Cross-polarization Conversion Research Articles

Comment on “A novel ultrathin wideband metamaterial absorber for X-band applications”

Recently, Ranjan et al. [A novel ultrathin wideband metamaterial absorber for X-band applications. J Electromagn Waves Appl. 2019;33:2341–2353. DOI:10.1080/09205071.2019.1681299] have designed a wideband metamaterial absorber for X-band applications. In this comment, we demonstrate that a linear reflective polarization converter is erroneously interpreted as a wideband metamaterial absorber by Ranjan et al. They have shown that the proposed structure is a metamaterial absorber due to the ignorance of cross-polarized component of the reflected wave. Furthermore, we have shown that due to anisotropic geometry and high cross-polarization of the reflected wave, the proposed design is a cross-polarization converter.

Dynamically tuning polarizations of electromagnetic fields based on hybrid skew-resonator-graphene meta-surfaces.

We demonstrate the enhanced polarization modulation of electromagnetic fields through hybrid skew-ring-resonator-graphene meta-surfaces that can dynamically transform the linearly polarized waves into its cross-linearly polarized counterparts or the circularly polarized waves. Such a meta-surface consists of a grounded skew-ring resonator array inserted with a monolayer graphene sheet that controls the electromagnetic interactions between the skew-ring resonators and the ground. Especially, the reconfigurable characteristic of graphene enables the reflections to be capable of converting from the cross-linearly polarized fields to the circularly polarized waves by setting different Fermi energies with the same original co-linearly polarized incidence. Finally, we demonstrate that the bandwidth of the cross-polarization conversion would be greatly expanded when the monolayer graphene sheet is integrated with skew-bar-resonator meta-surfaces.

A Multifunctional Integrated Design of Simultaneous Unity Absorption and Polarization Conversion

Herein, an integrated multifunctional design for simultaneous perfect absorption and polarization conversion is proposed that worked in the Ku band: the proposed structure consisted of two asymmetric dielectric semi-rings which are supported on a ground plane by two dielectric cylinders with different heights. Simulated results demonstrate that unity absorption and linear cross-polarization conversion can be integrated into one multifunctional structure: absorption and polarization conversion operate at different frequencies. Furthermore, these different functions under the different polarized modes (TE and TM) are integrated into the single structure without adjusting any parameters, while also at a large range of incident angles. The integrated design is more conducive to the miniaturization and multi-functionality of devices and there are also practical applications in other areas.

Vanadium Dioxide-Based Bifunctional Metamaterial for Terahertz Waves

A vanadium dioxide-based multilayer metamaterial is proposed with bifunctional properties of absorption and polarization conversion. When vanadium dioxide is in the metallic state, the designed system behaves as a single-band absorber which is composed of a vanadium dioxide disk-shaped array, a silica spacer, and a vanadium dioxide continuous film. The performance of absorption can be tuned by changing either the diameter of disk or the thickness of silica. The design of this absorber is robust against incident polarization and incident angle. The proposed single-band absorber may be generally applied for plasmonic detection, cavity resonator, and optical band-stop filter. When vanadium dioxide is in the insulating state, the designed system behaves as a cross polarization converter which mainly consists of a one-dimensional metallic strip-shaped array, a silica spacer, and a metallic continuous film. The designed metamaterial can convert a linear plane wave into its corresponding cross-polarized wave with the efficiency of >90% in the frequency of 2.0-3.0 THz. The physical mechanism of polarization conversion is explained by a simple picture. The proposed metamaterial could be a potential candidate for the modern device of polarization control.

