初始啁啾对双曲正割光脉冲线性传输特性的影响

Effect of initial frequency chirp on the linear propagation characteristics of the hyperbolic secant optical pulse

采用分步傅里叶方法数值研究了初始线性啁啾和非线性啁啾双曲正割光脉冲在单模光纤反常色散区的线性传输特性,并与啁啾高斯脉冲的线性传输特性作了比较.给出了双曲正割光脉冲频谱宽度和时间带宽积随初始线性啁啾变化的表达式.结果表明,双曲正割脉冲在线性啁啾|C|>0·1时随传输距离的增加逐渐演化成近高斯型,在0≤|C|≤0·1时最后将演化为近双曲正割脉冲.|C|越小,脉冲时域波形越趋近双曲正割曲线.负啁啾对脉冲时域展宽的影响比正啁啾要大得多.当|C|≥0·5时,初始啁啾对双曲正割光脉冲展宽的影响比对高斯脉冲的影响更大.非线性啁啾双曲正割光脉冲在线性传输过程中会出现时域波形分裂现象,比具有相同啁啾的高斯脉冲时域波形分裂严重.

The linear propagation characteristics of the hyperbolic secant optical pulse with initial linear and nonlinear frequency chirps are numerically studied in the anomalous-dispersion regime of a single mode fiber by use of the split-step Fourier method. It is found that the linear chirped hyperbolic secant pulse gradually evolves into near Gaussian pulse for ｜C｜ 〉 0.1, and evolves into near hyperbolic secant pulse for 0 ≤ ｜C｜ ≤ 0.1. The smaller ｜C｜ is, the more the waveform approaches to hyperbolic secant curve. The effect of the negative linear chirp on the pulse broadening is greater than that of the positive chirp. The effect of the initial linear chirp on broadening of hyperbolic secant pulse is greater than that of Gaussian pulse for ｜C｜ ≥ 0.5. The temporal waveform splitting of the hyperbolic secant pulse with nonlinear chirp is more obvious than that of Gaussian pulse during linear propagation. Furthermore, the expression of the time-bandwidth product of the pulse with the linear chirp is given.