Circular Polarization Conversion Research Articles

Ultrathin Bi‐Switchable Vanadium Dioxide‐Based Multifunctional Metamaterial for Terahertz Polarization Modulation

AbstractA broadband multi‐functional bi‐switchable ultrathin optical metamaterial design is investigated, which can achieve a high polarization conversion efficiency over a wide band of frequencies in the terahertz (THz) regime. The proposed design switches from a linear and circular polarization converter (LPC/CPC) to an efficient absorber by using the phase change property of a functional material, vanadium dioxide (VO2). The proposed design shows switching from an absorber to a reflector using the mechanical configuration of the functional material, and therefore the design can be used as a bi‐switchable device. The first type of switching is accomplished by changing the conductivity of the functional material, while the second type of switching is achieved with the help of the mechanical configuration of the functional material. Moreover, the structure is responsive to wide incident angles. The proposed switchable design has the potential to contribute to the development of tunable polarization rotating devices and on/off switching LPC devices, which have wide applications in detection, sensing, and communications.

A Multiband and Multifunctional Metasurface for Linear and Circular Polarization Conversion in Reflection Modes

Multifunctional integrated meta-devices are the demand of modern communication systems and are given a lot of attention nowadays. Most of the research has focused on either cross-polarization conversion (CPC) or linear-to-circular (LP–CP) conversion. However, simultaneously realizing multiple bands with good conversion efficiency remains crucial. This paper proposes a multiband and multifunctional dual reflective polarization converter surface capable of converting a linearly polarized (LP) wave into a circularly polarized (CP) wave, in frequency bands of 12.29–12.63 GHz, 16.08–24.16 GHz, 27.82–32.21 GHz, 33.75–38.74 GHz, and 39.70–39.79 GHz, with 3 dB axial ratio bandwidths of 2.7%, 40.15%, 14.6%, 13.76%, and 0.2%, respectively. Moreover, the converter is capable of achieving CPC with a polarization conversion ratio (PCR) that exceeds 95%, within the frequency ranges of 13.10–14.72 GHz, 25.43–26.00, 32.46–32.56 GHz, and 39.14–39.59 GHz. In addition, to identify the fundamental cause of the CPC and LP–CP conversion, a comprehensive theoretical investigation is provided. Furthermore, the surface current distribution patterns at different frequencies are investigated to analyze the conversion phenomena. A sample prototype consisting of 20 × 20 unit cells was fabricated and measured, verifying our design and the simulated results. The proposed structure has potential applications in satellite communications, radar, stealth technologies, and reflector antennas.

Maximal circular polarization isolation and asymmetric polarization conversion by chiral meta-structure

Chiral objects hold immense significance in modern optical technology, particularly due to their ability to manipulate circularly polarized waves. The chiroptical effects observed in naturally known chiral structures are typically very weak, however, the use of engineered meta-structures has proven to be highly effective in overcoming these shortcomings. Despite extensive research efforts, the construction of chiroptical phenomena approaching maximum performance has proven to be challenging, mostly due to the lack of optimal design choices and the existence of material losses. Here we present a metasurface constituting S-shaped building blocks capable of realizing virtually maximum chiroptical phenomena. The structure demonstrates nearly full polarization transmission, conversion to an opposite spin state, and reflection of the opposite spin state at a wavelength of 1549 nm. As a result, the maximum circular dichroism (CD) value reaches up to ≈1 (0.9993) for a given polarization state. Furthermore, reduced symmetry enables the one-way flow of a given polarization state resulting in about unity (0.998) asymmetric transmission (AT) value. Through rigorous numerical simulations, we elucidate the underlying principles driving these extraordinary optical properties. The CD and AT values are record-high demonstrated so far. The single-layer design offers an ultrathin profile, making it compatible with integrated photonics and providing opportunities for applications in compact, lightweight optical devices such as circular polarizers, half-wave plates, and self-polarizing reflectors.

Yansıma Modunda Doğrusal ve Dairesel Polarizasyon için Çok Fonksiyonlu Çok Bantlı Metasurface

A new metasurface design is presented in multi and broad frequency bands. Metasurface has been designed on Roger 5880 substrate with a thickness of 1.575 mm. The top of the designed metasurface consists of two diagonal mirror m-shaped unit cells. The background plane covers the whole metasurface. Numerical results demonstrate the metasurface's capability for both linear (12.48-13.62 GHz, 19.00-27.64 GHz, 39.45-41.72 GHz, 44.68-45.18 GHz, and 47.52-48.28 GHz) and circular (11.5-12.07 GHz, 30.01-37.77 GHz, 42.3-44.2 GHz, 45.45-47.1 GHz, 48.7-49.54 GHz) polarization conversion with over 90% efficiency. At the same time, the metasurface has good angular stability up 45^0.

