Design Of Laser Radar Ranging System Based On Linear Frequency Modulation

Laser Radar(Ladar)has developed rapidly since it was proposed in the 1960 s,and its research directions and fields are numerous.The research of Linear frequency modulation continuous wave Ladar(LFMCW Ladar)has become an important research direction.The application of LFMCW Ladar for laser ranging is a research hotspot in recent years.It has the advantages of high resolution,high ranging precision,and no distance blind zone.It is widely used in environmental sensing,meteorological research,high precision ranging and other fields.After this topic has made a thorough research in connection with the generation of large broadband Linear Frequency Modulation(LFM)signals from a Distributed Feedback(DFB)semiconductor laser in a LFM-based laser radar ranging system.We designed a linear frequency modulation system based on an optoelectronic phase-locked loop.Moreover,we have made the iterative compensation of the semiconductor laser drive signal further optimizing the linear frequency modulation system so that the laser emits large broadband chirped light.The laser linear frequency modulation system designed in this thesis is an important basis of the linear frequency modulation laser radar ranging system.This article mainly completes the following aspects:Firstly,the thesis introduces the theorys of LFM continuous-wave laser ranging and DFB laser current-modulation characteristics,and points out and analyzes the influence of semiconductor FM's current-frequency nonlinearity on the difference-frequency signal and ranging.Secondly,aiming at the problem of nonlinearity of current-frequency modulation of DFB lasers,a linear frequency-modulation system based on optoelectronic phase-locked loop is designed,and the theory of the photoelectric phase-locked loop in the linear frequency modulation system is analyzed in detail.Thirdly,the thesis designs the concrete hardware circuit design of the LFM system based on the optoelectronic phase-locked loop.According to the block diagram of the LFM system,the module selection and circuit design details of each module are introduced,including the optical path design,the voltage conversion circuit design,integrator and adder circuit design,photodetector circuit design and phase detector circuit design in the opto-electronic phaselocked loop module,as well as DAC and DDS signal circuit design and power supply clock design in the FPGA + AD9106 signal generation module.Finally,the thesis iteratively compensates the driving signal of the semiconductor laser to further reduce the nonlinearity of the current-frequency modulation of the semiconductor laser,shows and analyses the experimental results of the linear frequency-modulation system optimized through multiple iterations of compensation.