Self-complementary Metasurface Research Articles

Bidirectional and Circularly Polarized Fabry–Perot Antenna Based on Self-Complementary Metasurface for Millimeter-Wave Applications

Bidirectional and Circularly Polarized Fabry–Perot Antenna Based on Self-Complementary Metasurface for Millimeter-Wave Applications

Excitation of Surface Waves With On-Demand Polarization at Self-Complementary Metasurface

Surface electromagnetic waves are the main carriers of the highly localized in-plane signal in planar antennas and photonic devices. However, the polarization degree of freedom is generally absent for surface waves as far as it is still a challenge to excite the surface waves with a necessary polarization state. In this letter, for the first time, we propose a method to excite the surface waves of arbitrary polarization using the self-complementary metasurfaces obeying Babinet's duality principle. Namely, we demonstrate the excitation of surface waves with i) linear horizontal and vertical, ii) linear diagonal, iii) right- and left-handed circular, and iv) elliptical polarizations covering, in principle, a whole Poincaré sphere of polarization states. Finally, we analyze the impact of substrate on the efficiency of polarization-demanded surface waves excitation. The results obtained may find the numerous applications in planar photonic and flat optical polarization devices.

Dual-mode hyperbolicity, supercanalization, and leakage in self-complementary metasurfaces

Abstract Anisotropic Self-Complementary Metasurfaces (SC-MTSs) are structures constituted by an alternation of complementary inductive and capacitive strips, which are “self-dual” according to Babinet’s duality principle. They support the propagation of two orthogonally polarized surface-wave modes with the same phase velocity along the principal directions (i.e., along the strips and normal to them). The isofrequency dispersion curves of these modes are hyperbolas, and therefore, these MTSs fall in the category of hyperbolic MTSs. It is shown here that the hyperbolic dispersion curves may degenerate in same cases into almost straight lines, which implies that the velocity of energy transport is constantly directed along the same direction for any possible phasing orthogonal to the strips. In this circumstance, the SC-MTS can be conveniently used to design dual-polarized leaky-wave antennas by modulating the impedances of the complementary strips.

Self-Complementary Hyperbolic Metasurface Antennas

Anisotropic Self-Complementary Metasurfaces (SCM) are structures constituted by a “self-dual” (according to Babinet’s duality principle) alternance of inductive and capacitive complementary strips. They support orthogonally polarized surface-wave modes with the same phase velocity in the principal direction of propagation. The isofrequency dispersion curves of these modes are hyperbolas, and therefore these metasurfaces (MTSs) fall in the category of hyperbolic MTSs. It is shown here that the hyperbolas may degenerate in same cases into almost straight lines, which implies that the velocity of energy transport is constantly directed along the complementary strips at any frequency and for any possible phasing orthogonal to the strips. In this circumstance, the SCM can be conveniently used to design dual-polarized leaky-wave antennas by modulating the impedances of the complementary strips. Each strip behaves as a channel, which can be independently fed with the desired phase and amplitude. We demonstrate here that these antennas exhibit a strong decoupling between both co-polar and cross-polar channels, even when the distance between strips is electrically small. This increases the performance of the antenna, especially in azimuthal beam scanning. A prototype at 2.6 GHz has been constructed and successfully measured confirming the theoretical conjectures.

Surface Waves on Self-Complementary Metasurfaces: All-Frequency Hyperbolicity, Extreme Canalization, and TE-TM Polarization Degeneracy

A new platform for routing surface electromagnetic waves does so efficiently across a planar surface while maintaining control of polarization, key steps toward the realization of flat optical devices.

Self-complementary metasurfaces for designing terahertz deflecting circular-polarization beam splitters

Metasurfaces provide a broad range of functionalities related to wavefront manipulation in different frequency ranges with the advantage of subwavelength thickness. In this work, we numerically and experimentally investigate a terahertz splitter of circularly polarized beams based on a spatially nonuniform metasurface composed of self-complementary unit cells. When illuminated with circular polarization, the metasurface creates a deflected cross-polarized beam while transmitting a co-polarized beam in the normal direction. Despite the existence of two reflected beams leading to reflective losses, the metasurface is single-layer and is easy to design and fabricate. A required linear phase gradient for the cross-polarized beam can be obtained by adjusting only one design parameter of unit cells.

A Focusing Circular-Polarization THz Beam Splitter Based on a Self-Complementary Metasurface

Quasi-optical polarization beam splitters are important components of terahertz instrumentation widely used in interferometric and polarimetric measurements. Recently metasurfaces, i.e., two-dimensional periodic or quasi-periodic optically dense structures composed of unit cells with subwavelength dimensions, have been shown to operate as compact and efficient beam splitters. Typically, their design was based on careful optimization of anisotropic metal or dielectric resonant scatterers confined in each unit cell. In this work, we propose and experimentally demonstrate a simple and useful approach to designing circular-polarization beam splitters taking advantage of intrinsically frequency-independent properties of single-layer self-complementary metasurfaces (SCMSs). Theoretically, when illuminated with a circularly polarized beam, any SCMS at any frequency transmits a copolarized beam with a complex transmission coefficient of 1/2. At the same time, a cross-polarized beam of the same magnitude is produced, with a transmission phase that can be controlled at every point of a metasurface aperture. In this work, to split the copolarized and cross-polarized transmitted beams, we spatially modulate this phase by constructing a spatially nonuniform metasurface of self-complementary unit cells. With this approach, we experimentally demonstrate a focusing circular-polarization beam splitter operating near 0.345 THz.

