On the limitations of the first-order nonlinear Schrödinger equation in slow-light photonic crystal structures

Abstract

We investigate the limitations of the first-order nonlinear Schrodinger equation for describing slow-light enhanced optical nonlinearities in photonic crystal structures. We do this by introducing the concept of generalized Bloch modes to describe light propagation in nonlinear photonic crystal structures. By considering how the nonlinear effects perturb the eigenproblem that describes such generalized Bloch modes, we derive a formalism that allows us to determine the impact of nonlinearities up to an arbitrary order. Based on our formalism, we derive expressions for the first- and second-order nonlinear terms experienced by a single generalized Bloch mode. We then theoretically demonstrate that the second-order terms can in silicon-based slow-light photonic crystal waveguides already become significant at optical powers as small as 100 mW. Additionally, we show that the significance of the second-order term is closely related with the structural group index dispersion or second-order dispersion parameter of the structures considered.