Investigating extraordinary optical transmission and sensing performance through periodic bilayer magneto-plasmonic structure

Abstract

This paper proposes the phenomenon of extraordinary optical transmission via a magneto-plasmonic nanostructure, which combines magnetic and plasmonic functionalities. The structure includes an active magnetic film magnetized perpendicular to its surface and a plasmonic metal film, perforated with subwavelength circular annular arrays, with a ring placed in the middle of each annular circle. We use the finite element method and the finite-difference time-domain method for simulation of the structure. Numerical analysis shows an improvement in the Faraday rotation and optical transmission, simultaneously, in a magneto-plasmonic structure based on a silver- and bismuth-substituted ferrite garnet. Simultaneous improvement is achieved by coupling the TE and TM waveguide-plasmon modes. The amount of enhancement is adjusted by changing the dimensions, the periodicity of the hole arrays, and the refractive index of the materials filled in the holes. The influence of excitation of the two kinds of plasmon modes and the application of the external magnetic field are used to enhance the optical response. The resulting investigation shows two resonance peaks in the near-infrared range of the Faraday effect spectrum. Because of the strong Faraday rotation coinciding with the dual-band transmission of approximately 90%, the maximum figure of merit can also be obtained. Finally, this structure is investigated as a sensor in different reflective indexes from 1 to 1.5 RIU, and sensitivity of 45.97 nm/RIU was achieved. The potential applications of these nanostructures include, for example, subwavelength optics, optoelectronic devices, biosensing devices, and magneto-optical devices.