Broadband Spin-Decoupled Metasurface for Dual-Circularly Polarized Reflector Antenna Design

In this article, we theoretically and experimentally demonstrate a single-layered spin-decoupled metasurface and its application to a dual-circularly polarized reflector antenna. A developed method is first analyzed to guide the design of broadband spin-decoupled metasurface. Then, a quasi-I-shaped meta-atom, which exhibits a phase coverage of $2\pi $ and high cross-polarization conversion efficiency within 12–21 GHz, is accordingly designed to actualize spin-decoupled phase change by simultaneously tuning the structural parameters and self-rotation of the element. To illustrate the independent phase control of orthogonal spins, a dual-circularly polarized multiplexing reflector antenna is designed with offset configuration. The experimentally measured results of the assembled reflector antenna are in good agreement with the simulated ones, showing a peak gain of 29.5 and 29.6 dBic, peak aperture efficiency (AE) of 53% and 54%, 3 dB gain bandwidth (BW) of 13.2–20.2 GHz (41.9%) and 13.4–20.2 GHz (40.5%), and 3 dB axial ratio (AR) BW of 11.8–21 GHz (56.1%) and 11.5–22 GHz (62.7%) for left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) radiations, respectively. The design strategy and the well-performed multiplexing reflector antenna may have promising perspective in many practical applications, for example, satellite communication system and long-distance wireless communication system.

Multifunctional Single Layer Metasurface Based on Hexagonal Split Ring Resonator

We present a single-layer metasurface, which performs both cross and circular polarization conversion at multiple frequency bands. The unit cell of the proposed metasurface consists of periodic array of a uniquely designed hexagonal split ring resonator (SRR). The proposed metasurface behaves as an efficient 90° polarization rotator at dual frequency bands of 6.36-6.59 GHz and 10.54-13.56 GHz. The polarization conversion efficiency approaches 90% within these two operating bands. Moreover, linear-to-circular polarization conversion is also achieved in other three wide frequency bands from 6.10-6.20 GHz, 6.84-9.02 GHz and 14.10-15.48 GHz. The novel features of the subject hexagonal metasurface, which qualify it for numerous practical applications are high cross-polarization conversion (CPC) efficiency, wideband operation and angular stability for oblique incidence up to 45°.

A Solid State Plasma Multifunctional Metamaterial and Its Application for Energy Absorbing and Cross Polarization Conversion

With the increasing expectations of electromagnetic devices, the defects of monofunctional devices that are susceptibly limited by external constraints are becoming more and more obvious and the integration of multiple functions has gradually become the pursuit of researchers. In this paper, a novel multifunctional metamaterial tailored by the solid state plasma (SSP) is proposed. By inspiring the particular SSP resonators, such a metamaterial can be handily switched back and forth among two functions and form three working states. When the proposed SSP metamaterial is served in State I, its function embodies as an energy absorber and the absorption which is over 90% for TE and TM modes are 5.84-7.30 GHz and 5.41-6.34 GHz whose relative bandwidths (RBs) are 22.22% and 15.83%, respectively. States II and III keep the same functionality of cross-polarization conversion but a distinct operating band. The polarization conversion rate (PCR) of State II which is higher than 90% is 7.40-12.20 GHz (the RB is 48.98%) and this operational range will be shifted to 5.71-8.47 GHz (the RB is 38.92%) after switching to State III. Compared with the conventional tunable devices, this SSP metamaterial has the advantage of functional diversity and it provides a new design idea of absorber and polarization converter to promote potential applications of multifunctional devices.

A reconfigurable terahertz polarization converter based on metal–graphene hybrid metasurface

A metal–graphene hybrid metasurface polarization converter is designed in this Letter. The unit cell of the hybrid metasurface is composed of a butterfly-shaped structure whose branches are connected by multi-layer graphene sheets. The proposed device can be reconfigured from linear-to-circular polarization to cross-polarization by changing the Fermi energy of graphene. The simulation results show that for three-layer graphene, the device acts as a linear-to-circular polarization converter when EF = 0 eV and switches to a cross-polarization converter when EF = 0.5 eV. Compared with single-layer graphene, the device with three-layer graphene can maintain the cross-polarization conversion performance under low Fermi energy. Furthermore, two equivalent circuits in the x and y directions are developed to understand the working mechanism of the device.

