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(Color online) Isoindex gyrotropic spectral filters. (a) In conventional filters of this type, a uniaxial optically active birefringent crystal with accidental birefringence zero-crossing λ 0 is sandwiched between two orthogonal linear polarizers P 1 and P 2. The crystal birefringence must change sign at wavelength λ 0, while optical activity (circular birefringence) should remain non-zero. (b) In metamaterial-based isoindex spectral filters, planar metamaterial tilted with respect to the filter’s optical axis replaces the crystal. The metamaterial exhibits strong resonant optical activity, which coincides with a birefringence zero-crossing isoindex point λ 0.
(Color online) Metamaterial characteristics near the isoindex point. (a) Linear and (b) circular birefringence represented as differential phase delay for orthogonal polarizations. (c) Linear and (d) circular dichroism represented as differential transmission amplitudes. (e) Ellipticity angle and (f) azimuth of the metamaterial’s polarization eigenstates. Circular eigenstates illustrate negligible linear dichroism and zero linear birefringence at the isoindex point. All quantities are plotted for α = 20° oblique incidence onto the metamaterial shown in Fig. 3(a). tii are the metamaterial’s direct transmission coefficients for electric fields which are linearly polarized perpendicular (x)/parallel (y) to the metamaterial’s symmetry axis or right (+)/left (−) circularly polarized.
(Color online) Metamaterial-based isoindex filters for microwaves and optics. Transmission characteristics of the (a) microwave and (b) optical filters for various angles of the metamaterial tilt α. The insets show fragments of the actual metamaterial patterns.
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