Research On Gain-Switched TM³⁺-Doped Fiber Laser

Nanosecond pulsed Tm3+ -doped lasers in the 2μm spectral region have extensive application demands in many fields such as eye-safe lidars and optical countermeasures. All fiber pulsed Tm3+-doped fiber lasers (TDFLs) are of particular interest for its compactness and good maintainability. Experiments results at home and abroad show that the best way to realize all-fiber TDFL is through fast gain switching technique by using pulsed fiber source in the 1.55μm wavelength-range as a pump source. In the dissertation, pulsed Er3+ -doped fiber amplifier (EDFA) and its pumped TDFL are studied theoretically and experimentally.In theory, Firstly, theoretical model of pulsed Er3+ -doped fiber amplifier is introduced in detail, then the influences of amplifier parameters on the operating characteristics are discussed under low and high repetition rate conditions respectively based on the model. For the low repetition rate case, evolution equation of pulse energy along the EDFA is derived, the influences of pump power and the length of active fiber on the output characteristic are analyzed using the equation. For the high repetition rate case, model equations are solved using finite difference method, and the effects of repetition rate and input energy on the output characteristic are analyzed. Secondly, dynamics of gain-switched TDFL is studied, the influences of pump and cavity parameters on the width and built-up time of the output pulse are mainly analyzed.Experiments on two stage single mode EDFA seeded by a directly modulated 1.558μm diode laser are performed, for the first stage EDFA, single pass and double pass designs are applied respectively, the maximum output powers obtained are 20.4mW and 25.7mW correspondingly, Forward pump and single pass structure is used for the second stage, the maximum output energy is 18μJ at 5kHz with 3m Er3+ -doped fiber and 400mW pump power, the slope efficiency is about 22%. The output of the two stage pulsed EDFA is then used to pump Tm3+- -doped fiber for gain-switching experiment. Stable pulse with 5kHz repetition rate,80ns pulse width,0.5μJ energy at 1.94μm is achieved.