Study On Nonlinear Rectification Technology Of LFM DFB Semiconductor Laser

Laser ranging is an important part of modern measurement technology.Compared with the traditional ranging methods,the laser ranging technology does not need to contact the measured object,and can be used in harsh environment.The laser ranging technology also has larger ranging rang,higher accuracy and resolution.Laser ranging technology can be classified into pulse method,phase method,double frequency interference method and linear frequency modulation method.Linear frequency modulation(LFM)laser ranging technology has a large range of measurement and ranging accuracy which is an important research direction.LFM laser ranging technology has high requirements for lasers.There are few lasers that can meet all the requirements.Each laser source has its own disadvantages.Current modulation DFB semiconductor laser has the advantages of high modulation rate,wide modulation band and narrow line width.It is very suitable as a linear frequency modulation laser ranging light source and has been widely used and studied.In the process of frequency modulation,the variation of the laser frequency is nonlinear.The nonlinearity will result in the spectrum broadening of the measured signal and finally makes the ranging resolution lower.The nonlinear problem in the process of linear frequency modulation of current modulated DFB semiconductor laser is studied in this thesis.The mechanism of the nonlinearity as well as the influence of laser parameters on frequency modulation nonlinearity are both simulated and studied.Through the calculation,the method of nonlinear correction is obtained.The dynamic feedback compensation technique is used to realize the nonlinear correction in the process of LFM.The main research works of this paper:1.The research progress of LFM laser ranging technology is investigated,and the working principle of LFM laser ranging technology is discussed.The research work on nonlinear correction at home and abroad is investigated as well.The development of this technology and the mainly used technical methods are analyzed and discussed.2.Based on the research progress,the frequency modulation principle of DFB semiconductor laser is studied,and the mathematical model of frequency modulation of DFB semiconductor laser is established.After built the mathematical model,the effects of bias,amplitude and frequency of input current on the frequency modulation bandwidth and nonlinearity are theoretically researched.3.Theoretical simulation of the frequency modulation nonlinear precorrection method is carried out.The mathematical relationship between injection current and frequency modulation nonlinearity is obtained by theoretical simulation.On this basis,the linear equation of frequency modulation is set,and the injection current waveform is derived reversely through the mathematical relations.The derived current waveform is input into the mathematical model of frequency modulation to obtain the frequency modulation curve after the pre-correction.The correction effect of pre-correction method on frequency modulation nonlinearity is verified.4.On the basis of theoretical research,the experimental study of currentmodulated linear frequency-modulated DFB semiconductor laser is carried out.The frequency modulation nonlinearity of the triangular wave current-driven DFB semiconductor laser is corrected by real-time dynamic feedback technique.The nonlinearity in frequency modulation of DFB semiconductor laser is reduced obviously.