Research On Pulse Characteristics Of Q-switched Random Laser Based On Doped Fiber

Q-switched fiber laser has a wide application prospect in optical fiber sensing,medical laser,national defense and military and other fields because of its high output beam energy and high conversion efficiency.Random fiber laser(RFL)is a difficult and hot topic of current research because it has no fixed resonant cavity and has longitudinal mode free output characteristics.In this thesis,aiming at the difficulty of generating and controlling pulse output in RFL,the pulse generation and pulse characteristics of Q-switched random laser based on doped fiber are studied.1.An actively Q-switched ring cavity fiber laser based on electro-optic modulator is studied theoretically and experimentally.According to the rate equation of Qswitched laser,the effects of pump power,modulation frequency and modulation index on the pulse characteristics are analyzed.The results show that the output of Q-switched laser shows multi-pulse splitting,single-period pulse,period-doubling pulse and chaos.At the same time,under the combined action of pump power,modulation frequency and modulation index,Q-switched laser can be easily switched in the dynamic response of pulse splitting,chaos and special period-doubling pulse.2.An actively Q-switched ring cavity RFL based on random phase-shifted grating is studied experimentally.The Q-switched random laser output is realized by introducing random phase-shift grating to provide random feedback.The effects of pump power and modulation frequency on pulse output characteristics are studied.The results show that pulse splitting,period-doubling pulse and chaotic pulse output can also be observed in RFL.However,due to the introduction of random phase-shifted grating,the intracavity loss increases,higher pump power is needed to produce the same pulse splitting state,and the frequency corresponding to period doubling shifts to a smaller modulation frequency.3.A passively Q-switched ring cavity RFL laser based on random phase-shifted grating is studied experimentally.The output of passively Q-switched random laser is realized by using the saturable absorption characteristics of cascaded doped fiber.The stable pulse output with adjustable repetition rate in the 5.1 k Hz-29 k Hz range is obtained under different pump power.