Anisotropic coding metamaterials and their powerful manipulation of differently polarized terahertz waves

Abstract

Metamaterials based on effective media can be used to produce a number of unusual physical properties (for example, negative refraction and invisibility cloaking) because they can be tailored with effective medium parameters that do not occur in nature. Recently, the use of coding metamaterials has been suggested for the control of electromagnetic waves through the design of coding sequences using digital elements ‘0’ and ‘1,' which possess opposite phase responses. Here we propose the concept of an anisotropic coding metamaterial in which the coding behaviors in different directions are dependent on the polarization status of the electromagnetic waves. We experimentally demonstrate an ultrathin and flexible polarization-controlled anisotropic coding metasurface that functions in the terahertz regime using specially designed coding elements. By encoding the elements with elaborately designed coding sequences (both 1-bit and 2-bit sequences), the x- and y-polarized waves can be anomalously reflected or independently diffused in three dimensions. The simulated far-field scattering patterns and near-field distributions are presented to illustrate the dual-functional performance of the encoded metasurface, and the results are consistent with the measured results. We further demonstrate the ability of the anisotropic coding metasurfaces to generate a beam splitter and realize simultaneous anomalous reflections and polarization conversions, thus providing powerful control of differently polarized electromagnetic waves. The proposed method enables versatile beam behaviors under orthogonal polarizations using a single metasurface and has the potential for use in the development of interesting terahertz devices.

Polarization‐Induced Chirality in Metamaterials via Optomechanical Interaction

“…The great design flexibility of these structures allows one to manipulate the amplitude, phase, and polarization of waves on demand. [1][2][3][4][5][6][7][8] In the design of metamaterials, structural symmetry sets fundamental bounds on the electromagnetic properties that can be achieved. For example, optical chiral effects, including circular dichroism and circular birefringence, typically require stereoscopic structures with broken mirror symmetry (3D chirality), [9][10][11][12][13] while circular conversion dichroism (elliptical dichroism) can be found in planar chiral geometries (2D chirality).…”

Polarization State Manipulation of Electromagnetic Waves with Metamaterials and Its Applications in Nanophotonics

“…Another approach named "coding metamaterial" has also been paid great atention by the scientiic community, which is composed of several types of unit cells, with diferent constant phase responses, respectively [67][68][69][70]. Figure 9h shows a 1-bit coding metamaterial, composed of two types of unit cells, with 0 and π phase responses (as shown in Figure 9i), which is named "0" and "1" elements, respectively [67].…”

Microwave metamaterials

“…Then, the functionality of a metamaterial can be controlled in large dynamics by changing the coding sequences of '0' and '1'. The coding metamaterial has been extended from microwave to terahertz frequencies [15], from isotropic to anisotropic [16] and even with full tensor, from reflection type to transmission type, from single band to dual band, and from spatial coding to frequency coding [17], demonstrating the powerful ability and large potential of coding metamaterials in manipulating the wave fronts, polarization states, numbers and directions of scattering beams, diffusions, and conversions from spatial waves to surface waves.…”