Broadband polarization transformation via enhanced asymmetric   transmission through arrays of twisted complementary split-ring resonators
  This study proposes an ultrathin chiral metamaterial slab stacked with twisted complementary split-ring resonators (CSRRs) for highly efficient broadband polarization transformation. The polarization of linearly polarized electromagnetic waves can be rotated in a specific direction by passing it through such a slab having a thickness of about one-tenth the operational wavelength. Microwave experiments verified the theoretically predicted conversion efficiency of up to 96% covering a bandwidth of 24% of the central wavelength. CSRRs with circular symmetry provide increased interlayer coupling strength, which produces a high-efficiency broadband response and strong isolation of the original polarization. 
Wei Zeyong, Cao Yang, Fan Yuancheng, Yu Xing and Li Hongqiang
physics.optics