Optical hygrometer using light-sheet skew-ray probed multimode fiber with polyelectrolyte coating
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Date
2019
Authors
Chen, G.Y.
Wu, X.
Codemard, C.A.
Yu, L.
Liu, X.
Xu, H.
Monro, T.M.
Lancaster, D.G.
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Sensors and Actuators, B: Chemical, 2019; 296(126685):1-6
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The measurement of humidity provides valuable information to a range of industries. Existing hygrometers lack the combination of high sensitivity/low detection-limit, temperature insensitivity, fast response, high robustness and low cost. We present a new design of humidity sensors based on the combination of a polymer-coated multimode fiber interrogated by a light sheet (i.e. thin plane of light) designed to precision excite the optimum group of skew rays for enhanced sensitivity. The sensing mechanism is water absorption of light via evanescent-wave interaction mediated by a polymer-coated multimode fiber. For a 10.0 bilayer poly(diallyldimethylammonium) (PDDA)/poly(styrenesulfonate) (PSS)-coated sensing fiber, we demonstrated a sensitivity of up to 0.14 dB/%RH/cm, a detection limit of 0.007%RH, a temperature cross-sensitivity of less than ˜0.13%/°C, and response/recovery times of 115 ms and 200 ms. The tested dynamic range is between 10%RH and 94%RH. The dependence on the total optical power rather than the phase of light makes such sensors relatively insensitive to temperature while remaining sensitive to humidity. The PDDA/PSS functional coating inherently offers fast response. The use of multimode fibers and power meters make such fiber-optic sensors highly robust and relatively inexpensive, easing the translation to practical applications.
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Copyright 2019 Elsevier BV
Access Condition Notes: Accepted manuscript available after 1 July 2021