Matthew Mitchell

High-Q/V Monolithic Diamond Microdisks Fabricated with Quasi-isotropic Etching.

Optical microcavities enhance light-matter interactions and are essential for many experiments in solid state quantum optics, optomechanics, and nonlinear optics. Single crystal diamond microcavities are particularly sought after for applications involving diamond quantum emitters, such as nitrogen vacancy centers, and for experiments that benefit from diamonds excellent optical and mechanical properties. Light-matter coupling rates in experiments involving microcavities typically scale with Q/V, where Q and V are the microcavity quality-factor and mode-volume, respectively. Here we demonstrate that microdisk whispering gallery mode cavities with high Q/V can be fabricated directly from bulk single crystal diamond. By using a quasi-isotropic oxygen plasma to etch along diamond crystal planes and undercut passivated diamond structures, we create monolithic diamond microdisks. Fiber taper based measurements show that these devices support TE- and TM-like optical modes with Q > 1.1 × 10(5) and V < 11(λ/n) (3) at a wavelength of 1.5 μm.

Cavity optomechanics in gallium phosphide microdisks

We demonstrate gallium phosphide (GaP) microdisk optical cavities with intrinsic quality factors >2.8 × 105 and mode volumes <10(λ/n)3, and study their nonlinear and optomechanical properties. For optical intensities up to 8.0 × 104 intracavity photons, we observe optical loss in the microcavity to decrease with increasing intensity, indicating that saturable absorption sites are present in the GaP material, and that two-photon absorption is not significant. We observe optomechanical coupling between optical modes of the microdisk around 1.5 μm and several mechanical resonances, and measure an optical spring effect consistent with a theoretically predicted optomechanical coupling rate g0/2π∼30 kHz for the fundamental mechanical radial breathing mode at 488 MHz.

Efficient telecom to visible wavelength conversion in doubly resonant gallium phosphide microdisks

Resonant second harmonic generation between 1550 nm and 775 nm with normalized outside efficiency >3.8×10−4 mW−1 is demonstrated in a gallium phosphide microdisk supporting high-Q modes at visible ( Q∼104) and infrared ( Q∼105) wavelengths. The double resonance condition is satisfied for a specific pump power through intracavity photothermal temperature tuning using ∼360 μW of 1550 nm light input to a fiber taper and coupled to a microdisk resonance. Power dependent efficiency consistent with a simple model for thermal tuning of the double resonance condition is observed.

Monolithic single crystal diamond high-Q optical microcavities

Monolithic whispering gallery mode (WGM) optical microcavities are fabricated from bulk single crystal diamond (SCD) via a scalable process. Optical quality factors of Q_i ~ 1.15×10⁵ at 1.5 μm are demonstrated.

Design and experimental demonstration of optomechanical paddle nanocavities

We present the design, fabrication, and initial characterization of a paddle nanocavity consisting of a suspended sub-picogram nanomechanical resonator optomechanically coupled to a photonic crystal nanocavity. The optical and mechanical properties of the paddle nanocavity can be systematically designed and optimized, and the key characteristics including mechanical frequency can be easily tailored. Measurements under ambient conditions of a silicon paddle nanocavity demonstrate an optical mode with a quality factor Qo∼6000 near 1550 nm and optomechanical coupling to several mechanical resonances with frequencies ωm/2π∼ 12−64 MHz, effective masses meff∼350−650 fg, and mechanical quality factors Qm∼ 44−327. Paddle nanocavities are promising for optomechanical sensing and nonlinear optomechanics experiments.

Optomechanics in gallium phosphide microdisks

Gallium phosphide microdisk optical cavities with intrinsic quality factors Q_i ~ 2.8 × 10⁵ at 1.5 μm are demonstrated. No two-photon absorption is observed. Saturation of internal optical loss, and optomechanical coupling to radial breathing modes with g₀ ~ 30 kHz is observed.