Circularly Polarized Wave Research Articles

Tailoring spin-sensitive focusings by optical metasurfaces

Metalens is composed of artificially subwavelength metal or dielectric meta-atoms arranged according to phase distribution of lens, and it can focus wave in a compact and flexible manner. However, conventional geometric phase-based metalens cannot focus spin-sensitive splitting beams, hindering the simultaneous control of two spins. Here, spin-sensitive plasmonic metasurfaces are presented with independent phase modulation capability for circularly polarized channels. These metasurfaces encode phase information by integrating propagating phase and geometric phase to achieve arbitrarily independent control of focal length and focal position for circularly polarized waves (CPWs). Three metasurfaces, including longitudinally splitting focusing, multidimensional spin-sensitive splitting focusing, and multifocal metasurface, are numerically displayed to confirm these predictions. Firstly, a longitudinally splitting focusing is designed with focal length 3 μm under left-handed circular polarization (LCP) incidence and focal length 5 μm under right-handed circular polarization (RCP) incidence. Secondly, two anomalously reflected converging beams are formed by superimposing different gradient phases on a multidimensional spin-sensitive splitting focusing under LCP and RCP illuminations. Finally, a multifocal metasurface is presented, and it has bifocal points and four focal points under LCP and RCP incidences. This work provides novel methods for flexible control of circular polarization-sensitive focusing.

Dual-band and high-efficiency metasurface-based circular-to-linear polarization converter.

In this paper, to achieve circular-to-linear polarization conversion, a novel polarization converter based on an anisotropic metasurface is proposed. Because the polarization converter is an orthotropic anisotropic structure with a pair of mutually perpendicular symmetric axes u and v, theoretical analysis shows that the polarization converter can achieve circular-to-linear polarization conversion if its reflection phase difference Δφuv under u-polarized and v-polarized incidences is close to ±90°. Numerical simulations show that the reflection phase difference Δφuv of the polarization converter is very close to +90° in two separated frequency ranges, so the polarization converter can achieve high-efficiency and dual-band CP-to-LP polarization conversion, it can convert right-handed circular-polarized (RHCP) and left-handed circular-polarized (LHCP) waves into y-polarized and x-polarized waves respectively in the two separated frequency bands of 8.08-9.27 GHz and 13.80-27.11 GHz; moreover, its polarization conversion rate (PCR) is kept larger than 99.7% in the two frequency bands. Finally, to validate the design, a prototype is manufactured and measured, the measured results are in good agreement with the simulated ones.

Polarization-mismatching transmissive metasurface for independent amplitude and phase control of circular polarization.

This work presents a strategy for independent control of the amplitude and phase of transmissive circular-polarization (CP) waves. The designed meta-atom consists of an elliptical-polarization receiver and a CP transmitter. By changing the axial ratio (AR) and polarization of the receiver, amplitude modulation can be realized based on polarization mismatching theory, with negligible cumbrous components. While by rotating the element, a full phase coverage enabled by the geometric phase is achieved. Subsequently, a CP transmitarray antenna (TA) with high gain and low side-lobe level (SLL) is implemented to experimentally validate our strategy, and the tested results match well with the simulated ones. During the operating band from 9.6 to 10.4 GHz, the proposed TA obtains an average SLL of -24.5 dB, a lowest SLL of -27.7 dB at 9.9 GHz, and a maximum gain of 19 dBi at 10.3 GHz, with the measured AR lower than 1 dB, which mainly benefits from high polarization purity (HPP) of the proposed elements. The proposed strategy for full amplitude-phase manipulation of CP waves together with HPP paves a way for complicated field manipulations and indicates a promising candidate in antenna applications, such as anti-jamming systems and wireless communications.

