Dipole Radiation Near Anisotropic Low-Permittivity Media

Abstract

Abstract-We investigate radiation of a dipole at or below the interface of (an)isotropic Epsilon Near Zero (ENZ) media, akin to the classic problem of a dipole above a dielectric half-space. To this end, the radiation patterns of dipoles at the interface of air and a general anisotropic medium (or immersed inside the medium) are derived using the Lorentz reciprocity method. By using an ENZ half-space, air takes on the role of the denser medium. Thus we obtain shaped radiation patterns in air which were only previously attainable inside the dielectric half-space. We then follow the early work of Collin on anisotropic artificial dielectrics which readily enables the implementation of practical anisotropic ENZs by simply stacking sub-wavelength periodic bi-layers of metal and dielectric at optical frequencies. We show that when such a realistic anisotropic ENZ has a low longitudinal permittivity, the desired shaped radiation patterns are achieved in air. In such cases the radiation is also much stronger in air than in the ENZ media, as air is the denser medium. Moreover, we investigate the subtle differences of the dipolar patterns when the anisotropic ENZ dispersion is either elliptic or hyperbolic.

Dirac leaky-wave antennas for continuous beam scanning from photonic crystals

“…It is also possible to enhance and shape the air-side radiation patterns of radiators by placing them on (an)isotropic ENZs and ZIMs 8 . It has even been proposed that ENZs can enable electric levitation of a dipole 9 .…”

Generation of light in spatially dispersive materials

“…The problem of dipole radiation in optically anisotropic layered media without spatial dispersion has been previously considered using the Green function formalism [19][20][21][22][23][24]. When using the formalism, the materials are described by single electric permittivity and magnetic permeability tensors.…”

“…However, they only determine the field in some specific types of materials, including homogeneous anisotropic materials [19][20][21][22][23][24], lossless photonic crystals with known Bloch modes [25], and one-dimensional nanomaterials, such as dielectric-metal stacks [26]. More complex media, especially spatially dispersive ones, are out of reach of these methods.…”

Analysis of anisotropic epsilon-near-zero hetero-junction lens for concentration and beam splitting

“…The material parameters ϵ x 0 1 and ϵ z 0 → 0 − , however, lead to a hyperbolic dispersion, matching, and an atypical extremely oblique refraction because of the near zero longitudinal permittivity. The reflection properties and dispersion of these anisotropic ENZs are reported in [9]. The transverse permittivity component of the ENZ slabs in the x-z plane is close to 1, and the device is thus externally matched for incident light.…”

“…Depending on the frequency of operation, these anisotropic ENZs can be realized with periodic structures that have a similar effective electromagnetic response. At optical frequencies, a simple way is to utilize periodic layers of a plasmonic metal and dielectric, as was done in [8,9] for red light using silver and glass layers.…”