Sub-wavelength grating cavity optomechanics

Abstract

Cavity optomechanics explores reciprocal interactions between light and mechanical vibrations, down to the quantum level. It constitutes a very promising research field on both fundamental and applied physics, in areas ranging from quantum coherent control over bulky mechanical objects to ultra-sensitive on-chip inertial sensors. In most optomechanical systems, the resonance frequency of an optical cavity is shifted due to the oscillations of a mechanical resonator, which is in turn put into motion through optical forces such as radiation pressure or optical gradient forces. This interaction is quantified by the said optomechanical vacuum coupling rate, that is a measurement of the interaction between a single photon and phonon. Increasing this factor is mandatory for both quantum and classical applications. In order to do so, low volume and high quality factors cavities and resonators are required. The optomechanical strength is also proportional to the intra-cavity power, and it is then advantageous to avoid any non-linear or thermal effect to insure the stability of the system. Here, we investigate the use of sub-wavelength grating (SWG) structures as a way to induce optomechanical coupling. This paper will present the design, realization, and characterization of various geometries fabricated on standard SOI wafers and working over the telecom C-band. We expect a strong optomechanical vacuum coupling rate, that we believe will open new perspectives towards highly sensitive and stable on-chip optomechanical systems, optical signal processing, or even quasi room temperature back-action cooling.