Orthogonal Circular Polarizations Research Articles

A Dual Ka/Q-Band Reflectarray

Introduction. Duplex satellite communication is commonly arranged using two spaced frequency bands, with one band receiving and the other band transmitting signals to a satellite. The main task of a communications satellite antenna system consists in providing an identical coverage area across all involved frequency bands, which is often a challenging task for conventional parabolic reflector antennas. Reflectarrays allow an independent control of the reradiated wave phase in spaced frequency bands, which can be used to create efficient multi-band antenna systems for modern communication satellites.Aim. To develop a Ka/Q-frequency range phase-correcting element and to create on its basis a dual-band reflectarray for operation with orthogonal circular polarizations and identical gains in a given sector of angles in significantly spaced frequency ranges.Materials and methods. Numerical studies were carried out using the finite element analysis method. Radiation patterns were measured using the near field scanning method.Results. A single-layer dual-band phase-correcting reflectarray element was developed for operation with orthogonal circular polarizations with low losses and a weak dependence of the relative position of the elements on the phase characteristic. On the basis of the proposed element, a reflectarray consisting of 24 465 two-frequency elements was synthesized and manufactured. The developed prototype of a single-layer dual-band reflectarray demonstrated good characteristics, with the efficiency reaching 56 and 36 % in the Ka- and Q-frequency ranges, respectively, and an almost identical minimum gain in the ±0.75° angle sector.Conclusion. The research results confirm the potential of the developed reflectarray to successfully replace conventional parabolic reflectors installed both on modern communication satellites and as part of ground-based satellite terminals in the millimeter wavelength range.

Bifunctional Integration Performed by a Broadband High‐Efficiency Spin‐Decoupled Metasurface

AbstractAchieving broadband multitasked integration on an ultrathin interface is pivotal to increasing data capacity. However, broadband bifunctional metasurfaces exhibiting high‐efficiency and crosstalk‐free characteristics are rarely seen. Here, three broadband spin‐decoupled criteria are developed to design the meta‐atoms of high‐efficiency bifunctional metasurfaces. Specifically, six dipole‐loaded quasi‐I‐shaped meta‐atoms are proposed to satisfy the broadband spin‐decoupled criteria in radio band from 8.6 to 17.8 GHz (about 70% bandwidth) with more than 90% efficiency. The metasurface equipped with the proposed meta‐atoms can keep dispersionless phase gradients and crosstalk‐free characteristics in two orthogonal circular polarizations. This work demonstrates the broadband scheme with spin‐decoupled bifunctional metasurface, yielding two independent broadband multimode vortex beams in two completely decoupled helicities. Besides, other possible applications of the proposed meta‐atoms are illustrated from the perspective of the half‐wave plant (polarization control). Accordingly, the other multitasked‐type bifunctional metasurface is fabricated to achieve the broadband integration of two different functionalities: polarization conversion and full‐polarization anomalous refraction. The proposed schemes offer broadband, polarization‐multiplexing, and multitasked‐integration routes for complex electromagnetic wave manipulations within a subwavelength thickness, which can stimulate the development of electromagnetic/optical integration devices with broadband multiplexing techniques.

Independent control of both amplitude and phase for orthogonal circularly polarized electromagnetic waves through polarization conversions

Spin-selective multi-functional integrated metasurfaces have attracted much research attention due to its promising application prospects. However, the goal of independent and arbitrary control of both amplitude and phase for orthogonal circularly polarized (CP) waves still has not been achieved fully. This is because it requires mirror asymmetric structure to achieve such a goal but there is no apparent physical relation between the unit cell structure and the spin-selective properties. A simple method with clear physical pictures is proposed in this paper to achieve the goal of arbitrary spin-selective manipulations. The idea is to convert the incident orthogonal CP waves to orthogonal linearly polarized (LP) waves first, then manipulate the LP waves with matured techniques, and finally convert the LP waves back to the corresponding CP waves. Simulations and experiments have been carried out to validate the method. Using this idea, spin-selective focusing, spin-selective deflection and spin-selective orbital angular momentum vortex beam have been demonstrated.

