Reflective Polarization Converter Research Articles

A reflective multilayer polarization converter with switchable frequency band

A multilayer polarization converter operating in the reflection mode with a switchable frequency band is proposed, where the unit cell consists of layers of a polarizer, active frequency selective surface (AFSS), and metallic ground, separately. The polarizer layer is designed in the form of a periodic split circular loop structure. The AFSS layer is constructed by a three-layer second-order passband structure with PIN diodes loaded orthogonally on the top and bottom layers. In this design, the AFSS can be switched between the transmission and reflection modes by controlling the bias, resulting in a change in the effective permittivity of the dielectric substrate. The switchable polarization converter is verified by both simulations and experimental results. It is found that when the PIN diodes are in the ON/OFF-state, the proposal converter can change the linearly polarized wave from 9 GHz to 17.1 GHz and from 5.5 GHz to 11.6 GHz, respectively.

Broadband and wide-angle reflective linear polarization converter for terahertz waves

Polarization control of electromagnetic waves has wide applications in the field of communications, imaging, and remote sensing. Recent designs of periodic two-dimensional devices or metasurfaces employed for polarization control are limited in efficiency, bandwidth, and allowable incidence angle. This is attributed to high dissipation in the dielectric material used and to less-optimal device configuration. We propose and experimentally validate a reflective linear polarization converter metasurface with high efficiency, wide bandwidth, and wide acceptance angle in the terahertz regime. Our device is composed of three layers: an array of oriented metallic T-shaped resonators, cyclic olefin copolymer (COC) as a low loss dielectric layer, and a ground plane. For the normal and 45° incidence angles, a fabricated sample shows a bandwidth of 95% and 100%, with the average polarization conversion ratio above 80%, covering a frequency range of 0.38–1.07 and 0.36–1.08 THz, respectively. The wide-angle stability is attributed to a phase difference between a single resonance along the T-shaped resonator and a smooth phase response in the low-loss COC dielectric layer. For broad bandwidth performance, a resonator arm extending to adjacent unit cells introduces the fundamental resonance at a lower frequency, while the packed unit cell size shifts the grating lobe onset to a higher frequency. These design aspects can significantly improve the performance of other metasurfaces operating in any frequency range.

Broadband terahertz tunable metasurface linear polarization converter based on graphene

A terahertz broadband tunable reflective linear polarization converter based on oval-shape-hollowed graphene metasurface is proposed and verified by simulation and Fabry-Perot multiple interference theory in this paper. Our designed metasurface model is similar to a sandwiched structure, which is consisted of the top layer of anisotropic elliptical perforated graphene structure, an intermediate dielectric layer and a metal ground plane. The simulation results show that when the given graphene relaxation time and Fermi energy are τ=1 ps and μc=0.9 eV, respectively, the polarization conversion rate (PCR) of the designed metasurface structure is over 90% in the frequency range of 0.98 THz~1.34 THz, and the relative bandwidth is 36.7%. In addition, at resonance frequencies of 1.04 THz and 1.29 THz, PCR is up to 99.8% and 97.7%, respectively, indicating that the metasurface we designed can convert incident vertical (horizontal) linearly polarized waves into reflected horizontal (vertical) linearly polarized waves. We used the Fabry-Perot multi-interference theory to further verify the metasurface model. The theoretical predictions are in good agreement with the numerical simulation results. In addition, the designed metasurface reflective linear polarization conversion characteristics can be dynamically adjusted by changing the Fermi energy and electron relaxation time of graphene. Therefore, our designed graphene-based tunable metasurface polarization converter is expected to have potential application value in terahertz communication, sensing and terahertz spectroscopy.

Ultrathin and broadband highly efficient terahertz reflective polarization converter based on four L-shaped metamaterials

We propose a simple ultrathin design of reflective linear polarization converter with broadband and high efficiency based on four L-shaped anisotropic metamaterials. Simulated results demonstrate our design can convert a linearly polarized wave to its cross-polarized wave and the polarization conversion ratio over 98% is achieved from 4.2 to 5.2 THz. The further simulated results indicate that the deflection angles relative to y axis have greater impact on the cross-polarization reflection coefficient. Our design will provide an important reference for the practical applications of the metamaterials in polarization manipulation.

