Efficient telecom to visible wavelength conversion in doubly resonant GaP microdisks

Resonant second harmonic generation between 1550 nm and 775 nm with outside efficiency $>4.4\times {10}^{-4}{\text{mW}}^{-1}$ is demonstrated in a gallium phosphide microdisk cavity supporting high-$Q$ modes at visible ($Q\sim {10}^4$) and infrared ($Q\sim {10}^5$) wavelengths. The double resonance condition was satisfied through intracavity photothermal temperature tuning using $\sim 360,\mu$W of 1550 nm light input to a fiber taper and resonantly coupled to the microdisk. Above this pump power efficiency was observed to decrease. The observed behavior is consistent with a simple model for thermal tuning of the double resonance condition.