Surface plasmon resonance sensor composed of a D-type photonic crystal fiber with a three-layer coating

A surface plasmon resonance sensor composed of photonic crystal fibers (PCF-SPR) with an A u-T i O ₂-A u triple layer is designed for refractive index (RI) sensing and analyzed theoretically by the finite element method. The sensor exhibits enhanced resonance coupling between the core mode and surface plasmon polariton (SPP) mode as well as better sensitivity than the structure with a single gold coating. Furthermore, the A u-T i O ₂-A u tri-layer structure narrows the linewidth of the loss spectrum and improves the figure of merit (FOM). In the analyte RI range of 1.30-1.42, the maximum wavelength sensitivity is 20,300 nm/RIU, resolution is 4.93×10^-6, amplitude sensitivity is 6427R I U ^-1, and FOM is 559R I U ^-1. The results provide insights into the design of high-performance PCF-SPR sensors.