Dynamics of nonlinear optical properties in ${\mathrm{In}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As/InP quantum-well waveguides

We report the dynamics of the optical nonlinearity, measured by a weak probe propagating in single-mode ${\mathrm{In}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As/InP quantum-well waveguides, at wavelengths corresponding to the heavy-hole exciton resonance or longer. The experiments are conducted at moderate pump energies (ranging from 0.1 to a few pJ/pulse). We discovered a contribution from the weak longitudinal component of the waveguided TM mode to the dynamical behavior, and show that this dominates the absorption of TM-polarized light and the relevant optical nonlinearities at wavelengths close to the heavy-hole exciton resonance. Moreover, while at the heavy-hole exciton resonance we observe induced transmission, in the transparent region, we observe an induced-absorption behavior. We evaluate the strong impact on the optical response of waveguides of this behavior, whose origin is purely excitonic, as we show in the framework of a simple model. We further show that the diffusion of carriers out of the waveguiding region is negligible with respect to carrier recombination processes.