Chen, G.Y.Wu, X.Schartner, E.P.Shahnia, S.Hebert, N.B.Yu, L.Liu, X.Shahraam, A.V.Newson, T.P.Ebendorff-Heidepriem, H.Xu, H.Lancaster, D.G.Monro, T.M.2019-06-162019-06-162019Journal of Lightwave Technology, 2019; 37(9):2014-20220733-87241558-2213http://hdl.handle.net/2440/119492Existing sensing technologies lack the ability to spatially resolve multiple sources of water or humidity without relying on the deployment of numerous inline sensors. A fully distributed approach has the potential to unlock a diverse range of applications, such as humidity mapping and liquid-depth measurements. We have explored a new direction toward what is, to the best of our knowledge, the first non-bending fully distributed water/humidity sensors. This new class of sensors was made possible from the first combination of small-core exposed-core fiber, a hydrophilic polyelectrolyte multilayer coating, and coherent optical frequency-domain reflectometry. Their non-bending nature enables deployment in a wider range of environments compared to the bending type based on water-induced fiber bending. The sensing mechanism involves monitoring back-reflected optical signals created by changes in the local reflectivity due to water-induced reduction in the local refractive-index of the coating. The demonstrated average sensitivity of the sensing fiber with 10.0 bilayer polyelectrolyte multilayer coating to relative humidity varies from 0.060 to 0.001/%RH (0-38 cm distance) within a dynamic range of 26-95%RH. The distance-dependent detection limit varies between 0.3-10.0%RH (0-38 cm distance), and the spatial resolution of 4.6 mm is the smallest demonstrated for exposed-core fibers and can be vastly improved by simply broadening the swept range. The response time is 4-6 s, and the recovery time is 3-5 s. The sensing range (i.e., distance) is -0.5 m, which is more suitable for water-depth monitoring.EN© 2019 IEEE. Translations and content mining are permitted for academic research only. Personal use is also permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information.Distributed; exposed core; frequency; humidity; hygrometer; OFDR; optical fiber; polyelectrolyte coating; reflectometry; sensor; waterJournal article003011387910.1109/JLT.2019.28973460004650308000202-s2.0-85064605775470618Schartner, E.P. [0000-0003-1669-4302]Hebert, N.B. [0000-0002-6168-8510]Ebendorff-Heidepriem, H. [0000-0002-4877-7770]