A stepped Mach-Zehnder interferometric humidity sensor based on lateral offset fusion splicing

A novel optical fiber relative humidity (RH) sensor based on a Mach-Zehnder interferometer (MZI) is proposed and demonstrated in this paper. The sensor head is formed by a single-mode-multimode-single-mode-single-mode(SM-MM-SM-SM) fiber structure through lateral offset fusion splicing. The intermodal interference is achieved by two lateral offset points. The change of relative humidity will cause the optical path difference changed of the core mode and cladding modes, which gives rise to the interference pattern change. The ambient RH change can be determined by monitoring the energy variation of the interference pattern. The experimental results show the dip energy of the transmission spectrum changes with respect to surrounding RH with good linearity. The MZI with a interferometer length of 15 mm offers the enhanced RH sensitivity of −0.0487 dB/%RH in the range of 35-95%RH with linearity of 0.9966. The proposed humidity has compact size, simple fabrication procedure and does not need any functional coating, making it a good candidate for RH measurements.