Left-hand Circular Polarization Research Articles

A tunable versatile metasurface in terahertz frequency based on graphene–metal hybrid structures

The increasing demands for device integration and reusability have led to the development of freely switchable and dynamically tunable diverse functions in both modern optics and wireless communications. This study proposes a versatile metasurface that integrates with four tunable functions in the terahertz region based on graphene patch and metal split-ring hybrid structures. By adjusting the Fermi level of the graphene patches through electrostatic gating, the proposed metasurface can effectively achieve free switching among four different functions and dynamic tuning of each function's characteristics over a broad frequency band. Moreover, the metasurface operates smoothly in reflection mode for x-polarization, y-polarization, and left-hand and right-hand circular polarization illuminations. All expected performances, including resonant absorption with tunable frequency (relative bandwidth is about 20 %) and regulable absorbance (from 10 % to 100 %), arbitrary interconversion of four polarization states (relative bandwidth is over 48 %), regulation of cross-polarization conversion rate (from 0 % to 100 %), tunable spatial power division (three-way outputs), and dual-channel high-efficiency signal modulation (modulation depth is over 81 %), are demonstrated through full-wave simulation experiments. This study opens up a new avenue for exploring tunable multifunctional integrated devices with graphene materials, with potential applications in various domains, such as wireless communication, terahertz sensing, and imaging.

Broadband intelligent programmable metasurface with polarization-modulated self-adaptive electromagnetic functionality switching

Programmable metasurfaces have received a great deal of attention due to their ability to dynamically manipulate electromagnetic (EM) waves. Despite the rapid growth, most of the existing metasurfaces require manual control to switch among different functionalities, which poses severe limitations on practical applications. Here, we put forth an intelligent metasurface that has self-adaptive EM functionality switching in broadband without human participation. It is equipped with polarization discrimination antennas (PDAs) and feedback components to automatically adjust functionalities for the different incident polarization information. The PDA module can first perceive the polarization of incident EM waves, e.g., linear or circular polarization, and then provide the feedback signal to the controlling platform for switching the EM functionality. As exemplary demonstrations, a series of functionalities in the 9–22 GHz band has been realized, including beam scanning for x-polarization, specular reflection for y-polarization, diffuse scattering for left-handed circular polarization (LCP), and vortex beam generation for right-handed circular polarization (RCP) waves. Experiments verify the good self-adaptive reaction capability of the intelligent metasurface and are in good agreement with the designs. Our strategy provides an avenue toward future unmanned devices that are consistent with the ambient environment.

Decoding the Nature of Coherent Radio Emission in Pulsars I: Observational Constraints

Radio observations from normal pulsars indicate that the coherent radio emission is excited by curvature radiation from charge bunches. In this review, we provide a systematic description of the various observational constraints on the radio emission mechanism. We have discussed the presence of highly polarized time samples where the polarization position angle follow two orthogonal well-defined tracks across the profile that closely match the rotating vector model in an identical manner. The observations also show the presence of circular polarization, with both the right and left handed circular polarization seen across the profile. Other constraints on the emission mechanism are provided by the detailed measurements of the spectral index variation across the profile window, where the central part of the profile, corresponding to the core component, has a steeper spectrum than the surrounding cones. Finally, the detailed measurements of the subpulse drifting behaviour can be explained by considering the presence of non-dipolar field on the stellar surface and the formation of the partially screened gap (PSG) above the polar cap region. The PSG gives rise to a non-stationary plasma flow that has a multi-component nature, consisting of highly energetic primary particles, secondary pair plasma, and iron ions discharged from the surface, with large fragmentation resulting in dense plasma clouds and lower-density inter-cloud regions. The physical properties of the outflowing plasma and the observational constraints lead us to consider coherent curvature radiation as the most viable explanation for the emission mechanism in normal pulsars, where propagation effects due to adiabatic walking and refraction are largely inconsequential.

