高相干度超连续谱产生的理论研究

Theoretical research on the generation of coherent supercontinuum

超连续谱的相干性直接影响到很多光学测量器件的分辨率及准确性,如何获得高相干度的超连续谱是当前非线性光学领域的研究热点之一.本文首先分析超连续谱产生的机理,认为调制不稳现象是降低超连续谱相干性的重要因素.因此抑制调制不稳定性,利用其他非线性效应(如自相位调制)是得到高相干性超连续谱的有效方法.最后设计了一种全波段正常色散光子晶体光纤,仿真结果表明,在脉宽400 fs无啁啾高斯脉冲抽运,50 cm长该光子晶体光纤的条件下,产生的超连续谱具有在相对功率大于-80 dB的全波段高度相干的特性.

The degree of coherence of the supercontinuum（SC） directly determine the resolution and the precision in many optical apparatus, so how to achieve highly coherent SC is one of the focuses in nonlinear optics. It is shown that modulation instability （MI） is the key element that influences the coherence of SC. Therefore an effective way of achieving coherent SC is to avoid MI and to use other nonlinear effects such as self-phase modulation （SPM）. We design a kind of photonic crystal fiber （PCF） which has an all-normal group velocity dispersion （GVD） profile. After numerical investigation on the generation of SC in the PCF we obtain the degrees of the SC in different lengths. Results indicate that for the generated SC by pumping 50 cm of this PCF with TFWHM = 400 fs unchirped pulse Gaussian pulse can realize high coherence in the entire broadening area on condition that relative power is larger than -80 dB.