Asymmetric transmission of radially polarized THz radiation through a double circular grating

Abstract

We report on unidirectional and asymmetric transmission of radially polarized THz radiation through a dual circular metallic grating with sub-wavelength slits. Unidirectional transmission is shown theoretically for a super-Gaussian incident beam, and an asymmetric transmission is demonstrated experimentally, when the radially polarized beam of 0.1 THz is obtained by converting a linearly polarized beam with a discontinuous phase retarder and a tapered waveguide. The dual grating does not include nonlinear materials, its operation is reciprocal, and analogous to that of some planar metallic gratings.

Experimental verification of asymmetric transmission in continuous omega-shaped metamaterials

“…8 Recently, metamaterials have been studied widely by simulation methods; most of the sample fabrications and experimental measurements were just realized at microwave and terahertz regions by both two-dimensional (2D) and three-dimensional (3D) metamaterials. 1,2,9 In contrast, the fabrication of nanoscale metastructures at infrared and optical regions primarily involve planar metasurfaces rather than 3D metamaterials. 7,10,11 However, it is of great signicance to overcome the challenges of fabricating 3D metamaterials at nanoscale, which have presented or enhanced a variety of electromagnetic properties not realized in planar metamaterials, such as AT effect of linearly polarized light 12,13 and the enhanced optical activity.…”

“…However, these studies usually involve a material whose size is bigger than the desired wavelength; hence, they cannot be used in the micro-nano optical system and other optical communication systems. In addition, the gradient metasurface, 25 asymmetric gratings, 9,26,27 and chiral metamaterials 28,29 have been proposed to realize AT effects without breaking Lorentz's reciprocity theorem. It is complicated to properly design the phase gradient of the metasurface 25 or to avoid the higher diffraction modes of asymmetric gratings.…”