Surface plasmon resonance-induced high sensitivity refractive index sensor with adjustable measurement range based on an evanescent field-enhanced D-shaped five-hole photonic crystal fiber

A simple configuration of a D-shaped five-hole photonic crystal fiber (DFPCF)-based surface plasmon resonance (SPR) refractive index (RI) sensor is proposed. A full vector finite element method is applied to simulate the resonant coupling characteristics of the core modes and the surface plasmon polariton (SPP) modes. In addition to its simple structure, a very small polishing depth can introduce a sufficiently strong evanescent field to excite surface plasmon waves, thus ensuring the mechanical strength of the polished fiber. These two key factors lay the foundation for mass production of the sensors. Further, two air holes above the core induce a tunable evanescent field from the core leakage to the polished surface that adjusts the resonance between core modes and SPP modes. A thin layer of gold film is applied to the polished surface to provide a detection platform for liquid analytes without filling pores, forming the SPR effect. Numerical simulation results show that the proposed DFPCF-based SPR RI sensor exhibits sensing performance that is tunable with the film thickness. A maximum wavelength sensitivity of 20 786 nm RIU⁻¹ and widest detection range of 1.30–1.50 are achieved. Due to its improved sensing performance, the liquid RI sensor could be a potential candidate for use in biochemical analyte detection, industrial production, and food and environmental quality monitoring. (paper)