Measurement of the Electro-Optic Coefficient for Gallium Arsenide and Cadmium Telluride Modulator Rods

Abstract

ABSTRACTCadmium telluride and gallium arsenide remain the only viable materials for electro-optic modulator applications in the 10 μm wavelength range. Primarily the modulators are used as Q switches, cavity dumpers, amplitude modulators, and frequency modulators for infrared applications, such as laser radar and guidance systems. Designers of optical and electrical systems incorporating these modulators require accurate values for the electro-optic coefficient, r41.A test arrangement, based on a modified version of the cross polarizer technique, was used to measure the electro-optic coefficients for cadmium telluride and gallium arsenide single crystals. The first part of this paper describes our test arrangement for measuring the r41 coefficient. The second part of the paper will discuss the test results. The r41 coefficient for CdTe was found to be 5.5 × 10−12 m/V in the unclamped region and 4.1 × 10−12 m/V in the clamped reion. Values for the r41 coefficient in GaAs were found to be 1.3 × 10−12 m/V and 1.9 × 10−12 m/V in the unclamped and clamped regions, respectively. All measurements were at 10.6 μm. Also investigated are the piezoelectric resonance values for both materials and the effect the resonances have on the measured r41 coefficient in the clamped and unclamped regions.