Efficient telecom to visible wavelength conversion in doubly resonant GaP microdisks

Resonant second harmonic generation between 1550 nm and 775 nm with outside efficiency \(> 4.4\times10^{-4}\, \text{mW}^{-1}\) 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.