A hollow dual-core PCF-SPR sensor with gold layers on the inner and outer surfaces of the thin cladding

A hollow dual-core photonic crystal fiber (PCF) with high sensitivity based on surface plasmon resonance (SPR) sensing is designed and analyzed numerically by the finite element method (FEM). This double-sided gold structure has not been reported before and provides a novel mechanism of SPR excitation. In order to increase coupling effects between the plasmonic mode and the fundamental mode, double-sided gold films deposited on both inner and outer surface are selected. The sensing properties are enhanced remarkably by depositing gold films on the inner and outer surfaces of the thin cladding as manifested by more than 50 times improvement in the average sensitivity compared to the single-sided gold structure. The working wavelength of the sensor is controllable in the near-infrared region (1550–2700 nm) for analyte refractive indices (RIs) ranging from 1.36 to 1.41. Numercal simulation reveals that the average and maximum spectral sensitivities rise to 23,000 nm/RIU and 30,000 nm/RIU and the corresponding resolution is improved to 3.33 × 10−6 RIU. Compared with the unilaterally coated sensor with the same structural parameters, this bilaterally coated sensor offers distinctive advantages that are beneficial to the development of photonic sensors with ultrahigh sensitivity.