Multimode gradient-index fiber coated with a blend of PEG and PVP as a humidity sensor

A novel humidity sensor based on a multimode graded index unclad fiber optic coated with polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) was proposed. During synthesis process, the fiber diameter underwent optical control resulting in an enhanced repeatability. The achieved sensitivity was found to be 0.219 microwatts per relative humidity percent (µW/%RH), equivalent to 0.212 dB per relative humidity (dB/RH) within a humidity range of 65–95% RH. The response time was 0.02 s per relative humidity percent (s/%RH), indicating rapid detection capabilities. Therefore, this sensor could be used for respiration monitoring. The new sensor has low hysteresis and good repeatability and linearity.