▎ 摘　　要

We report on relative humidity (RH) sensing probe based on a cladding etched no-core fiber (NCF) multimode interferometer. The sensor structure was constructed by fusion splicing a section of NCF between two segments of single-mode fibers (SMF). Then a part of the NCF's cladding was chemically etched with hydrofluoric acid (HF) solution until it reaches 50 mu m in diameter. Thin-film of graphene-polyvinyl alcohol (G-PVA) was coated onto the etched zone of the bare NCF. The experimental results revealed that sensitivity enhanced more than 3 times compared to bare fiber at the proposed diameter. The strong interaction of G-PVA with the evanescent field of the etched NCF results in higher sensitivity. The maximum sensitivity of 0.412 nm/RH% with good stability at the RH range of 40%-100% was obtained. To the best of our knowledge, this is the first demonstration of an RH sensor based on an etched NCF coated with G-PVA film. This work presents a method to improve the sensitivity of a single-mode- no-core -single-mode (SNCS) fiber structure based RH sensor featuring a low- cost, compact size, and good reversibility.