Wideband and wide-angle reflective metasurface for efficient linear and circular polarization conversion in X, Ku, and K bands

A single-layer wideband and wide-angle reflective metasurface exhibiting linear to cross-polarization conversion (CPC) and linear-to-circular polarization (LP-to-CP) conversion in the X, Ku, and K bands is presented in this research. The devised metasurface serves as a multifunctional platform, achieving CPC over a substantial fractional bandwidth of 64.34% (9.75–19 GHz) with remarkable efficiency exceeding 90% within the 9.75–16 GHz range, reaching a remarkable 100% at resonant frequencies of 11 GHz and 14.6 GHz. Additionally, linear-to-circular polarization conversion is achieved over a significant bandwidth of 9.54 GHz. Notably, the carefully optimized unit cell structure ensures robust polarization transformation, maintaining stability against variations in the incidence angle of up to 45° for both transverse-electric (TE) and transverse-magnetic (TM) polarizations. The proposed metasurface, characterized by its simplicity, compactness, angular stability, and multifunctionality, demonstrates the considerable potential for various microwave communications, antenna design, radar invisibility, and remote sensing device applications.

A Low Profile Wideband Linear to Circular Polarization Converter Metasurface with Wide Axial Ratio and High Ellipticity

This paper introduces an ultra-wideband (UWB) reflective metasurface that exhibits the characteristics of a linear to circular (LTC) polarization conversion. The LTC polarization conversion is an orthotropic pattern comprising two equal axes, v and u, which are mutually orthogonal. Additionally, it possesses a 45° rotation with respect to the y-axis which extends vertically. The observed unit cell of the metasurface resembles a basic dipole shape. The converter has the capability to transform LP (linear polarized) waves into CP (circular polarized) waves within the frequency range 15.41–25.23 GHz. The band that contains its 3dB axial ratio lies within 15.41–25.23 GHz, which corresponds to an axial ratio (AR) bandwidth of 49.1%, and the resulting circular polarized wave is specifically a right-hand circular polarization (RHCP). Additionally, an LTC polarization conversion ratio (PCR) of over 98% is achieved within the frequency range between 15 and 24 GHz. A thorough theoretical investigation was performed to discover the underlying mechanism of the LTC polarization conversion. The phase difference Δφμν among the reflection coefficients of both the v- as well as the u-polarized incidences is approximately ±90° that is accurately predictive of the AR of the reflected wave. This study highlights that the reflective metasurfaces can be used as an efficient LTC polarization conversion when the Δφμν approaches ±90°. The performance of the proposed metasurface enables versatile applications, especially in antenna design and polarization devices, through LTC polarization conversion.

Broadband circular polarization selector and converter based on multilayer metamaterials with stacked split-rings

Broadband circular polarization selector and converter based on multilayer metamaterials with stacked split-rings

Single Layer Multi-Band Transmissive Type Linear to Circular Polarization Converter With Wide Angular Stability for C-, X-, and Ku-Band Applications

Single Layer Multi-Band Transmissive Type Linear to Circular Polarization Converter With Wide Angular Stability for C-, X-, and Ku-Band Applications

Multi-Functional Wideband Metasurface: Perfect Absorber and Linear to Linear and Linear to Circular Polarization Converter

Multi-Functional Wideband Metasurface: Perfect Absorber and Linear to Linear and Linear to Circular Polarization Converter

An efficient and low-profile metasurface-based polarization converter with linear and circular polarization efficiencies for X- and Ku-Band applications

In this study, a metasurface-based linear and circular polarization converter operating on the reflection mode is proposed for X- and Ku-band microwave applications. The proposed converter offers an optimum performance with a polarization conversion ratio (PCR) and polarization matching ratio (PMR) greater than 93 in the bandwidth for a linearly polarized in the y-direction and right-handed circular polarized (RHCP) incident waves. Besides, the design performs over 80 PCR performance up to under oblique incidence. Moreover, the proposed converter is capable of left-handed circular polarization conversion between 7.42 and 7.68 GHz for a y-polarized incident wave. The design offers a relative bandwidth (RBW) of 71.36. The converter design is constructed with metal termination, an easily accessible FR-4 substrate and a simple design metasurface. Surface currents of the polarization converter at resonance frequencies of 8.77, 12.88 and were examined to understand its working mechanism. In addition, when the proposed design is rearranged with the appropriate geometry, the monostatic RCS reduction value in the 8.0–17.7 range is observed to be higher than 10 dB. CST program (a commercial 3D electromagnetic simulator) was used in simulations. The simulated device was fabricated with a traditional board fabrication technique. Simulation results were verified with free space measurements calibrated by the thru-reflect-line calibration procedure. The performance and efficiency of the proposed polarization converter were compared with other converters in the literature.

