Investigation of polyimide coated fibre Bragg gratings for relative humidity sensing

This paper reports the development of a polyimide coated fibre Bragg grating for relative humidity sensing. The humidity response was measured for several polyimide coatings including P84 and P84 HT. The P84 HT polyimide coating proved the most promising with a large coefficient of moisture expansion measured at 73.8 ppm/%rh. The effect of coating thickness and optical fibre diameter were also investigated.