| Given its ultra-fast temporal characteristics,excellent heat dissipation,simple operation,no need for maintenance,excellent stability and high output power,femtosecond fiber lasers have an important position in the laser field and have a broad application market,so researching and developing the femtosecond fiber laser system are especially important.Based on the design and development of new fiber lasers and amplifiers,this paper includes the design concept of lasers from the principle of modelocking to the evolution of pulses in optical fibers.A series of experimental studies based on novel fiber lasers are carried out to optimize the structure of lasers for better output characteristics,and successfully developed a high-power full polarizationmaintaining fiber structure femtosecond laser amplification system.(1)This paper introduces the current mode-locking technologies commonly used in full polarization-maintaining fiber lasers,and proposes a new mode-locking approach combining their respective advantages.The dynamic behavior of the pulse in the fiber subjected to dispersion and nonlinearity is also studied,in virtue of the photon chromatography technology we observe the mode-locked transient process successfully,which provides an experimental basis for studying the mode-locking technique.(2)The effects of dispersion distributions on pulse evolution are studied.The experimental study on ytterbium-doped and erbium-doped linear cavity lasers based on the mode-locking of saturable absorbers are carried out.The exploration of the best working conditions is obtained by applying space components.And the corresponding linear cavity laser with full polarization-maintaining fiber structure have been constructed further,which accumulated rich experimental data for the development of new type of lasers.(3)The hybrid mode-locked ring cavity laser combined with the nonlinear amplifying ring mirror and the semiconductor saturable absorber is studied.The lasers consisting of ytterbium-doped full normal dispersion distribution fiber and the erbiumdoped total negative dispersion distribution fiber are developed,and the output ultrashort pulses are of excellent performance.Then the self-similar pulse amplifier is further developed by using the erbium-doped total negative dispersion laser as the seed source.The pulse output with the repetition frequency of 100.09 MHz,the average power of 225.6mW and the spectral width of 55.72 nm was obtained.(4)To improve the structure of the ring cavity laser with a full negative dispersion distribution,and increase the degree of freedom of adjustment,we build a laser which can passively adjust the output power by inserting a highly nonlinear fiber into the cavity.Furthermore,we add an additional amplification unit in the nonlinear amplifying loop mirror.By adjusting the pump power respectively to build a laser structure with an tunable output ratio,the mode-locking range is broadened,and the pulse output characteristics is optimized.(5)The amplifier design model is established by using the step-by-step amplification method to improve the gain of pulses.The nonlinear phase is used to compensate the gain narrowing effect,which gives the requirement of the width of the chirped pulse.The design scheme of chirped pulse amplification and the method of amplifying pulse based on self-similar evolution are studied.A three-stage cascade pulse amplification system with output power of 20.66 W is developed in the laboratory. |
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