Fabrication, experimental investigation and computer modeling of gallium-arsenide nonlinear optical devices.

Abstract

Nonlinear-optical switching and logic devices based on GaAs nonlinear Fabry-Perot etalons have been investigated theoretically and experimentally. The theoretical modeling has been performed with the first realistic and easily computed theory of GaAs nonlinear optical properties near the band edge. Both steady-state and dynamic calculations have been performed for optical bistability with GaAs etalons. High-transmission operation is predicted for certain etalon detunings from the excitation wavelength. Various logic-gate functions have simulated with the model. An investigation of differential energy gain in transient, one-wavelength operation was performed. The conclusion is that useful differential gain is not achievable in transient, one-wavelength operation if the pulse width is less than about ten times the carrier lifetime in the material. Waveguide structures with single-mode transverse confinement were designed and optical bistability was predicted for long GaAs etalons similar to cleaved waveguides. GaAs nonlinear optical devices were fabricated in forms of interest for application to optical parallel processing and guided wave signal processing. The fabrication work included etalon arrays and waveguide devices fabricated by reactive ion etching. The photolithography and reactive ion etching processes used and developed are described. Preliminary work on ultra-small quantum-confinement structures is described. Optical experiments were performed on the devices fabricated. The etalon arrays demonstrated extremely fast relaxation times for GaAs etalon devices, and demonstrated the ability to control material parameters through the fabrication process, by increasing the surface recombination rate of charge carriers. Fast optical bistability at low powers was also demonstrated in the array devices. Strip-loaded waveguides with cleaved ends were operated as optical bistable devices with conclusive evidence that the mechanism was electronic in origin. Nonlinear phase shifts of greater than $2\pi$ were observed in some waveguides. Such large nonlinear phase shifts are of great interest for the development of other nonlinear-optical waveguide devices.