Nonlinear photonic crystal fibres: pushing the zero-dispersion toward the visible
The strong waveguide dispersion in photonic crystal fibres provides unique opportunities for nonlinear optics with a zero-dispersion wavelength $λ_0$ far below the limit of ~1.3 micron set by the material dispersion of silica. By tuning the air-hole diameter d, the pitch Lambda, and the number of rings of air holes N, the strong waveguide dispersion can in principle be used to extend lambda_0 well into the visible, albeit to some extend at the cost of multimode operation. We study in detail the interplay of the zero-dispersion wavelength, the cut-off wavelength lambda_c, and the leakage loss in the parameter space spanned by d, Lambda, and N. As a particular result we identify values of d (~500 nm) and Lambda (~700 nm) which facilitate the shortest possible zero-dispersion wavelength (~700 nm) while the fibre is still single-mode for longer wavelengths.