Long Period Fiber Grating Humidity Sensor With Gelatin/Cobalt Chloride Coating

A long period fiber grating (LPFG) coated with a combination of cobalt chloride and gelatin is proposed and demonstrated for the monitoring of relative humidity (RH) levels. The thin overlay of the combination and its spectral properties with respect to different ambient humidity levels are observed. Field emission scanning electron microscope and atomic force microscope have provided detailed evidence of attachment of the amalgamation on LPFG surface using adapted coating methodology. The results show a significant shift in the resonance wavelength of the coated LPFG when the RH is varied from 35% to 90%, with a sensitivity of 0.18 nm/% RH and accuracy of 98.55%.