Metasurfaces in terahertz waveband

Metasurface, composed of subwavelength antennas, allows us to obtain arbitrary permittivity and permeability in electromagnetic (EM) waveband. It can be used to control the polarization, frequency, amplitude, and phase of the EM wave. Conventional terahertz (THz) components, such as high-impedance silicon lens, polyethylene lens, and quartz wave plate, rely on the phase accumulation along the wave propagation to reshape the THz wavefront. The metasurface employs the localized surface plasmon resonance to modulate the wavefront. Compared with conventional THz components, metasurface has the advantages of being ultrathin, ultralight, and low cost. In recent years, a large number of THz devices based on metasurface have been proposed. We review in broad outline the metasurface devices in the THz region and describe the progress of static and tunable THz field-modulated metasurfaces in detail. Finally, we discuss current challenges and opportunities in this rapidly developing research field.