Bright Second Harmonic Emission from Photonic Crystal Vertical Cavity

This study presents photonic vertical cavities consisting of nonlinear materials embedded in photonic crystals (PhCs) for resonantly enhancing second harmonic generation (SHG). Previous attempts at SHG in such structures have been limited to efficiencies of 10−7 to 10−5, but a high SHG efficiency of 0.28% by constructing a vertical cavity with a lithium niobate membrane placed between two PhCs is demonstrated, which exhibits high‐quality resonances. The results open up new possibilities for compact laser frequency converters that can have a revolutionary impact on the fields of nonlinear optics and photonics. A strong second harmonic generation up to 0.28% is obtained from a photonic crystal vertical cavity embedded with lithium niobate thin film. This is a significant improvement compared with previous ones with a similar framework, which provides a promising platform to develop ultracompact efficient nonlinear light sources.