Optomechanical cantilever device for displacement sensing and variable attenuator

Abstract

An optomechanical double cantilever device has been fabricated with applications as a displacement sensor and variable attenuator. The device is based on a silica glass on silicon substrate. A novel fabrication approach using a precision dicing saw is used, which has benefits in terms of cost, fabrication time and energy consumption compared to cleanroom based lithography techniques. The silica cantilevers contain integrated optical waveguides and Bragg gratings fabricated using a Direct UV Writing process. The cantilevers are deflected out of plane by thin film stress effects, providing a suitable geometry for use in sensing. Displacement causes both cantilevers to move simultaneously resulting in variable coupling due to the angular alignment of the waveguide modes. Using a developed ratiometric approach based on fitting to Gaussian apodized Bragg gratings, the measured displacement is completely independent of fluctuations in light source power as well as insensitive to detector noise. The device is optically interrogated at a wavelength band around 1550nm. As a sensor the device has a sensitivity of 0.8 dB/micron and can be accurately modelled using fiber optic coupling misalignment theory. When operating as an attenuator, a suppression ratio of over 20dB can be obtained. If combined with integrated optical components such as X-couplers, multiple double cantilever arrays can be placed on the same chip for distributed sensing. We will report detailed fabrication procedures as well as optical characterization of the device including the performance metrics of the force sensor.

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Identifiers

ORCID for C. Holmes: orcid.org/0000-0001-9021-3760

ORCID for J.C. Gates: orcid.org/0000-0001-8671-5987

ORCID for P.G.R. Smith: orcid.org/0000-0003-0319-718X

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