Dual-band transmissive linear to circular polarization converter with angular-stable and orthogonal polarizations

Abstract A dual-band angular-stable transmissive linear to circular polarization converter based on metasurface is proposed and demonstrated in this work. The converter consists of three layers. The top and bottom layers are formed by an array of double split-ring layers. The unit cell of the central layer contains a square loop nesting a slant dipole. The split-rings create two resonances, enabling dual-band operation. The slant dipole and square loop are useful for improving the quality of circular polarization conversion. It is shown that the proposed polarization converter converts the incident linearly polarized wave into circularly polarized wave with opposite polarization modes over the frequency ranges of 8.77–10.58 and 17.59–19.88 GHz. The angular stability is up to 60° for 3 dB axial ratio. Moreover, the thickness of unit cell has a wavelength below 0.06 at the lower band. Compared with other designs in the literature, the structure bears merits of wideband response, high angular stability, and low-profile property within dual-band operational region. To validate the design, a sample prototype was designed, fabricated, and measured. The measured results are in good agreement with the simulated ones.

Broadband metasurface based on metallic stereo split-ring structure for full-space terahertz beam deflection and focusing effect

In this paper, we proposed an all-metal metasurface that enables circular polarization (CP) conversion and wavefront manipulation of the both transmitted and reflected terahertz (THz) waves over a wide frequency range. The proposed metasurface consists of a periodic array of the metallic stereo split-ring (MSSR) structure adhered on an ultrathin dielectric substrate made of benzocyclobutene (BCB). Numerical simulations show that the incident CP waves through the proposed MSSR can be converted into their orthogonal components in the full-space in a broadband range, with transmission conversion coefficients exceeding 40 % and reflection conversion coefficients exceeding 50 % between 0.8 and 1.1 THz (relative bandwidth of 31.6 %). Based on the geometric phase principle, 2π-phase full coverage can be realized by changing the rotation angle of the MSSR structure in the operating frequency range. Specifically, to demonstrate the multifunctional wavefront manipulation, we numerically simulated the anomalous deflection of THz beams and the full-space planar focusing functionality, respectively. Our research provides a valuable reference for the study of multifunctional components that possess full-space amplitude and phase modulation capabilities. This work holds particular significance in the field of device research in the THz region.

Tunable multifunctional polarization conversion inbilayer chiral metamaterials.

A chiral metamaterial composed of bilayer twisted split-ring resonators is proposed and demonstrated to realize tunable, dual-directional, and multifunctional polarization conversion for terahertz waves. Simulations show that the converter can selectively achieve linear-to-linear, linear-to-right-handed circular, or linear-to-left-handed circular polarization conversion by tuning the polarization and propagating direction of the incident waves. Stokes parameters, ellipticity, and a polarization rotation angle are introduced to determine the output polarization. The circular polarization transmission coefficients and surface current distribution are employed to demonstrate the physical mechanisms of the phenomena above. The proposed converter can find potential applications in terahertz imaging and communications.

Active anisotropic polarization conversion meta-surface for 6G communication bandgap in the reflection mode

This paper investigates a single-layered active anisotropic meta-surface design capable of achieving high polarization conversion efficiency in the 6 G communication band gap. Additionally, the designed structure can convert the linear polarization of the incoming wave fronts to its cross-polarization and linear polarization to circular polarization in the reflection mode. The polarization conversion characteristic is achieved due to the strong anisotropic behavior of the meta-surface. Such a simple design can achieve a 90% to 100% cross-polarization conversion efficiency over a frequency region of [0.28–0.36] THz. The linear to circular polarization conversion is performed near 0.26 THz and 0.40 THz. Between these two frequencies, band linear to cross-polarization conversion is more prominent. The proposed design can be tuned from a half-wave plate (HWP) or linear polarization converter to a quarter-wave plate (QWP) or circular polarization converter using the chemical potential of graphene. The optical response of the meta-surface behaves differently from different incident angles. The proposed polarization converter can contribute to the development of active polarization device.

Dual-mode dual-band circular polarization device based on three-layer plasmonic metasurface

In this work, we proposed a three-layer metasurface with rotated gold split-rings as a polarization device that has two adjacent operating bands in two different modes. The proposed metasurface can be used as a circular polarization selector in transmission mode as well as a circular polarization converter in reflection mode. In transmission mode, it can transmit right- and left-handed circularly polarized light at the corresponding wavelengths of 2130 and 3040 nm with transmission efficiencies of 85.3% and 83.8%, respectively. In reflection mode, it can convert two types of circularly polarized light into those of the orthogonal state with conversion efficiencies of 70.3% and 77.3% in the opposite bands, respectively. The results of the theoretical calculation by transfer matrix method are consistent with these simulation results, and the current distribution results illustrate the coupling mechanism under the proposed chiral structure. In addition, the influence of parameters on circular dichroism was investigated, demonstrating the strong robustness of the structure. The proposed metasurface provides a new degree of freedom for multifunctional photonic integrated devices, which can be used for applications in optical communication and imaging.

