Study of electro-optic effect in asymmetrically ramped AlInGaAs multiple quantum well structures

We investigate the electro-optic properties of two oppositely ramped asymmetric quantum well structures in the AlInGaAs material system. The grading of the bandgap in the quantum wells has been achieved by changing the ratio of Al to Ga in the quaternary alloy during the epitaxial growth. The surface normal photo-response and the Fabry-Perot fringe shift in straight waveguides are compared for both structures as a function of applied voltage at 1550 nm for TE-polarized light. The measurements show a change in the refractive index due to a red shift of the excitonic resonances due to the quantum-confined Stark effect. The 10 quantum well structure with a ramp up of the bandgap in the growth direction leads to the figure of merit of the voltage for a π phase shift, V_π by length, L, V_π× L, of 6 as compared to 7 V · mm in the structure with a ramp in opposite direction. Further investigations show that the reduction in V_π is due to increased absorption at high reverse bias which induces a non-linear phase change.