Optical fiber relative humidity sensor based on FBG embedded in SMS fiber structure

A novel optical fiber humidity sensor based on fiber Bragg grating (FBG) embedded in single-mode-multimode-single-mode (SMS) fiber structure is proposed. With relative humidity (RH) changing, the transmission spectrum of the SMS fiber structure shifts while the central wavelength of FBG remains unchanged. Numerical simulations of light distribution of the SMS structure have been carried out, analyzing the effects of different wavelengths of the input light, lengths and core diameters of the multimode fiber (MMF). The cross-sensitive problem of temperature has also been solved.