Graphene-coated terahertz photonic crystal fiber for refractive index sensor applications

A graphene-coated terahertz photonic crystal fiber (G-PCF) for refractive index (RI) sensing is proposed and numerically simulated by the finite element method (FEM). To enhance the sensitivity and produce birefringence, two larger air-holes are introduced in the innermost ring of holes around the solid core. Inner surface of the larger air-holes is coated with multilayer graphene and used for analyte filling. The guided modes of the designed G-PCF are distributed mainly in the larger air-holes as a result of the high permittivity and carrier mobility of graphene. The relative sensitivity coefficient can be improved more than 5 times by introducing the graphene coating for analytes with a RI in the range of 1.00 to 1.50. The highest relative sensitivity coefficient about 90% is obtained when RI is equal to 1.37. The relative sensitivity coefficient can be improved more than 15 times with RI equals to 1.03. The propagation properties and RI sensitivities of the G-PCF can be electrically and thermally controlled. Our results provide references for RI sensor applications of the designed GPCF in terahertz range.