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通过数值计算,对色散平坦渐减光纤(DFDF)产生平坦超连续谱(SC)进行了研究。结果表明,该光纤中抽运脉冲峰值功率对超连续谱的形成有着重要的影响,超连续谱的产生存在阈值功率,抽运脉冲峰值功率由阈值逐步增大,超连续谱随之愈宽,平坦度愈好,但增大到一定值时,超连续谱的平坦度会开始劣化,综合考虑各因素找到了产生平坦超连续谱的最佳功率;四阶和五阶群速度色散(GVD)是该种光纤产生平坦超连续谱的决定因素,三阶及五阶以上群速度色散的作用可以忽略;进一步研究发现,超连续谱频谱展宽的机理主要来自脉冲的自相位调制效应,自变陡、受激拉曼散射等高阶非线性效应对平坦超连续谱的产生没有显著影响,在计算的时候完全可以忽略。
Through the numerical calculation, a flattened supercontinuum (SC) is generated by the dispersion-flattened decreasing fiber (DFDF). The results show that the peak power of pumping pulse has an important influence on the formation of supercontinuum. The supercontinuum generation has threshold power, the peak power of pumping pulse increases gradually from the threshold, The flatness is better, but when it reaches a certain value, the flatness of supercontinuum will start to deteriorate. The best power to produce flat supercontinuum is found by considering all factors. The fourth and fifth order group velocity dispersion (GVD) Is the determinant of the flat supercontinuum produced by this kind of fiber. The effect of the third-order and the fifth-order group velocity dispersion can be ignored. The further study shows that the mechanism of spectrum broadening of the supercontinuum mainly comes from the pulse self-phase modulation effect, , Higher-order nonlinear effects such as stimulated Raman scattering have no significant effect on the generation of flat supercontinuum, which can be completely neglected in the calculation.