Circular Polarization Conversion Research Articles

A metasurface for linear-to-circular polarization conversion and sensing based on quasi-BIC

This work presents a multifunctional metastructure (MS) which realizes linear to circular polarization conversion and sensing function based on quasi-bound states in the continuum (quasi-BIC). MS is made of silicon dioxide as substrate, and silicon as surface material, by etching cross holes and square holes on it to form a 2 × 2 structure, through the transmission of terahertz (THz) band, to form an ultrahigh quality factor (Q-factor), and realize the conversion of linearly polarized waves to circularly polarized ones. At 178.190 THz, it achieves a Q value of 2969, and in the range 178.193 TH to 178.200 THz, the axial ratio (AR) is less than 3 dB and the insertion loss is less than 0.0001. In addition, by changing the permittivity of the surrounding environment, the minimum of the output wave will produce a good linear frequency shift. Using this feature, the given device can also be used as a dielectric constant sensor to detect air quality. The device has a sensing sensitivity (S) of 6.415 THz RIU−1 and a figure of merit (FOM) of 106.9. The parameters (H, w2, L2, g2), incidence angle (θ) and the polarization angle (φ) are discussed. The effects of different parameters on the Q-factor and AR were analyzed, which helped to select the optimal parameters. The design can also be used in communication and biosensing.

Gain improvement of conformal circularly polarized Fabry-Perot resonator antenna based on metasurface

Conformal antenna can keep consistent with the shape of the carrier perfectly, which greatly saves the space of the carrier, so it is widely used in military, aerospace and other fields. In this paper, a cylindrical conformal circular polarization Fabry-Perot resonator antenna is designed, and the adverse effect of conformal on antenna gain is overcome by transmission phase compensation. Firstly, a linear to circular polarization conversion metasurface with adjustable transmission phase is designed. The main reason for choosing the metasurface here is to take advantage of its excellent electromagnetic control ability. The metal structures of the metasurface are printed on the ultra-thin dielectric plates, and then attached to the support structure machined by 3D printing, so as to achieve the conformal design of the metasurface. Secondly, the proposed metasurface is used as the superstructure and is combined with a conformal feed to form a cylindrical conformal circularly polarized Fabry Perot resonator antenna. The conformal feed is a patch antenna which is conformal designed in the same way as the metasurface. The conformal feeder is placed under the conformal metasurface to ensure that the electromagnetic wave radiated by the feeder can enter the resonant cavity composed of the feeder and the metasurface. The curvature of the cylindrical conformal of feed and metasurface is the same, which can ensure the high unity of the different positions in the resonator. Next, by adjusting the transmission phase of the unit on the metaurface, the phase compensation of the transmitted electromagnetic wave is realized, so that the electromagnetic wave radiated by the conformal antenna still presents the characteristic of plane wave. Finally, the conformal Fabry-Perot resonator antenna obtains the same high-gain radiation characteristics as the planar resonator antenna. The designed antenna achieves a maximum gain of 13.1dBic at 10 GHz. The size of the antenna is 2.9λ × 2.9λ, so the aperture efficiency is about 19.9 %. The antenna proposed in this paper overcomes the influence of conformal design on the gain of the antenna, so that it can be conformal on the surface of a cylindrical object and obtain better gain characteristics.

Performance Enhancement of Graphene-based Linear to Circular Polarization Converter for Terahertz Frequency Using a Novel Parameter Prediction Methodology

Performance Enhancement of Graphene-based Linear to Circular Polarization Converter for Terahertz Frequency Using a Novel Parameter Prediction Methodology

A wavefront processing coding metasurface with independent dynamic control of circularly and linearly polarized

To address the current issue of complex coding metasurface structure and deficiency of independent phase control for distinct polarized light within the broadband range, we present a wavefront processing coding metasurface with independent dynamic control of circularly and linearly polarized. The results demonstrate that when VO2 is in the metallic state and circularly polarized (CP) is incident, the metasurface can achieve efficient broadband circular polarization conversion in the 0.48–1.19 THz range, with a relative bandwidth of 85.02 %. It can achieve full 0-2π phase coverage by leveraging the P-B phase principle. When VO2 is in the dielectric state and linearly polarized (LP) is incident, x-LP can attain full 0-2π phase coverage in the range of 1.54–1.60 THz and y-LP can reach full 0-2π phase coverage in the range of 0.65–1.05 THz, which can be adjusted independently. Through encoding and arranging the metasurface, abnormal reflection and vortex beam generation of different polarized light in the same device are realized.

