Design and Analysis of a Biosensor Based on Surface Plasmon Resonance in a Photonic Crystal Fiber

This study introduces the design and analysis of two surface plasmon resonance (SPR) biosensors based on photonic crystal fibers (PCFs) coated with a gold layer, utilizing the finite element method (FEM) in COMSOL Multiphysics. The investigation focuses on two structural configurations: circular and elliptical air holes in the first cladding ring. The \(\:y\)-polarized mode, due to stronger coupling with the surface plasmon polariton (SPP) mode, provided enhanced sensitivity. Phase matching occurred at ~ 0.67µm for an analyte refractive index of 1.37. The elliptical design showed higher confinement loss (131.8dB/cm) compared to the circular one (120.4dB/cm). As the analyte refractive index increased from 1.33 to 1.37, both confinement loss and wavelength sensitivity increased, with a red shift in resonance wavelength. Polynomial fitting showed strong linearity between resonance wavelength and analyte index, with adjusted \(\:{R}^{2}\) values of 0.9923 and 0.9927 for circular and elliptical designs, respectively. Final sensor resolutions were 3.22 × 10⁻⁶RIU and 3.15 × 10⁻⁶RIU. These results highlight the critical role of hole geometry in optimizing SPR-PCF biosensor performance.