A dual-band dual-sense circularly polarized patch antenna using hybrid capacitive-inductive proximity-coupling feed

This paper presents a new proximity-coupling mechanism between a rectangular patch and a microstrip line with an open circuit terminal. The patch is located to cover both adjacent maximum-voltage (capacitive coupling) and maximum-current (inductive coupling) points of the standing wave on the feedline, and consequently, two orthogonal resonant modes with 90° phase difference are excited on the patch for generating a circularly polarized (CP) radiation. Based on this feeding mechanism, a dual-band dual-sense CP antenna is designed, which is composed of two linear rectangular patch arrays coupled to an open-ending microstrip line. It is realized on a single-layer substrate and its CP rotating sense in each band is opposite to each other. For verification, the antenna operating at 5.0 and 8.0 GHz are designed, fabricated, and tested. Noting that the design concept can be easily implemented to other frequency bands. The measurements result in an impedance-matching bandwidth of 4.72 – 5.10 GHz and 7.50 – 8.20 GHz. The antenna is left-hand CP for the lower band and right-hand CP for the upper band. In addition, the prototype shows a 3-dB axial ratio bandwidth of 4.93 – 5.02 GHz and 7.40 – 8.10 GHz and peak gains of 11.4 and 12.7 dBic at the lower and upper bands, respectively.

Self-Powered Circularly Polarized Light Detection Enabled by Chiral Two-Dimensional Perovskites with Mixed Chiral-Achiral Organic Cations.

Direct detection of circularly polarized light (CPL) holds great promise for the development of various optical technologies. Chiral 2D organic-inorganic halide perovskites make it possible to fabricate CPL-sensitive photodetectors. However, selectively detecting left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) light remains a significant challenge. Herein, we demonstrate a greatly enhanced distinguishability of photodiode-type CPL photodetectors based on chiral 2D perovskites with mixed chiral aryl (R)-(+),(S)-(-)-α-methylbenzylammonium (R,S-MBA) and achiral alkyl n-butylammonium (nBA) cations. The (R,S-MBA0.5nBA0.5)2PbI4 perovskites exhibit a 10-fold increase in circular dichroism signals compared to (R,S-MBA)2PbI4 perovskites. The CPL photodetectors based on the mixed-cation perovskites exhibit self-powered capabilities with a specific detectivity of 2.45 × 1012 Jones at a 0 V bias. Notably, these devices show high distinguishability (gres) factors of -0.58 and +0.54 based on (R,S-MBA0.5nBA0.5)2PbI4 perovskites, respectively, surpassing the performance of (R-MBA)2PbI4-based devices by over 3-fold and setting a record for CPL detectors based on chiral 2D n = 1 perovskites.

A Two-Port Dual-Band Dual-Circularly-Polarized Dielectric Resonator Antenna

A Two-Port Dual-Band Dual-Circularly-Polarized Dielectric Resonator Antenna

A compound reconfigurable electronically switched parasitic monopole antenna for sub 6 GHz wireless and vehicular applications

In this paper, a compound reconfigurable electronically switched parasitic monopole antenna is reported for sub-6 GHz (n77/n78 bands) wireless standards and vehicular communication. The antenna comprises a half-hexagonal-shaped radiating element and two inverted L-shaped parasitic stubs. These stubs are connected through two PIN diodes, allowing for control over frequency. An additional pair of PIN diodes incorporates analogous parasitic stubs into the ground plane to facilitate pattern tilting and polarization. By switching these PIN diodes across seven operating states (OS), the antenna structure could resonate in a single band, spanning 4.5–5.8 GHz (sub-6 GHz higher band), with an omnidirectional pattern specific to OS1. In OS2 and OS3, the antenna resonates in a single band within the range of 4.1–5.7 GHz, featuring beam tilting with linear polarization. In OS4 and OS5, the structure has two bands: one covers 3.3–4.2 GHz (5G-n77 band) with linear polarization, and the other covers 5.1–6.1 GHz (5G WLAN band) with right-hand circular polarization (RHCP) in OS5 and left-hand circular polarization (LHCP) in OS4 with an axial ratio bandwidth of 14.5 %, including pattern tilting within the range of ± 340. Finally, in the OS6 and OS7 structure introduce dual bands of 3.3–3.8 GHz (5G–n78 band) and 4.8–5.8 GHz (sub-6 GHz higher band). Both bands feature LHCP/RHCP with an axial ratio bandwidth of 8.57 % for the lower resonant band and 7.4 % for the higher resonant band. Additionally, it incorporates radiation pattern reconfiguration capabilities. The structure is printed on an FR-4 substrate and measures various associated parameters. The experimental results closely match the simulated results.