Multi-band ultrathin reflective metasurface for linear and circular polarization conversion in Ku, K, and Ka bands

Linear polarization (LP) and circular polarization (CP) holds paramount importance in Ku, K, and Ka bands for satellite based communication, and remote sensing applications. Satellite based remote sensing applications face challenges like atmospheric attenuation, noise & interference, and signal degradation. Moreover, satellite based communication application demands CP in two distinct, non-adjacent frequency bands with orthogonal polarizations at greater oblique angles, considering the unpredictable incidence angles of electromagnetic (EM) waves. Addressing these challenges, an innovative metasurface polarization converter is proposed to operate efficiently across the Ku-band (13.5–18.0 GHz), K-band (18.0–26.5 GHz), and Ka-band (26.5–38.5 GHz) frequency ranges. The converter achieves left-handed circular polarization (LHCP) in the Ku- and Ka-bands within the frequency ranges of 14.57–15.65 GHz and 27.47–33.85 GHz for y-polarized incident EM waves. Additionally, it provides right-handed circular polarization (RHCP) in the K- and Ka-bands at 17.27–23.92 GHz and 35.87–38.32 GHz for y-polarized incident EM waves. The LP conversion ratio exceeds 95% in the frequency bands of 15.97–16.85 GHz, 24.70–26.65 GHz, and 34.37–35.45 GHz for y-polarized, LHCP, and RHCP incident EM waves, respectively. The metasurface exhibits robust performance up to incidence angles of 45 degrees under oblique conditions. Experimental validation using traditional board-circuit manufacturing demonstrates close agreement between measured co- and cross-polarized reflection coefficients and simulations in the 13.5–18 GHz, and 24–38.5 GHz frequency range. Thin metasurface with a thickness of only 0.64 = 0.013λo mm, the proposed design outperforms existing studies in the literature, establishing its competitive edge in terms of structure and performance.

A near-infrared metastructure to realizing polarization conversion and sensing based on the electromagnetic induced reflection

A multifunctional metastructure (MS) working in the near-infrared band is proposed that achieves linear to circular polarization conversion (LTCPC) and electromagnetically induced reflection (EIR). In addition, due to the use of reflected electric fields to overcome the influences of near-infrared band thermal radiation, MS has a good multifunctional sensing detection. The given MS is composed of a four-layer stacked structure. From the substrate to the top layer (along the +z-direction), it consists of silver, a silicon dioxide layer, and two layers of silicon (Si) resonators. Each layer of the Si resonator has four holes created by rotation. By breaking the symmetry of the upper and lower Si layers of MS, the deviation of the rotation angle of the upper and lower holes is introduced, so the MS achieved a near-infrared EIR with an ultrahigh quality factor (Q-factor). Under electromagnetic wave incidence, at 187.89 THz, the Q-factor of MS's reflection peak reaches 2441.25. Due to the unique shapes of the two resonator layers' holes, the axial ratio (AR) is less than 3 dB between 187.844 THz and 187.871 THz, realizing LTCPC. Utilizing the relationship between the optimal polarization conversion frequency point (the frequency corresponding to the lowest AR) and the environmental refractive index, the MS can be used for detecting cancer cells with a sensing sensitivity (S) of 37.24 THz/RIU (36.06 THz/RIU). By introducing the alcohol into the MS, the refractive index of the alcohol to be measured. MS achieved the detection function of the alcohol solution volume fraction, with an S reaching 33.32 THz/RIU, and a figure of merit as high as 154.202. Finally, the related parameters and polarization angle are discussed. The effects of different parameters on EIR and AR also are analyzed. The innovation of this paper lies in the realization of EIR, and a method to improve the Q-factor of near-infrared EIR by rotating the structure is proposed. The combination of a high Q-factor and polarization conversion overcomes the disadvantage that both are difficult to achieve together, and the EIR is easier to detect than the electromagnetically induced transparency. The design also has potential applications in biomedical sensors and industrial production.

