Highly efficient vectorial field manipulation using a transmitted tri-layer metasurface in the terahertz band

Polarization is a basic characteristic of electromagnetic waves that conveys much optical information owing to its many states. The polarization state is manipulated and controlled for optical information security, optical encryption, and optical communication. Metasurface devices provide a new way to manipulate wave-fronts of light. A single ultrathin metasurface device can generate and modulate several differently polarized light fields, and thus carries optical information in several different channels. Terahertz (THz) waves have become widely used as carrier waves for wireless communication. Compact and functional metasurface devices are in high demand for THz elements and systems. This paper proposes a tri-layer metallic THz metasurface for multi-channel polarization generation and phase modulation with a high efficiency of approximately 80%. An azimuthally polarized THz vectorial beam generator is realized and characterized for use as a THz polarization analyzer. The incident polarization angle can be observed graphically with high accuracy. Moreover, a vectorial hologram with eight channels for different linear polarization states is demonstrated experimentally. The information in different holograms can be hidden by choosing the polarization channel for detection. This work contributes to achieving multi-functional metasurface in the THz band and can benefit THz communication and optical information security.