Physics

Relative humidity

Plastic optical fiber

Composite number

Optics

Humidity

Engineering

Long-period fiber grating

Composite material

Fiber optic sensor

Materials science

Optical fiber

Polyethylene glycol

Grating

Polyvinyl alcohol

Fiber Bragg grating

Refractive index

Chemical engineering

Optoelectronics

Fiber

Polymer

Wavelength

Thermodynamics

Sensors

We demonstrate a simple and highly sensitive optical fiber relative humidity (RH) sensor based on a long-period fiber grating (LPFG) coated with polyethylene glycol (PEG)/polyvinyl alcohol (PVA) composite films. The resonance wavelength of the LPFG is sensitive to environmental humidity due to the change in effective refractive index caused by the strong surface absorption and desorption of the porous PEG/PVA coatings. The sensor is sensitive in a wide range from 50% to 95% RH, with a highest sensitivity of 2.485 nm/%RH in the range 50-75% RH. The proposed RH sensor has the advantages of compact size, good reversibility, and stability, which makes it attractive for high-humidity environments.

Humidity Sensor Based on a Long-Period Fiber Grating Coated with Polymer Composite Film