High-Sensitivity Refractive Index Sensing and Broadband Tunable Polarization Filtering Characteristics of D-Shaped Micro-Structured Fiber With Single-Layer Air-Holes and Gold Film Based on SPR

An easy-to-implement side-polished micro-structured fiber MSF)based on surface plasmon resonance (SPR) is proposed. The influence of fiber structure parameters on transmission performance is investigated by finite element method (FEM). The chemical stable gold is deposited on the side polished plane to provide the plasmonic material required for SPR. Ten cladding air-holes are used to confine light transmission and improve the coupling strength between the core mode and surface plasmon polaritons (SPP) mode. The optimization results show that the MSF integrates the characteristics of high refractive index (RI) sensing and broadband tunable polarization filtering. In addition, the RI detection range of the sensor can be further extended by depositing a $Si_{3}N_{4}$ dielectric layer on the gold film. The RI detection range of the sensor with gold coating is 1.20--1.325 with the maximum sensitivity of 12,000 nm/RIU. The RI measurement range of the sensor with gold-$Si_{3}N_{4}$ bilayer film can be extended to 1.20--1.37, and the maximum sensitivity is 10,000 nm/RIU. Furthermore, by changing the ambient RI of gold-coated fiber or the polishing depth of fiber, a broadband tunable filter with excellent performance can be obtained. Therefore, the proposed MSF not only has application value in the detection of biochemical liquid samples, but also has broad application potential in broadband communication networks, which is helpful to promote the development of miniaturization and integration of optical devices.