Cavity Optomechanical Bistability with an Ultrahigh Reflectivity Photonic Crystal Membrane

Photonic crystal (PhC) membranes patterned with sub-wavelength periods offer a unique combination of high reflectivity, low mass, and high mechanical quality factor. Using a PhC membrane as one mirror of a Fabry-Perot cavity, a finesse as high as $F=35000\left(500\right)$ is demonstrated, corresponding to a record high PhC reflectivity of $R=0.999835\left(6\right)$ and an optical quality factor of $Q_{\text{opt}}\approx {10}^9$ . The fundamental mechanical frequency is 426 kHz, more than twice the optical linewidth, placing it firmly in the resolved-sideband regime required for ground-state optical cooling. The mechanical quality factor in vacuum is $Q=1.1\left(1\right)\times {10}^6$ , allowing values of the single-photon cooperativity as high as $C_0=6.6\times {10}^{-3}$ . Optomechanical bistability is easily observed as hysteresis in the cavity transmission. As the input power is raised well beyond the bistability threshold, dynamical backaction induces strong mechanical oscillation above 1 MHz, even in the presence of air damping. This platform will facilitate advances in optomechanics, precision sensing, and applications of optomechanically-induced bistability.