Index of refraction of GaAs/AlxGa1−xAs multiple quantum wells with an applied electric field using the grating coupling technique

Abstract

The grating coupling technique is used to determine the index of refraction under an applied electric field. Light is coupled into a GaAs/AlxGa1−xAs multiple quantum well slab waveguide using a conducting grating which has been etched onto the waveguide. The coupling angle is measured with high precision and the effective index of the mode is calculated with the mode coupling equation. The technique is very sensitive, allowing the index to be determined to within ±2×10−5. The strong absorption of the quantum wells prevents measurements at photon energies near the quantum well absorption peaks. This is not a serious limitation as the measurable range is the most technologically important region for electro-optic devices which utilize refractive index changes. The linear and quadratic electro-optic coefficients, evaluated from the change in index with electric field, agree well with previous measurements by other methods.