CW Supercontinuum Generation in Photonic Crystal Fibres with Two Zero-Dispersion Wavelengths

Abstract

This study is devoted to supercontinuum generation in photonic crystal fibres using a continuous‐wave pumping scheme. We demonstrate that the spectral broadening of a continuous‐wave laser can be more efficiently achieved in a short piece of photonic crystal fibre with two zero‐dispersion wavelengths rather than in a fibre with a single one. This is due to efficient self‐frequency shift of the solitons initially created by modulation instability, because their peak power is kept high in fibres with two zero‐dispersion wavelengths. We then focus on the dynamics of the supercontinuum evolution under continuous‐wave pumping in a series of different photonic crystal fibres exhibiting two zero‐dispersion wavelengths. Control of the supercontinuum spectral extension is demonstrated as well as the changing dynamics as the zero‐dispersion wavelengths are brought closer together. For closest zero‐dispersion wavelengths, the spectral broadening is mainly due to parametric processes. For increasing spectral separation between the two zero‐dispersion wavelengths, the soliton self‐frequency shift due to intrapulse Raman scattering becomes more important. The soliton self‐frequency shift is canceled just before the second zero‐dispersion wavelength and some energy is transferred to a phase‐matched dispersive wave. We also pay particular attention to the effect of the water absorption band located around 1380 nm.