Asymmetric Quantum Wells for Second-Order Optical Nonlinearities

Abstract

Second-order optical nonlinearities are increasingly important for a number of applications including second-harmonic generation, optical rectification, and self-phase modulation using the second-order cascade effect. Implementation of any second-order nonlinearity generally requires phase-matching, which may be quite difficult to achieve in a solid-state medium lacking linear birefringence. In such cases phase-matching must be engineered into the material in some way, either during the material growth stage, or post-growth in the form of a quasi-phase-matching grating. Semiconductor materials such as gallium arsenide are attractive for nonlinear optical applications because they have a fundamental bandgap in the region of the optical part of the electromagnetic spectrum, so that near-resonant excitation can be achieved, resulting in high nonlinear responses; in addition semiconductors support mature fabrication technologies which can be used to make devices in waveguide form, which can in principle be integrated with laser sources on the same substrate.