Research On Q-switched Random Fiber Laser Based On Gain Fiber

Q-switched fiber lasers have a crucial position in many application domains such as laser medical treatment,mechanical processing,national defense and military due to their high beam energy,good quality and many other advantages.Random Fiber Laser(RFL)has a significant non-longitudinal mode because it has no fixed resonator.The pulse output of RFL has potential application value in next-generation laser processing,ultra-fast optical communication and medical applications.There are a large number of complex patterns in random lasers that make the generation and control of RFL pulse output challenging.In this thesis,the following researches are conducted on the above issues:1?An actively Q-switched ring cavity fiber laser based on an electro-optic modulator(EOM)is studied.Due to the short response time of the modulator,multiple completely separated pulses were observed in experimentally.The influence of pump power,modulation frequency and other parameters on the characteristics of output pulse amplitude,number of pulses and sub-pulse spacing is studied.By improving pump power,up to 6 separate multi-pulses can be obtained in one modulation period.By increasing the frequency of the modulation signal,a single pulse is obtained in two to three modulation cycles.2?An actively Q-switched ring cavity RFL based on two feedback mechanisms of random phase shift grating and Rayleigh scattering is studied.In both RFLs,multiple completely separated pulses were also observed.The influence of pump power,modulation frequency and other parameters on the characteristics of output pulse amplitude and number of pulses is studied.By improving pump power,up to 3and 8 pulses can be observed in one modulation period.The waveform and polarization state of the modulated signal will also affect the pulse amplitude accordingly.3?An actively Q-switched linear cavity RFL based on erbium-doped fiber is studied,and the pulse is controlled by pump power and laser cavity loss.By adjusting pump power and loss in the laser cavity,the pulse shape is adjusted from the square wave to a quasi-passive Q-switched pulse.When the pump power increases and additional attenuation is added,the combination of stimulated Brillouin scattering(SBS)and EOM in the fiber produces a regular and stable output pulse.The pulse width ranges from 1.66?s to 6.8?s,and its amplitude ranges from 0.016 V to 4.32 V.