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 Dual-Frequency Reflective Linear Polarization Converter Based on Metasurface for Microwave Bands

A dual-broadband and high-efficiency reflective linear polarization converter based on an anisotropic metasurface is presented. The device consists of two symmetrical, double-slotted metallic split-rings and one criss-cross structure, a dielectric layer, and a completely reflective metallic ground. The converter exhibits four resonances and can near-perfectly convert x- or y-polarized incident waves into cross-polarized waves in the frequency ranges of 9.38–13.36 GHz and 14.84–20.36 GHz. The polarization conversion ratios (PCRs) of the two bands are 98.21% and 99.32%, respectively. The energy conversion ratio (ECR) for energy loss measurement is almost 100% in these frequency bands. The polarization conversion principle is studied. The bandwidths and PCRs of the two bands are determined by varying the dielectric layer thickness. The simulation results are consistent with experimental observations. The designed dual-broadband and high-efficiency metasurface has great potential in the application of electromagnetic polarization control.

Ultra-wideband and high-efficiency reflective polarization converter for both linear and circular polarized waves

In this work, an ultra-wideband and high-efficiency reflective polarization converter is proposed based on an orthotropic anisotropic metasurface for both linear and circular polarized waves, which is a symmetric structure with a pair of mutually perpendicular symmetric axes. Both the simulated and measured results show that the polarization converter can realize linear polarization conversion at x- and y-polarized incidences in the frequency range from 8.77 to 24.71 GHz, which is corresponding to a 95.2% relative bandwidth; moreover, it can keep the handedness of the reflected wave the same as that of the incident wave in this band and realize reflection-type circular polarization conversion at circular polarized (CP) incidence. We have explained the root cause of these polarization conversions, and made it clear that it is just the symmetry of the metasurface structure which makes the magnitude of co-polarized reflection coefficient at CP incidence equal to that of the cross-polarized reflection coefficient at x- and y-polarized incidences, thus it is shown that the previously proposed various reflective linear polarization converters based on orthotropic anisotropic metasurfaces can all realize reflection-type circular polarization conversion.

Design of broadband polarization converter for terahertz waves

A broadband reflective polarization converter is proposed. The unit cell of polarization converter is composed of a single-split resonant ring, a double-split resonant ring, a dielectric substrate and a metallic ground. The simulated results show that the polarization converter can convert x-polarized waves into y-polarized waves and obtain a broadband polarization conversion from 0.501 0 THz to 1.390 0 THz with the polarization conversion ratio (PCR) beyond 80% at normal incidence. Moreover, the surface current distributions are investigated to explain the polarization conversion mechanism. Finally, a good agreement is achieved between simulated and measured results. The polarization converter can be applied in terahertz imaging, communication and stealthy technology.

Wideband Metasurface-Based Reflective Polarization Converter for Linear-to-Linear and Linear-to-Circular Polarization Conversion

A wideband reflective polarization converter based on metasurface is proposed in this letter. This converter can transform a linearly polarized (LP) incident electromagnetic (EM) wave into its orthogonal LP reflection wave in a lower band, and a circularly polarized (CP) reflection wave in a higher band. The unit cell of this converter is comprised of two meander lines and one cut wire printed on a dielectric substrate, backed with metallic ground sheet. The simulation results show that the y / x -polarized incident EM wave can be converted to the x/y -polarized reflected wave over a fractional bandwidth of 59.6% from 6.53 to 12.07 GHz with a polarization conversion ratio over 0.88. Besides, the y / x -polarized incident EM wave is converted to a CP reflected wave from 13.70 to 15.60 GHz (a fractional bandwidth of 13.0%). To verify the polarization conversion performance, a sample consisting of 30 × 30 unit cells is fabricated and measured. The experimental and simulation results obtained are in a reasonable agreement, which verifies the properties of the design.

An ultra-broadband and highly-efficient tunable terahertz polarization converter based on composite metamaterial

A near perfect, ultra-broadband and highly-efficient terahertz reflective polarization converter based on multilayer metamaterial is proposed in this paper. The hybrid metamaterial unit structure consists of a split-ring metal pattern and a metal sheet separated by a dielectric resonator spacer. The polarization conversion ratio (PCR) is above 90% from 2.06 to 4.26 THz, with an optimal range between 2.98 and 4.16 THz where the efficiency is above 98% for normal incidence. It also shows excellent performance for oblique incidences. Moreover, the working band and the optimized frequency range for the polarization conversion can be manipulated by changing the open angle between the metallic arcs and the substrate thickness, respectively. Based on this design, two types of hybrid metamaterial converters are also investigated to swith off polarization conversion altogether or modify the polarization conversion bandwidth. A polarization converter with temperature controlled PCR is realized by adding a vanadium oxide (VO2) mask on the designed structure. In addition, by integrating photoconductive silicon islands between the split-ring and metal bar a dual-band polarization converter can be realized. Combining with a polarizer, this window can act as an active THz filter.

