Optical property of X-two ring structure

In this paper, the metal periodic array structure of X-two ring based on the principle of Fano resonance is proposed, which is composed of two concentric rings around the center X. The optical properties of the structure are investigated by using the finite difference time domain method. According to the simulated transmission spectra, electric field distribution and charge distribution, when linearly polarized light is incident to the metal surface, Fano resonance can be excited and the interaction between resonance modes can be produced in the structure of X-two ring, which can make resonance valleys generated at different positions. Fano resonance is mainly formed by the coherent interference between a bright mode with the larger radiation broadening and a dark mode with the weak radiation broadening, thus the structural resonance valley of X-two ring based on Fano resonance is strongly dependent on the relative parameters of the structure (the arm length of X, the distance between the inner ring and outer ring, the width of the inner ring and outer ring, the period, the number of ring, and the angle of X). In other words, over the wavelength range of 450 nm to 3000 nm, the intensity and position of the structural resonance valley are adjustable as the change of the relative geometric parameters of the structure. In addition, due to weak radiation damping and strong local electromagnetic field enhancement of Fano resonance, the resonance frequency and line type can significantly shift with the change of the environmental refractive index. Therefore, the further analysis of the variation of the structural resonance valley under the conditions of different refractive indices can be concluded that the structure of X-two ring has a higher sensitivity to the refractive index of surrounding environment, up to 1300 nm/RIU. The above results show that the structure of X-two ring not only is simple, economical, compact and efficient, but also has great potential applications in refractive index sensors and some photonic devices.