Hydrogel Coated Long Period Grating Sensor for High Relative Humidity Measurement

A very sensitive hydrogel coated long period grating (LPG) humidity sensor is developed and experimentally investigated for high relative humidity monitoring. A thin-film of PINPAM hydrogel is deposited onto the cladding of LPG by using dip-coating technique. The transmission spectrum of the coated LPG is studied at different humidity levels. For humidity levels greater than 95%, the resonant dip depth suffers a sharp linear increase with a span of 10.26 dB and the resonant wavelength suffers a redshift of 8.6nm.The proposed hydrogel coated LPG humidity sensor shows a high sensitivity of 2.86dB/%RH at high relative humidity region.