We demonstrate enormously strong
chiral effects from a photonic
metamaterial consisting of an array of dual-layer twisted-arcs with
a total thickness of ∼λ/6. Experimental results reveal
a circular dichroism of ∼0.35 in the absolute value and a maximum
polarization rotation of ∼305°/λ in a near-infrared
wavelength region. A transmission of greater than 50% is achieved
at the frequency where the polarization rotation peaks. Retrieved
parameters from measured quantities further indicate an actual optical
activity of 76° per λ and a difference of 0.42 in the indices
of refraction for the two circularly polarized waves of opposite handedness