Broadband and high-efficiency thermal switchable InSb metasurface for terahertz wave anomalous reflection and focusing effect

In this paper, a reflective metasurface composed of a dielectric substrate sandwiched with a double-split-ring (DSR) structure InSb and a metal ground plane was proposed in terahertz (THz) region, which can realize a high-efficient thermal switchability of circular-polarization (CP) conversion, anomalous reflection, and planar reflective focusing effect in a broadband manner. Simulation results demonstrated that the designed InSb metasurface structure can achieve high-efficient reflective CP conversion, with the magnitude of the reflected orthogonal CP wave being over 0.8 on average from 0.7 THz to 1.55 THz under the external higher thermal (T = 320 K, “On” state). Conversely, the magnitude of the reflected orthogonal CP wave is nearly zero under external lower thermal conditions (T = 240 K, “Off” state). Furthermore, the proposed InSb metasurface structure can achieve a high-efficient reflective CP conversion with an efficiency of about 0.7 under the “On” state, and a 2π phase full coverage by adjusting the oriented rotation angle (α) of the DSR structure InSb. As evidences of the concept, two InSb metasurfaces have been constructed to achieve the broadband switchable anomalous reflection phenomenon and reflective focusing effect based on Pancharatnam-Berry (PB) phase principle. The proposed metasurface has great potential in developing a dynamically tunable device for THz wavefront modulation applications in the future.

Multifunctional Device for Circular to Linear Polarization Conversion and Absorption

AbstractIn this paper, a metastructure multifunctional device for circular‐to‐linear polarization conversion (PC) and perfect absorption is proposed in which the electrical conductivity of the silicon material is controlled by light, thus changing the function of the device. The paper also explores three methods of optimizing bandwidth and their mechanisms, which are analyzed by means of current and energy density diagrams. The unit structure of this device adopts a 2 × 2 array, which is used for differentiated reflection of circular polarization waves, and forms linear polarization waves after reflection. In the other state, ultrawideband absorption can be achieved by changing the conductivity of silicon by external optical pumping, and the bandwidth is widened by inserting air resonators. In general, the device can form a PC at 0.89–1.31 THz with a relative bandwidth of 38% when there is no illumination. The resulting linear polarization wave has an axial ratio greater than 19 dB. When the silicon is excited by light resulting in a stable conductivity of around 9000 S m−1, the absorption band is 0.89–2.01 THz, the relative bandwidth is 77%, and the absorption rate is above 90%. This device can be used for communication, electromagnetic cloaking, and modulation.

Interconversion between dual-peak electromagnetically induced transparency and dual-peak electromagnetically induced absorption utilizing metasurface

Utilizing metasurface (MS), the transition between dual-peak electromagnetically induced transparency (EIT) and dual-peak electromagnetically induced absorption (EIA) in four states has been proposed in the terahertz (THz) band with the incidence of a circularly polarized (CP) wave. Additionally, the phase-change material vanadium dioxide (VO2) and photosensitive material silicon (Si) have been adopted. The four state transitions can be achieved by adjusting the pump light and the temperature which is not affected by incident CP waves. With the incidence of the pump light, Si can transform from the insulating state to the metallic state. Similarly, when the temperature exceeds 68 °C, VO2 enters the metallic state. Two different dual-peak EIT (State 1 and State 2) accompanied by slow light effect can be observed by modulating the state of VO2 without the action of Si. However, once Si is in metallic state, two different states of dual-peak EIA (State 3 and State 4) are achieved by changing the state of VO2. Notably, the MS has the property of polarization insensitivity. The theoretical oscillator model and equivalent RLC-circuit model verify the feasibility of dual-peak EIT and EIA.

