Zhaoyang WANG^*, Hiroyasu SONE¹, Yasuhide TSUJI², and Masaaki IMAI

Department of Electrical and Electronic Engineering, Muroran Institute of Technology, 27-1 Mizumoto-cho, Muroran, Hokkaido 050-8585, Japan
¹Department of Computer Science, Kitami Institute of Technology, 165 Koen-cho, Kitami, Hokkaido 090-8507, Japan
²Department of Electrical and Electronic Engineering, Kitami Institute of Technology, 165 Koen-cho, Kitami, Hokkaido 090-8507, Japan

(Received November 29, 2006; Accepted February 6, 2007)

Supercontinuum (SC) spectrum generation in a biconical tapered fiber is theoretically studied by taking into account the varying dispersion characteristics. Our numerical model is based on the extended nonlinear Schrödinger equation including higher-order dispersive terms, self-steepening, and Raman nonlinearity terms. We demonstrate how the group velocity dispersion and effective core area vary in the input taper region, which is significant for the broadening of the SC spectrum in the subsequent waist region. The evolutions of the unwrapped spectral phase and the spectral intensity along the transition and waist regions of the tapered fiber are also investigated in detail. It is found that the output taper has a considerable effect on the nonlinear variation of the spectral phase, e.g., 6.5 rad/THz in the infrared range of 280–300 THz (i.e., 1071–1000 nm in wavelength) and 21 rad/THz in the visible range of 600–620 THz (i.e., 500–484 nm).

Key words: nonlinear fiber optics, supercontinuum generation, tapered fiber, femtosecond pulse, spectral phase and intensity, finite element method, split-step Fourier method

^*E-mail address: s1461016@mmm.muroran-it.ac.jp