Terahertz-absorbing,dual-polarization converting supersurface structures based on the phase-change material VO2

Dynamically tunable multifunctional hypersurface structures have attracted the interest of researchers due to their good control of electromagnetic waves. Based on this, we have designed a dynamically tunable multifunctional hypersurface structure using the phase change material vanadium dioxide. By changing the state of vanadium dioxide, three functions of efficient broadband wave absorption, linear polarization conversion (LPC) and linear circular polarization conversion (LCPC) can be achieved. At room temperature, the hypersurface is used as a polarization converter to achieve broadband linear polarization conversion in the 0.903 THz range and line-circular polarization conversion with a total bandwidth of 0.608 THz in the 0.522 THz, 0.964 THz and 1.448 THz bands. When the temperature is raised to 68 °C, the hypersurface structure can be used as a broadband absorber, absorbing more than 90% of the incident wave in a wide frequency range of 1.348 THz and showing a large tolerance to variations in the angle of incidence and polarization. The electromagnetic field distribution is used to illustrate the absorption mechanism, and Stokes analysis is introduced to evaluate the polarization transition state. The designed structure can realize three electromagnetic modulation functions by changing the excitation conditions and can cover a wide range of frequency bands. Finally, we used coding to simulate the effect of loss on the wave absorption results in real applications and verified the stability of the structure. Our design provides new ideas for the development of terahertz communication and multifunctional integrated devices.

Multi-functional active frequency reconfigurable polarization converter using a simple DC bias circuit

A multi-functional active converter with frequency reconfiguration is proposed and experimentally verified. The unit cell is composed of two T-shaped metal patches connected with a PIN diode. Two metal vias are designed to connect the T-shaped metal to the ground. The T-shaped metal patches are slantly arranged to provide circular polarization conversion. By switching on and off the PIN diode, frequency reconfiguration can be realized. The DC bias is exerted to the PIN diode through two metal vias connecting to the ground. The ground is gracefully designed so that a very simple bias circuit is developed. It is demonstrated that three frequency bands are generated for both off and on states. An incident linear polarization can be converted to right-hand circular polarization, linear polarization, and left-hand circular polarization in these frequency bands, respectively. A circuit model is established to understand the principle of this design. It is found that circuit simulation is consistent with full wave simulation. Measurements conducted during the frequency range of 20-40 GHz shows that good agreement with simulation has been reached.

Wideband LP to CP Converter Using a Reflectarray Based on Modulated Admittance Surfaces Capable of Wide‐Range Beam‐Scanning for Ku/K Band Applications

AbstractThis study provides the design and demonstration of a Ku/K band horn‐fed linear polarization (LP) to circular polarization (CP) converter using a reflectarray antenna based on the holographic technique and the generalized law of total reflection without any iterative algorithms. The proposed hologram performs wide‐range frequency beam scanning with minimum gain losses and cross‐polarization levels. It comprises 2,500 diagonal slotted octagonal subwavelength metasurfaces with a periodicity of 0.266λ0 = 4 mm at 20 GHz as the center frequency. Two equations are defined to compute Y11 of the proposed unit cell regarding its dimensions for TE(0,0) and TM(0,0) Floquet modes. They significantly simplify the coding procedure and reduce the computational time for synthesizing the hologram. The antenna is simulated using the CST software from 14 to 25 GHz. As a confirmation, a prototype is manufactured and measured at 16, 18, 20, 22, and 24 GHz to verify its performance. The simulated and measured results are well‐matched. The presented hologram achieves 40% 1.8‐dB axial ratio (AR) bandwidth (16–25 GHz), 40% 3.3‐dB gain bandwidth (16–24 GHz), and above 30% 2‐dB gain bandwidth (16–22 GHz). Moreover, the antenna can perform beam scanning from 42° to 24° by changing the frequency from 16 to 24 GHz with peak gain values greater than 20.33 dBi. The LHCP pencil beams are at least 24° off‐broadside, so the proposed hologram avoids the feed blockage. These achievements make the hologram one of the best candidates for satellite communications, radar applications, short‐range communication, and point‐to‐point communication.

