High sensitivity FBG humidity sensor coated with graphene and polyimide films

A high sensitivity FBG humidity sensor coated with polyimide and graphene films is proposed. The sensing probe is based on a fiber Bragg grating coated with an inner polyimide film and an outer graphene film. The sensor shows the high humidity sensitivity and experimental results show that its sensitivity is 1.80 times that of the sensor coated with only polyimide film. Within the humidity range of 30%–70%RH, its sensitivity reaches 19.8 pm/%RH and is almost 25 times that of the other lower sensitivity FBG humidity sensor.