Abstract

Recent theoretical studies¹,² and experimental measurements³,⁴,⁵ have shown that there is a large inherent anisotropy in the absorption coefficient of excitons in biaxially strained quantum wells (QWs) grown on (110) surfaces. Due to the symmetry properties of the excitonic wavefunctions, there is no such anisotropy in the absorption spectra of unstrained or biaxially strained QWs grown on (100) or (111) surfaces. Such an anisotropy in the absorption coefficient can be exploited to construct optical switches or modulators. For example, a contrast ratio of 330:1 between on and off states has been achieved in uniaxially strained [100]-oriented QW structures using 100 wells.⁶ In this work, we present the first measurements of optically-induced and intrinsic anisotropies in the nonlinear absorption of a biaxially strained, [110]-oriented MQW structure using picosecond pump-probe and differential transmission spectroscopy. We also demonstrate how the polarization rotation associated with these anisotropies can be used to construct an all optical on/off switch or modulator with a contrast ratio of 25:1 using only 50 wells.

© 1995 Optical Society of America