Comparison of solution approaches for distributed humidity sensing in perfluorinated graded-index polymer optical fibers

We compare four different sensing solutions suitable for distributed fiber optic humidity sensing in perfluorinated graded-index polymer optical fibers (PFGI-POFs). Compared to silica fibers, polymer optical fibers offer advantageous benefits including significantly higher break down strain, fracture toughness and humidity sensitivity. Various humidity-related effects in PFGI-POFs have been reported in the last years including measured attenuation and length changes as well as Brillouin frequency and Bragg wavelength shifts. The four aforementioned methods could serve as a basis for distributed and quasi-distributed humidity sensing and are described here closely with an emphasis on plausible cross effects to temperature and strain. The main focus of this paper lies on the comparison of four approaches with regard to method complexity, sensitivity to humidity, spatial resolution, real-time capability and effort to compensate for cross effects.