正常色散光纤放大器中超短脉冲的自相似演化条件

Ultra-Short Pulses Self-Similar Evolution Conditions in Normal Dispersive Fiber Amplifiers

在正常色散条件下,超短光脉冲在光纤放大器中可以演化成具有线性啁啾的自相似抛物脉冲,其演化结果可影响脉冲的压缩质量.采用分步傅里叶方法数值研究了正常色散光纤放大器中,初始输入脉冲宽度、能量、光纤增益和色散系数对超短脉冲自相似演化结果的影响.发现色散长度是脉冲能否实现自相似演化的关键因素.当色散长度与光纤长度相近(几倍)时,脉冲可以实现自相似演化;两者相差越大,脉冲的自相似演化程度越差.增加初始脉冲能量可以加速脉冲的自相似演化,缩短自相似演化的距离.放大器总增益一定时,增益系数越大,脉冲受非线性扭曲的影响越大,使脉冲的自相似演化结果越差;增益系数为0.95 m-1时放大器可获得的总增益比3.8 m-1时大3.3 dB.

Ultrashort pulses can evolve into self-similar parabolic pulses with a linear chirp in optical fiber amplifiers with normal group velocity dispersion, and the evolution result can affect the consequent pulse compression. The influences of the initial pulse width and energy as well as fiber dispersion and gain coefficient on the pulse self-similar evolution were numerically studied by split-step Fourier method, and the results reveal that dispersion length is the key factor determining whether the pulse can evolve self-similarly or not. When the dispersion length is close to fiber length （just severalfold）, the initial pulse can evolve into a parabolic pulse; the larger the difference between the dispersion length and fiber length, the worse the self-similar evolution. Increasing the initial pulse energy can accelerate the pulse self-similar evolution, and therefore decrease the distance for self-similar evolution. Under a given amplifier total gain the higher the gain coefficient is, for the effect of nonlinear distortion, the worse the self- similar evolution is. When the gain coefficient is 0.95 m^-1 , the total gain of the amplifier is 3.3 dB larger than that when the gain coefficient is 3.8 m^-1.