OAM mode-excited surface plasmon resonance for refractive index sensing based on a photonic quasi-crystal fiber

In this paper, a novel, to the best of our knowledge, surface plasmon resonance (SPR) fiber biosensor is theoretically proposed to detect the surrounding refractive index based on a Stampfli-type photonic quasi-crystal fiber with one air hole coated gold thin film. Surface plasmon polaritons (SPPs) at the metal/dielectric interface are excited by the orbital angular momentum (OAM) mode (other than Gaussian mode) that propagates very robustly along the fiber with helical phase, facilitating the energy transformation of OAM mode to SPP mode and then realization of the typical resonant loss peak. The proposed OAM-SPR fiber sensor exhibits a refractive index sensitivity of 4466.5 nm/RIU and a resolution of 2.3 × 1 0 − 5 RIU in a broad refractive index range from 1.36 to 1.435. Numeric results show that both structure parameters of the fiber and thickness of the gold layer influence sensing performance as the phase matching condition varies. This work offers theoretical guidance for the design of an OAM-SPR fiber biosensor and has great potential applications in sensing bio-molecular and bio-chemical liquids.