High-Q silicon photonic crystal cavity for enhanced optical nonlinearities

We fabricate and experimentally characterize a $H0$ photonic crystal slab nanocavity with a design optimized for maximal quality factor, $Q = 1.7$ million. The cavity, fabricated from a silicon slab, has a resonant mode at $\lambda = 1.59 \mathrm{\mu m}$ and a measured $Q$-factor of $400,000$. It displays nonlinear effects, including high-contrast optical bistability, at a threshold power among the lowest ever reported for a silicon device. With a theoretical modal volume as small as $V = 0.34(\lambda/n)^3$, this cavity ranks among those with the highest $Q/V$ ratios ever demonstrated, while having a small footprint suited for integration in photonic circuits.