Thermal index changes by optical absorption in group III-V semiconductor waveguides

Large fast-relaxing intensity-dependent refractive index changes would make certain all-optical signal processing devices in waveguides feasible. In III-V compound materials, light-induced index changes can arise from any of several physical mechanisms which have different strengths and relaxation times. Index changes from 1.06-μm pulsed and CW Nd: YAG laser excitation were measured in single-mode low-loss InP and GaAs waveguide Fabry-Perot structures. The dominant effect was found to be due to heating of the waveguide volume which accompanies an extremely small amount of free-carrier absorption.