Demonstration of a Wideband Multipolarization Transmitarray Antenna for Satellite Communication

To meet the requirements of satellite communication (SATCOM), in this paper, a wideband high stability transmitarray antenna (TA) for SATCOM is proposed. The TA is composed of 225 metal-only unit cells that comprise three metallic layers with an air spacer in between. High stability is capable by adopting a simple metallic square loop and two pairs of orthogonal stubs with a 1 mm thickness of the layer, which ensures lower assembly complexity and higher integration. The proposed unit cell can also support linear polarization (LP) wave excitation and circular polarization (CP) wave excitation simultaneously. Meanwhile, the metal-only unit cell can operate without dielectric loss, which leads to higher working efficiency. By adjusting feature sizes, eight different kinds of the unit cell are designed to realize a 3-bit TA which enables obtaining a gain of 23.53 dBi. Finally, four TA prototypes have been fabricated and tested successfully. The measured result shows a 28.5% 3 dB gain bandwidth from 30 GHz to 40 GHz, which is in good consistency with the simulated design. This compact and mechanical robustness design provides an alternative proposal for SATCOM.

Wideband OAM Generator Design Using a Low Q-Factor and C-Shaped Element

Reflective metasurfaces have been widely explored for generating orbital angular momentum (OAM) carried by vortex beams. However, the most OAM generators have narrow bandwidth or major for circular polarization waves, which are caused by the propagation phase and Pancharatnam–Berry (PB) phase. In this letter, by combining the propagation phase and reflection polarization conversion metasurface, a novel OAM generator operating at microwave band is proposed, which is based on a low <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$</tex-math> </inline-formula> -factor C-shaped element. A proof-of-concept prototype is fabricated and measured. This generator not only covers a broad bandwidth from 12 to 18 GHz (40%) but can also be used for dual-linear and dual-circular polarized waves.

Wideband Circularly Polarized Reflectarray Antenna Using Rotational Symmetrical Crossed Dipoles

A wideband circularly polarized (CP) reflectarray (RA) antenna using rotational symmetrical crossed dipoles is presented. This is the first time investigating coupled crossed dipoles as the unit cell for wideband reflection bandwidth in the CP RA design. Equivalent circuit analysis shows that when a CP wave impinges on the designed unit cell, two series resonances and two parallel resonances are simultaneously excited on the crossed dipoles. Owing to these four different resonances, the CP reflection bandwidth is greatly improved and elaborately adjusted by controlling the coupling between the crossed dipoles. The CP reflection bandwidth ratio of the unit cell is enhanced up to 2:1 for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S_x</i> <-15 dB with a thin thickness of 0.12λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . Based on this unit cell, a wideband -20° collimated CP RA antenna with a circular aperture of 316 unit cells was designed, fabricated, and measured for final performance verification. The measured results show that a wide CP bandwidth of 7.6-15.9 GHz is achieved with the axial ratio <3 dB. In addition, the measured 3dB gain bandwidth is better than 43.7% with the peak realized gain of 26.3 dBic and the maximum aperture efficiency of 58.3%.

Multifunctional terahertz metamaterial based onvanadium dioxide and silicon.

This paper proposes a multifunctional metamaterial device operating in the terahertz (THz) band. The metamaterial device can switch functions by using the phase transition properties of vanadium dioxide (V O 2) and the photoconductive effect of silicon. An intermediate metal layer divides the device into the I side and II side. When V O 2 is in the insulating state, the I side can achieve polarization conversion from linear polarization waves to linear polarization waves at 0.408-0.970THz. When V O 2 is in the metal-like state, the I side can perform polarization conversion from linear polarization waves to circular polarization waves at 0.469-1.127THz. When silicon is not excited in the absence of light, the II side can perform polarization conversion from linear polarization waves to linear polarization waves at 0.799-1.336THz. As the light intensity increases, the II side can realize stable broadband absorption at 0.697-1.483THz when silicon is in the conductive state. The device can be applied to wireless communications, electromagnetic stealth, THz modulation, THz sensing, and THz imaging. Moreover, it provides a fresh idea for the design of multifunctional metamaterial devices.

