High-sensitivity humidity sensing of side-polished optical fiber with polymer nanostructure cladding.

This paper presented a high-sensitivity humidity sensor comprised of a side-polished fiber with polymer nanostructure cladding, which was constructed by dehydrating dichromate gelatin film on the polished surface. Due to the intermodal interference of the core mode and cladding mode, two main transmission dips were observed at 1184.4 nm and 1325.6 nm. These two transmission dips showed significant sensitivity to humidity. The position of transmission dip at 1325.6 nm shifted 22 nm while the relative humidity (RH) changed from 30% RH to 50% RH. The humidity sensitivity was up to 1.12 nm/% RH, and its linear correlation was 98.45%. The humidity sensing characteristic of nanostructure cladding fiber was successfully demonstrated. This novel sensor is compatible with optical fiber systems and has high potential in optical sensing applications.