Design of Optomechanical Cavities and Waveguides on a Simultaneous Bandgap Phononic-Photonic Crystal Slab

TL;DR

This paper presents the design of 2D optomechanical crystals with simultaneous optical and mechanical bandgaps, enabling high-Q resonant cavities with strong optomechanical coupling for potential quantum applications.

Contribution

It introduces a novel design of optomechanical crystals with coexisting pseudo-bandgaps and demonstrates high-Q cavities with significant optomechanical coupling in silicon slabs.

Findings

Achieved optical and mechanical Q-factors > 10^7 in simulations

Designed cavities with optical resonance at 1.5 microns and mechanical at 9.5 GHz

Calculated a quantum conversion rate of 292 kHz for optomechanical interaction

Abstract

In this paper we study and design quasi-2D optomechanical crystals, waveguides, and resonant cavities formed from patterned slabs. Two-dimensional periodicity allows for in-plane pseudo-bandgaps in frequency where resonant optical and mechanical excitations localized to the slab are forbidden. By tailoring the unit cell geometry, we show that it is possible to have a slab crystal with simultaneous optical and mechanical pseudo-bandgaps, and for which optical waveguiding is not compromised. We then use these crystals to design optomechanical cavities in which strongly interacting, co-localized photonic-phononic resonances occur. A resonant cavity structure formed by perturbing a "linear defect" waveguide of optical and acoustic waves in a silicon optomechanical crystal slab is shown to support an optical resonance at wavelength 1.5 micron and a mechanical resonance of frequency 9.5 GHz. These resonances, due to the simultaneous pseudo-bandgap of the waveguide structure, are simulated to have optical and mechanical radiation-limited Q-factors greater than 10^7. The optomechanical coupling of the optical and acoustic resonances in this cavity due to radiation pressure is also studied, with a quantum conversion rate, corresponding to the scattering rate of a single cavity photon via a single cavity phonon, calculated to be 292 kHz.