Design of a Dual Polarized Gold-Coated Four-Channel PCF-SPR Sensor with Ultra-High Sensitivity and Broad RI Coverage

Photonic crystal fiber-based surface plasmon resonance (PCF-SPR) sensors have emerged as a promising class of optical sensors due to their high sensitivity, compact structure and compatibility with a wide range of analytes. Their performance can be significantly enhanced by carefully engineering the fiber geometry to improve the coupling between the guided core mode and the surface plasmon mode. In this work, a polarization-dependent PCF-SPR sensor is numerically designed and analyzed using the finite element method (FEM) to achieve strong mode coupling, wide detection range and high refractive index (RI) sensitivity. The proposed structure incorporates air holes of varying diameters and a rectangular core slot to induce birefringence, while four outer microchannels coated with a 30 nm gold layer form separate plasmonic regions for multiple resonance excitation. Simulation results demonstrate maximum wavelength sensitivities of 77500 nm/RIU and 92500 nm/RIU for x and y-polarizations, respectively and amplitude sensitivities of 3930 1/RIU and 3139 1/RIU, with corresponding figures of merit of 517 1/RIU and 356 1/RIU across an analyte RI range of 1.32-1.42. Parametric analysis confirms strong fabrication tolerance, with coupling mainly influenced by the smallest air holes and the core slot height. The external sensing configuration enables easy analyte handling and reuse, while the design remains compatible with existing fabrication techniques. The proposed sensor thus offers a compact, highly sensitive and fabrication-feasible platform for biochemical and chemical sensing applications.