A refractive-index fiber sensor by using no-core fibers

A simple, small-size, compact and high-sensitivity refractive-index sensor composed of a short no-core fiber (NCF) about 20 mm in length sandwiched between two pieces of single-mode fibers is proposed in this paper. The index measurement is experimentally demonstrated with the sensitivity of 7792.85 nm/ RIU in the range from 1.440 to 1.454 and 227.14 nm/ RIU in the range from 1.300 to 1.430. This sensing mechanism is based on the induced multi-mode interfering wavelength shift in the no-core fiber when the reflective index of the fiber outside is changed.