Surface Acoustic Wave Induced Birefringence in In0.21Ga0.79As-GaAs Multiple Quantum Wells for Optical Modulation ≈1000 nm under Normal Incidence

Abstract

This paper presents observation of quantum Confined Stark effect induced by the surface acoustic waves (SAW) propagating in multiple quantum well (MQW) layers. It also presents the evidence for the first time of SAW induced birefringence under surface normal mode operation in MQWs. MQW layers usually do not exhibit significant birefringence when the light is normally incident. The launching of surface acoustic waves in In0.21Ga0.79As-GaAs MQW layers produces significantly different strain along the direction of propagation (y) as compared to the lateral direction (x), and this in turn results in differential absorption coefficient Δα (= αx - αy) and birefringence (Δnbir). The enhanced birefringence due to excitonic effect depends on the magnitude of RF power exciting the SAW transducer. An interdigitated transducer operating at 119 MHz with an aperture (w) to wavelength (Λ) ratio of 25 was used to launch the surface acoustic waves. Typical values of Δn are in the range of 0.01-0.02 for polarized light at ≈1.01 μm wavelength when the RF power is varied between 0.5-1.2 Watt. Computations of Δn are in agreement with experimental data. The SAW propagation also induces a perpendicular component Ez of electric field which results in conventional Stark effect producing absorption and index changes in MQWs that vary as a function of SAW power.