We experimentally demonstrate a three-dimensional chiral optical metamaterial that exhibits an asymmetric transmission for forwardly and backwardly propagating linearly polarized light. The observation of this novel effect requires a metamaterial composed of three-dimensional chiral metaatoms without any rotational symmetry. Our analysis is supported by a systematic investigation of the transmission matrices for arbitrarily complex, lossy media that allows deriving a simple criterion for asymmetric transmission in an arbitrary polarization base. Contrary to physical intuition, in general the polarization eigenstates in such three-dimensional and low-symmetry metamaterials do not obey fixed relations and the associated transmission matrices cannot be symmetrized.PACS numbers: XX.XX.XX During the past several years optical metamaterials (MMs) have attracted an enormous interest since they promise to allow for a manipulation of light propagation to a seemingly arbitrary extent. MMs are usually obtained by assembling sub-wavelength unit cell structures called metaatoms. Initial studies on MMs were based on rather simple and highly symmetric metaatoms [1][2][3]. Recently, more and more sophisticated structures were explored in order to achieve customized functionalities like, e.g. a negative refractive index due to chirality [4-6]. Also, a large variety of plasmonic metaatoms were investigated that evoke a huge polarization rotation like gammadions, omega shaped particles or helices [7][8][9]. Studying the characteristics of light propagation in such low-symmetry MMs also revealed unexpected phenomena like asymmetric transmission for circularly polarized light [10][11][12]. Although at first sight this effect of nonreciprocal transmission, to date not observed for linearly polarized light, is counterintuitive, it does not violate Lorentz' reciprocity theorem. This asymmetric transmission of circularly polarized light was demonstrated at so-called planar chiral MMs. Such MMs are composed of metaatoms without structural variation in the principal propagation direction. They preserve symmetry in this direction and are only chiral in the two-dimensional space [13]; thus, strictly speaking, they are intrinsically achiral in three dimensions since the mirror image of a structure is congruent with the structure itself if operated from the backside. The remaining mirroring plane is perpendicular to the propagation direction.In this Letter we theoretically and experimentally demonstrate a novel MM design which breaks the latter symmetry. For the first time our approach reveals that the very structures exhibit asymmetric transmission for linearly polarized light. We emphasize that also in this case the reciprocity theorem is not violated since only reciprocal materials are involved.Prior to any further considerations we concisely discuss the effect of a potential MM substrate that is, after all, in most cases required for fabricating planar MMs. Generally speaking, just this supporting substrate breaks the mirror symmetry for ...

defined polarization state is a key requirement in numerous photonic applications. For example, linear optical polarizers are frequently utilized in lithography, [7,8] industrial vision, [9] microscopy, ellipsometry [10] or astronomic remote sensing systems. [11] All these applications substantially benefit from efficient nano-optical wire grid polarizers.A wire grid polarizer (WGP) is a grating type metasurface (see Figure 1). The typical operation principle for such elements requires the transmittance of TM polarized light T TM (TM transversal magneticelectrical field orthogonal to the ridges) to be much larger than that of TE polarized light T TE (transversal electric-electrical field parallel to the ridges) to achieve a significant anisotropic filter functionality. Here, the extinction ratio E r = T TM /T TE is used to express the suppression of TE polarized light. [12] WGPs are highly beneficial because of large achievable element sizes (wafer size), compactness (wafer thickness), and large acceptance angles. [13] Furthermore, their nano-optical nature allows an easy integration into other (nano-)optical elements, such as litho graphy masks, [14] enabling local polarization control. Currently, applications advance toward shorter wavelengths in order to benefit from smaller foci and characteristic electronic transitions, which can be utilized for material analysis. While WGPs are well established in the VIS and IR, suitable ones were not available in the deep ultraviolet (DUV) spectral range until very recently. [12,15,16] The lack of applicable DUV WGPs originates from challenging requirements on both structure and material properties.A structural period of the polarizer has to fulfilling the zero order conditionto avoid propagation of diffraction orders greater than the zeroth one.[17] For a normal incidence of light (ϕ = 0°) with a wavelength λ in the DUV and a fused silica substrate with a refractive index n sub a period p in the order of 100 nm is necessary. Additionally, an aspect ratio (see Figure 1: ratio of height and ridge width) larger than five is typically required. [12] The simultaneous realization of large aspect ratio and small periods is technologically extremely challenging. Fortunately however, advances in nanotechnology do allow the fabrication of such structures. [18] Pelletier et al. [15] demonstrated aluminum WGPsWire grid polarizers (WGPs), periodic nano-optical metasurfaces, are convenient polarizing elements for many optical applications. However, they are still inadequate in the deep ultraviolet spectral range. It is shown that to achieve high performance ultraviolet WGPs a material with large absolute value of the complex permittivity and extinction coefficient at the wavelength of interest has to be utilized. This requirement is compared to refractive index models considering intraband and interband absorption processes. It is elucidated why the extinction ratio of metallic WGPs intrinsically humble in the deep ultraviolet, whereas wide bandgap semiconductors are superior materia...

Plasmonic metamaterials exhibit strong and tunable dispersion, as a result of their pronounced resonances. This dispersion is used to construct an ultrathin light-shaping element that produces different waves at two distinct wavelengths in the near IR range. The optical response of the pixelated element is adjusted by variations in the geometry of the metamaterial's unit cell. Applications requiring spatial and spectral control of light become feasible.

In this paper, the Comsol Multiphysics version 5.0 is used to study the effect of geometric parameters on transmission of chiral met-amaterial nanostructures. The angle of the chiral metamaterial element was varied to see his effect. Transmission coefficient (S21) and reflection coefficient (S11) are computed. In the case of nano chiral metamaterial structure, and depending on the application, the electromagnetic behavior can be adjusted by changing the angle of the chiral element.

This paper describes in a very easy and intelligible way, how the diffraction efficiencies of binary dielectric transmission gratings depend on the geometrical groove parameters and how a high efficiency can be obtained. The phenomenological explanation is based on the modal method. The mechanism of excitation of modes by the incident wave, their propagation constants and how they couple into the diffraction orders helps to understand the diffraction process of such gratings and enables a grating design without complicated numerical calculations.