A Wideband High-Efficiency Transmit-Reflect-Array Antenna for Bidirectional Radiations With Distinct Circular Polarizations Based on a Metasurface

In this communication, we present the modeling, design, and experiments of a wideband high-efficiency transmit-reflect-array (TRA) antenna with independent manipulations for transmitted and reflected beams with distinct circular polarizations working in the millimeter-waveband. A polarization-dependent full-space metasurface is designed to transmit the left-handed circularly-polarized (LCP) wave for a transmitarray (TA) operation, and at the same time to reflect the right-handed circularly-polarized (RCP) wave for a reflectarray (RA) operation. The TRA is then optimized with a rectangular shape for a high aperture efficiency (AE) based on a system-level analysis combining the characteristics of a Fermi feed antenna. The experimentally measured results are in good agreement with the simulated ones, achieving a peak gain of 22 dBi (21.5 dBi), a 1 dB gain bandwidth of 18.2% (24.6%), and a 3 dB axial ratio (AR) bandwidth of 38.6% (38.5%) for TA (RA) operation. A total AE as high as 61.2% is realized by comprehensively considering TA and RA operations. The design strategy and the well-performed TRA may find promising applications in wireless and satellite communication systems with bidirectional communication scenarios.

Terahertz linear to circular polarization converter based on reflective metasurface

Metasurfaces are two-dimensional artificial structures which have extraordinary electromagnetic properties. They have been used in myriad of devices such as nano-antennas, cloaking coatings, imaging devices, flat lenses, and polarization converters over a wide range of frequency. Due to high dependency of many devices on incident wave polarization, manipulating the polarization of electromagnetic waves would be useful, especially in the THz regime. In this study, we propose a linear to circular polarization converter (LTC-PC) based on a THz reflective metasurface. For a TE linear polarization incident wave, this structure has two distinct bands; the first one lays in a wideband frequency range of 0.5-1.41 THz, in which the reflected wave would be a left-handed circular polarization (LHCP) with minimum efficiency of 89% and maximum efficiency of more than 95% in 80% of the bandwidth. The second band lays in the narrowband frequency range of 1.45-1.55 THz, resulting a right-handed circular polarization (RHCP) wave with a minimum efficiency of 82%. The proposed polarization converter can be used in optical communication and electronic devices.

Ring slot CP antenna for the hybrid electromagnetic solar energy harvesting and IoT application

The research proposed a compact antenna integrated with dual-function solar cells to optimize internet of things (IoT) communication devices and energy harvesting. The use of integrated solar cells with electromagnetic elements as antennas and energy-gathering in a design is a solution for wireless communication sensors and simultaneously electromagnetic and solar energy harvesting. Radiation performance testing of solar cell antennas and optical experiments were carried out to test the ability of solar energy collection. A double feed ring slot circular polarization (CP) antenna coplanar antenna with a configuration has highly sensitive to vertical and horizontal waves. It is to accommodate the impact of circular polarization wave and solar cell distortion on antenna performance. This technology promises green communications, renewable energy, and environmental protection to combine wireless communication and green battery components. The study presents the performance and design results of a double line-feed microstrip antenna circuit connected with CP antenna on the S-band for IoT communication by accommodating electromagnetic energy transmission. The importance of adopting an integrated radio frequency (RF) solar energy harvesting strategy rather than a single source method makes this research very significant in its novelty by optimizing the analysis of multiple signal access in IoT communications.

Orthogonal Adjacent-Order Filtering Element-Based Wideband Transmissive Linear-to-Circular Polarization Converter

