Polyvinyl Alcohol Nanofibers Wrapped Microtapered Long-period Fiber Grating for High-linearity Humidity and Temperature Sensing

A simple, reversible and highly sensitive sensor with excellent linearity and stability in response to temperature and relative humidity (RH) is successfully proposed and demonstrated, for the first time, by electrospinning a layer of polyvinyl alcohol (PVA) nanofiber film coated on a microtapered long-period fiber grating (MT-LPFG). Owing to the change in effective refractive index(RI) and stress of microtapered region caused by strong surface absorption and desorption of the PVA coating, the resonance wavelength of the MT-LPFG is more linearly sensitive to environmental humidity and temperature fluctuation. In the experiment, the temperature sensitivity of the sensor is 63.3 pm/°C and 0.162 dB/°C in the range of 30°C-70°C, which has an excellent linearity of 0.997. In addition, RH rise causes changes both in the RI and geometry size of the film. The RH sensitivity is above 13.2 pm/%RH and 0.021 dB/%RH when the humidity ranges from 30%RH to 70%RH with a linearity of 0.998. Compared with traditional sensors, the results show that the grating with a micro-nano structure has a higher sensitivity, linearity, and repeatability. Therefore, this sensor with high linear response of power and wavelength, simple fabrication and stable performance may find great application potential in industrial production, environmental monitoring, civil fields, etc.