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Extrinsically chiral optically active metamaterial: circular birefringence and dichroism are seen when the metamaterial plane is tilted around its symmetry axis, so that the plane normal forms an angle with the wave vector of the incident wave .
Circular transmission and polarization conversion measured for electromagnetic waves incident at a tilt angle of (see Fig. 1). The dashed line marks a frequency of pure optical activity; here circular dichroism and linear anisotropy are virtually absent.
Circular dichroism and birefringence in the non-chiral planar metamaterial structure measured for tilt angles from to in steps of . Tilt angles of opposite sign result in reversed signs of circular dichroism and azimuth rotation. The frequency at which pure optical activity on a background of vanishing anisotropy can be seen is marked by a vertical dashed line.
Electric and magnetic responses of asymmetrically split rings. (a) Oscillating currents in a split ring can be represented as a sum of symmetric and antisymmetric currents, corresponding to an electric dipole (green arrow) and a magnetic dipole (red arrow). Optical activity is controlled by the projections of and onto the plane perpendicular to the -vector (green and red dashed arrows correspondingly): it is absent either when one of the projections is zero (b) or if the projections are orthogonal (c); the strongest polarization rotations, of opposite sign, occur if these projections are either parallel (d) or antiparallel (e).
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