We present the design specifications and in-depth analysis of a terahertz (THz) broadband cross-polarization converter composed of a single-layer metasurface. This device can convert linearly polarized light into its cross-polarization in transmission mode. Different from other polarization conversion devices, this effect results from the suppression and enhancement for different electric components. The broadband characteristic is also achieved by specific partial symmetries designed in the structure. The proposed polarization converter can aid in the development of novel plasmonic polarization devices, and can help to overcome certain limitations of the customary designs that have been proposed thus far.

Graphene, a two-dimensional carbon atom sheet, has attracted tremendous attention and research interest because of its exceptional physical properties. Graphene has high mobility and optical transparency, in addition to flexibility, robustness and environmental stability. The main focus so far has been on fundamental physics and electronic devices. However, because the linear dispersion of the Dirac electrons enables ultrawideband tunability, we believe its true potential lies in photonics and optoelectronics. In this review, we introduce recent advances in the nonlinear optical properties of graphene-based materials. The rise of graphene in nonlinear optics is shown by several recent results, ranging from saturable absorbers and the four-wave mixing effect to giant two-photon absorption, reverse saturable absorption and optical limiting. The relevant forms of the graphene-based materials include pure graphene, graphene oxide and graphene hybrids.