A chitosan-coated humidity sensor based on Michelson interferometer with thin-core optical fiber

A novel humidity sensor, which is based on Michelson interferometer (MI) with thin core fiber (TCF) coated with chitosanis proposed and experimentally demonstrated. Its principle is that the light in the single-mode fiber (SMF) core is excited into the cladding of the TCF, and the light transmitted from the end face of the TCF is reflected back to the SMF core. When the chitosan is coated on the end face of the TCF, its refractive index (RI) is changed, causing the shift of the wavelength and intensity of the interference pattern. The structure can be double demodulated, and the sensitivity is highest achievable is 0.058dB/%RH (relative humidity unit), 0.043nm/%RH respectively. The sensor is low cost, easy to make.