A study of non-linear optical properties of GaAs/AlₓGa₁₋ₓAs quantum well waveguide devices

Includes bibliographical references.An experimental study of the optical properties of GaAs/AlₓGa₁₋ₓAs slab and laterally confining waveguides is presented. The structures were grown by molecular beam epitaxy which allowed the incorporation of quantum wells in the devices. The absorption properties of quantum well slab waveguides were experimentally determined. Light polarized parallel to the layers was found to have two strong, sharp absorption peaks which are identified as transitions of electrons from the quantized energy levels in the valance band wells to the conduction band well. The peak positions compare well with a simple one-dimensional quantum well model based on the effective mass approximation. Absorption spectra for light polarized perpendicular to the growth layers are found to have only one absorption peak. When an electric field is applied perpendicular to the quantum well, the absorption peaks are found to shift to lower energy. This is known as the quantum confined Stark effect, which can be used to make voltage-dependent intensity modulators. The positions of the absorption peaks were found to shift quadratically with electric field. Photocurrent spectra were also made. It was found that a single 65Ȧ quantum well waveguide had a ABSTRACT responsivity of at best 0.33A/W. Using a multiple quantum well slab waveguide device, an optical absorption modulator was constructed that had a modulation depth of 30:1. This device was then used to transmit data between two personal computers. Initial measurements have been made on laterally confining waveguides. The number of laterally confined waveguide modes was studied as a function of ridge width and etch depth and then compared to a model based on the effective index method with favorable results.M.S. (Master of Science