Dual wideband circularly polarized reconfigurable antenna using gap loaded annular ring

This work presents a novel proposal for a dual wideband circularly polarized (CP) reconfigurable antenna for wideband wireless communication applications. The circularly polarized characteristic is achieved by introducing a gap in the annular ring, which leads to the generation of traveling waves in circular patterns. The concentric annular ring patch is fed using a tapered 50 Ω microstrip line. Dual wideband characteristics are obtained by incorporating concentric annular rings and additional DGS (defective ground structure) to achieve wideband characteristics. By employing PIN diodes, the proposed approach facilitates reconfiguration, allowing for both left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) in either single or dual wideband operations. The CP antenna exhibits an impressive measured axial ratio bandwidth (ARBW) of 35 % (3438–4900 MHz) and 18.75 % (5154–6252 MHz). The measured return loss bandwidths of the proposed antenna are 18.40 % (3990–4799 MHz) and 35.17 % (5161–7364 MHz). The antenna, fabricated using FR4, is compact in size, measuring 0.56 λo*0.56 λo*0.01 λo, and has a peak gain of 6.33 dBic. The simulated outcomes and hardware measurement findings agreed well.

Fiber end integrated surface plasma lens for circular airy beam shaping

This paper presents a circular Airy beam generator based on a fiber end integrated surface plasma lens. The surface plasma lens consists of a nano-annular slot and an array of series concentric circular grooves etched on the gold film coated on the fiber end. When the fiber light field illuminates the nano-annular slot, surface plasmon polaritons (SPPs) will be excited, then the SPPs propagates along the surface of the gold film, and will finally be decoupled into free space to generate circular Airy beam by the array of concentric circular grooves. The effect of the parameters of the plasma lens on the properties of the output circular Airy beam, such as self-focusing, focal spot size, is studied in detail via FDTD simulations. In addition, we found that the proposed plasma lens has a high tolerance to manufacturing errors. The case that instead of the nano-annular slit with a circular wheat-spike shaped structure is also investigated. In this case, due to the different photon spin response of the circular wheat-spike shaped structure, the device can generate circular Airy beam when the input fiber light field is right-handed circularly polarized (RHCP) light, and subwavelength Bessel-like nondiffracting beam when the input fiber light field is left-handed circularly polarized (LHCP) light. These results provide a highly integrated all-fiber circular Airy beam and subwavelength Bessel-like nondiffracting beam generation scheme, which may be useful in the areas of fiber end structured light beam shaping and fiber-integrated photonic devices.

C-Slot Circular Polarized Antenna for Hybrid Energy Harvesting and Wireless Sensing

This paper presents a new hybrid energy harvesting on electromagnetic solar for wireless energy harvesting of ambient from sensors of low-power devices. The axial ratio (AR) requirements produce Left-Hand Circular Polarization (LHCP) and Right-Hand Circular Polarization (RHCP) and simultaneously produce a 90-degree phase difference during energy harvesting, adopting a new design in designing a dual-feed broadband circular polarized (CP) antenna. To get the frequency band 2.3–2.4 GHz, we propose a C-Slot antenna with a circular patch dual feed. To estimate the diversity of the phase and magnitude output of the feed configuration under AR value, we used a 50 Ohm feed network output of the characteristic analysis for a dual feed CP antenna. An Axial ratio frequency range of less than 3 dB is achieved using polarization analysis with different branch channel couplers. To produce a DC output voltage, a high-frequency rectifier circuit embedded with a thin-film solar cell on the antenna is then connected to two T-junction power divider rectifiers, resulting in a high-efficiency design. A complete system-level analysis will include multiple signal classification methods of powered ambient RF energy using a wireless energy harvesting array that proposes a compact structure and demonstrates optimal configuration. Reliable operation in typical indoor environments indicates a self-contained sensor Node. Therefore, it has significant implications for powering small electronics and wireless sensor applications independently of the IoT Network or real implementation telecommunications industry.

