Abstract
An optical fiber humidity sensor with a microfiber knot resonator (MKR) nested U-shaped Mach-Zehnder (MZ) interferometer based on the Vernier effect is proposed. While the reference arm is protected by cured ultraviolet glue, the sensing arm is coated by agarose. The Vernier effect is realized by superimposing the comb-like transmission spectra of the MKR and MZ interfernce, which are designed to have slightly different free spectral ranges. Experimental results indicate that the proposed sensor can provide a maximum humidity sensitivity of 2.442 nm/%RH with a measurement range from 60% RH to 95% RH. The sensor temperature response, reversibility and repeatability are also investigated. The response time is found to be 102 ms for a change of ∼30% RH. This sensor not only retains key features and merits of the MKR, including low cost and small footprint, but also has a simpler preparation process compared with conventional sensors based on the Vernier effect.
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