Multifunctional Metasurface Polarizers Synthesis Using Effective Data Generation with Adaptive Attention and Space‐To‐Depth Enhanced Network

AbstractConventional approaches for designing metasurfaces with the desired scattering response are often a time‐consuming and onerous process that heavily relies on the design experience and empirical methods. In this paper, a time and resource‐efficient design method is proposed for the synthesis of multiple metasurface polarizers with an efficient automated data generation process by utilizing the structure validation surrogate model (SVSM). Moreover, a novel attention and space‐to‐depth enhanced adaptive tandem network (ASE‐ATN) is proposed which integrates symmetry‐aware space‐to‐depth (SA‐SPD) along with the attention mechanism for efficient feature extraction. Several design examples of metasurfaces with linear polarization to orthogonal linear polarization (LP‐OLP) and/or linear polarization to circular polarization (LP‐CP) conversion capabilities are provided to verify the performance of the proposed method. The feasibility of the proposed method is demonstrated through the fabrication and measurement of a dual‐band dual‐polarization converter.

Bidirectional triple-band truly incident angle insensitive polarization converter using graphene-based transmissive metasurface for terahertz frequency

Abstract The design and response of a triple-band linear-to-circular polarization converter (LTCPC) in the terahertz frequency regime using a graphene-based transmission-type metasurface have been studied numerically and analytically. The unit cell of the converter is constructed using lossy silicon dioxide (SiO2) with a relative permittivity of 3.9 as the substrate. And two similar layers of graphene-based sub-wavelength structures are used at the top and bottom of it. Multiband linear to circular polarization conversion is achieved from 0.74 THz to 0.98 THz, 1.70 THz to 2.33 THz, and 4.06 THz to 5.19 THz, i.e., about 28 %, 31 %, and 24 % fractional bandwidths, respectively. As the same metasurface configuration is used at the top and bottom layers of the transmission-type unit cell, it can be used as a bidirectional polarization converter with identical responses from both sides. The geometrical optimization of the unit cell is done, and an equivalent lumped parameter circuit model is also proposed for the same, considering analogous responses. Tunability over the operating frequency is achieved by varying the chemical potential and relaxation time of graphene. Moreover, due to the ultrathin width and special types of identical configuration of the metasurfaces, the response of the system remains excellent over a wide range of incident angle variations up to 80° angle of incidence.

Quad‐band reflective metasurface for linear to circular polarization conversion

AbstractA quad‐band linear to circular polarization (CP) conversion based on a reflective metasurface is presented. The unit cell of proposed reflective metasurface consists of two unequal tilted and crossed bi‐directional arrow strips with an elliptical ring printed on a grounded dielectric slab. The operating bandwidth of the proposed structure is enhanced by introducing two small slits into the long arrow. A reflective metasurface sheet is fabricated and measured for verification. The simulated and measured results show that the reflective metasurface converter successfully transforms linearly polarized incident waves into right‐hand circularly‐polarized waves in frequency bands 9.49–9.96 GHz and 20–31.8 GHz and into left hand circular polarized waves in frequency bands 12.2–14.44 and 31.8–32.1 GHz. Also, wide angular stability up to 50° oblique incidence along with high efficiency reveals the good applicability of the structure. The proposed reflective structure can be used in multiband satellite communication systems and multifunctional dual‐circularly polarized antenna systems.

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.

Multi-functional Multi-band Metasurface for Linear and Circular Polarization in Reflection Mode

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

Circular Polarization Conversion Using Dual Frequency Selective Surfaces for Full-Duplex Satellite Communications

Circular Polarization Conversion Using Dual Frequency Selective Surfaces for Full-Duplex Satellite Communications