Mid-infrared optical sensing using sub-wavelength gratings

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Hogan, Brian
Lewis, Liam
McAuliffe, Michael
Hegarty, Stephen P.
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OSA - The Optical Society
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Optical sensing has shown great potential for both quantitative and qualitative analysis of compounds. In particular sensors which are capable of detecting changes in refractive index at a surface as well as in bulk material have received much attention. Much of the recent research has focused on developing technologies that enable such sensors to be deployed in an integrated photonic device. In this work we demonstrate experimentally, using a sub-wavelength grating the detection of ethanol in aqueous solution by interrogating its large absorption band at 9.54 μm. Theoretical investigation of the operating principle of our grating sensor shows that in general, as the total field interacting with the analyte is increased, the corresponding absorption is also increased. We also theoretically demonstrate how sub-wavelength gratings can detect changes in the real part of the refractive index, similar to conventional refractive index (RI) sensors.
Extinction coefficients , Reflectivity , Refractive index , Rigorous coupled wave analysis , Sensor performance , Total internal reflection
Hogan, B., Lewis, L., McAuliffe, M. and Hegarty, S.P., 2019. Mid-infrared optical sensing using sub-wavelength gratings. Optics express, 27(3), (10pp). DOI:10.1364/OE.27.003169