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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 impulsive pulses in an exponentially increasing nonlinearly-increasing fiber (NIF) was investigated by a combination of theoretical derivation and numerical simulation. The results show that parabolic self-similar impulses with strictly linear chirp can be obtained by using exponentially increasing NIF, similar to the hyperbolic descending forward dispersion reducing fiber (ND-DDF). The effects of ND-DDF and NIF gain on self-similar evolution are studied in depth. The results show that: 1) The equivalent gain determines the pulse self-similar evolution, and the equivalent mode determines the evolution of pulse self- Speed; 2) Under equal equivalent gain, the pulse evolves into the same self-similar pulse in exponential increasing NIF and hyperbolic decreasing ND-DDF, but the former is more efficient at self-similar evolution of the pulse, The length of the fiber needed to achieve self-similar evolution is shorter; 3) The required fiber length for the two gain-equivalent modes is such that they each have the same fiber “effective amplification factor.”