Research On Generation And Amplification Of Narrow Bandwidth Picosecond Pulse Based On Fiber Laser Technology

High-energy narrow-band picosecond pulses have important applications in micro-machining,biomedical,spectroscopy,and precision ranging due to their short duration,high peak power,and high spectral purity.Passive mode-locked fiber laser is one of the main solutions for generating picosecond pulses,which has the advantages of compact,high efficiency,low cost and maintenance-free,and recived much attention recent years.This dissertation focuses on the research of narrow-band picosecond fiber lasers and amplification.The main work includes:Firstly,The properties of narrow-band dissipative soliton and the boundary problem of single-pulse operation region are studied based on theoretical and numerical methods.The dominant effect of filter bandwidth on pulse duration and bandwidth is revealed.The weak nonlinear region operating characteristic is the root cause of high repetition rate and low pulse energy.Second,we propose and demonstrate a method to reduce the repetition rate of an all-PM picosecond DS passively mode-locked fiber laser without changing the pulse characteristics.Our experimental results will show that,by inserting an optical coupler(OC)to extract pulse energy from a cavity and using a large mode area(LMA)fiber to increase cavity length and placing it at the rear end of the OC where the propagated pulse has lower energy,the nonlinear phase shift can be effectively reduced,and thus,the laser repetition rate can be significantly decreased.For an all-PM linear-cavity DS passively mode-locked fiber laser based on a 0.3-nm FBG,the repetition rate is successfully reduced to 1.77 MHz while pulse duration and bandwidth are basically unchanged.This method is applicable to lasers with any filter bandwidth.Third,a method for suppressing the self phase modulation in the amplifier by spectrally shaping the seed pulse is proposed and demonstrated,and then the amplification capability of the fiber amplifier while maintaining the narrowband output is improved.A pulsed time domain waveform transform scheme by spectral intensity shaping through a tunable notch filter is designed,which effectively reduces the spectral broadening slope caused by self-phase modulation and improves the narrowband amplification capability of the fiber amplifier.The experimental results show that for the 11.2 ps seed source,the spectral pulse shaping technique can increase the energy of the output pulse from 14 nJ to 25.5 nJ under the 0.4 nm rms spectral width.Fourth,the nonlinear fiber amplification technology is studied.Based on the 10 ps near-transform limited source,a pulse train with an average power of 5 W and a pulse duration of 200 fs is obtained by a nonlinear amplification technique.The above research results have important value for the development of high-quality all-fiber picosecond lasers to meet the needs of micro-machining,medical,ranging and spectroscopy applications.