Investigation of a Highly Sensitive D-Type Photonic Crystal Fiber Utilizing Surface Plasmon Resonance

Due to the limited application of sensors in the low-refractive-index range, accurate detection of certain low-refractive-index objects remains challenging. To address this limitation, this study proposes a novel D-shaped photonic crystal fiber (PCF) operating on the surface plasmon resonance (SPR) principle. Distinct from conventional D-type PCF designs, the proposed structure employs an open-loop channel coated with a gold film to enable efficient excitation. Finite element analysis shows that the sensor’s detection range of refractive index is between 1.23 and 1.32. With increasing analyte refractive index, the loss peak exhibits progressive broadening and eventual stabilization. A maximum spectral sensitivity of 18,500 nm/RIU and a resolution of 5.41 × 10−6 RIU are attained at a refractive index of 1.32. The sensor features a straightforward design and exhibits excellent performance characteristics. Its exceptional sensing capabilities make it highly competitive for use in applications with a low refractive index. At the same time, to optimize the sensing performance, this study investigates how structural parameters affect the resonant spectrum.