Highly tunable low-threshold optical parametric oscillation in radially poled whispering gallery resonators

Whispering-gallery resonators (WGRs), based on total internal reflection, possess high quality factors in a broad spectral range. Thus, nonlinear-optical processes in such cavities are ideally suited for the generation of broadband or tunable electromagnetic radiation. Experimentally and theoretically, we investigate the tunability of optical parametric oscillation in a radially structured WGR made of lithium niobate. With a 1.04 µm pump wave, the signal and idler waves are tuned from 1.78 to 2.5 µm including the point of degeneracy by varying the temperature between 20 and 62 °C. Aweak off centering of the radial domain structure extends considerably the tuning capabilities. The oscillation threshold lies in themW-power range