Polarization Control in Terahertz Metasurfaces with the Lowest Order Rotational Symmetry

Abstract

wileyonlinelibrary.com COMMUNICATIONwith specifi c symmetry to control the polarization state of the incoming light. Owing to the 2D feature of metasurfaces, we could degenerate the tensor χ from complex 3 × 3 matrix to 2 × 2 matrix. [ 10 ] The transmission response through a metasurface can be described by transmittance, polarization ellipses, averaged polarization rotation, and polarization conversion, [22][23][24][25] which can easily be determined from the frequencydependent 2 × 2 Jones matrix. [ 26,27 ] In the recent past, there have been several works on chiral metamolecules that consist of 2D and 3D designs. [ 28,29 ] For the 2D metasurfaces with planar chirality, the most commonly employed designs have fourfold rotational symmetry. [30][31][32][33] Asymmetric transmission of circular polarization in planar metamaterial structures has been discussed in the past. [34][35][36][37][38][39] Another approach to obtain the optical activity by planar metasurfaces is to tilt the metamaterial plane with respect to the incident light so that the excited magnetic and electric dipoles in the asymmetric metamolecule interact with each other. [ 40 ] However, the optical activity and birefringence are not strong enough in these metamaterials to have a functionality such as a circular polarizer and polarization rotator. Therefore, 3D designs and multilayer metamaterials were proposed to improve the optical activity and birefringence. [ 31,41,42 ] Circular polarizers with broadband operation were also realized due to the giant circular dichroism of the 3D and multilayer designs. A major advantage of 3D chiral metamolecules over planar chiral design is that the asymmetric transmission of linearly polarized light can be achieved by breaking the symmetry of the unit cell in the propagation direction. [43][44][45] However, the complex fabrication process limits the application of these devices to a large extent. Therefore, a simple planar design with giant optical activity and asymmetric transmission of circularly polarized light becomes highly desirable.Unlike the previously employed designs, we propose a planar metamolecule with the lowest order rotational symmetry, i.e., twofold rotational symmetry, and demonstrate a giant optical activity and asymmetric transmission of the terahertz waves. We observed a giant cross polarization transmission response, which is the most straightforward way to determine the optical activity, the polarization control as well as realize high effi ciency wave defl ection using planar metasurfaces. The major advantage of the twofold rotational symmetric planar structure is due to the additional degree of freedom that allows us to tailor the optical axes of the metamolecule that can in turn modulate the cross polarization transmission amplitude. By varying the orientation of the split gaps in the split-ring resonator (SRR) metamolecule and preserving the rotational symmetry, the intrinsic optical activity and asymmetric transmission is easily modulated. The optimized design allows the strongest op...

Fundamentals and Applications of Metasurfaces

“…Consider an anisotropic nanostructure under normal incidence, and t o and t e represent its complex transmission coefficients when the polarization of incoming light is along the two principle axes of the nanostructure, respectively. As the nanoresonator is rotated an angle θ from the x axis shown in Figure f, the transmission coefficients for this rotated system can be deduced via the operation of Jones matrix:where R (θ) is the rotation matrix. When the incident wave is circularly polarized (CP), the transmitted electric field () can be derived by applying matrix multiplication of Equation and the Jones' vectors of left‐handed CP (LCP) or right‐handed CP (RCP) light …”

Advances in Full Control of Electromagnetic Waves with Metasurfaces

“…[ 39,40 ] Because of the geometrical nature of the PB phase, such concept can be easily extended to other frequency. [41][42][43] It is noted that the PB phase can only be imparted to CP light. Signifi cantly, when a linearly polarized Figure 1.…”

Near‐Field Inductive Coupling Induced Polarization Control in Metasurfaces

“…[ 29 ] We obtained the time-domain waveforms and then converted them into frequency domain spectra with both amplitude and phase information using Fourier transform. The transmission amplitude spectra | ( )| t ji ω and the phase informa- ω is the complex transmitted reference signal, respectively.…”

“…[ 22,23 ] Arbitrary manipulation of local and global polarization of output radiation has been a very important research hot spot that fi nds applications in holography, [24][25][26] beam splitter, [ 27 ] vector beam generation, [ 28 ] and polarization control. [29][30][31][32][33][34][35] In this work, we provide a new perspective of near-fi eld coupling where we demonstrate a passive switching of the near-fi eld inductive coupling induced excitation in orthogonally twisted meta-atoms where the coupling channel is switched on in one confi guration (MM1, See Figure 1) and switched off in another confi guration (MM2) without any change in the geometrical distance between the near-fi eld coupled meta-atoms. The electromagnetic nearfi eld coupling between the meta-atom induces the crosspolarized radiation that is switched on and off as the coupling channel is switched on and off, which plays a dominant role in determining the output polarization state of light.…”