Polarization properties in helical metamaterials

In the last few years, there has been growing interest in the research of helical metamaterials due to the advantages of giant circular dichroism, broad operation bands, and compact structures. However, most of the researches were in the cases of single-, circular-helical metamaterials, and normal incidences. In this paper, we reviewed recent simulation works in the helical metamaterials with the finite-difference time-domain (FDTD) method, which mainly included the optical performances of double-, three-, four-helical metamaterials, performances of elliptical-helical metamaterials, and the polarization properties under the condition of oblique incidences. The results demonstrate that the double-helical metamaterials have operation bands more than 50%, which is broader than those of the single-helical structures. But both of them have low signal-to-noise ratios about 10 dB. The three-and four-helical metamaterials have significant improvement in overall performance. For ellipticalhelixes, simulation results suggest that the transmitted light can have elliptical polarization states. On the condition of oblique incidences, the novel property of tunable polarization states occurred in the helical metamaterials, which could have much broader potential applications such as tunable optical polarizers, tunable beam splitters, and tunable optical attenuators.