Research On Signal Generation And Processing Technologies Of High Linearity FMCW Lidar System

High-precision measurement methods are the core technology for promoting scientific and technological development,realizing industrial upgrading,and building a military power.Laser radar has shown excellent application prospects in engineering measurement,military inspection,automatic driving and other fields to meet the needs of high-precision measurement in complex scenes.Frequency Modulated Continuous Wave(FMCW)laser radar has the superiority of narrow laser light source line width and strong coherence,as well as strong environmental adaptability and anti-noise capacity in terms of ranging technology.Therefore,it has significant measurement advantages over the widely used time of flight radars.However,the light intensity variation and frequency nonlinearity induced by the modulation process of FMCW laser radar light source become the core factors affecting the measurement accuracy and resolution.This thesis builds a laser radar system based on the principle of FMCW ranging,and investigates the above key problem.Firstly,this thesis analyzes the current research status of FMCW laser radar ranging technology,and investigate extensively the key issues and methods in the high linearity FMCW laser radar signal generation and processing system.This thesis studies the relevant theories,discusses the influencing factors of the corresponding index parameters,and builds the FMCW modulated light source model under external disturbance.Secondly,this thesis builds a signal source module with a Distributed Feedback(DFB)laser as the light source,and this thesis develops a signal generation,acquisition and processing module based on FPGA.Then,this thesis constructs the FMCW laser radar simulation model based on the relevant ranging theory,and study the measurement error caused by the light intensity variation of the frequency modulated laser.This thesis expounds the theory of the precorrection open-loop control and closed-loop negative feedback optical power control,and design an FPGA-based open-closed-loop joint optical power control algorithm.This thesis tests the control algorithm numerically based on the system simulation model.Furthermore,this thesis studies the characteristics of the power control device experimentally for improving the performance of the control algorithm.This thesis develops the technology to balance the laser output power based on the open-loop precorrection and closed-loop optoelectronic negative feedback joint control.The experimental results indicate that the light intensity stability is improved by 71.7 times with a modulation period of 1 ms and a modulation bandwidth of 90 GHz.Finally,this thesis studies the measurement error caused by the frequency nonlinearity of the frequency modulated laser,and establish the corresponding quantitative evaluation index.Combined with the idea of nonlinear modulation to suppress nonlinear frequency sweep and iterative correction,this thesis designs a nonlinear frequency modulation algorithm which is numerically test on MATLAB and realized with FPGA.The experiment results indicate an excellent improvement in the linearity of the FMCW system,and the ranging resolution improved to 8.4 times of the original base,reaching 0.003 m.