Arc and rotation together induce phase-modulated terahertz metasurfaces

Abstract

Metasurfaces have the characteristics of simple structure, easy fabrication, easy integration etc., and can flexibly control electromagnetic waves. It is widely used in terahertz filters, lenses, polarization converters, wavefront adjustment, terahertz imaging and so on. By encoding and arranging unit cells with different amplitudes and phases according to a certain rule, the metasurfaces can achieve various functions such as imaging, focusing, beam splitting, vortex beam, etc. The reported coding metasurfaces are phase-modulated according to geometric phase or transmission phase theory. However, geometric phase has spin-locking property and transmission phase has single-frequency property, which hinders the application of a unified metasurface to simultaneously regulate geometric and transmission phases.<br>To address the above issues, in this letter, we proposed an arc and rotation co-induced phase modulation metasurface, whose unit cell independently modulate the cross-polarized reflection phases of LCP and RCP waves and has a certain bandwidth, which meets the demands in frequency region of 1-1.2 THz. Through the principle of phase convolution and shared aperture, the metasurface realize vortex beams with a topological charge of ±1, focusing with a focal length of 1500 μm, deflected vortex beams with a topological charge of ±2, and quasi-perfect vortex beams, and multichannel vortex beams. The structure has the advantages of simple structure, flexible and convenient regulation, and compact size, which improves the utilization of the electromagnetic space and has a broad application prospect in the future terahertz communication system.