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...

We show that in the visible to near-IR part of the spectrum, normal incidence transmission of circularly polarized light through a nanostructured anisotropic planar chiral metamaterial is asymmetric in the opposite directions. The new effect is fundamentally different from the conventional gyrotropy of bulk chiral media and the Faraday effect. It has a resonance nature associated with a new type of excitation in the metal nanostructure:  the enantiomerically sensitive plasmon.

The authors demonstrate a chiral photonic metamaterial with chirality provided by electromagnetic coupling between mutually twisted unconnected layers. In the visible and near-IR spectral ranges, the material exhibits polarization rotatory power of up to 2500°∕mm and shows relatively low losses and negligible circular dichroism, making it a promising candidate for the development of chiral negative index media.

We demonstrate for the first time a nanostructured planar photonic metamaterial transmitting light differently in forward and backward directions.