Strong optomechanical coupling in a slotted photonic crystal nanobeam cavity with an ultrahigh quality factor-to-mode volume ratio.

Katharina Schneider,Paul Seidler

doi:10.1364/oe.24.013850

Abstract

We describe the design, fabrication, and characterization of a one-dimensional silicon photonic crystal cavity in which a central slot is used to enhance the overlap between highly localized optical and mechanical modes. The optical mode has an extremely small mode volume of 0.017(λvac / n)3, and an optomechanical vacuum coupling rate of 310 kHz is measured for a mechanical mode at 2.69 GHz. With optical quality factors up to 1.2 × 105, fabricated devices are in the resolved-sideband regime. The electric field has its maximum at the slot wall and couples to the in-plane breathing motion of the slot. The optomechanical coupling is thus dominated by the moving-boundary effect, which we simulate to be six times greater than the photoelastic effect, in contrast to most structures, where the photoelastic effect is often the primary coupling mechanism.

Highlights

Sophisticated fabrication methods have led in recent years to the ability to make ever-smaller optomechanical systems [1]
We have determined the optomechanical vacuum coupling rate g0 for the slotted photonic crystal cavities to be greater than 300 kHz using two independent methods
The Optomechanically induced absorption (OMIA) and calibration tone techniques yield results, which are consistent within the range of uncertainty of the measurements and generally in agreement with the simulated value of g0⁄2π = 342 kHz

Summary

Introduction

Sophisticated fabrication methods have led in recent years to the ability to make ever-smaller optomechanical systems [1]. Interaction of small mechanical resonators with a strongly confined electromagnetic field enables light modulation at frequencies up to several gigahertz. Such high frequencies are required for applications in communication [2], radio astronomy [3] or the transduction of superconducting qubits [4,5]. An approach has been presented, where propagating acoustic waves with frequencies up to 12 GHz exhibit optomechanical coupling with a photonic cavity [17]

Methods

Results

Conclusion