Broadband waveplate operation by orthotropic metasurface reflector

We present an anisotropic metasurface offering a simultaneous linear to cross-polarization conversion and linear to circular polarization conversion operations on large bandwidths of microwave frequencies. The proposed orthotropic structure consists of metallic bow tie shaped patches with embedded circular patches enabling diagonal structure symmetry. We demonstrate through numerical simulations and experiments that the metasurface can be used as a high efficiency linear to cross-polarization reflective converter within the two broad frequency bands of 7.48–10.55 GHz and 18.47–19.52 GHz with a polarization conversion ratio above 90%. Simultaneously, the designed metasurface acts as a circular polarizer for linearly polarized incident waves in triple frequency bands of 6.10–7.46 GHz, 10.55–18.42 GHz, and 19.60–22.39 GHz with an axial ratio below the 3 dB threshold. To the best of our knowledge, the second band from 10.55 to 18.42 GHz of circular polarization conversion “has the highest reported (to date) bandwidth of 54.3% for an axial ratio below 3 dB.” The designed metasurface remains angular stable up to 75° over most of the part of the above-mentioned operating bands for both transverse-electric and transverse-magnetic polarized wave incidences.

Tunable mid-infrared dual-band and broadband cross-polarization converters based on U-shaped graphene metamaterials.

We propose a tunable dual-band reflective cross-polarization converter composed of periodically arranged single layer U-shaped graphene nanostructures in mid-infrared region. The proposed dual-band reflective cross-polarization converter can convert the polarization state of an incident wave from the linear polarization state to its cross polarization state at the operating frequencies of 34.67 and 44.13 THz with the high-efficiency polarization conversion ratio (PCR) approaching 100%. Furthermore, as a complementary structure, a reflective cross-polarization converter with a hollow-carved U-shaped graphene sheet shows a broadband polarization conversion performance with a bandwidth of 1 THz and the PCR over 90%. The bandwidth of this broadband converter can be further extended to 2 THz after certain geometric parameter optimization. More importantly, both the dual-band and broadband cross-polarization converters not only can dynamically tune their PCR peak frequencies and magnitudes by adjusting the chemical potential and relaxation time of graphene without changing the geometric structure but also have good angular stability with high PCR in a wide range of incident angle up to 55°. These polarization converters may have great potential applications in mid-infrared spectroscopy, radiometer, sensor, and other photonic devices.

Broadband high-efficiency cross-polarization conversion and multi-functional wavefront manipulation based on chiral structure metasurface for terahertz wave

In this paper, a broadband and high-efficient tri-layered chiral structure metasurface (CSM) for linear polarization conversion and multi-functional wavefront manipulation was proposed and investigated numerically in terahertz region. The unit-cell of the proposed CSM consist of two orthogonal metal wires sandwiched with square split-ring resonator (SRR) structure, which can manipulate the polarization and wavefront of the transmitted wave simultaneously. Based on the Fabry–Perot-like cavity-enhanced effect of proposed CSM, broadband and high-efficiency cross-polarization conversion can be achieved. Numerical simulation results indicate that the cross-polarization transmission coefficient is higher than 0.9 from 0.4 THz to 1.0 THz, with a fractional bandwidth of 85.7%. The proposed CSM can achieve complete 2π phase coverage by adjusting the geometric parameters of the unit-cell structure. Anomalous refraction with a wide angle, two kinds of focusing metalenses and vortex beam generation are investigated to verify the multi-functional wavefront manipulation performance of the proposed CSM. Our work provides an effective method of enhancing the performance of transmission-type metasurface and the proposed devices show endless potential in wavefront control and communication applications in terahertz region.

Selective interaction between graphene and a multifunctional metamirror in the near-infrared region

The chiroptical response is ubiquitous and offers additional degrees of freedom in modern optics systems which require high efficiency and moderate modulation. Exhibiting a fascinating electromagnetic performance, a graphene–metamaterial hybrid structure is an ideal candidate to satisfy the requirements for chiroptical response. Herein, the interaction between a graphene layer and a multifunctional metamirror is investigated in the near-infrared region. The simulation results show that the graphene layer can moderately modulate the circular dichroism effect in the short wavelength region, while leaving cross-polarization conversion almost unaffected in the long wavelength region. This selective interaction can be well understood with the electromagnetic models and graphene surface conductivity. This work provides a guide for selectively modulating the multifunctional chiroptical response and presents a new strategy to detect the layers of graphene.

