GaAs photonic crystal cavity with ultra-high Q: microwatt nonlinearity at 1.55 $\mu$m

We have realized and measured a GaAs nanocavity in a slab photonic crystal based on the design by Kuramochi et al. [Appl. Phys.Lett., $\mathbf{\text{88}}$, 041112, (2006)]. We measure a quality factor Q=700,000, which proves that ultra-high Q nanocavities are also feasible in GaAs. We show that, due to larger two-photon absorption (TPA) in GaAs, nonlinearities appear at the microwatt-level and will be more functional in gallium arsenide than in silicon nanocavities.