Double quantum well phase modulators using surface acoustic waves

Abstract

Electro-optic modulators using the interaction of surface acoustic waves (SAWs) with III-V semiconductor multiple quantum well structures have gained interests. A SAW induces potential field which provides the phase modulation. In order to improve the phase modulation, an AlGaAs/GaAs asymmetric double quantum well (DQW) optical phase modulator using SAWs is investigated theoretically. The optimization steps of the DQW structure are discussed. The optimized phase modulator structure is found to contain a five-period DQW active region. Analysis of the modulation characteristics show that by using the asymmetric DQW, the large change of the induced potential at the surface and thus large modification of the QW structure can be utilized. The modification of each QW structure is consistent, although this consistency is not always preserved in typical SAW devices. Consequently, the change of refractive index in each of the five DQWs is almost identical. Besides, the change of effective refractive index is 10 times larger here in comparison to a modulator with a five periods single QW as the active region and thus produces a larger phase modulation. In addition, a long wavelength and a low SAW power required here increase the size of the SAW transducer and simplify its fabrication.