Characteristics of electric quadrupole and magnetic quadrupole coupling in a symmetric silicon structure

Abstract

Abstract Multipole interferences have attracted a lot of interests in last decade due to extraordinary performance on beam control and scattering shaping. However, most of previous works focused on the dipole-based interferences while the quadrupole modes and other high-order multipole modes with unique properties were of less attention. In this work, we aim to expand the present dipole-based multipole-interference regime to the quadrupole-interference regime. We study the interference between an electric quadrupole (EQ) and a magnetic quadrupole (MQ) in both isolated and periodically arranged homogeneous cross dielectric structure. Through structural parametric control, the EQ and MQ can be precisely tuned to share the same resonant intensity at a specific wavelength, resulting in a generalized Kerker effect. Moreover, a dark MQ mode, which is orthogonal with the original MQ mode, arises when we increase the interaction between structure. We find that the spectral approaching between dark MQ and original bright EQ results in an EIT effect and Fano-shaped spectral reflection response. The induced Fano spectrum possesses tunable quality factors varying from ∼10 to >105 with the variation of EQ–MQ coupling efficiency. The numerically derived maximum quality factor (238, 618) of the dielectric EQ–MQ coupling system even exceeds the quality factors of many plasmonic resonant systems. We also prove that such spectrum can be adopted to refractive index sensing. Besides, we show that EQ–MQ coupling can bring about rapid 2π phase change, which can be applied in metasurface designs. These results and conclusions about the EQ–MQ interference systems can provide a promising avenue for advanced optical devices.