探索利用大模场光子晶体光纤产生大功率、高光束质量的超连续谱。采用分步傅里叶方法求解广义非线性薛定谔方程(GNLSE), 模拟了光脉冲在大模场光子晶体光纤中非线性传输和超连续谱的产生过程。着重分析了光子晶体光纤长度和抽运脉冲的峰值功率、啁啾等对超连续谱产生的影响, 讨论了大模场光子晶体光纤中光谱的非线性展宽机制。发现可将超连续谱产生过程分为初始展宽、剧烈展宽和饱和展宽三个阶段。合理选择光纤长度, 使产生的超连续谱处于剧烈展宽阶段时输出, 既能够得到较宽的光谱, 又能够保证较高的效率。抽运峰值功率对超连续谱的产生有重要影响, 当输入功率较小时, 脉冲的频谱成对称展宽, 仅有自相位调制(SPM)效应起作用, 其他高阶效应的影响都很弱。随着脉冲功率的增加, 频谱短波方向变化较小, 光谱向长波方向展宽。同时, 脉冲时域出现振荡调制, 振荡的起因与光波分裂现象有关。抽运光初始啁啾对超连续谱的产生也有重要影响。当啁啾为正时, 啁啾量的大小对产生超连续谱的影响较小, 蓝移方向基本没有影响, 而红移部分能量随着啁啾量的增大向长波方向转移, 超连续谱总的宽度变化较小; 当啁啾为负且满足一定条件时, 其中的非线性作用得到增强, 有利于光谱展宽。

Large-mode-area photonic crystal fiber is used to generate high power, high beam quality supercontinuum. Propagation and supercontinuum generation process of laser pulse in large-mode-area (LMA) photonic crystal fiber (PCF) is simulated by solving the general nonlinear Schrdinger equation (GNLSE) using the split-step Fourier method. Effects of the pump pulse parameters (peak power and chirp) and the length of photonic crystal fiber used on supercontinuum generation are particularly estimated. Nonlinear spectral broadening mechanism of laser pulse in large-mode-area photonic crystal fiber is discussed. The results show that the process of supercontinuum generation can be divided into three stages: initial broadening, dramatic broadening and saturation broadening. The spectrum width and efficiency can be achieved by the optimized length of LMA PCF to insure output of the generated supercontinuum at the dramatic broadening stage. The pump peak power and chirp have important impact on supercontinuum generation. When a small peak power pump is input, the spectrum broadens symmetrically. When the pump peak power increases, it brings little changes with the shorter wavelength component but broader of the longer wavelength component. The time-domain shape of the pulse exhibits concussion modulation as the effect of pulse breakup. When the pump chirp is positive, little influence is shown, except a shift of longer wavelength power by increasing the chirp. But the full width of the supercontinuum has little changes. While the pump chirp is negative and satisfy certain condition, the nonlinear is enhanced to facilitate the supercontinuum generation.