Refractive index sensor based on all-fiber multimode interference

This paper reports the work on the development of refractive index sensors using the multimode interference technology in an optical fiber. The sensor consists of a short section of multimode fiber (MMF), from which the cladding around the core is removed, inserted between two single-mode fibers (SMF). The proposed refractive index sensor is theoretically and experimentally investigated in terms of its ability to shift the re-imaging resonant wavelength as a function of refractive index. It shows that the proposed sensor has a measurement resolution of 5.3 × 10−5 refractive index unit (RIU) for the changes of refractive indices from 1.336 to 1.372. The proposed sensor has a great potential for biological and chemical applications.