We report the first experiential observation and theoretical analysis of the new phenomenon of planar chiral circular conversion dichroism, which in some aspects resembles the Faraday effect in magnetized media, but does not require the presence of a magnetic field for its observation. It results from the interaction of an electromagnetic wave with a planar chiral structure patterned on the sub-wavelength scale, and manifests itself in asymmetric transmission of circularly polarized waves in the opposite directions through the structure and elliptically polarized eigenstates. The new effect is radically different from conventional gyrotropy of three-dimensional chiral media.Since Hetch and Barron [1] and Arnaut and Davis [2] first introduced planar chiral structures to electromagnetic research they have become the subject of intense theoretical [3,4] and experimental investigations with respect to the polarization properties of scattered fields [5,6,7]. It was understood by many that planar chirality is essentially different in symmetry from threedimensional chirality. Whereas in three-dimensional chiral structures the sense of perceived rotation remains unchanged for opposing directions of observation (think, for example, of a helix observed along its axis), planar chiral structures possess a sense of twist that is reversed when they are observed from opposite sides of the plane to which the structure belongs. Consequently, if planar chiral structures were to exhibit a polarization effect (due to this twist) for light incident normal to the plane, the sense of the effect would be reversed for light propagating in opposite directions. Such behavior has never been observed before, but if proven would be of profound benefit to the development of a new class of microwave and optical devices.In this paper we report such a polarization sensitive effect. It is a previously unknown fundamental phenomenon of electromagnetism that asymmetric materials can generate behaviors that in some ways resemble the famous non-reciprocity of the Faraday effect, which emerges when a wave propagates through a magnetized medium. However, the phenomenon reported here does not require the presence of a magnetic field and results from an electromagnetic wave's transmission through a chiral planar structure patterned on the sub-wavelength scale. Both in the Faraday effect and in that produced by planar chirality, the transmission and retardation of a circularly polarized wave are different in opposite directions. In both cases the polarization eigenstates, i.e. polarization states conserved on propagation, are elliptical (circular).There are also essential differences between the two phenomena. The asymmetry of the Faraday effect with respect to propagation in opposite directions applies to the transmission and retardation of the incident circularly polarized wave itself. The planar chirality effect leads to the (partial) conversion of the incident wave into one of opposite handedness, and it is the efficiency of this conversion that is as...
We report the first experimental evidence that electromagnetic coupling between physically separated planar metal patterns located in parallel planes provides for exceptionally strong polarization rotatory power if one pattern is twisted in respect to the other, creating a 3D chiral object. In terms of optical rotary power per sample of thickness equal to one wavelength, the bi-layered structure rotates five orders of magnitude stronger than a gyrotropic crystal of quartz in the visible spectrum. We also saw a signature of negative refraction for circularly polarized waves propagating through the chiral slab.The ability to rotate the polarization state of light (gyrotropy) by chiral molecules is one of the most fundamental phenomena of electrodynamics. It was discovered by F. Aragot in 1811 and is now widely used in analytical chemistry, biology and crystallography for identifying the spatial structure of molecules. Recent explosive increase in the interest in gyrotropic media is driven by an opportunity for the development of negative index metamaterials, where simultaneous electric and magnetic response of gyrotropic structures are required to achieve negative refraction [1,2,3,4,5,6,7]. Sculptured helical pillars for the optical part of the spectrum [8], helical wire springs [9,10] and twisted Swiss-role metal structures [2] for microwave applications have been discussed as possible candidates for achieving strong artificial gyrotropy that can be used for implementing negative refraction. However, from meta-material prospective it would be very desirable if chirality could be achieved by planar patterning using well-established planar technologies, thus making nano-fabrication of such structures for the optical part of the spectrum a practical proposition. The opportunity of creating true 3D chirality in non-contacting layers of planar metal structures was first identified in Ref. [11]. It was suggested that inductive coupling between two identical mutually twisted metal patterns can create an optically active chiral object and thus provide for gyrotropy.In this letter we show the first experiential demonstration that giant optical gyrotropy can be achieved in a bilayered chiral structure through electromagnetic coupling between the layers and that there is no need to sculpture continuous helix-like volume three-dimensional chiral objects to achieve strong polarization rotatory power. We also saw clear evidence of negative refraction in the structure. The experiments were performed in the microwave part of the spectrum. Although we expect the effect to be seen with a large variety of patterns, we investigated a structure consisting of two identical metal rosettes of 4-fold rotational symmetry located in parallel planes, as presented on Fig. 1. The 4-fold symmetry of the rosette ensures that the structure is isotropic for observations at normal incidence and therefore shows no birefringence. Due to curved lines rosette-like structure exhibit resonant properties at wavelengths larger than the overall size of th...
Engaging strongly resonant interactions allows dramatic enhancement of functionalities of many electromagnetic devices. However, resonances can be dampened by Joule and radiation losses. While in many cases Joule losses may be minimized by the choice of constituting materials, controlling radiation losses is often a bigger problem. Recent solutions include the use of coupled radiant and sub-radiant modes yielding narrow asymmetric Fano resonances in a wide range of systems, from defect states in photonic crystals and optical waveguides with mesoscopic ring resonators to nanoscale plasmonic and metamaterial systems exhibiting interference effects akin to electromagnetically-induced transparency. Here we demonstrate theoretically and confirm experimentally a new mechanism of resonant electromagnetic transparency, which yields very narrow isolated symmetric Lorentzian transmission lines in toroidal metamaterials. It exploits the long sought non-trivial non-radiating charge-current excitation based on interfering electric and toroidal dipoles that was first proposed by Afanasiev and Stepanovsky in [J. Phys. A Math. Gen. 28, 4565 (1995)].
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