A compact refractive index sensor with high sensitivity based on multimode interference

Abstract

A compact refractive index sensor is proposed and investigated based on multimode fiber-micro tapered single-mode fiber-multimode fiber (MTSM) structure. The micro tapered single-mode fiber excites the high-order cladding mode and induces a compact size of 2.2 mm. The influence of multimode fiber (MMF) for the interference fringe is studied numerically and verified experimentally. The experimental and simulated results show that the appropriate MMF length is conducive to form a clear interference fringe. At the same time, the results of refractive index test show that the maximal sensitivity reaches 1879.87 nm/RIU under external refractive index of 1.437. Due to the advantages of small size and high sensitivity, the novel fiber sensor has the potential in the application of refractive index sensing.