A simple feed orthogonal excitation X-band dual circular polarized microstrip patch array antenna

This work represents a microstrip patch array antenna which is designed and analyzed for the application of circular polarization in X band frequency range. The proposed antenna array has a very simple microstrip line feeding mechanism and each patch is energized orthogonally to acquire circular polarization without the need for any phase shifters. The array antenna has a slot line in the ground to electrically couple the signals from the microstrip feed line to feed each patch. The outcome demonstrates that the antenna is capable of radiating both left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP). The designed work has a return loss of -41.88 dB, that is the antenna is perfectly matched. The outcome also demonstrates the antenna’s strong gain and directivity capabilities, which are 12.87 dBi and 13.30 dBi, respectively. The antenna resonates circularly at a frequency of 10 GHz.

Controlled circular dichroism with graphene-based metamaterial for terahertz wave

This article explores the design and analysis of a metal-graphene hybrid metamaterial structure tailored for tunable circular dichroism (CD) effects in the terahertz (THz) frequency regime. Chiral metamaterials have garnered considerable interest in photonics due to their versatile applications, including sensing, polarization manipulation, and chiral imaging. The proposed metamaterial unit cell features four meta-atoms with C4 rotational symmetry, composed of gold on a polyimide substrate. By strategically integrating the graphene sheets above the gold patterns, selective control over the absorption efficiency for the incident wave of left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) light is achieved. The study demonstrates that adjusting graphene chemical potential enables precise modulation of CD from 0.80 to 0.10 across a wide THz frequency spectrum. Furthermore, the article investigates the structure optical response for incident angles ranging up to 75°, revealing stable CD behavior up to 30° and intriguing dual-band effects beyond 50°. These findings underscore the potential of the proposed metamaterial for practical applications in photonics, sensing, and chiral imaging, offering tunable control over the CD effects in the THz regime.

Spin-splitting and spin Hall effect of reflected Airy beams on the surface of topological insulator

We present an analysis of the enhanced spin Hall effect of light (SHEL) resulting from a reflected Airy beam off the interface of an air-topological insulator (TI). Our study suggests that the surface conductivity of TI film and the decay factors of Airy beams are crucial in increasing the spin-splitting distance and the spatial shifts of the left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) components. An apparent spatial shift asymmetry depending on the decay factors can be observed between the LCP and RCP components, where the coupling of intrinsic and extrinsic angular momentum will play a significant impact. The connection among the thickness of TI film, chemical potential and the incident frequency at the fixed decay factors is thoroughly examined to achieve the maximum of spatial shifts. We find that the coupling between the upper and lower surfaces’ conductivity could be responsible for the pronounced SHEL. These conclusions can be extended to other interfaces of comparable structures, such as insulators coated with a layer of two-dimensional Dirac material. Our work provides novel insights into the use of innovative beams incident on the surface of TI film and their potential applications in optical detection.

Design of dual circular polarized stacked patch antenna for BeiDou navigation satellite systems

In this article, a design of two-layered, dual circular-polarization (CP) and dual-band path antenna is presented for BeiDou navigation satellite (BDS) system applications. A single 50-Ω Co-axial probe feeding arrangement is employed to achieve dual-band operation and it feeds both the antennas simultaneously. This mode introduces the CP radiation on both upper (RHCP) and lower (LHCP) operation bands. The impedance bandwidth is further widened by accommodating two semi-circular stubs on the top patch. The fabricated and experimentally validated prototype radiates at 1.82 and 3.45 GHz (center frequency). The upper and lower operating band exhibits right and left-handed CP radiations, which constructs dual-band operation. The fabricated prototype has a physical size of πr2 × 0.024 λg with an antenna profile of 2.38 mm (0.024 λg). The experimentally validated upper and lower bands impedance bandwidth with |S11| < −10 dB are 21.1% and 11.1%, respectively. The fabricated prototype is a good candidate to use in BDS applications. [Q2

