Dispersive coupling and optimization of femtogram L3-nanobeam optomechanical cavities

TL;DR

This paper designs a femtogram L3-nanobeam photonic crystal cavity with high optical and mechanical quality factors, demonstrating strong dispersive coupling suitable for ultrasensitive sensing applications.

Contribution

The paper introduces a novel femtogram L3-nanobeam cavity with optimized optical and mechanical properties, achieving high vacuum optomechanical coupling rates and evaluating mechanical Q limits.

Findings

Optical quality factor up to 52,000 achieved.

Mechanical frequencies exceed 600 MHz.

Vacuum optomechanical coupling rate g0/2π > 200 kHz.

Abstract

We present the design of a femtogram L3-nanobeam photonic crystal cavity for optomechanical studies. Two symmetric nanobeams are created by placing three air slots in a silicon photonic crystal slab where three holes are removed. The optical quality factor (Q) is optimized up to 52,000. The nanobeams' mechanical frequencies are higher than 600 MHz due to their femtogram effective modal masses. The optical and mechanical modes are dispersively coupled with a vacuum optomechanical coupling rate g0/2pi exceeding 200 kHz. The anchor-loss-limited mechanical Q of the differential beam mode is evaluated to be greater than 10,000 for structures with ideally symmetric beams. The influence of variations on the air slot width and position is also investigated. The devices can be used as ultrasensitive sensors of mass, force, and displacement.