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A highly sensitive, reversible, and linear sensor, exhibiting excellent stability in response to temperature and humidity, has been successfully proposed and demonstrated for the first time. This sensor is achieved by wrapping a polyvinyl alcohol/graphene nanofiber film onto a chiral long-period fiber grating (CLPG), which is fabricated by periodically twisting single mode fiber. In the experiment, the CLPG sensor demonstrates a temperature sensitivity of 74 pm/°C , which is approximately twice as high as that of conventional fiber grating sensors. Note that, by wrapping the graphene nanofiber film on CLPG, the temperature sensitivity of the sensor is up to 115.23 pm/°C in the range of 30°C to 75°C. In addition, CLPG using for humidity sensing is first demonstrated. The humidity sensitivity measures −9.92 pm/%RH with linearity of 0.995 during a change from 40%RH to 80%RH. In comparison to other humidity sensors, the sensitivity of the CLPG is comparable, whereas its sensing linearity stands out notably above the rest. The results show that CLPG has the characteristics of simple fabrication, easy combination with materials, stable performance, and high sensitivity and holds significant development potential in optical fiber sensing application fields. [ABSTRACT FROM AUTHOR]

A fiber-optic humidity sensor based on excessively tilted fiber grating (Ex-TFG) wrapped with tin dioxide (SnO 2)/polyvinyl alcohol (PVA) hybrid nanofibers is presented. Relative humidity (RH) rise causes the changes both in refractive index (RI) and geometry size of the film. The transmitted spectrum of the Ex-TFG changes as a result, owing to the strong interaction of the excited forward propagating cladding modes to the surface coating. Experimental results demonstrate the maximum intensity sensitivity of 0.43 dB/%RH in RH range of 35%−75%. Compared with pure PVA film coated ones, the RH sensitivity of the SnO 2 /PVA wrapped grating is vastly enhanced by one order of magnitude. The reticular morphology of electrospun SnO 2 /PVA film around the Ex-TFG promises the unimpeded permeation of water molecules, and then the sensor exhibits an ultrafast response of ∼67 ms and recovery times of ∼83 ms, by monitoring the human breathing with different rhythms. Lastly, the negligible spectral deformation to temperature perturbations verifies the temperature de-correlation of the designed RH sensor. This work indicates that the proposed SnO 2 /PVA nanofibers wrapped Ex-TFG can provide a simple, robust and high-sensitive optic device for healthcare monitoring, environmental and biochemical sensing applications. • Wrapping SnO 2 /PVA nanofibers on an excessively tilted fiber grating. • High intensity sensitivity up to 0.43 dB/%RH with negligible temperature crosstalk. • Monitoring human breathing with ultrafast response speed of 67 ms. • Performing the merits of long-term stability, reliability, and easy fabrication. [ABSTRACT FROM AUTHOR]