The Study On Adaptive Manipulation Of Fiber Laser Time-Frequency Characteristics

Fiber laser has been widely used in various fields,such as industrial processing,remote sensing,biological medicine and so on.These applications have their unique requirements for the characteristics of fiber lasers(such as power,polarization,spatial domain,time domain and frequency domain,etc.).Therefore,manipulation techniques of laser characteristics is of great importance for practical applications.In this paper,based on the Master Oscillator Power Amplifier(MOPA)structure and adaptive manipulation technique,the pulse shaping and spectral manipulation are studied theoretically and experimentally.Specific research contents are as follows:1.The application and research status of manipulation technology for time-frequency characteristic of fiber laser is introduced,which indicates the value of pulse shaping and spectrum manipulation in the compensation of laser pulse shape distortion and the suppression of nonlinear effect existing in narrow-linewidth fiber laser,respectively.2.A design scheme of fiber laser time-frequency characteristic manipulation system is proposed.The instrument communication system based on Local Area Net(LAN),Transmission Control Protocol/Internet(TCP/IP)Protocol is built to realize the stable data exchange between the modules of the hardware system.Based on the "top-down" design idea,the hierarchical structure and core functions of adaptive manipulation system for time-frequency characteristics are analyzed,and then the software system of adaptive manipulation system is designed by using LabVIEW.The measurement method of the vectors similarity is proposed to design the evaluation function of time-frequency characteristic manipulation system.3.Adaptive manipulation technology of pulse shape has been studied theoretically and experimentally.The physical mechanism of shape distortion in pulse fiber amplifiers is analyzed and based on electro-optic modulation,the scheme of adaptive manipulation for pulse shape distortion is proposed.A numerical simulation model is established,and the numerical simulation of pulse manipulation is carried out that verifies the feasibility of the proposed scheme theoretically.An experimental system for the adaptive manipulation of pulse shape is built,and the effectiveness of the proposed scheme is verified.The distance between output pulse and target pulse vectors is proposed and used to describe the effect of pulse shape manipulation.In the experiment,a variety of target pulse shapes are generated adaptively,and the relative error distance between the peak power vector of target pulse and actual output pulse are all less than 1%.4.Adaptive spectral manipulation technique for narrow-linewidth fiber laser is studied theoretically.Based on electro-optic modulation,a scheme for adaptive manipulation of narrow-linewidth fiber laser spectrum is proposed for the first time.The validity of this scheme is verified theoretically.Through the optimization of the phase modulation signals,the spectra with 11,19 and 29 equal-amplitude lines are obtained.The mean square error of spectral lines power density are less than 3%,and the energy of the equal-amplitude lines are all beyond 85%.The method can adjust the peak power and linewidth of the spectrum flexibly,providing theoretical guidance for further improving the output power level of narrow linewidth fiber laser.