Design and analysis of a refractive index sensor based on dual-core large-mode-area fiber

•Co-axial dual-core LMA fiber has been designed for refractive index sensing.•Resonant coupling between the two cores results in high sensitivity.•Transfer matrix method has been used to analyze the structure.•Proposed sensor is highly sensitive with the resolution of 2.0 × 10−6.

We present a novel co-axial dual core large-mode-area (LMA) fiber design for refractive index sensing. In a dual-core fiber there is resonant coupling between the two cores, which is strongly affected by the refractive index (RI) of the outermost region. The transmittance of the fiber, therefore, varies sharply with the refractive index of surrounding medium. This characteristic of the proposed structure has been utilized to design a RI sensor. We have analyzed the structure by using the transfer matrix method. Our numerical results show that the proposed sensor is highly sensitive with the resolution of 2.0 × 10−6 around nex = 1.44376. Effect of design parameters on sensitivity of the proposed sensor has also been investigated.