Planar metamaterial with transmission and reflection that depend on the direction of incidence

Abstract

We report that normal incidence reflection and transmission of circularly polarized electromagnetic waves from and through planar split-ring microwave metamaterials with chiral symmetry breaking depends on the incidence direction and handedness of circular polarization. The effect has a resonant nature and is linked to the lack of mirror symmetry in the metamaterial pattern leading to a polarization-sensitive excitation of electric and magnetic dipolar responses in the meta-molecules. It has striking phenomenological resemblance with the reflective circular dichroism of high-temperature "anyon" superconductors. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3109780͔ Directional asymmetry of transmission and reflection is normally associated with the presence of a static magnetization of the medium which breaks the reciprocity of the light-matter interaction. Here the optical Faraday effect is the most important example. However, it was recently understood that asymmetric transmission of circularly polarized electromagnetic waves is also possible in reciprocal systems if circular polarization conversion is involved. 1 This has been investigated for lossy, planar chiral metamaterial structures. 2-4 Several other ideas using chirality in asymmetric and polarization-sensitive devices have recently been suggested. [5][6][7][8] In this letter we demonstrate a type of microwave metamaterial that shows strong resonant asymmetric transmission at normal incidence and we report that this is accompanied by asymmetric reflection. Transmission and reflection of circularly polarized waves are both controlled by the chiral asymmetry of the metamaterial pattern and depend on the direction of incidence and on the handedness of the incident circular polarization state in exactly the same way. We show that such behavior is associated with the asymmetric nature of dissipation in the substrate imposed by twodimensionally chiral ͑2D-chiral͒ patterning and we provide a detailed description of the effect's microscopic mechanism along with a complete characterization of its eigenstates.The effect has been observed in a planar metamaterial based on asymmetrically split rings, which belongs to a recently identified class of structures supporting high-Q trapped-mode resonances of collective/coherent nature. 9,10 To see the asymmetric effects we modified a previously used design by introducing an asymmetry in both arcs and gaps so that the resulting metamaterial has no line of mirror symmetry and is thus 2D-chiral. A "twist vector" W governed by the corkscrew law ͑rotation from small gap towards large gap along the short arc͒ may be associated with the handedness ͑twist͒ of the pattern ͓see Fig. 1͑b͔͒. In our structures the metal rings had a radius of 6 mm and a width of 0.8 mm and were split to create two arcs of 160°and 140°with gaps corresponding to 30°and 10°. They were etched from 35 m copper cladding covering 1.6 mm thick FR4 PCB substrate ͑ Ӎ 4.5͒. The metamaterial was formed by a regular array of these rings with an overall si...

Dual-Band Circular Polarizer and Asymmetric Spectrum Filter Using Ultrathin Compact Chiral Metamaterial

“…These drawbacks make them not good candidates in this area. An asymmetry was recently introduced in both arc and gaps so that the resulting metamaterial has no line of mirror symmetry [10,14,30], enabling the asymmetric transmission of circularly polarized wave, however, this leads to exceptionally large meta-atoms.…”

“…due to their unique electromagnetic (EM) properties and a wider set of functionalities such as giant optical activity [1], elliptical or circular dichroism [2], giant gyrotropy [3], negative refraction without simultaneous negative permittivity and permeability [4][5][6][7][8][9], and asymmetric transmission [10][11][12][13][14][15], etc. The unusual polarization functionalities and chirality not found in natural medium arise from the magneto-electric cross coupling of chiral structures due to their bianisotropy and lack of any mirror symmetry.…”

“…Among them, several chiral structures have been available to tailor the cross coupling between electric and magnetic fields such as the commonly utilized U-shaped structures [1,15,21,29], conjugated metallic pairs and conjugated gammadion resonators combining cut-wire pairs [27,28], twisted rosettes [2,3,5], cross-wire structure (gammadion) and its complementary variations [9,11,20,31], twisted foil structure [7,26], L-shaped chiral structure [8], fishscale pattern [10,11], twisted split ring resonators (SRRs), twist Hilbert patterns, and twisted complementary SRRs with symmetric or asymmetric geometry [12-14, 23, 24, 30, 33], Metallic helix array [16,18], stacked nanorod arrays [19], twist arc structure [22], and I-shaped structure [25]. However, most "meta-atoms" or "meta-molecule" of CMMs are extremely large, this is especially true when arrange the four U-shaped rings in four-fold rotational symmetry (C4) to obtain the optical activity insensitive to the linear polarization of the incident wave.…”

Chiral mirrors

“…Lossy, anisotropic, 2D-chiral metasurfaces exhibit a corresponding optical effect, where the same circularly polarized wave will be transmitted and absorbed differently when illuminating opposite sides of the metasurface. [19][20][21][22][23][24][25][26][27] In particular, such 2D-chiral metasurfaces predominantly absorb RCP incident on one side and LCP incident on the opposite side. We note that also the Faraday effect enables differential absorption of circularly polarized waves, which would aggregate during both passes through the Faraday medium, however, such a "Faraday absorber mirror" would still reverse the handedness of the reflected wave.…”

Broadband asymmetric waveguiding of light without polarization limitations

“…Great efforts have been made to realize such 'optical diodes' with non-reciprocal propagation of light by breaking the time-reversal symmetry, such as indirect interband photonic transition 1,2 , magneto-optic effect [3][4][5][6][7] , optical nonlinearity [8][9][10] or photonic crystals 11 . In addition, numerous reciprocal structures are designed as alternatives to achieve asymmetric propagation of light by employing metamaterials [12][13][14][15][16][17][18][19][20] for either circularly polarized waves or linearly polarized waves.…”