LAUSR

Abstract. We report on a humidity sensor based on passband spectrum resulting due to self-imaging effect in single-mode–multimode–single-mode fiber structure experimentally. The sensor performance with varying NCF diameter was investigated to find appropriate size of maximized evanescent fields. Different tuned diameters of NCF of 100, 80, 60, and 40  μm were obtained by chemical etching process based on hydrofluoric (HF) acid immersion. The experimental results reveal that almost a threefold increase in sensitivity was obtained at the proposed optimum NCF diameter of 60  μm coated with copper oxide nanoparticles embedded in poly polyvinyl alcohol. The highest wavelength and intensity sensitivity of −0.581  nm  /  RH  %   and −0.456  dB  /  RH  %   were obtained, respectively, in the RH range of 30% to 100% with 8.11-s response time. To the best of our knowledge, this is the first demonstration of RH sensor based on NCF coated with CuO NPs thin film.