38 research outputs found
Resonance Properties of Optical All-Dielectric Metamaterials Using Two-Dimensional Multipole Expansion
We examine the electromagnetic response of metamaterial unit elements consisting of dielectric rods embedded in a non-magnetic background medium. We establish a theoretical framework where the response is described through the electric and magnetic multipole moments that are simultaneously generated via the polarization currents that are excited upon the incidence of plane waves. The corresponding dipole and quadrupole polarizabilities are then calculated as a function of the Mie scattering coefficients, and their resonances are mapped for the case of dielectric cylindrical rods as a function of the geometry and the material parameters utilized. The results provide critical insight on the anisotropic response of two-dimensional rod-type metamaterials and can be used as a unified methodology in the calculation of exotic effective electromagnetic parameters involved in phenomena such as optical magnetism
Topological bands in two-dimensional networks of metamaterial elements
We show that topological frequency band structures emerge in two-dimensional
electromagnetic lattices of metamaterial components without the application of
an external magnetic field. The topological nature of the band structure
manifests itself by the occurrence of exceptional points in the band structure
or by the emergence of one-way guided modes. Based on an EM network with nearly
flat frequency bands of nontrivial topology, we propose a coupled-cavity
lattice made of superconducting transmission lines and cavity QED components
which is described by the Janes-Cummings-Hubbard model and can serve as
simulator of the fractional quantum Hall effect
Computing the T-matrix of a scattering object with multiple plane wave illuminations
Given an arbitrarily complicated object, it is often difficult to say immediately how it interacts with a specific illumination. Optically small objects, e.g., spheres, can often be modeled as electric dipoles, but which multipole moments are excited for larger particles possessing a much more complicated shape? The T-matrix answers this question, as it contains the entire information about how an object interacts with any electromagnetic illumination. Moreover, a multitude of interesting properties can be derived from the T-matrix such as the scattering cross section for a specific illumination and information about symmetries of the object. Here, we present a method to calculate the T-matrix of an arbitrary object numerically, solely by illuminating it with multiple plane waves and analyzing the scattered fields. Calculating these fields is readily done by widely available tools. The finite element method is particularly advantageous, because it is fast and efficient. We demonstrate the T-matrix calculation at four examples of relevant optical nanostructures currently at the focus of research interest. We show the advantages of the method to obtain useful information, which is hard to access when relying solely on full wave solvers
Circular dichroism in planar nonchiral plasmonic metamaterials
It is shown theoretically that a nonchiral, two-dimensional array of metallic
spheres exhibits optical activity as manifested in calculations of circular
dichroism. The metallic spheres occupy the sites of a rectangular lattice and
for off-normal incidence they show a strong circular-dichroism effect around
the surface plasmon frequencies. The optical activity is a result of the
rectangular symmetry of the lattice which gives rise to different polarizations
modes of the crystal along the two orthogonal primitive lattice vectors. These
two polarization modes result in a net polar vector, which forms a chiral triad
with the wavevector and the vector normal to the plane of spheres. The
formation of this chiral triad is responsible for the observed circular
dichroism, although the structure itself is intrinsically nonchiral.Comment: 7 pages, 4 figures, to appear in Optics Letter