Improving the Sensitivity of Humidity Sensor Based on Mach-Zehnder Interferometer Coated with a Methylcellulose

Abstract

A novel humidity sensor based on Mach-Zehnder interferometer (MZI) with the single-mode fiber (SMF) coated with methylcellulose (MC) is proposed and experimentally demonstrated. The MZI consists of two waist enlarged structures. Such an all-fiber MZI incorporates an intermodal interference between the core mode and cladding modes. The MC is coated on the surface of the SMF. External humidity changes the refractive index of MC, causing the intensity changes of the interference pattern. The proposed sensor is linearly responsive to refractive humidity (RH) within the range from 45% to 85% RH, with sensitivity of 0.094 dB/%RH. Moreover the insensitivity of the fiber to the temperature makes this structure more suitable for practical measurement.