Demonstration of a highly efficient terahertz flat lens employing tri-layer metasurfaces

Abstract

We demonstrate a terahertz flat lens based on tri-layer metasurfaces allowing for broadband linear polarization conversion, where the phase can be tuned through a full 2π range by tailoring the geometry of the subwavelength resonators. The lens functionality is realized by arranging these resonators to create a parabolic spatial phase profile. The fabricated 124-μm-thick device is characterized by scanning the beam profile and cross section, showing diffraction-limited focusing and ∼68% overall efficiency at the operating frequency of 400 GHz. This device has potential for applications in terahertz imaging and communications, as well as beam control in general.

Unveiling the Properties of Metagratings via a Detailed Analytical Model for Synthesis and Analysis

“…Finally, it is important to note that although the syn-thesis and analysis presented herein were demonstrated using metagratings operating at microwave frequencies, the derivation and observations are not restricted to this frequency range. More than that, the same meta-atom structures have been used in the past to devise metasurfaces for terahertz and optical applications [12,[52][53][54].…”

“…Focusing on electrically-polarizable particles in the form of loaded conductive wires has two merits. First, such structures are more practical from a realization point of view, as they can be naturally integrated into planar devices, as was vastly demonstrated for microwave, terahertz, and optical metasurfaces (e.g., [12,15,24,[52][53][54]). Second, it allows harnessing of wellestablished analytical models [30,55,56] for formulation of efficient and insightful synthesis and analysis schemes.…”

Tutorial: Terahertz beamforming, from concepts to realizations

“…185 Subsequently, this methodology was employed to realize a flat lens device with a center frequency of 400 GHz and overall focusing efficiency of 68%. 186 A micrograph of a portion of this array is given in Fig. 14(b).…”

“…14. Terahertz-range transmitarrays that operate in cross-polarization, showing (a) a micrograph of a nonuniform array of C-shaped resonators, which is a portion of a transmitarray device, after Zhang et al, 44 and (b) a multi-layer metallic transmitarray, where the top and bottom layers are orthogonal wire-grid polarizers that enhance the yield of cross-polarized radiation, after Chang et al 186 at terahertz frequencies, 14 and hence the addition of more resonator layers engenders an increase in Ohmic loss. For example, a three-layer device consisting of "I"-shaped resonator unit cells has been employed for a frequency-scanning beam steerer operating around 0.9 THz, with a peak efficiency of 44%.…”

Planar Porous Components for Low‐Loss Terahertz Optics

“…Thanks to the micrometer scale of the THz wavelength, THz metamaterials are easier to manufacture in the THz band than in the visible range. Recently, several designs of metamaterial beamforming devices have been proposed for the THz range, including lenses, deflectors, polarization controllers, orbital angular momentum phase plates, beam splitters, etc. Typically, these metamaterial devices function via a resonant mechanism that can lead to high ohmic losses in metallic metamaterials, as well as relatively narrowband operation.…”