Polarization-Independent Electro-optic Waveguide Switch Using Strained InGaAs/InP Quantum Wells

Abstract

Most current applications for electro-optic space-division switches call for polarization-independence as a top systems requirement. However, in both LiNbO3[l] and bulk semiconductor [2] devices polarization-independent switching has thus far been achieved only at the expense of greatly increased switching voltage. Moreover in these materials there is no means, other than substrate orientation, for adjusting the relative strength of TE and TM electro-optic coefficients. In this paper we demonstrate a novel approach to polarization independence: control of electro-optic coefficients via bandgap engineering. By design of layer thicknesses and composition in a quantum well heterostructure, we show that it is possible to use strain to adjust the ratio of refractive index changes in the TE and TM polarizations such that (ΔnTΕ)/(ΔnTΜ) ~1. At the same time, we make use of the same enhanced excitonic electro-optic effects found in unstrained quantum wells [3,4] to produce a polarization-independent 2×2 switch with voltage-length product 30 times smaller than in bulk semiconductors and 150 times smaller than in LiNbO3.