Optical fiber relative-humidity sensor with polyvinyl alcohol film.

We describe a fiber-optic relative-humidity (RH) sensor comprising a moisture-sensitive overlay on a single-mode side-polished fiber. The hygroscopic polymeric material deposited was polyvinyl alcohol (PVA), which proved to have good adherence and stability. The film reached a fast equilibrium with atmospheric moisture (in less than 1 min), inducing changes in the output optical power of approximately 10 dB for the 70%-90% RH range.