A Coated Spherical Microresonator for Measurement of Water Vapor Concentration at PPM Levels in Very Low Humidity Environments

Arun Kumar Mallik, Gerald Farrell, Dejun Liu, Vishnu Kavungal, Qiang Wu, Yuliya Semenova

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9 Citations (Scopus)
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Abstract

This paper presents a novel approach to measurements of low relative humidity (RH) values based on the whispering gallery modes (WGMs) effect in a small silica microsphere coated with a thin layer of Agarose hydrogel. The light from a narrow-linewidth tunable laser with a few GHz tuning range is launched into an adiabatic tapered fiber, which excites WGMs in the Agarose layer via evanescent coupling. Adsorption and desorption of water vapor by the Agarose layer in response to changes in ambient humidity lead to changes in the layer's refractive index, which in turn leads to a spectral shift of the WGM resonances. We experimentally demonstrate the WGMs spectral shift over a range of RH values from 1%RH to 25%RH. The proposed sensor displays linear response and is capable of measurement of low concentrations of water vapor (corresponding to about 11.7 ± 0.32 ppm water molecules in air). In addition, the proposed sensor offers the advantages of a very small form factor and good repeatability. Detailed studies of the sensor stability, cross sensitivity to temperature, response times, and hysteresis are also presented.
Original languageEnglish
Pages (from-to)2667-2674
JournalJournal of Lightwave Technology
Volume36
Issue number13
Early online date30 Mar 2018
DOIs
Publication statusPublished - 1 Jul 2018

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