Slot-mode-coupled optomechanical crystals

TL;DR

This paper introduces a flexible design for cavity optomechanical systems using separate nanobeams, achieving strong coupling and enabling applications like wide-band optical frequency conversion.

Contribution

It presents a novel approach to independently optimize optical and mechanical components in nanobeam resonators with high coupling strengths.

Findings

Achieved large zero-point optomechanical coupling g/2pi > 300 kHz in Si3N4.

Demonstrated high coupling g/2pi approx. 900 kHz in silicon at 1550 nm.

Enabled potential for wide-band optical frequency conversion.

Abstract

We present a design methodology and analysis of a cavity optomechanical system in which a localized GHz frequency mechanical mode of a nanobeam resonator is evanescently coupled to a high quality factor (Q>10^6) optical mode of a separate nanobeam optical cavity. Using separate nanobeams provides flexibility, enabling the independent design and optimization of the optics and mechanics of the system. In addition, the small gap (approx. 25 nm) between the two resonators gives rise to a slot mode effect that enables a large zero-point optomechanical coupling strength to be achieved, with g/2pi > 300 kHz in a Si3N4 system at 980 nm and g/2pi approx. 900 kHz in a Si system at 1550 nm. The fact that large coupling strengths to GHz mechanical oscillators can be achieved in SiN is important, as this material has a broad optical transparency window, which allows operation throughout the visible and near-infrared. As an application of this platform, we consider wide-band optical frequency conversion between 1300 nm and 980 nm, using two optical nanobeam cavities coupled on either side to the breathing mode of a mechanical nanobeam resonator.