Acousto-optic interactions in semicondutor multi-layer optical waveguides for device applications

• Main Author: Thompson, Cameron
• Published: University of Surrey 1996
• Subjects: 530.41; Solid-state physics
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336496

This thesis reports on work undertaken over the last three years on the modelling of the physical processes relevant to acousto-optic diffraction in multi-layered, single and multiple quantum well (QW) structures, and is mainly concerned with the AlGaAs/GaAs material system. The propagation of surface acoustic waves (SAWs) on top of a general multi-layer structure is modelled using a basis of orthonormal polynomials to represent the appropriate solutions. The guided optical mode profiles are then determined through Maxwell's equations and matching of optical fields and field gradients at layer interfaces. The acousto-optic diffraction efficiency as a function of the wavelength of the SAW is calculated from the framework of coupled mode theory and the effects of compositional variations to the structure are considered. The effect of the SAWs on the electron/hole energy eigenvalues and envelope functions in QW structures is then considered in more detail, using a simple static approximation for the SAW. The change in complex refractive index of the QW structures is then calculated using the results of a density matrix theory expressed within the context of a semi-classical approach. Results show that multi-layer structures have distinct advantages over single layer structures for acousto-optic applications in terms of the added control available over both the SAW induced field quantities and the guided optical mode profiles. In addition, the possibilities for constructing multiple quantum well (MQW) structures within the multi-layer structure will lead to enhanced changes in refractive index due to the presence of a SAW induced electric field. It is shown that these refractive index changes are significantly larger than those possible in bulk materials for the same acoustic powers. Also, the results indicate that the non-linearity of the SAW induced fields will, for high enough acoustic frequencies, produce different SAW induced electric fields within adjacent quantum wells of the MQW structure, an effect not suggested previously when such devices have been proposed.