Photo-Excited Metasurface for Tunable Terahertz Reflective Circular Polarization Conversion and Anomalous Beam Deflection at Two Frequencies Independently

Abstract

In this paper, a photo-excited metasurface (MS) based on hybrid patterned photoconductive silicon (Si) structures was proposed in the terahertz (THz) region, which can realize the tunable reflective circular polarization (CP) conversion and beam deflection effect at two frequencies independently. The unit cell of the proposed MS consists of a metal circular-ring (CR), Si ellipse-shaped-patch (ESP) and circular-double-split-ring (CDSR) structure, a middle dielectric substrate, and a bottom metal ground plane. By altering the external infrared-beam pumping power, it is possible to modify the electric conductivity of both the Si ESP and CDSR components. By varying the conductivity of the Si array in this manner, the proposed MS can achieve a reflective CP conversion efficiency that ranges from 0% to 96.6% at a lower frequency of 0.65 THz, and from 0% to 89.3% at a higher frequency of 1.37 THz. Furthermore, the corresponding modulation depth of this MS is as high as 96.6% and 89.3% at two distinct and independent frequencies, respectively. Moreover, at the lower and higher frequencies, the 2π phase shift can also be achieved by respectively rotating the oriented angle (αi) of the Si ESP and CDSR structures. Finally, an MS supercell is constructed for the reflective CP beam deflection, and the efficiency is dynamically tuned from 0% to 99% at the two independent frequencies. Due to its excellent photo-excited response, the proposed MS may find potential applications in active functional THz wavefront devices, such as modulators, switches, and deflectors.

Recent Advances in Terahertz Manipulations Using C‐Shape‐Split‐Ring‐Resonator Metasurfaces (Review)

“…Recently, metasurfaces have garnered significant attention for their ability to manipulate electromagnetic waves. [ 39–42 ] Composed of subwavelength‐scale elements arranged in a periodic or aperiodic pattern, metasurfaces offer unique capabilities in controlling electromagnetic waves such as the amplitude, [ 43–45 ] phase, [ 46–52 ] and polarization [ 53,54 ] of electromagnetic waves. In the context of manipulating THz waves, metasurfaces have demonstrated tremendous potential.…”

Metamaterial terahertz device with temperature regulation function that can achieve perfect absorption and complete reflection conversion of ultrawideband

“…Terahertz waves are a type of electromagnetic wave characterized by frequencies ranging from 0.1 to 10 THz and corresponding wavelengths of 0.03-3 mm [1][2][3][4][5]. These waves possess notable attributes, such as low energy, strong penetration, and coherence, which contribute to their wide-ranging potential applications [6][7][8][9][10].…”

Ultrathin Narrowband and Bidirectional Perfect Metasurface Absorber

“…By altering the geometrical shape and dimensions of the unit cell structures, MSs can tailor the effective EM parameters (complex permittivity and permeability) and provide much more design flexibility than conventional materials. Over the past few decades, MSs have gained considerable attention due to their numerous promising applications, such as in flat metalenses [2,3], imaging [4], filters [5,6], wavefront manipulating devices [7][8][9][10], detectors [11], sensors [12], polarization convertors [13][14][15], and absorbers [16,17]. In particular, since the invention of the concept of a perfect absorber based on MMs by Landy [16], numerous metasurface absorbers (MSAs) have been proposed and implemented for the microwave, THz, and even for the visible frequency regions [17][18][19][20][21][22][23][24][25][26].…”