Symmetrical dual-D and dual-core single-mode fiber surface plasmon resonance liquid sensor

A symmetrical dual-D and dual-core single-mode fiber surface plasmon resonance (SPR) liquid sensor is designed for biological detection. The dual-core design optimizes the transmission path, improves the momentum matching between free electrons and photons, and facilitates bidirectional coupling, consequently amplifying the SPR effect and enabling sensitive monitoring of the refractive index changes of biological solutions. In this structure, a gold wire is placed in the middle of the polished surface of the double-D-shaped single-mode fiber (SMF) to produce high-quality free electrons and promote the mode-coupling excitation of the SPR effect. The characteristics of the sensor are analyzed by the finite element method, and the important structural parameters are optimized systematically. The sensor can be operated in the near-infrared region for a refractive index (RI) range of 1.31–1.40 with a maximum wavelength sensitivity (WS) of 21,000 nm/RIU, amplitude sensitivity of 586.62RIU −1 , as well as resolution of 4.76×10 −6 RIU. Small changes in the refractive index can be detected by the sensor and it can be produced easily by conventional manufacturing techniques. The sensor thus has wide application prospects in biomedical and chemical analysis and related applications.