Optomechanical electrometer based on optical mode-localization sensing

Abstract

This work explores the feasibility of the optomechanical electrometer based on a novel sensing mechanism named optical mode-localization that originates from the mechanical mode-localization sensing mechanism. The electrometer is constructed by integrating coupled optical ring resonators and a suspended slot modulator on a silicon chip. The slot modulator is a Nano-Opto-Electrical-Mechanical-Systems (NOEMS) actuator that can tune the effective index and phase of the waveguide, and thus the perturbation in electrical charge can be transferred to the phase perturbation in the optical ring resonators. We use the modulator to create the mode-localization in the coupled optical ring resonators to accomplish ultra-high sensitivity charge sensing. We established an analytical approximation of the index and phase change induced by the NOEMS slot modulator using the finite element analysis (FEA), including the Casimir force, optical force, electrostatic force and pull-in effect. The modulator can be configured in different ways to make the design flexible. COMSOL Multiphysics and Lumerical are used to analyze the possible configurations. The modulating performance of the fully suspended slot configurations are thoroughly analyzed. Based on the signal flow graph analysis (Mason’s rule), analytical model of the optical mode localization based on coupled ring resonators is established. The correctness of the theoretical model is proved by Lumerical simulation. The optical mode-localization sensing has the advantages in sensitivity, accuracy, anti-aliasing and noise immunity compared with the mechanical mode localization one. The optomechanical electrometer designed from coupled ring resonators and NOEMS slot modulator is more sensitive among other on-chip electrometers in theory. We carried out few test runs to investigate the capability of the device fabrication. The specific structural releasing process based on HF vapour etching is developed for suspended waveguide. The specific ring resonators designed successfully extract the parameters of the necessary components. The scanning electron microscopy (SEM) pictures and output spectrum indicated that the surface roughness caused by fabrication imperfections would significantly affect the performance of the devices.

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Identifiers

ORCID for Jize Yan: orcid.org/0000-0002-2886-2847

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