Guided-wave measurements of real-excitation optical nonlinearities in a tensile strained InGaAs on InP quantum well at 1.5 μm

Abstract

Reported are measurements, in the 1.5 μm wavelength region, of the nonlinear refractive and absorptive changes, associated with real excitation processes, in a tensile-strained 6.7 nm thick In 0.47Ga 0.53As/InP single quantum well centred within a linear InGaAs/InP multiple quantum well waveguide Fabry-Pérot (PF) cavity. The refractive index changes were determined using two different pump/probe techniques: direct measurement of the refractive index changes in a FP cavity, and also via a Kramers-Kronig transformation of the absorption changes in the wavelength region of the bandgap resonance. Comparing these two measurements, reveals that there is a significant non-resonant contribution to the total refractive index changes in the SQW material, which is attributed to an enhanced free carrier absorption contribution due to carrier confinement in the two-dimensional quantum well. At wavelengths near the bandedge, index and absorption changes of Δ n= -0.12 and Δα=8300 cm -1, respectively, were observed, while Δ n=-0.07 was measured at a wavelength over 90 nm from the bandedge. These index changes are sufficient to allow the design of, polarisation independent, optical switches based on carrier induced refractive index changes such as bistable Fabry-Pérots, with predicted sub-mW switch powers.