Enhancement of second harmonic generation in self-suspended lithium niobate photonic crystal cavities

Lithium niobate is a ferroelectric material widely used in nonlinear and integrated optics due to its transparency over a large wavelength range and its high optical nonlinearity. However, since the conversion efficiency of nonlinear processes is usually very weak, further enhancement mechanisms are required. Here we demonstrate the enhancement of second harmonic generation in self-suspended lithium niobate photonic crystal cavities. The structures, fabricated by ion-beam enhanced etching and focused ion beam milling, possess several resonances. The multi-modal properties of the cavities are theoretically and experimentally investigated. Second harmonic generation, measured with a low power continuous wave pump, undergoes an enhancement scaling as the square of the quality factor of the resonance.