Dual-band reflective polarization converter based on slotted wire resonators

A dual-band and high-efficiency reflective linear polarization converter composed of a layer of slotted metal wires has been proposed. Both the simulated and experimental results indicate that the structure can convert a linearly polarized wave to its cross-polarized state for two distinct frequency bands under normal incidence: 9.8–15.1 and 19.2–25.7 GHz. This phenomenon is attributed to a resonance that corresponds to the “trapped mode” at 15.8 GHz. This mode is stable with structural parameters and incident angle at a relatively wide range, and thus becomes promising for dual-band (also multiband) devices design. By surface current distribution and electric field analysis, the operation mechanism has been illuminated, especially for the “trapped mode”, identified by the equally but also oppositely directed currents in each unit cell.

A tunable reflective polarization converter based on hybrid metamaterial

A hybrid metamaterial converter based on a hybrid layer, a gold (Au) film and a dielectric substrate is proposed to realize linear and circular polarization conversions in the terahertz (THz) band. The hybrid layer is composed of a vanadium dioxide (VO2) plane and I-shaped resonators. The polarization conversion ratio (PCR) above 90% is achieved in a broad band range from 2.10 to 5.03 THz under both linearly and circularly polarized waves. And, the PCR is up to near unity around the resonant frequency. Meanwhile, the metamaterial convertor is sensitive to the incident angles. Moreover, a controlled modulation characteristic can be realized by the proposed polarization converter. In addition, the physical mechanism of the polarization conversion is analyzed by the distributions of surface currents. These features pave a novel way for the broad band polarization converter and hold application in the area of sensing, THz communication and tunable polarizers.

Ultra-wideband high-efficiency reflective linear-to-circular polarization converter based on metasurface at terahertz frequencies.

The polarization conversion of electromagnetic (EM) waves, especially linear-to-circular (LTC) polarization conversion, is of great significance in practical applications. In this study, we propose an ultra-wideband high-efficiency reflective LTC polarization converter based on a metasurface in the terahertz regime. It consists of periodic unit cells, each cell of which is formed by a double split resonant square ring, dielectric layer, and fully reflective gold mirror. In the frequency range of 0.60 - 1.41 THz, the magnitudes of the reflection coefficients reach approximately 0.7, and the phase difference between the two orthogonal electric field components of the reflected wave is close to 90° or -270°. The results indicate that the relative bandwidth reaches 80% and the efficiency is greater than 88%, thus, ultra-wideband high-efficiency LTC polarization conversion has been realized. Finally, the physical mechanism of the polarization conversion is revealed. This converter has potential applications in antenna design, EM measurement, and stealth technology.

Design of ultrathin dual-resonant reflective polarization converter with customized bandwidths

In this paper, an ultrathin dual-resonant reflective polarization converter is proposed to obtain customized bandwidths using precise space-filling technique to its top geometry. The unit cell of the dual-resonant prototype consists of conductive square ring with two diagonally arranged slits, supported by metal-backed thin dielectric layer. It offers two narrow bands with fractional bandwidths of 3.98 and 6.65% and polarization conversion ratio (PCR) of 97.16 and 98.87% at 4.52 and 6.97 GHz, respectively. The resonances are brought in proximity to each other by changing the length of surface current paths of the two resonances. By virtue of this mechanism, two polarization converters with two different types of bandwidths are obtained. One polarization converter produces a full-width at half-maxima PCR bandwidth of 34%, whereas another polarization converter produces a 90% PCR bandwidth of 19%. All the proposed polarization converters are insensitive to wide variations of incident angle for both TE- and TM-polarized incident waves. Measured results show good agreement with the numerically simulated results.

Dual-broadband and near-perfect polarization converter based on anisotropic metasurface

A novel dual-broadband and near-perfect reflective polarization converter based on anisotropic metasurface is presented and analyzed in this paper. The unit cell of the proposed converter is composed of a double-cut slotted metallic split-ring and a metallic ground sheet separated by an F4B-2 substrate. Both numerical analysis and measured results demonstrate that the proposed converter has five plasmon resonance frequencies, and can near-completely convert the x- or y-polarized incident wave to its orthogonal counterpart in two frequency bands (9.5–12.9 GHz, 16.1–20.2 GHz). The corresponding polarization conversion ratio is more than 98.3% in the first frequency band and 99.7% in the second one. In addition, the bandwidths and central frequencies of the two frequency bands can be effectively tuned over a wide range by adjusting the geometrical dimensions of the metasurface, while the high conversion efficiency is preserved. The proposed polarization converter may have great potentials in electromagnetic polarization control applications.

