Research On Narrowband Picosecond Pulsed Figure-9 Fiber Laser

Due to the advantages of narrow pulse duration and high peak power,picosecond pulse has important applications in precision machining,ranging,medical imaging and other fields.Passively mode-locked fiber lasers are one of the mainstream solutions for obtaining picosecond pulses.Among them,the Figure-9 fiber laser based on nonlinear loop mirror mode locking has gradually become a research hotspot in recent years because that it can be made in an all polarization-maintaining fiber design,which has the advantages of good stability,compact structure,and high damage threshold.This thesis focuses on the narrow-band picosecond Figure-9 fiber laser based on nonlinear amplifying loop mirror.The main contents include:First,a lumped laser model based on nonlinear amplifying loop mirror mode locking is established,and the effects of different parameters of the Figure-9 fiber laser on the output pulse characteristic of the laser is studied through theoretical analysis and numerical simulations.Second,we construct an all polarization-maintaining fiber Figure-9 fiber laser.By adding a non-reciprocal phase shifter to the nonlinear amplifying loop mirror,it is easy to realize self-start mode-locking.By separately optimizing the length and asymmetry of the fiber in the nonlinear amplification loop mirror and the length of the fiber in the linear arm,picosecond pulse with the repetition frequency of?10MHz,center wavelength?1064nm,average power of 4.00mW,pulse width of 21.07ps,and 3dB spectrum of 0.20nm is obtained.Third,through a single-stage single-mode fiber amplifier,the output pulse of the picosecond laser is effectively amplified and a single pulse energy greater than 10nJ is obtained.At the same time,the pulse spectrum width is still less than 0.6nm.Thus it can be used directly as the fiber front end for solid-state amplification to generate high energy picosecond pulses.The above research results have important reference value for the design and development of a practical picosecond laser source with compact structure and good stability.