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

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.