Efficient Humidity Sensor Based on An Etched No-core Fiber Coated with SiO2- nanoparticles

This work presents the simple architecture of a relative humidity detection probe based on a Mach-Zehnder interferometer (MZI). The interferometer structure is made of non-core multimode fibre (NCF) sandwiched between two pieces of single-mode fibre to create the SMF sensor structure. A chemical etching process using hydrofluoric acid (HF) reduces the diameter of the NCF to 64.2 μm. Then, the etched NCF was coated with a thin layer of polyvinylpyrrolidone (PVP)/silica (SiO2). Results show that the PVP/SiO2 NLs coating is a moisture coating material, which allows a significant improvement in sensitivity compared with an uncoated probe due to the improvement in the evanescent field. Experimental results indicate an excellent sensitivity of - 0.2718 dB/% RH at R2 of about 94% and an ultra-fast response time of 2 s for the PVP/SiO2 NLs-coated sensor at RH ranging from 47% to 100%. The sensor also shows good stability