Fano interferences of electromagnetic modes in dielectric nanoblock dimers

Abstract

The optical properties of a dielectric dimer consisting of two parallel identical nanoblocks are theoretically investigated. Each dielectric nanoblock has a magnetic dipole mode and a broad electric dipole mode, when the polarization of the plane wave excitation is along the long axis of the nanoblock. The two modes are spectrally overlapped. In such a dimer, the magnetic fields associated with the magnetic dipole modes on the two nanoblocks will rotate and form a subradiant mode. Multipole decomposition calculations show that the subradiant mode is induced by the spatial combination of the magnetic fields of a magnetic quadrupole mode and a toroidal dipole mode. The electric field associated with the subradiant mode undergoes destructive Fano interference with that of a broad electric dipole mode and results in a pronounced Fano dip on the scattering spectrum of the dimer. The Fano resonance varies with the distance between the two nanoblocks and the size of each nanoblock. The case with the polarization along the short axis of each nanoblock is also considered. Fano interference between a subradiant mode and a radiant electric mode can also appear in this configuration. But here the subradiant mode corresponds to the combined magnetic quadrupole and toroidal dipole modes on each nanoblock. Our study reveals complex electromagnetic interactions in simple dielectric nanostructures and could find applications in dielectric photonic devices.