采用分步傅里叶方法,对飞秒脉冲在高非线性光纤中超连续谱(SC)的形成过程进行了研究,分析了脉冲峰值功率,脉冲宽度及初始频率啁啾对超连续谱特性的影响.结果表明,脉冲峰值功率,脉冲宽度以及初始啁瞅对超连续谱的形成有着极其重要的影响;当脉冲峰值功率逐渐增大,超连续谱随之愈宽(-20 dB处谱宽从170 nm展宽到400 nm以上),平坦度愈好.与之相反,脉冲宽度逐渐增大,超连续谱展宽范围减小,其平坦度也逐渐劣化;初始负啁啾有利于脉冲SC谱的展宽而正啁啾使脉冲SC谱的展宽受到一定抑制.进一步研究表明,适当的峰值功率超短啁啾脉冲在高非线性光纤传输时,得到没有泵浦成份残余的超宽且平坦超连续谱.
The supercontinuum generation in high nonlinear fiber with the normal dispersion is investigated using the split-step Fourier method. The effect of the peak power of pump pulse, pulse width and the frequency chirp on characteristics of supercontinuum spectrum is analyzed. The results show that the pulse width, peak power and initial chirp of the pump pulse are very important to flat wideband supercontinuum generation. With the increase of the peak power, the spectral width becomes wider (170 nm to more than 400 nm at -20 dB) and the flatness of supercontinuum becomes better. By contrast, the spectral width becomes narrower and the flatness of supercontinuum becomes worser when the pulse width increases gradually. The negative initial chirp is profitable for spectrum broadening, but the positive chirp has certain impact on spectrum broadening. It is further investigated that a broadband and fiat supercontinuum without residual pump is generated from such a high nonlinear fiber pumped at the normal dispersion region.
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