This article proposes a unified design method for a highly efficient wideband transmissive linear-to-circular polarization converter composed of two orthogonal adjacent-order bandpass filtering elements for the first time. First, the linear-to-circular polarization converter is constructed to convert two orthogonal linearly polarized (LP) spatial waves split from a 45°-slant incident plane wave into a desired circularly polarized (CP) wave. Taking advantage of the wideband filter synthesis method and phase shifter theory, polarization converter elements with prescribed specifications [e.g., fractional bandwidth (FBW) and Chebyshev passband ripple] are then synthesized by the corresponding low-characteristic-impedance bandpass filtering networks with the loading of shunt short-circuited stubs on quarter-wavelength transmission line (TL) sections. The adjacent-order phase difference function with a natural ±90° value at a center frequency can be simultaneously manipulated by a filtering bandwidth. The theoretical axial ratio (AR) curve is calculated by the synthesized magnitude responses and phase deviation (PD) function. The design guideline is then summarized. Finally, based on the third- and fourth-order bandpass filtering networks, a prototype of the proposed linear-to-circular polarization converter operating at 5 GHz with a designable 70% 3 dB AR bandwidth is implemented, fabricated, and tested by the free-space measurement method. The transmitted CP wave with three in-band AR minima and relatively stable angular performances can be efficiently converted from the incident LP spatial wave as well verified in the experiment. The AR curves and design requirements of different adjacent-order bandpass filtering combinations are further explored according to the proposed design guideline.

Study on the Absorption Properties of Terahertz Circularly Polarized Wave in FPL Model Fully Ionized Dusty Plasma

In this article, Boltzmann’s general plasma kinetics and the Fokker–Planck–Landau (FPL) collision model of dusty plasma are used to obtain the expression of the dielectric coefficient of dusty plasma under the influence of an external magnetic field and the collision condition of the fully ionized FPL model. The charging effect of dusty plasma is fully considered. The absorption characteristics of circularly polarized waves in the terahertz band under different plasma parameters are calculated and analyzed by using the transfer matrix method. Results show that the intensity of the external magnetic field, the size and concentration of dust particles, the effective collision frequency and thickness of dusty plasma, the incidence angle of the electromagnetic waves, and the electron temperature greatly influence the absorption characteristics of circularly polarized electromagnetic waves. The propagation characteristics of circularly polarized waves caused by different external magnetic fields are evaluated. An absorption band is formed near the cyclotron frequency when the external magnetic field increases to a certain extent, and the direction of the electron cyclotron and the rotation direction of the polarized wave are consistent. The position and frequency band of dusty plasma can be controlled by artificially changing the magnitude of the external magnetic field. These results provide a theoretical basis for the study of electromagnetic wave propagation in weakly colliding, fully ionized dusty plasma and the propagation mechanism of an electromagnetic wave in the local high-temperature area of the hypersonic target.

Manipulation of Arbitrary Polarizations and Phases Based on Metasurfaces

AbstractPolarization and phase are two essential properties of electromagnetic (EM) waves. A transmissive metasurface is proposed that can simultaneously manipulate the polarization and phase of the EM waves. The design has a powerful capability of rotating the polarization to any desired azimuth direction for a linearly polarized (LP) wave and achieving the cross‐polarization conversion for a circularly polarized (CP) wave. Meanwhile, the transmission phase of the cross‐polarization can be dynamically controlled for the CP wave. The proposed metasurface is composed of two types of substrate‐integrated waveguides (SIW) in a cross arrangement, which has an insertion loss of less than 0.3 dB from 9.7 to 10.3 GHz. Some samples are fabricated and measurements are performed, which are in satisfactory agreement with the theoretical and simulated results, indicating the feasibility of the proposed method. It is believed that the proposed design has many potential applications in the fields of imaging, communication, and radar systems.

Tri-band terahertz vortex beam generator based on a completely independent geometric phase metasurface

A vortex beam carrying orbital angular momentum (OAM) is an effective way to increase wireless communication capacity. The existing terahertz (THz) metasurface (MS)-based vortex beam generator is limited to operating at a single or two frequency points, and also has wavelength-dependent behavior, thus limiting its application. Here, a transmissive MS is proposed to generate THz vortex beams carrying OAM with different topological charges l = − 1 , − 2 , and − 3 ( l = + 1 , + 2 , and + 3 ) under left/right-handed circular polarization (CP) incidence at three different frequencies. The mode purity of the generated vortex beam with topological charges of all orders is greater than 60% under CP wave incidence at 0.6 THz, 0.857 THz, and 1.892 THz, respectively. Both theoretical prediction and simulation results verify that the designed MS can independently manipulate CP waves at three different THz frequencies. The proposed unit-cell structure is preferable for increasing the number of operation frequencies while guaranteeing the manipulation of electromagnetic waves. The compact system of unit-cell structure provides ideas for the fabrication of multifunctional THz MS-based devices with higher integration and smaller size.

