Optical Bistability in a MQW Etalon with Optical Half-wave Periodicity

Abstract

Optical bistability (OB) in passive nonlinear etalons such as those containing multiple quantum wells (MQW) of GaAs/AlGaAs is a promising alternative to other bistable optical switching mechanisms such as those which occur in semiconductor lasers and laser amplifiers [1]. Although OB in passive nonlinear etalons is somewhat slower, it is much more easily extendable to one- and two-dimensional arrays of switches. To realize this advantage, it is necessary to minimize the switching thresholds and optical absorption (and hence the power dissipation) in the MQW etalon. Following an approach which has already proven successful in reducing thresholds and increasing power efficiencies of vertical-cavity surface-emitting semiconductor lasers (VCSELs) [2], here we consider a MQW structure with several quantum wells (or closely-spaced groups of quantum wells) spaced one-half wavelength apart in the resonant cavity, positioned so that they align optimally with the antinodes of the standing wave optical field in the etalon. We have analyzed the system numerically using a wave propagation model in a thin-film matrix formalism. The spacers are assumed to have constant indices, the unsaturated QW absorption α0 follows the semi-empirical description of Chemla et al. [3], and the excitonic features saturate according to the simple rule α(I) = α0/(1 + I/Isat). In contrast to the situation where optically-pumped lasing occurs, here the spacers are non-absorbing and the input optical beam(s) for holding and switching are tuned close to the heavy-hole excitonic absorption peak in the quantum wells. As in the VCSEL, significant excitation of the quantum wells occurs primarily along the cavity axis, reducing the switching threshold. This reduction, together with the low background absorption of the structure, should enable efficient arrays of bistable optical switches to be constructed.