Multipoint fiber optics refractive index sensor based on multimode interference effects

Abstract

We demonstrate a fiber optics sensing structure for the measurement of the refractive index of liquid samples at multiple spatial locations simultaneously. The sensing architecture is all-fiber and consists of standard single-mode–multimode-single-mode multimodal interference (MMI) devices working in parallel. The spectral response of each MMI device is carefully engineered to have nonoverlapping responses, such that the entire system can be interrogated with a single broadband light source and single optical spectrum analyzer. In proof-of-concept experiments, we tested the proposed system with aqueous saline solutions and binary solutions of water–glycerol and water–ethylene glycol. Our results validate the use of the proposed platform for the simultaneous monitoring of the refractive index of liquid samples at different locations.