Whispering gallery optical parametric oscillators for the mid-infrared spectral range

The tunability of cw optical parametric oscillators can be extended in the mid-infrared spectral range by using whispering gallery resonators (WGRs) made of non-oxide crystals. We demonstrate the fabrication of WGRs from silver gallium selenide, cadmium silicon phosphide and orientation-patterned gallium phosphide with quality factors above 106. The resonators made of the first two provide optical parametric oscillation in the mid-infrared pumped by a compact laser diode at 1.57 mm wavelength. The wavelength tunability of the device based on silver gallium selenide provides a tuning range beyond 8 mm wavelength. These achievements are considered as the first steps of cw optical parametric oscillators into this important spectral region.