Coherent mid-infrared broadband continuum generation in non-uniform ZBLAN fiber taper

Abstract

A simple method is described for efficient, asymmetric and coherent continuum generation in the mid-infrared region based on the dynamics of a stabilized soliton in the vicinity of a second dispersion zero of a nonlinear fiber. The mechanism involves nonlinear soliton compression, Raman self-frequency shift and resonant emission of a dispersive (Cherenkov) wave in a non-uniformly tapered ZBLAN fluoride fiber pumped by a low-power compact femtosecond laser at 1.55 microm. The fiber taper features a continuous shift of the second zero dispersion wavelength, which facilitates the progressive shift in the wavelength of the dispersive wave generated by the stabilized soliton. Numerical solution of the generalized nonlinear Schrödinger equation, which accounts for the exact wave-length dependence of dispersion and nonlinear coefficients, shows robust generation of near-octave continuum spanning 1.5-3 microm wavelength range.