D-shaped photonic crystal fiber-based SPR sensor with an embedded microchannel for refractive index sensing

Abstract Refractive index is a fundamental parameter for identifying the composition of a substance. Hence, developing a sensor capable of accurately and reliably measuring RI is of great importance. This study proposes a D-shaped photonic crystal fiber sensor for enhanced surface plasmon resonance (SPR) sensing. The structure incorporates dual-sized air holes ( D ₁ and D ₂) within a silica core to optimize light confinement, mode coupling, and propagation characteristics. One side of the fiber is polished to form a D-shaped profile, exposing the inner air holes and allowing direct interaction between the guided light and a thin gold layer, which supports efficient SPR excitation. The sensor is capable of detecting RI variations in the range of 1.28 – 1.44. It achieves an average wavelength sensitivity of 3875 nm RIU −1 , highlighting its effectiveness in monitoring ambient RI changes. The results confirm the sensor’s suitability for a wide range of applications, including biochemical analysis, environmental monitoring, and medical diagnostics.