Vortex beam generator based on exceptional topological phase in terahertz all-dielectric metasurface

In this study, an all-dielectric metasurface with an F-shaped chiral structure in the terahertz region has been proposed. The coupling between the electric and magnetic dipole modes supported by the metasurface can be adjusted by varying the structural parameters. In the parameter space composed of l l and s, any closed path around exceptional point in the circular polarization conversion channel t rl generates a topologically protected exceptional topological phase. A vortex beam generator with a unit topological charge was proposed to provide a novel concept for designing terahertz metasurface wavefront modulation devices.

A Circularly Polarized Dielectric Discrete Lens Antenna With Wide Axial Ratio and Gain Bandwidths

This letter presents a novel circularly polarized (CP) discrete lens antenna, which exhibits wide axial ratio and gain bandwidths. It consists of a transmitting surface (TS) and a linearly polarized feeding source. For the former, it is based on a dielectric unit cell (UC) which is composed of two parallel slabs. This UC is anisotropic in its cross-section and variable in its height, which provide two degrees of freedom to manipulate the phase difference and the phase shifts of two orthogonal electric field components, and thus the TS can seamlessly attain linear to circular polarization conversion and collimated beam. In the design of the TS, 3-bit phase quantization is adopted. Owing to the non-dispersive characteristic of the UCs, the proposed TS shows superior bandwidth performance over the existing studies. For the latter, it is a commercial wideband double-ridged horn antenna which matches with the TS in terms of bandwidth. As a proof of concept, a 9×9 prototype is fabricated by using 3-D printing technology. Experimental results show that the proposed antenna has a 3-dB axial ratio bandwidth (ARBW) of 44.2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> (8.8-13.8 GHz). The 1-dB and 3-dB gain bandwidths are 16.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> (11.7-13.8 GHz) and 40 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> (9.2-13.8 GHz), respectively.

Ultra-thin single-layer compact metasurface based on a meander structure for multifunctional polarization conversion

In this paper, we proposed and investigated an ultra-thin, single-layer and compact metasurface (MS) based on a meander structure that achieves linear-polarization to linear-polarization (LP-to-LP) and linear-polarization to circular-polarization (LP-to-CP) conversion for both transmission and reflection simultaneously in the microwave region. Simulation and experimental results demonstrated that the cross-polarization coefficients of both transmission and reflection are approximately 0.49 for the normal incident LP wave passing through the MS at approximately 7 GHz, indicating a near LP-to-LP conversion in both reflection and transmission modes. Furthermore, the linear-to-circular polarization coefficients for both transmission and reflection are about 0.65 at approximately 8 GHz, indicating a near LP-to-CP conversion when the incident LP wave passes through the designed MS after transmission and reflection. The simulation results are in good agreement with the experiment. This design provides a valuable reference for the practical applications of MSs in full-space multifunctional polarization conversion and wavefront manipulation.

Leveraging Symmetry in the Analysis of Mirror-Symmetric Multilayered Periodic Structures With Application to LP-to-CP Converter Design

This communication proves that the analysis of the scattering by a mirror-symmetric multilayered periodic structure can be replaced by the analysis of the scattering by two semi-structures with half the size in which the symmetry plane behaves either as a perfect magnetic conductor (PMC) or as a perfect electric conductor (PEC). The proof is based on the reflection properties of the electric and magnetic fields through PMCs and PECs, and it is valid for arbitrary oblique incidence. As an application of this concept, the spectral domain Method of Moments (SD-MoM) is reformulated to deal with MPSs limited by PMCs and PECs, and it is used in the design of a mirror-symmetric multilayered linear to circular polarization (LP-to-CP) converter. The results obtained with SD-MoM are validated by comparison with commercial software CST. Numerical simulations show that the CPU time required by both SD-MoM and CST in the analysis of half the LP-to-CP converter limited by PMC and PEC is between 30 and 42 per cent smaller than that required by the analysis of the complete LP-to-CP converter, which shows the numerical advantage gained in exploiting the symmetry when it is present.

An efficient cost effective wide-angle metasurface-based linear and circular polarization converter for X-, Ku- and K-band applications

An efficient cost effective wide-angle metasurface-based linear and circular polarization converter for X-, Ku- and K-band applications