A dual-wideband bi-layered chiral metamaterial to develop cross-polarization conversion and asymmetric transmission functionalities for the linearly polarized electromagnetic waves

A novel modified bi-layered chiral metamaterial (CMM) with dual-wideband cross-polarization conversion and asymmetric transmission (AT) operations is introduced for the transmission of the linearly polarized electromagnetic (EM) waves. To this end, any unit cell of the presented CMM includes a pair of twisted meander-shaped metallic layers arranged on two opposite sides of a thin dielectric slab. The proposed CMM can cover two frequency bands from 8 GHz to 12 GHz and 14 GHz to 15 GHz, which makes it appropriate to be used in X-band and Ku–band applications. The simulated and measured results with acceptable coincidence indicate that the suggested CMM has a significant potential to transform an incident linearly x− (y−) polarized wave into the orthogonal polarization by transmission across the sample along −z (+z) propagation. Parametric studies of the applied structural modifications are investigated to achieve desirable asymmetric transmission. The realized polarization conversion ratio (PCR) has values above 86% at both operating frequency bands. Also, the obtained polarization rotation azimuth angleθ confirms that the plane of the polarization for the transmitted linearly polarized wave rotates relative to the incident one. Furthermore, the procedures of the cross-polarization conversions are investigated by the surface current distributions at two resonant frequencies.

Chiral metasurfaces formed by 3D-printed square helices: A flexible tool to manipulate wave polarization

The transmission of linearly and circularly polarized waves is studied both theoretically and experimentally for chiral metasurfaces formed by arrays of metallic square helices. The helical particles of the metasurfaces are constructed of rectangular bars manufactured by direct three-dimensional printing in solid metals. The transmittance of the metasurface is found to depend critically on the number of bars forming the square helical particles. In the case of an even number of bars, the chiral metasurface exhibits identical co-polarized transmittance of orthogonal linearly polarized waves, which are characterized by a dual-band asymmetric transmission. For an odd number of bars, the metasurface provides the same cross-polarization conversion for any polarization orientation of the incident field and thus serves as a polarization-independent twist polarizer. Finally, the transmittance of this polarizer is investigated with respect to the dimensions of the square helices. The investigated chiral metasurfaces are characterized by strong broadband circular dichroism regardless of the number of bars in the helical particles. The wide variety of transmission properties observed in the metasurfaces makes them particularly attractive for use in polarization conversion and separation devices.

All-metal metasurface polarization converter in visible region with an in-band function

We propose an ultrathin and high-efficiency all-metal metasurface polarization converter, by which cross-polarization conversion in reflection mode is achieved for linearly-polarized lights. The simulated result shows that the polarization conversion ratio for normal incidence is nearly 100% in the visible region. Moreover, strong coupling between nanobars with metallic ground plane, make it possible to provide novel application of in-band switch function. The proposed all-metal polarization converter not only improves the feasibility of nanofabrication due to its simple nanostructure, but demonstrates a reflection-type avenue to design optoelectronic devices up to the visible spectrum.

Tunable dual-frequency cross polarization converters based on graphene metasurface in infrared range

A tunable dual-frequency metamaterial graphene polarization converter in the infrared range is put forward in this paper. The proposed converter is made up of 3 layers—the bottom gold layer, the middle silicon dioxide layer and the upper graphene layer. The simulated results show that the polarization converter can simultaneously work at two resonant frequencies of 36.82 and 41.38 THz. The polarization conversion rates are up to 0.9992 at 36.82 THz and 0.9969 at 41.38 THz under the certain normal condition when Fermi energy is given to 1.0 eV, showing the high efficiency of the polarization converter. Moreover, the converter shows its stable working performance under the change of the incident angle and the geometrical size. Meanwhile, without varying the nanostructure, the resonant frequencies can be flexibly adjusted by controlling the Fermi energy. The superior performance of the proposed graphene polarization converter indicates a broad prospect that a large number of applications such as infrared imaging sensors, modulators, switches, photonic and biochemical sensors, light harvesting, thermal detection and electromagnetic energy converter will apply it.

