基于非线性渐增原理获得抛物线型自相似脉冲的研究

Study on Parabolic Self-Similar Pulse Generation in a Nonlinearity Increasing Fiber

采用理论推导和数值模拟相结合的方法研究了脉冲在指数渐增的非线性渐增光纤(NIF)中的自相似演化。结果表明,与双曲渐减的正色散渐减光纤(ND-DDF)类似,利用指数渐增的NIF也可获得具有严格线性啁啾的抛物线型自相似脉冲。同时深入研究了ND-DDF和NIF两种增益等效方式对自相似演化特性的影响,结果表明:1)等效增益决定了脉冲自相似演化的结果,等效方式决定了脉冲自相似演化进程快慢;2)在具有相等的等效增益条件下,脉冲在指数渐增NIF和双曲渐减ND-DDF中演化为相同的自相似脉冲,但是前者对脉冲的自相似演化更高效,即前者实现自相似演化所需光纤长度更短;3)两种增益等效方式所需光纤长度的关系是使得各自具有相同的光纤"有效放大因子"。

The self-similar evolution of an initial Gaussian pulse propagating in a nonlinearity increasing fiber （NIF） with an exponential nonlinearity profile is studied theoretically and numerically. As well as the dispersion decreasing fiber with normal group velocity dispersion （ND-DDF with a hyperbolic dispersion profile）, the NIF is also equivalent to a fiber amplifier, which can generate a parabolic self-similar pulse with strictly linear chirp. Furthermore, the impacts of two equivalent ways of ND-DDF and NIF on characteristics of the self-similar evolution are studied. The theoretical and simulation results show that： 1） the equivalent gain determines the results of self-similar evolution while the equivalent method determines the process speed; 2） with the same equivalent gain, the initial pulses in ND- DDF and NIF both evolve into the same parabolic self-similar pulse, but the process of NIF is more efficient, needing a shorter fiber length; 3） the relationship of fiber lengths of NIF and ND-DDF is to make the two fibers have the same ＂effective amplification＂.