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

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 (D₁ and D₂) 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.