利用单模光纤中SBS效应进行被动调Q的掺铒光纤激光器研究

分析了利用光纤中的受激布里渊散射(SBS)相位共轭效应进行激光腔内调Q,产生ns量级脉冲激光的原理,并对利用该效应产生的激光脉冲波形和脉冲形成过程进行了数值模拟,得到的脉冲波形与SBS相位共轭反射率随时间变化曲线基本一致,表明利用光纤中的SBS相位共轭作用调Q具有可行性。据此,对采用单模光纤(SMF)作为SBS池的掺Er3＋调Q光纤激光器进行实验研究,当单模光纤长度为1.5 m时,在45 mW的抽运光功率下得到脉宽约2.6 ns,脉冲周期58.23 ns,平均功率7.35 mW的激光脉冲。进一步的研究表明：激光器中相位共轭镜的形成与SBS介质长度有关,SBS介质过长,斯托克斯线之间无固定的相位关系,不能形成相干叠加,SBS相位共轭腔不能形成; SBS介质过短,腔内正交偏振模光子寿命的改变使脉冲出现双峰现象。脉冲形成后其属性只与SBS动态属性有关。

Investigation of a Self-Q-Witched Fiber Laser Based on the Stimulated-Brillouin-Scattering Phase Conjugation in Single-Mode-Fibers

The generation of nanosecond-scale pulsed laser with stimulated-Brillouin-scattering (SBS) phase conjugation in fiber was investigated theoretically and experimentally. Numerical simulation was performed to study the waveform and the sequence of laser pulse. The obtained waveform is coincident with the curve describing the relationship between reflectivity of SBS phase conjugation mirror and time. The results show that changing Q value in resonant cavity by utilizing SBS phase conjugation is feasible. To investigate the output laser at different lengths of SBS medium, an all-fiber Er3+-doped Q-switched laser was designed. When the length of single-mode-fiber (SMF) is 1.5 m, laser pulse are generated with pulse duration of 2.6 ns, pulse period of 58.23 ns, average output power of 7.35 mW at pump power of 45 mW. When the length of SMF is decreased to 1 m, pulsed laser with remarkable dual-peaks is obtained with pulse period of 26.47 ns. While the length of SMF is increased to 2 m, only irregular stochastic pulsations are observed. Experimental data indicate that the length of SBS medium is vital to the formation of phase conjugation mirror. If it is too long, pulsed laser can not be generated for the lack of fixed conjugation relation between Stokes lines, and on the contrary, dual-peaks laser pulses occur for the change of photon lifetime in orthogonally polarized modes. Once the laser pulses are generated, their characteristics are only correlated with the stochastic characteristics of SBS and the pulse profile maintains constant with the increase of pump power.