Reconfigurable transmissive metasurface with a combination of scissor and rotation actuators for independently controlling beam scanning and polarization conversion

Polarization conversion and beam scanning metasurfaces are commonly used to reduce polarization mismatch and direct electromagnetic waves in a specific direction to improve the strength of a wireless signal. However, identifying suitable active and mechanically reconfigurable metasurfaces for polarization conversion and beam scanning is a considerable challenge, and the reported metasurfaces have narrow scanning ranges, are expensive, and cannot be independently controlled. In this paper, we propose a reconfigurable transmissive metasurface combined with a scissor and rotation actuator for independently controlling beam scanning and polarization conversion functions. The metasurface is constructed with rotatable unit cells (UCs) that can switch the polarization state between right-handed (RHCP) and left-handed circular polarization (LHCP) by flipping the UCs to reverse their phase variation. Moreover, independent beam scanning is achieved using the scissor actuator to linearly change the distance between the UCs. Numerical and experimental results confirm that the proposed metasurface can perform beam scanning in the range of 28° for both the positive and negative regions of a radiation pattern (RHCP and LHCP beams) at an operational frequency of 10.5 GHz.

Chiral metasurface absorber with near-infrared excitation-induced dual circular dichroism

Microscopic components in metasurfaces allow precise control of electromagnetic waves, enabling chiral metasurface absorbers to adapt to different frequencies and wavelengths of electromagnetic waves, providing higher controllability. In this paper, we present a near-infrared chiral absorber utilizing a Metal-Insulator-Metal (MIM) structure, achieving selective absorption in the dual wavelength ranges of 1500–1750 nm and 2250–2750 nm. The absorber's structural layout adopts a pseudo-π configuration, featuring a unique design that establishes distinct resonance cavities between structural periods. This results in disparate responses to left-handed circularly polarized (LCP) light and right-handed circularly polarized (RCP) light, thereby attaining dual-band selectivity and adjustability. To illustrate the physical mechanism, we explore the electric and magnetic field distributions within this structure, offering deeper insights into the fundamental mechanism of selective absorption. This analysis illustrates that the charge distribution in different wavelength bands can vary with the polarization direction, forming orthogonal electric dipoles. Under the incidence of LCP and RCP, we achieved circular dichroism (CD) of 0.75 and 0.7, respectively. By adjusting parameters within individual resonance cavities, we achieve independent control over each resonance wavelength. This near-infrared chiral absorber provides unparalleled design flexibility, with implications for advancements in applications such as molecular detection and optical switching.

Kinetic numerical analysis of electromagnetic ion cyclotron instability in non-thermal Vasyliunas-Cairns distributed plasmas

Enhanced fluctuations driven by non-thermal features of particle-distributions are reported frequently in the variety of space plasma observations. In the rare-collisional plasmas, these amplified fluctuations scatter the particles in various direction and governs the dynamics of space plasma environments effectively. Electromagnetic ion cyclotron (EMIC) waves usually responsible for low frequency interplanetary magnetic field fluctuations. These are natural emissions in numerous natural environments of plasmas which usually operates underneath the ion/proton cyclotron frequencies. These are identified as left hand circular polarization (L-mode) with a propagation directed towards the ambient magnetic field. Various space missions and in situ measurements unveil the perpendicular temperature anisotropies of non-thermal populations of ions/protons i.e. in heliospheric regions and solar wind. These proton temperature anisotropies excite EMIC instability which in turn the pitch angle scatters the ions and restrained the anisotropy in certain ranges. In Vasyliunas-Cairns distributed hybrid non-thermal electromagnetic proton plasma, the transverse dielectric response function (TDERF) is calculated for L-mode. It is then numerically solved in order to show the impact of non-thermal populations due to non-thermal parameters α and κ on the dispersion and growth rates of EMIC instability in low and high plasma beta β regimes. Possible variation in the real oscillatory and imaginary frequencies spectrum is also analyzed with the variation in the values of other pertinent parameters i.e. temperature anisotropy τ and β. The parametric numerical analysis of the present work has relevance about that plasma phenomena of space regions where non-thermal distributed populations are prevalent.

