Fiber optic interferometric humidity sensor by using gelatin

A fiber optic interferometric humidity sensor based on hollow core fiber (HCF) and gelatin humidity sensing film was studied. It was formed by fusion splicing a short length of HCF to the end of a single-mode fiber and coating gelatin film at the free end of HCF. Relative humidity was measured by measuring interference spectrum of the so-formed Fabry-Perot interferometer, which changes with humidity level. High sensitivity of 192 pm/%RH is achieved within the range of 20-80^%RH, as well as good stability and repeatability.