Second-harmonic generation in aluminum nitride microrings with 2500%/W conversion efficiency

Photonic integrated circuits hold promise as miniaturized and scalable platforms for classical and quantum photonic information processing. Second-order nonlinearity (χ(2)) is the basis of many important applications such as second-harmonic generation, spontaneous parametric down-conversion, and optical parametric oscillation. Here, we present systematical investigation and optimization of the second-harmonic generation in a dual-resonant aluminum nitride microring resonator. By optimizing the quality factor, independently engineering the coupling conditions for dual-band operation, and perfectly fulfilling phase-match conditions through thermal tuning, we demonstrate a second-harmonic generation efficiency of 2500%  W−1 in the low-pump-power regime. To the best of our knowledge, this is a state-of-the-art value among all the integrated photonic platforms. We also study the high-power regime where the pump power depletion is non-negligible. A conversion efficiency of 12% is realized with 27 mW pump power. Our high-efficiency second-harmonic generator enables integrated frequency conversion and frequency locking between visible and infrared systems, and our approach can also apply to other photonic platforms.