Analysis of a THz unit-structured grating metasurface wave plate

Conventional grating quarter-wave plates (QWPs) usually utilize the birefringence effect to achieve the modulation of the polarization state of the incident wave; however, the operating bandwidth is narrow. A metasurface is a two-dimensional material with periodically aligned structures characterized by thinner volume and larger operating bandwidth. In this paper, it is found that the combination of a conventional grating with a metasurface, which divides the entire conventional grating into multiple sets of unit-structured grating metasurfaces according to the number of grating stripe periods, leads to a certain increase in dispersion bandwidth of the QWP due to the differences in the model patterns formed. By comparing the working bandwidth of the grating metasurface QWP with different stripe periods, it is concluded that the fewer the stripe periods of the grating metasurface QWP, the larger the working bandwidth obtained at low rotational degrees, and the more stripe periods there are, the larger the working bandwidth can be maintained at high rotational angles. This research has design guidance for the next multilayer rotating ultra-broadband achromatic wave plate.