Point-top Shaped Photonic Crystal Fiber for Enhanced Surface Plasmon Resonance Biosensing

A point-top photonic crystal fiber (PCF)–based surface plasmon resonance (SPR) biosensor with a continuous gold coating is theoretically proposed and analyzed using the finite-element method. The asymmetric PCF geometry is optimized to enhance coupling between the guided core mode and the surface plasmon polariton at the metal–analyte interface. Sensor performance is evaluated for x- and y-polarized modes by varying the analyte refractive index from 1.35 to 1.40. Resonance wavelengths are observed near 0.67 μm (x-polarization) and 0.68 μm (y-polarization) at an analyte index of 1.37, corresponding to efficient phase matching and strong plasmonic excitation. The structure exhibits polarization-dependent confinement losses of 0.77 dB/cm and 33.4 dB/cm for x- and y-polarizations, respectively. Increasing the analyte refractive index results in a systematic redshift of the resonance wavelength and enhanced confinement loss. Maximum wavelength sensitivities of 1025.59 nm/RIU (x-polarized) and 864.39 nm/RIU (y-polarized) are achieved. Polynomial fitting confirms a stable nonlinear relationship between resonance wavelength and refractive index with adjusted values above 0.98. The results demonstrate that the proposed configuration provides improved sensitivity and reliable sensing performance for biochemical and biomedical refractive-index detection.