TEMPERATURE DEPENDENCE OF NONLINEAR REFRACTION, AND NOVEL BISTABLE OPTICAL DEVICES IN INDIUM-ANTIMONIDE.

Abstract

This dissertation presents the results of experimental research on the nonlinear refraction in InSb and the experimental demonstration of two nonlinear etalon devices using InSb as the active material. The first portion of the dissertation considers the Dynamic Burstein-Moss Shift model for nonlinearities in narrow-gap semiconductors. The physics and the equations are reviewed, and limitations in describing intensity dependent refraction in a semiconductor are considered. These limitations arise from the nonlinear dependence of charge carrier density upon irradiance. The second portion of the dissertation presents experimental measurements made on the nonlinear refraction of InSb at temperatures between 80 K and 182 K, for wavelengths from 5.75 μm to 6.10 μm, where the photon energy lay in the band tail below 100 cm⁻¹. Measurements of the linear absorption were first made with an infrared spectrometer for temperatures from 80 K to 300 K. The nonlinearity was measured by analyzing the transmission through InSb etalons. Nonlinear transmission curves were digitized and stored with an IBM PC-XT, then a curve fit was performed using the nonlinear refractive index as a fiting parameter. Observations are reported of increasing absorption, due in part to a thermal shift of the absorption edge. The second portion of the work presents the theory and demonstration of a bistable etalon using an edge-injected control beam. Plane-wave nonlinear etalon theory is used to describe the operation of such a device, illustrating the way in which switching and logic gate operation can be obtained. Two devices based on this concept are demonstrated: the 3-port device using a single control beam, and the 2SON gate using two control beams to perform two-input logic operation. The extension of the 2SON gate to an array of pixels, and some considerations for optimizing array performance, are considered. Two appendices follow the body of the dissertation, the first describing the preparation of the InSb etalon samples, and the second detailing several procedures for maintenance and operation of the CO laser used.