Slot-Mode Optomechanical Crystals: A Versatile Platform for Multimode Optomechanics

TL;DR

This paper introduces slot-mode optomechanical crystals with nanobeam resonators separated by a narrow slot, enabling high-quality optical and mechanical mode coupling, and demonstrates their versatility for multimode optomechanical systems.

Contribution

The work presents a new slot-mode design in Si3N4 platforms, achieving enhanced optomechanical coupling and multimode configurations with flexible design options.

Findings

Achieved slot widths down to 24 nm using high tensile stress.

Observed optomechanical self-oscillations at multiple frequencies.

Developed multimode systems with coupled optical and mechanical modes.

Abstract

We demonstrate slot-mode optomechanical crystals, a class of device in which photonic and phononic crystal nanobeam resonators separated by a narrow slot are coupled through optomechanical interactions. In these geometries, nanobeam pairs are patterned so that a mechanical breathing mode is confined at the center of one beam, and a high quality factor (Qo>10^5) optical mode is confined in the slot between the beams. Here, we produce slot-mode devices in a stoichiometric Si3N4 platform, with optical modes in the 980 nm band, coupled to breathing mechanical modes at 3.4 GHz, 1.8 GHz, and 400 MHz. We exploit the high Si3N4 tensile stress to achieve slot widths down to 24 nm, which leads to enhanced optomechanical coupling, sufficient for the observation of optomechanical self-oscillations at all studied frequencies. We utilize the slot mode concept to develop multimode optomechanical systems with triple-beam geometries, in which two optical modes are coupled to a single mechanical mode, and two mechanical modes are coupled to a single optical mode. This concept allows great flexibility in the design of multimode chip-scale optomechanical systems with large optomechanical coupling at a wide range of mechanical frequencies.