Improved material quality and OPO performance in orientation-patterned GaAs

摘要

The U.S. Air Force is developing orientation-patterned GaAs (OPGaAs) for nonlinear frequency conversion in the 2-5 μm and 8-12 μm regions. We report recent progress in OPO device performance which reflects continued improvement in material quality. Seven new OPGaAs samples, representing four distinct growth regimes, were evaluated in terms of threshold, slope efficiency, and output spectral content using a Q-switched Tm,Ho:YLF laser operating at 2 μm as the pump source. The samples were identical in base template, grating period, length, and AR coating, permitting direct comparison of results to identify favorable growth conditions. As anticipated, performance varied significantly among the sample set, with slope efficiencies from 12% to 35% and thresholds from 9 μJ to 40 μJ. Less anticipated was the low level of uniformity across each sample and between samples grown in the same growth run. Significant variations in slope efficiency and threshold were not uncommon. Still, most of the samples performed manifestly better than previously grown material, indicating an overall improvement in OPGaAs quality. Research continues on understanding growth processes, optical loss mechanisms, and how these translate into device performance.