Nanomechanical Design Strategy for Single-Mode Optomechanical Measurement

TL;DR

This paper introduces a mechanical design strategy for optomechanical sensors that isolates a single vibrational mode, significantly improving measurement sensitivity by suppressing unwanted modes in a nanobeam resonator.

Contribution

The authors develop a spectral design approach that enhances mode selectivity and robustness against disorder, demonstrated experimentally in a photonic crystal nanobeam resonator.

Findings

Four orders of magnitude increase in signal-to-noise ratio for the targeted mode

Effective suppression of spurious mechanical modes

Design strategy applicable to various mechanical systems

Abstract

The motion of a mechanical resonator is intrinsically decomposed over a collection of normal modes of vibration. When the resonator is used as a sensor, its multimode nature often deteriorates or limits its performance and sensitivity. This challenge is frequently encountered in state-of-the-art optomechanical sensing platforms. We present a mechanical design strategy that ensures that optomechanical measurements can retrieve information on a single mechanical degree of freedom, and implement it in a sliced photonic crystal nanobeam resonator. A spectral design approach is used to make mechanical symmetries robust against practical disorder. The effectiveness of the method is evaluated by deriving a relevant figure of merit for continuous and pulsed measurement application scenarios. The method can be employed in any mechanical design that presents unwanted spurious mechanical modes. In the nanobeam platform, we experimentally show an increase of the signal to noise ratio of the mode of interest over the first spurious mode by four orders of magnitudes.