the sweep period so as to eliminate polarity abrupt change of relative error; S5, calculating a frequency error between the actual instantaneous frequency and the smoothed ideal frequency, and converting the frequency error into a voltage error; S6, updating a driving voltage waveform of the next iteration according to the voltage error; and S7, repeating the steps S2 to S6 until the nonlinearity reaches a preset threshold value or the iteration times reach a preset value.
2. The method for iterative nonlinear correction of smooth predistortion of a linear frequency modulated DFB laser as set forth in claim 1, wherein the smoothing of the ideal frequency curve in step S4 is specifically: for the initial and final stages of upper or lower sweep, i.e. inflection point region, the ideal linear frequency curve is smoothly connected by using quadratic function, and the smoothed ideal frequency Expressed as: ; Wherein the method comprises the steps of In order to smooth the length of the region, For an ideal sweep frequency slope, For a half of the modulation period, And To smooth the fitting coefficients, specific settings are needed according to the experiment.
3. The method for iterative nonlinear correction of smooth predistortion of a linear frequency modulated DFB laser as set forth in claim 1, wherein the driving voltage update formula in step S6 is: ; Wherein the method comprises the steps of Is the first The driving voltage of the number of iterations, As an error factor, the error factor is, To the first calculated from the frequency error Secondary voltage correction.
4. A linear frequency modulation DFB laser smooth predistortion iteration nonlinear correction system is used for realizing the linear frequency modulation DFB laser smooth predistortion iteration nonlinear correction method in claim 1 and is characterized by comprising an FPGA control module, a driving circuit module, an optical path detection module and a data acquisition module.
5. The smooth predistortion iterative nonlinear correction system of a chirped DFB laser as set forth in claim 4 wherein said FPGA control module is adapted to generate a drive waveform, receive a feedback signal, perform a Hilbert transform, construct a smooth ideal frequency curve, and update a drive voltage algorithm.
6. The smooth predistortion iterative nonlinear correction system of a linear frequency modulation DFB laser as set forth in claim 4, wherein the drive circuit module comprises a DAC and an adder for driving the DFB laser after superimposing the modulated voltage generated by the FPGA control module with the DC bias voltage.
7. The system of claim 4, wherein the optical path detection module comprises an MZI interferometer comprising an optical fiber coupler and a delay fiber, and a Balanced Photodetector (BPD) for converting laser frequency variation into an electrical signal.
8. The system of claim 4, wherein the data acquisition module comprises an analog-to-digital converter for digitally transmitting analog voltage signals from a Balanced Photodetector (BPD) to the FPGA control module.

Description

Linear frequency modulation DFB laser smooth predistortion iteration nonlinear correction method Technical Field The invention relates to the technical field of photoelectrons and laser radars, in particular to a smooth predistortion iteration nonlinear correction method of a linear frequency modulation DFB laser. Background Frequency Modulated Continuous Wave (FMCW) lidars have important applications in the areas of autopilot and remote sensing due to their high resolution and anti-interference capabilities, however, directly modulated semiconductor lasers (e.g., DFB lasers) have inherent frequency modulation nonlinearities due to thermal and carrier effects, which can lead to spectral broadening, severely affecting ranging accuracy and imaging quality. In the existing nonlinear correction technology, an optical phase-locked loop (OPLL) is complex in structure and high in cost, the resampling technology is limited by the Nyquist sampling theorem, an iterative predistortion algorithm is paid attention to because of high hardware efficiency, but a traditional linear fitting-based iterative algorithm is easy to cause error symbol alternation at an inflection point (a peak and a trough of a triangular wave) of a sweep frequency signal due to discontinuity of an ideal frequency linear fitting and an actual physical process, and further drive voltage mutation is caused, high-frequency components are introduced by the mutation, so that the algorithm cannot converge at the inflection point, and final linearity improvement is limited, so that a linear frequency modulation DFB laser smooth predistortion iterative nonlinear correction method is provided for overcoming the defects in the prior art. Disclosure of Invention Aiming at the defects of the prior art, the invention provides a smooth predistortion iteration nonlinear correction method of a linear frequency modulation DFB laser, which solves the problems of poor convergence and easy generation of abrupt change of driving voltage of the prior iteration predistortion technology at the inflection point of a sweep frequency. In order to achieve the purpose, the invention is realized by the following technical scheme that the smooth predistortion iterative nonlinear correction method of the linear frequency modulation DFB laser comprises the following steps: s1, generating an initial ideal triangular wave driving voltage signal by an FPGA, and driving a DFB laser through a digital-to-analog converter (DAC); S2, coupling an optical signal output by a laser into an unbalanced Mach-Zehnder interferometer (MZI), obtaining a beat frequency signal through a Balanced Photoelectric Detector (BPD), and acquiring the beat frequency signal back to the FPGA through analog-digital conversion of an analog-digital converter; S3, performing Hilbert transformation on the acquired beat frequency signals, and demodulating to obtain the actual instantaneous frequency of the laser ; S4, constructing an ideal frequency curveThe ideal frequency curve is directly calculated based on bandwidth and period in the middle linear region of the sweep period, and is processed by adopting a smoothing function in the inflection point region of the sweep period so as to eliminate polarity abrupt change of relative error; S5, calculating a frequency error between the actual instantaneous frequency and the smoothed ideal frequency, and converting the frequency error into a voltage error; S6, updating a driving voltage waveform of the next iteration according to the voltage error; and S7, repeating the steps S2 to S6 until the nonlinearity reaches a preset threshold value or the iteration times reach a preset value. Preferably, the smoothing process for the ideal frequency curve in step S4 specifically includes: for the initial and final stages of upper or lower sweep, i.e. inflection point region, the ideal linear frequency curve is smoothly connected by using quadratic function, and the smoothed ideal frequency Expressed as: Wherein, the In order to smooth the length of the region,For an ideal sweep frequency slope,For a half of the modulation period,AndTo smooth the fitting coefficients, specific settings are needed according to the experiment. Preferably, the driving voltage update formula in step S6 is: Wherein the method comprises the steps of Is the firstThe driving voltage of the number of iterations,As an error factor, the error factor is,To the first calculated from the frequency errorSecondary voltage correction. A linear frequency modulation DFB laser smooth predistortion iteration nonlinear correction system comprises an FPGA control module, a driving circuit module, an optical path detection module and a data acquisition module. Preferably, the FPGA control module is configured to generate a driving waveform, receive a feedback signal, perform a hilbert transform, construct a smoothed ideal frequency curve, and update a driving voltage algorithm. Preferably, the driving circuit module co