Polarization Independent Optical Modulation with Tensile-Strained GaAs-InAIAs Quantum Wells grown on GaAs Substrate

Abstract

Large field-induced optical absorption and refractive index variations through the quantum confined Stark effect in quantum well structures have prompted the development of many high performance compact optical modulating devices1). However, several shortcomings are present and one of them is a strong polarization dependent characteristic in lattice-matched systems2). This is due to the fact that the dipole moments of electron-heavy/light hole transitions show a strong polarization dependence, such that while TE mode light, with the electric vector parallel to the quantum well layers, interacts with both heavy and light hole transitions, only electron-light hole transitions are involved in the TM mode polarization, where the electric vector is perpendicular to the quantum well layers3). Moreover, in an unstrained quantum well, the valence bands for the heavy and light holes are degenerate and hence the electron-heavy hole transition always lead the electron-light hole transition at the absorption edge due to the heavy hole’s larger effective mass. As a result, there exists a large difference in the optical absorption and refractive index variation at the absorption edge between the TE and TM mode polarizations.