Ultrafast synthesis and switching of light polarization in nonlinear anisotropic metamaterials

Optical communications, laser science, microscopy and metrology demand control of light polarization, which is also used as a probe of chemical and biological systems. Typically, certain polarization states of light are achieved using macroscopic anisotropic crystals. Metamaterials and metasurfaces
have recently been developed to act as efficient passive polarization components of subwavelength dimensions1–4. However, active polarization control has so far been mainly limited to microwave and terahertz wavelengths5–7. Here we demonstrate all-optical switching of visible light polarization, achieving up to 60° rotation of the polarization ellipse at picosecond timescales. This is accomplished both under control illumination and in a self-phase modulation regime, where the intensity of light affects its own polarization state, by exploiting the strong anisotropy and nonlinear response of a hyperbolic metamaterial3,8–10. The effects are general for any resonant, anisotropic, nonlinear nanoantennas and metasurfaces and are suited to numerous photonic applications and material characterization techniques where ultrafast polarization shaping is required.