0.02-wavelengths-thick transmission-type designer wave plate with high efficiency

The thin thickness and the working efficiency are always two key problems for transmission-type polarization conversion devices. Here, we propose a C-band ultrathin (0.02 λ0 in the thickness) and highly efficient circular-polarization conversion device in the transmission mode. The designer wave plate is composed of double layer surface structures printed on both sides of a single-layer substrate and the metallic layers are connected by a pair of through-via holes. The structure of the top layer is composed of a patch with a D-shape slot inside, and the bottom layer can be obtained by rotating the top layer with 180 degrees around the center. We demonstrate that the designer wave plate can achieve transmission polarization conversion from right-handed circularly polarized incident electromagnetic (EM) waves to left-handed ones or from left-handed circularly polarized incident EM waves to right-handed ones in the transmission mode. The results show that the maximum cross-polarization conversion efficiency of the designer wave plate at a working frequency of 5.8 GHz is 94.6%. This ultra-thin circular-polarization conversion device is expected to be applied to wireless systems that require circular polarization diversity.

A metasurface‐based broadband quasi nondispersive cross polarization converter for far infrared region

A broadband nondispersive cross polarization converter (CPC) structure using metasurface for far infrared region has been proposed in this article. The structure is transmittive in nature, which converts a linearly polarized incident wave to its mutually orthogonal linearly polarized wave over a band of frequency ranging from 10.25 to 22.7 THz maintaining a high polarization conversion ratio (PCR) of more than 0.95. The fractional bandwidth of 75.6% corresponding to the center frequency of PCR bandwidth having more than 0.9 PCR value has been realized. The structure is also studied for oblique incidences where it shows wide band polarization conversion up to 45° for both TE and TM polarized oblique incident waves. The electric field distributions at the top and bottom surfaces of the structure close to the center frequency of polarization conversion bandwidth indicate the orthogonal rotation of incident linearly polarized wave at the frequency of interest. For the given set of media interface a separate study on polarization conversion through Brewster angle concept has been carried out simultaneously. The structure exhibits high PCR by maintaining the compactness in thickness (~ λ/5) as well as periodicity (~ λ/3) compared to the existing reported ones.

Low-profile reflective polarization conversion metasurface with frequency selective characteristics

We proposed a low-profile reflective polarization converter based on anisotropic metasurfaces. By properly designing the unit cell structure, the proposed metasurface can achieve frequency selective polarization conversion. When the proposed metasurface is illuminated by a linear polarization incoming wave, the circular polarization outgoing waves are implemented in frequency-band-1 (6.87 to 16.83 GHz) and frequency-band-2 (19.72 to 23.64 GHz), but the rotation direction of the circularly polarized reflections are orthogonal over the two bands. In addition, cross polarization conversion is achieved in frequency-band-3 (17.38 to 18.6 GHz). Indeed, the proposed metasurface can also serve as a circular to linear polarization converter. The theoretical analysis and the physical mechanism are given to understand the polarization conversion phenomenon. The measured result is consistent with the simulation. The proposed metasurface can be utilized in the design of a circularly polarized reflectarray with linearly polarized feeding.

High‐efficiency cross and linear‐to‐circular polarization converters based on novel frequency selective surfaces

AbstractMost high‐efficiency polarization converters in literatures are based on reflective structures. Here we report the designs and experiments of high‐efficiency transmissive polarization converters using novel compact frequency‐selective surfaces (FSSs). By combining the common dipole and square ring based band‐pass FSSs, a novel FSS can be generated, whose high‐efficiency pass bands and transmissive phases for two orthogonal polarizations can be tuned by changing the dimensions of the FSS structure. As demonstrations of the concept, a transmissive cross polarization converter (a half‐wave plate) and a transmissive linear‐to‐circular polarization (LP‐CP) converter (a quarter‐wave plate) are designed and tested, respectively. Simulated results show that the polarization conversion ratio over 90% for the transmissive cross‐polarization converter is from 18.5 to 23.5 GHz, about 23.8%, and the 3‐dB LP‐CP conversion bandwidth is 19.6%. Experiments are carried out to validate both designs.