Investigating the impact of polarization on surface plasmon polariton characteristics in plasmonic waveguides under periodic driving fields

This study examines the impact of polarization in the driving field on the surface plasmon polariton (SPP) modes within plasmonic waveguides under the influence of a periodic driving field. Addressing a significant knowledge gap in the existing literature, we present a comprehensive investigation employing Floquet engineering techniques, with a specific emphasis on elliptically polarized fields as the dressing field. Our analysis reveals that the use of generalized Floquet states allows us to derive Floquet states for specific polarized dressing fields, such as linear, left-handed circular, and right-handed circular polarization. Remarkably, we demonstrate that Floquet states depend on the chirality of the dressing field’s polarization. Employing the Floquet-Fermi golden rule, we assess electron transport under various polarization types and find that the specific polarization type influence electron transport properties. However, we establish that the chirality of the polarization of the dressing field does not impact the transport properties. During our numerical analysis, we assess the alterations in SPP characteristics arising from two distinct types of polarization in dressing fields: linear polarization and circular polarization. Our results underscore the potential of employing a dressing field to effectively mitigate the propagation losses of SPPs in plasmonic metals, with the extent of improvement contingent on the specific polarization type. To quantify the performance enhancements of commonly used plasmonic metals under linearly and circularly polarized dressing fields, we employ a figure of merit (FoM). This study offers insights into the practical utilization of periodic driving fields as a powerful tool in advancing plasmonic communication within chip-scale environments.

A Whole W-Band Multi-Polarization Horn Antenna Based on Boifot-Type OMT.

A wideband multi-polarized square-horn antenna based on an orthogonal mode transducer (OMT) is developed for working in the whole W-band in this paper. The designed antenna is capable of radiating multiple polarization modes as horizontal polarization (HP) and vertical polarization (VP) when as single-port excitation and left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP) when as dual-port excitation, owing to the characteristic of the OMT with the transmitting of orthogonally polarized waves. A CNC-layered fabrication approach is proposed, which means that the antenna prototype integrating with a Boifot-type OMT, turning waveguide, twisting waveguide and phase shifter is divided into three layers along the vertical direction to be fabricated based on computerized numerical control (CNC) technology. In the design, the turning waveguide and twisting waveguide are employed to achieve plane consistency of the antenna branch ports. Furthermore, a phase shifter is designed to compensate the orthogonally polarized waves, which can keep the phase of the orthogonally polarized waves consistent in a wideband frequency range from 75 GHz to 110 GHz. A prototype is fabricated and measured to verify the performance of the proposed multi-polarization antenna, and the measured results agree well with the simulation ones. In the whole W-band, the value of return loss is better than 10 dB of all polarization modes, and the value of AR of the LHCP and RHCP is below 3.5 dB. The maximum gain of the antenna reaches up to 18.8 dBi at 110 GHz. In addition, regarding the layered structure, the possible layered assembly error analysis is discussed, which verifies the feasibility of the layered machining for this antenna.

Versatile polarization-converted non-diffractive Bessel beams based on fully phase-modulated metasurfaces.

The Bessel beam has become significant in optical research due to its properties such as a long focal depth, self-healing, and non-diffraction. However, conventional methods for generating Bessel beams have drawbacks such as limited flexibility and tunability and the use of bulky optics. These factors lead to the complexity of the optical systems. This paper presents what we believe is a novel approach to generating Bessel beams by utilizing a fully phase-modulated all-dielectric metasurface. The proposed method enables the arbitrary and independent manipulation of cross-polarized and co-polarized components, allowing the creation of Bessel beams featuring multiple polarization conversions when subjected to left-handed circularly polarized (LCP) incidence. To demonstrate the versatility and effectiveness of the method, three metasurfaces with distinct characteristics are designed. The simulated generated Bessel beams exhibit qualities including long focal depth, non-diffraction behavior, self-healing capabilities, and polarization conversion, which align with the theoretical predictions. This work presents novel possibilities for effectively generating and multi-functional application of Bessel beams.