Highly coherent flat supercontinuum generation in highly nonlinear silica fiber pumped by 1.5μm femtosecond fiber laser

Abstract

Supercontinuum light sources with both highly flatness and highly coherence have unique application advantages in biological imaging, optical frequency comb, and optical coherence tomography. We demonstrate the generation of a highly coherent flat supercontinuum spectrum. In order to achieve broadband flat spectrum generation, we used a highly nonlinear fiber with a nominal dispersion of zero at 1550 nm and a dispersion slope of less than 0.025 ps/(nm2·km). Meanwhile a sub 100 fs fiber laser was used as the pump source in the experiment to achieve good coherence. When the pump power was 134 mW, the supercontinuum emission was characterized between 1197 nm and 2242 nm, showing the flat spectrum with 10 dB uniformity was obtained at the wavelength region of 1603–2242 nm and wide spectrum with a conversion efficiency over 85%. The coherence of the supercontinuum spectrum was 1 in the range of 1200–2242 nm by theoretically studying the coherence characteristics of the supercontinuum spectrum. In addition, the effect of pump laser duration on spectral flatness was demonstrated through experiments. Our experiment provides a feasible method for the generation of near-infrared flat highly coherence supercontinuum spectrum with all optical fibers structure.