Multiband Terahertz Self-Complementary Metasurface

A self-complementary metasurface is presented for application in multiband terahertz filters. The unit cell structures of the self-complementary metasurface consist of a combination of an ordinary Jerusalem cross and its complementary counterpart that resonates in the THz regime. The columnar repetition of ordinary and complementary resonator structures enables complementary spectral responses for incident waves with mutually orthogonal linear polarizations. The operating principles of the self-complementary metamaterial with the interaction between the juxtaposed ordinary and complementary Jerusalem crosses are explained using an equivalent circuit method and are confirmed with a full-wave electromagnetic simulation. The designed self-complementary metasurface functions as a selective bandstop filter (BSF) or bandpass filter (BPF) depending on the polarization states of the incident wave. The fabricated metasurface exhibits high polarization purity, exemplified by a polarization extinction ratio as high as 24 dB. The transmittance phases of the two orthogonally polarized waves have phase differences between -73° and 83° within a broad frequency range.

Frequency-Controllable Polarization Rotation of THz Waves With an SCMS

In this article, we theoretically and experimentally study the conversion from a circularly polarized (CP) plane electromagnetic wave into a linearly polarized (LP) transmitted one using anisotropic self-complementary metasurfaces. For this purpose, a metasurface design operable at sub-terahertz frequencies is proposed and investigated in the range of 230-540 GHz. The metasurface is composed of alternating complementary rectangular patches and apertures patterned in an aluminum layer deposited on a thin polypropylene film. Our study shows that the translational symmetry of the metasurface results in unusual and useful electromagnetic properties under illumination with CP radiation beams. In particular, alongside with broadband circular-to-linear conversion, the transmitted wave exhibits a frequency-independent magnitude, while its polarization angle gradually changes with frequency that paves the way for new beam-splitting applications.

Broadband and Thin Linear-to-Circular Polarizers Based on Self-Complementary Zigzag Metasurfaces

In this paper, we have studied a practical design of a broadband linear-to-circular polarizer based on a self-complementary metasurface composed of zigzag-shaped metal strips printed on a dielectric substrate. The term self-complementary indicates that the structure is identical to its complement, except for some translation smaller than the periodicity. This property together with the nonresonant response of the unit cells ensures broadband conversion from linear polarization to circular polarization. Although we have experimentally achieved a relative 3-dB-axial-ratio (AR) bandwidth (BW) of 53%, in principle, it could reach up to 70.5%. Moreover, the studied metasurface has a very small periodicity, which avoids any higher order grating lobes and provides angular stability of the phenomenon. In fact, the relative 3-dB-AR BW obtained in experiments stays always above 40% for incidence angles within ±30°. An excellent agreement was achieved among theory, simulations, and experiments.

Broadband and energy-concentrating terahertz coherent perfect absorber based on a self-complementary metasurface.

We demonstrate that a self-complementary checkerboard-like metasurface works as a broadband coherent perfect absorber (CPA) when symmetrically illuminated by two counter-propagating incident waves. A theoretical analysis based on wave interference and the results of numerical simulations of the proposed metasurface are provided. In addition, we experimentally demonstrate the proposed CPA in the terahertz regime by using a time-domain spectroscopy technique. We observe that the metasurface can work as a CPA below its lowest diffraction frequency. The size of the absorptive areas of the proposed CPA can be much smaller than the incident wavelength. Unlike conventional CPAs, the presented one simultaneously achieves the broadband operation and energy concentration of electromagnetic waves at the deep-subwavelength scale.

Self-complementary metasurfaces for linear-to-circular polarization conversion

In this work, we have demonstrated that self-complementary metasurfaces can provide linear-to-circular polarization conversion. For illustration of this general approach, we studied several particular structures based on periodic self-complementary patterns etched on metal sheets of negligible thickness. The advantage of using self-complementary metasurfaces over previous proposals of thin polarizers is the rigorous constancy of the phase difference between transmission (or reflection) coefficients corresponding to orthogonal linear polarizations, which is just ${90}^{\ensuremath{\circ}}$ at any frequency. Also, this unusual phenomenon is stable under oblique incidence. The general proposed theory of self-complementary metasurfaces was first validated through numerical simulations for structures made of ideal lossless materials. Through simulations with realistic materials and experimental measurements, we have also demonstrated that this conversion can be reached in reality with high precision.

7pAD-2 テラヘルツ帯における自己補対型メタ表面の広帯域応答の観測(7pAD 領域5(2,3,12,14番目のみ領域1と合同)フォトニック結晶,領域1(原子分子・量子エレクトロニクス・放射線))

7pAD-2 テラヘルツ帯における自己補対型メタ表面の広帯域応答の観測(7pAD 領域5(2,3,12,14番目のみ領域1と合同)フォトニック結晶,領域1(原子分子・量子エレクトロニクス・放射線))

Plane-wave scattering by self-complementary metasurfaces in terms of electromagnetic duality and Babinet's principle

We investigate theoretically electromagnetic plane-wave scattering by self-complementary metasurfaces. By using Babinet's principle extended to metasurfaces with resistive elements, we show that the frequency-independent transmission and reflection are realized for normal incidence of a circularly polarized plane wave onto a self-complementary metasurface, even if there is diffraction. Next, we consider two special classes of self-complementary metasurfaces. We show that self-complementary metasurfaces with rotational symmetry can act as coherent perfect absorbers, and those with translational symmetry compatible with their self-complementarity can split the incident power equally, even for oblique incidences.

Self-Complementary Metasurface for Designing Narrow Band Pass/Stop Filters

A self-complementary metasurface is studied in this paper. The metasurface is a 2-D periodical arrangement of unit cells formed by a metallic printed split ring resonator and its complementary counterpart. It is demonstrated that this structure behaves like a very selective band-pass filter for a certain linear polarization while band-stop filtering is achieved for the orthogonal polarization over the same frequency range. This idea opens the door to a new class of frequency selective surfaces made of connected and unconnected elements, whose filtering properties are mechanically tunable from band-pass to band-stop by rotating the surface or the polarization.