Characteristic mode analysis of a compact circularly polarized rotated square slot antenna

AbstractPresented in this paper is a circularly polarized (CP) wide 45° rotated slot antenna with a broad bandwidth. Characteristic mode analysis is initially carried out to show that, by simply rotating a square slot, CP waves can be radiated if it is properly excited. A simple 50 Ω feedline is then designed to excite the slot for the generation of broadband CP waves. The antenna has a total volume of 30 × 30 × 1.6 mm3. Measurement results indicate a broad S11 ≤ −10 dB impedance bandwidth of 85.7% (3.2–8 GHz), a broadband 3 dB axial ratio bandwidth of 57.1% (3.5–6.3 GHz) and a peak gain of 3.6 dBi are obtained by the antenna. The proposed antenna possesses stable radiation patterns as well as relatively flat gain over its operational bandwidth in addition to being compact. It can thus be used for wireless technologies such as WiMAX 3.5 and 5.5 GHz, WLAN 5.2 and 5.8 GHz in addition to Industrial, Scientific, and Medical 5.8 GHz.

A dual‐band dual‐sense circularly polarized antenna based on chiral structure

AbstractA millimeter‐wave (MMW) dual‐band dual‐sense (DBDS) circular polarization (CP) antenna based on a chiral structure is presented. An arc parasitic patch is loaded around a circular patch to have chiral characteristics. This structure exhibits bi‐isotropy to the electromagnetic wave. The linear polarization (LP) wave passes through the chiral structure and excites the orthogonal left‐handed (LH) and right‐handed (RH) CP waves. The antenna is fabricated and measured. The LHCP radiation is achieved in the range between 23.75 and 24.25 GHz, and the RHCP radiation is between 27.75 and 28.25 GHz. The realized gains reach 6.9 dBic at 24 GHz and reach 7.1 dBic at 28 GHz. The proposed antenna has a profile of 1.044 mm (0.08 λ) and occupies an area of 0.54 λ × 0.54 λ, λ is the free‐space wavelength at the lower frequency and is convenient for array design.

Double-split-ring structure based ultra-broadband and ultra-thin dual-polarization terahertz metasurface with half-reflection and half-transmission

In this paper, we propose a dual-polarization ultra-wideband metasurface with half-reflection and half-transmission based on a double-split-ring (DSR) structure operating in a terahertz (THz) frequency range. The designed metasurface can simultaneously control the circularly polarized (CP) wave and linearly polarized (LP) wave in reflection mode and transmission mode, covering an extensive THz frequency range. The unit-cell architecture of the metasurface consists of a periodic arrangement of the DSR structure made of metal, which is affixed to an ultra-thin dielectric substrate. By manipulating the size and rotation direction of the DSR structure, we achieve full phase coverage of 0–2π of the orthogonally polarized LP wave and CP wave across a frequency span of 0.3–1.2 THz, encompassing transmission and reflection scenarios. The relative bandwidths of the corresponding orthogonal LP wave and CP wave with an average amplitude of 0.45 reach 86% and 120%, respectively. Specifically, through numerical simulations, we demonstrate that the designed metasurface has the ability to achieve THz beam deflection and vortex beam generation while reflecting and transmitting LP wave and CP wave. The proposed dual-polarization ultra-wideband metasurface holds great promise for various applications in the terahertz frequency range. These findings pave the way for the development of flexible and versatile THz devices with expanded functionality, thereby opening up new possibilities for wavefront manipulation in metasurfaces.