五阶非线性光纤中光扰动所致超短脉冲串的产生

Generation of Ultra-Short Optical Pulse Trains Induced by Optical Perturbations in Optical Fibers with Quintic Nonlinearity

从光纤中包含五阶非线性效应的扩展非线性薛定谔方程出发,采用分步傅里叶算法,数值模拟了连续光波的幅度受到正弦光扰动的调制后在光纤中演化分裂成超短脉冲串的过程,探讨了五阶非线性效应和正弦调制周期对脉冲串形成和演化特点以及相应频谱的影响。结果表明,与三阶非线性相比,正五阶非线性使形成超短脉冲串的最佳光纤长度缩短,形成的单个脉冲宽度更窄、峰值功率更高,负五阶非线性则相反。正弦调制周期将影响脉冲串的重复率和最佳光纤距离。随传输距离的增加,单个脉冲可能分裂成两个甚至三个分脉冲,在主脉冲之间还可能出现一定数量的峰值功率弱的次脉冲。就频谱特性而言,正(负)五阶非线性可增多(减小)光波频率成分、加宽(窄化)频谱;视主脉冲有无分裂以及次脉冲的存在与否,频谱的形状也会不同。

Starting from the extended nonlinear Schrodinger equation in which the quintic nonlinearity effect is included, the evolution and splitting process of continuous optical wave which is amplitude perturbed by the sine optical wave into ultra-short optical pulse trains in optical fibers is numerically simulated by adopting the split-step Fourier algorithm. The effects of the quintic nonlinearity and the modulation period of the sine optical wave on the generation and evolution of ultra-short optical pulse trains and the corresponding spectra are investigated. The results show that, in comparison with the case of cubic nonlinearity only, the positive quintic nonlinearity can shorten the optimal fiber length required to form the pulse trains and make every pulse shorter in width and higher in peak power, while the negative quintic nonlinearity takes the opposite. The sine modulation period may influence the pulse repetition rate and the optimal fiber length. With the increase of the propagation distance, every single pulse may split into two and even three sub-pulses. Moreover, some small pulses with weak peak powers may appear among the main pulses. In terms of the frequency spectra, the positive （negative） quintic nonlinearity can make the number of frequency components increase （decrease） and the spectral width wide （narrow）. Depending on whether the main pulses split and the small pulses exist or not, the spectra take on different shapes.