Abstract

Nonlinear optics in fibres has for decades been carried out predominantly in step-index glass cores that support just one transverse mode, or if the core supports higher-order modes (HOMs), careful launch alignment is used to minimize their excitation in practice. In gas-filled hollow-core fibres, however, single-mode propagation ceases to be valid at high intensities, even under perfect launch conditions. This is because self-focusing can be understood as being caused by transfer of energy from the fundamental mode to HOMs through nonlinear mode coupling [1,2].

© 2017 IEEE