High-sensitivity refractive index sensor based on 3 x 3 microfiber coupler structure

In this study, a 3 x 3 microfiber coupler sensing structure is fabricated by the fusion taper technology, and the mode coupling distribution of its light energy is numerically simulated by the beam propagation method. Results confirmed that the sensing structure produces regular and stable mode coupling within an 11-25 mu m effective coupling region. The 3 x 3 microfiber coupler is used as a light splitter. In addition, it can also perform refractive index (RI) sensing. The RI characteristics of the proposed sensor are further verified experimentally. Experimental findings reveal that the RI sensitivity is inversely proportional to the effective coupling region diameter, and the sensitivity is 5223.83 nm/RIU when the effective coupling region diameter is 11 mu m.