Agarose coated spherical micro resonator for humidity measurements

Mallik, Arun Kumar, Liu, Dejun, Kavungal, Vishnu, Wu, Qiang, Farrell, Gerald and Semenova, Yuliya (2016) Agarose coated spherical micro resonator for humidity measurements. Optics Express, 24 (19). pp. 21216-21227. ISSN 1094-4087

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Official URL: http://dx.doi.org/10.1364/OE.24.021216

Abstract

A new type of fiber optic relative humidity (RH) sensor based on an agarose coated silica microsphere resonator is proposed and experimentally demonstrated. Whispering gallery modes (WGMs) in the micro resonator are excited by evanescent coupling using a tapered fiber with ~3.3 µm waist diameter. A change in the relative humidity of the surrounding the resonator air induces changes in the refractive index (RI) and thickness of the Agarose coating layer. These changes in turn lead to a spectral shift of the WGM resonances, which can be related to the RH value after a suitable calibration. Studies of the repeatability, long-term stability, measurement accuracy and temperature dependence of the proposed sensor are carried out. The RH sensitivity of the proposed sensor depends on the concentration of the agarose gel which determines the initial thickness of the deposited coating layer. Studies of the micro- resonators with coating layers fabricated from gels with three different Agarose concentrations of 0.5%, 1.125% and 2.25 wt./vol.% showed that an increase in the initial thickness of the coating material results in an increase in sensitivity but also leads to a decrease of quality factor (Q) of the micro resonator. The highest sensitivity achieved in our experiments was 518 pm/%RH in the RH range from 30% to 70%. The proposed sensor offers the advantages of a very compact form factor, low hysteresis, good repeatability, and low cross sensitivity to temperature.

Item Type: Article
Uncontrolled Keywords: Optical resonators; Micro-optical devices; Fiber optics sensors; Microstructured fibers
Subjects: F200 Materials Science
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Becky Skoyles
Date Deposited: 25 Oct 2016 08:27
Last Modified: 24 Oct 2017 08:52
URI: http://nrl.northumbria.ac.uk/id/eprint/28155

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