Optomechanics with one-dimensional gallium phosphide photonic crystal cavities

Abstract

Gallium phosphide offers an attractive combination of a high refractive index ( > for vacuum wavelengths up to 4 µm) and a wide electronic bandgap (2.26 eV), enabling optical cavities with small mode volumes and low twophoton absorption at telecommunication wavelengths. Heating due to strongly confined light fields is therefore greatly reduced. Here, we investigate the benefits of these properties for cavity optomechanics. Utilizing a recently developed fabrication scheme based on direct wafer bonding, we realize integrated one-dimensional photonic crystal cavities made of gallium phosphide with optical quality factors as high as 1.1 × 10 5 . We optimize their design to couple the optical eigenmode at ~200 THz via radiation pressure to a co-localized mechanical mode with a frequency of 3 GHz, yielding sideband-resolved devices. The high vacuum optomechanical coupling rate ( = × kHz) permits amplification of the mechanical mode into the so-called mechanical lasing regime with input power as low as ~20 μW. The observation of mechanical lasing implies a multiphoton cooperativity of C > 1, an important threshold for the realization of quantum state transfer protocols. Because of the reduced thermo-optic resonance shift, optomechanically induced transparency can be detected at room temperature in addition to the normally observed optomechanically induced absorption.

Gallium Phosphide as a Piezoelectric Platform for Quantum Optomechanics

“…Owing to the wide electronic bandgap and piezoelectric properties of GaP the successful operation of our device in this parameter regime opens the door for novel quantum experiments as well as the potential for using such devices for microwave-to-optics conversion. Strong optical χ (2) and χ (3) non-linear coefficients [19,20] and the ability to integrate GaP with current silicon technologies [12] and technologies. Our device consists of an optomechanical crystal evanescently coupled to an optical waveguide, as shown in Fig.…”

Observation of phonon trapping in the continuum with topological charges

“…Based on these results and the scaling rule of Eq. (2), we expect mechanical BICs with Q ≥ 10 7 can be realized in millimeter-scale PnCs with improved fabrication and material quality, such as using single crystalline silicon 30 or epitaxially grown materials [31][32][33] . The mechanical quality factor can also be further improved using the technique of topological charge merging to suppress scattering losses 19 .…”

Microwave-to-Optical Transduction Using a Mechanical Supermode for Coupling Piezoelectric and Optomechanical Resonators

“…In GaAs, heating due to the optical field is also an issue, restricting n phot , but the significantly larger g 0 means that appreciable C OM can more readily be achieved, particularly considered its squared dependence on g 0 . Moreover, geometries that allow for better thermal dissipation such as two-dimensional photonic crystals [84] or higher bandgap materials such as gallium phosphide [85] might mitigate the heating problem. On the other hand, the electrical and mechanical resonance enhancement enables C EM > 1 even with low k 2 .…”