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A kind of dimer nanostructure similar to panda's eyes (P-Es), consisting two center biased elliptical rings, is proposed in this paper. The finite element method is used to study the nanostructure with the vertical incident light. The structure exhibits high order magnetic modes and the magnetic modes intensity can be manipulated independently by changing the structure parameters. The intensities of the magnetic dipole and magnetic quadrupole modes can be controlled by changing the angle between two rings and the distance of two cavity centers, respectively. Moreover, when two circular cavities increase simultaneously, the intensity of the magnetic octupole mode increases accordingly. Fano resonance can be induced when the electric mode couples with the magnetic mode. When the radius of the left circular cavity decreases, triple Fano resonance is formed. And when the whole structure is rotated, quintuple Fano resonance can be formed. More interesting, when the radii of the circular cavities of the two elliptical rings increase to 50 and 55 nm, the nanostructure becomes crescent dimer, and the enhancements of magnetic field and electric field reach 36 and 390, respectively. The P-Es structure has potential application value in multiwavelength surface enhanced spectroscopy and biochemical sensing.

The Optical properties of the Square Split Ring dimer (SSRD) nanostructure is studied by the finite element method (FEM). Fano resonance can be excited in the visible and near-infrared bands by changing geometrical parameters of the SSRD or the arrangement of two square split rings (SSR). The production mechanism of Fano resonance is illustrated by using the plasmon hybridization theory (PHT). At the meantime, a pair of reverse current circulation is formed in the SSRD nanostructures and the maximum magnetic field enhancement reaches 45.69. In addition, calculation results show that the maximum refractive index sensitivities and the figure of merit (FOM) of SSRD systems reached 2043 nm/RIU and 57.9, respectively. Based on these features of the SSRD system, it may have potential application in sensor devices and surface-enhanced Raman scattering (SERS).

In recent years, various nanostructures related to Fano resonance have been proposed by many researchers due to their outstanding optical properties. A structure consisting of two double-split rings (TD-SR) is researched by using finite element method in this paper. When the incident light is normal to the structure surface, a magnetic Fano resonance can be generated by the interference of bright electric mode and dark magnetic mode. In addition, when the symmetry of the structure is destroyed along x-axis or y-axis, double Fano resonances will be generated. At the same time, the maximum refractive index sensitivity (S) and the maximum figure of merit at resonance mode can reach 1200 nm/RIU and 30.61, respectively. More interestingly, the electromagnetically induced transparency (EIT)-like behavior can be induced when the cavity of inner split ring is biased and the corresponding electric and magnetic field enhancements can reach 229 and 52, respectively. The optical properties of our nanostructure make it has important application value in the fields of multi-wavelength sensor, ultra-sensitive biosensor, surface enhanced spectroscopy and slow light.