High-efficiency and multi-frequency polarization converters based on graphene metasurface with twisting double L-shaped unit structure array

In this work, a high-efficiency and tunable dual-frequency reflective polarization converter composed of graphene metasurface with twisting double L-shaped unit is firstly realized. Numerical results demonstrate that the device can convert a linearly polarized wave to its cross-polarized wave, and meantime it can also convert to a circularly polarized wave. Subsequently, one thickness of 500nm SiO2 layer sandwiched by two graphene metasurfaces with similar pattern is stacked on the top of the two-layered structure, a four-frequency efficient reflective polarization converters is realized. Above all, those working frequencies can also be dynamically tuned within a large frequency range by adjusting the Fermi energy of the graphene, without reoptimizing and refabricating the nanostructures, which paves a novel way toward developing a controllable polarization converter for mid-infrared applications.

Design of a wideband reflective linear polarization converter based on the ladder-shaped structure metasurface

In this paper, a ladder-shaped structure metasurface is proposed and investigated theoretically and experimentally, which can efficiently convert a linear polarized electromagnetic (EM) wave to its orthogonal component in a wideband range. The wideband reflective polarization convertibility is resulted from three resonance modes generated by the ladder-shaped structure MM for the normal incident waves. The mechanism of high-efficiency reflective polarization conversion is illustrated by surface current distribution and the destructive interference theory. The experimental measurement results show that the average polarization conversion ratio (PCR) is greater than 90% from 6.9 to 15.4GHz, which are in good agreement with the numerical simulations and theoretical predictions. The designed metasurface possesses the merits of wideband and high-efficiency, and thus has great application values in novel polarization-control devices.

Linearly Polarized Converters for Reflected and Transmitted Waves Based on Double-Split Ring Resonator

We propose and demonstrate the linearly polarized converters for reflected and transmitted waves based on a double-split ring resonator (DSRR). For reflective polarization converter, the three-layered metamaterial structure can rotate the polarization state of incident linearly polarized wave into its orthogonal one. The calculated results indicate that the polarization conversion ratio of reflective polarization rotator can reach unity (99.99%) at the resonant frequency. For transmissive polarization rotator, we propose a multi-layered metamaterial structure at terahertz frequencies which exhibits the incident y-polarized wave can be thoroughly and perfectly converted to the x-polarized output wave over the entire frequency range. The numerical simulation and theoretical calculation indicate that polarization conversion ratio of the y-polarized wave can be higher than 99.98% at the frequency range from 0.42 to 1.59 THz. Additionally, we investigate the polarization rotation properties based on optical activity and ellipticity. Specifically, the proposed structure can achieve simultaneously a multi-band 90o polarization rotation angle and an extremely low dispersion (lower than 0.25o, absolute value). The physical mechanism of polarization conversion is also analyzed based on the electronic field distribution at the resonance frequency.

Broadband and efficient reflective polarization converter based on a three-dimensional metamaterial

In this paper, a three-dimensional metamaterial was proposed to realize a broadband and efficient polarization conversion. The unit cell of the three-dimensional metamaterial is composed of pseudo-planar structure and a ground plane separated by a dielectric spacer. The linear polarization of incident waves can be converted to its orthogonal direction upon reflection. The simulated results show that the polarization conversion ratio of more than 95 % is observed in the broad frequency range from 7.39 to 13.87 THz. The novel pseudo-planar reflective polarization converter can improve the magnitude of the polarization conversion ratio compared to previous works. To explain the mechanism of the proposed structure, the surface current distributions are investigated. In addition, the right-hand circularly polarized incident waves can also be converted to left-hand circularly polarized wave with broadband and efficient polarization conversion. The proposed metamaterial provides an alternative platform to promote potential applications in the terahertz region.

Ultra-wideband reflective polarization converter based on anisotropic metasurface**Project supported by the National Natural Science Foundation of China (Grant Nos. 61471387, 61271250, and 61571460).

In this paper, we propose an ultra-wideband reflective linear cross-polarization converter based on anisotropic metasurface. Its unit cell is composed of a square-shaped resonator with intersectant diagonal and metallic ground sheet separated by dielectric substrate. Simulated results show that the converter can generate resonances at four frequencies under normal incident electromagnetic (EM) wave, leading to the bandwidth expansion of cross-polarization reflection. For verification, the designed polarization converter is fabricated and measured. The measured and simulated results agree well with each other, showing that the fabricated converter can convert x- or y-polarized incident wave into its cross polarized wave in a frequency range from 7.57 GHz to 20.46 GHz with a relative bandwidth of 91.2%, and the polarization conversion efficiency is greater than 90%. The proposed polarization converter has a simple geometry but an ultra wideband compared with the published designs, and hence possesses potential applications in novel polarization-control devices.