High sensitivity balloon-like refractometric sensor based on singlemode-tapered multimode-singlemode fiber

A high sensitivity refractive index (RI) sensor based on balloon-like singlemode-tapered multimode-singlemode (STMS) fiber structure is proposed. The configuration is formed by bending the tapered multimode fiber (MMF) like a balloon shape, which is sandwiched between two singlemode fibers (SMFs). Taking the advantage of tapering and bending, the sensitivity is dramatically improved. The maximum sensitivity of 6909 nm/RIU at RI = 1.42 is experimentally achieved. The proposed refractometer is promising and attractive in chemical and biological applications for its superior properties, such as high sensitivity, compact size, easy fabrication, and low cost.