Nonresonant propagation phase based metasurface design for independent manipulation of dual circularly polarized waves

Pancharatnam–Berry (PB) phase has attracted significant attentions due to its phase control characteristic for circularly polarized (CP) waves. PB phase structure usually provides equal but inverse phase shifts for the left-handed CP (LCP) and right-handed CP (RCP) waves. In this article, a method is proposed to decouple this correlation and to manipulate the wavefronts of interacting LCP and RCP waves independently and simultaneously. Nonresonant propagation phase realized through open-ended transmission line is introduced as an additional degree of freedom to achieve totally independent phase responses of the orthogonal CP waves. A metasurface is presented to shape the reflected orthogonal CP waves into vortex beam and pencil beam independently. Simulation and measurement results confirm with each other and demonstrate the proposed method.

Four-Port Orthogonal Circularly Polarized Dual-Band MIMO Antenna With Polarization and Spatial Diversity Using a Dual-Band Linear-to-Circular Polarization Converter

A dual-band circularly polarized (CP) four-port multiple-input-multiple-output (MIMO) antenna for K/Ka-bands fixed-satellite service is proposed in this communication. The single element of MIMO is composed of a cascade of two dipoles of different lengths resonating at around 20 and 30 GHz. An array of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7 \times 7$ </tex-math></inline-formula> elements of the unit cell of the dual-band linear-to-circular polarization converter is placed at a distance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{o}$ </tex-math></inline-formula> /4 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{o}$ </tex-math></inline-formula> is calculated with respect to 19.51 GHz) in the endfire direction of MIMO antenna to obtain an orthogonal CP wave at the two frequency bands. The proposed CP antenna shows good MIMO performance with a correlation coefficient (CC) of less than 0.19 and diversity gain (DG) of better than 0.99 at both the frequency bands. The proposed MIMO also agrees with polarization and spatial diversity, and the CP nature at lower and upper frequency bands can be interchanged by exciting the orthogonal ports. A prototype of the MIMO antenna is fabricated, and the measured CP bandwidths of 11.51% and 3.69% are obtained in the lower (19.65–22.05 GHz) and upper (29.25–30.35 GHz) frequency bands, respectively. The proposed antenna can be used for the Ka-band: 29.5–30.0 and 19.7–20.2 GHz fixed satellite service as uplink and downlink frequencies, respectively.

Generation and Superposition of Perfect Vortex Beams in Terahertz Region via Single-Layer All-Dielectric Metasurface.

Terahertz (THz) orbital angular momentum (OAM) technology provides promising applications in future wireless communication with large bandwidth and high capacity. However, the ring radius of the conventional THz vortex beam is related to the topological charge, limiting the co-propagation of multiple OAM modes in the THz communication systems. Although the perfect vortex beam (PVB) based on traditional methods can solve this problem, they are usually bulky and unstable. Here, we demonstrate two PVB generators based on a single all-dielectric metasurface to obtain polarization-independent PVB and spin multiplexed PVB, respectively. The former regulates the propagation phase by using isotropic unit cells; the latter simultaneously manipulates the propagation and geometric phase to achieve the spin-decoupled phase control by arranging anisotropic unit cells. In addition, we also demonstrate the stable generation of a perfect Poincaré beam with arbitrary polarization and phase distribution on a hybrid-order Poincaré Sphere via a spin-decoupled metasurface, which is achieved by the linear superposition of two PVBs with orthogonal circular polarizations. The proposed scheme provides a compact and efficient platform for the generation and superposition of PVBs in THz region, and will speed up the progress of THz communication systems, complex light field generation, and quantum information sciences.

