Photonic crystal fiber-based sensor with internal and external sensing for enhanced refractive index range

This study introduces a high-performance dual-channel surface plasmon resonance (SPR) sensor based on a photonic crystal fiber (PCF) platform, designed to detect analytes with refractive indices (RIs) both lower and higher than that of silica. The proposed configuration integrates two distinct analyte channels to achieve broad detection capability and enhanced structural adaptability. The first channel, positioned externally to the PCF, employs a gold layer to induce SPR excitation, whereas the second channel is embedded within the fiber at the centre. A gold film deposited along the inner wall of a neighboring air hole of the second channel works as a plasmonic medium. This indirect plasmonic configuration effectively eliminates direct contact between the metallic surface and liquid analytes, thereby mitigating oxidation and significantly improving the sensor’s operational stability. The optical performances of the sensor were numerically analyzed and optimized using the finite element method (FEM). Simulation outcomes reveal superior sensing performance, with the external channel exhibiting a maximum wavelength sensitivity (WS) of 16,000 nm/RIU and an amplitude sensitivity (AS) of 5030 RIU −1 , while the internal channel achieves 15,000 nm/RIU and 724 RIU −1 , corresponding to resolutions of 6.25×10 −6 RIU and 6.67×10 −6 RIU, respectively. The proposed sensor demonstrates wide detection ranges of 1.31–1.42 for the external channel and 1.44– 1.52 for the internal channel, enabling precise and reliable identification of analytes across diverse refractive indices. Owing to its wide sensing range, high sensitivity, and oxidation-resistant architecture, this dual-channel SPR sensor presents a promising platform for advanced applications in biochemical diagnostics, food quality control, environmental monitoring, and chemical analysis.