Noninterleaved Metasurface for Full‐Polarization Three‐Dimensional Vectorial Holography

AbstractMetasurface‐enabled full‐polarization vectorial holography has attracted numerous attention due to the promising applications for multichannel displays, enhanced information capacity, and optical encryption. However, recently showcased design strategies suffer from undesirable cross‐talk resulting from interleaved meta‐atoms and are restricted to a two‐dimensional plane. This work presents a general approach for full‐polarization beam shaping in three‐dimensional space by completely exploiting the capacity of a noninterleaved metasurface. The noninterleaved metasurface is spin‐decoupled, which is capable of achieving independent phase control for the two orthogonal circular polarizations by combining both propagation and geometric phases. As a proof‐of‐concept, a three‐dimensional vectorial holography capable of converting the linear polarized light to holographic images with arbitrary spatial polarization distributions is experimentally demonstrated. Taking use of the extended dimension, the z‐axis distance, which provides a new degree of flexibility for boosting information capacity and security, a double‐level optical encryption scheme is implemented. This work provides a compact and general scheme for full‐polarization channel wavefront steering, unlocking a new door for designing planar polarization functionality devices.

Wideband Polarization Agile Dielectric Resonator Antenna With Reconfigurable Broadside and Conical Beams

A new broadside and conical beam reconfigurable dielectric resonator antenna (DRA) with three orthogonal linear polarizations (LPs) and two orthogonal circular polarizations (CPs) agility is presented. It consists of a quad-strip-fed DRA element and a reconfigurable feeding network. First, the DRA element is designed to make unidirectional <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm{HEM}}_{11 \delta }$ </tex-math></inline-formula> mode and omnidirectional <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm{TM}}_{01 \delta }$ </tex-math></inline-formula> mode operate in the same wide band by tactfully removing a concentric annular column from its interior. Furthermore, a center-loaded metal post helps to improve the impedance matching of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm{TM}}_{01 \delta }$ </tex-math></inline-formula> resonance significantly. Afterward, the switchable feed network is designed to implement diverse phase distributions of four output ports, i.e., providing the quad-port in-phase excitation, dual-port differential excitations, and quad-port sequentially rotated phase excitation strategies for a vertical LP, ±45° slant horizontal LPs, and two CPs, respectively. Finally, a fully functional prototype is designed, fabricated, and measured to validate the design. The measured results show that the overlapping impedance bandwidth of 36.8% for all the states and the axial-ratio bandwidth of 33.8% for the CPs are obtained.

High-Order Mode Resonant Planar Dual-Sense Bidirectional Circularly Polarized Antenna With Arbitrary Orthogonal Polarization Flared Angles

A design approach to a planar dual-sense bidirectional circularly polarized (CP) antenna is advanced. The resultant antenna can exhibit orthogonal CP radiations in arbitrary directions between 90° and 180°, i.e., the flared angle formed by pure left-handed CP (LHCP) and right-handed CP (RHCP) directions could be set in a wide range from 90° to 180°. The operational principle is revealed by an equivalent source model at first. Then, prototype antennas are advanced by incorporating a high-order mode resonant, V-shape dipole to a planar magnetic dipole, and a parasitic electric dipole. As numerically simulated and experimentally validated, the flared angle formed by LHCP and RHCP directions can be adjusted as 90° and 135°. In the 90° case, the presented bidirectional CP antennas can exhibit impedance bandwidth of 6.6%, 3 dB axial ratio (AR) bandwidth of 13.0% in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$+ x$ </tex-math></inline-formula> -axis, and 8.9% in the +z-axis. The advanced low-profile (height < 0.05 wavelength) antenna can simultaneously provide spatial and polarization diversity abilities in one principal-cut elevation plane. Therefore, it would be a promising colocated, spatial/polarization diversity antenna in future wireless systems.

All dielectric metasurfaces for spin-dependent terahertz wavefront control

Metasurfaces consisting of artificial subwavelength structure arrays have shown unprecedented ability to manipulate the phase, amplitude, and polarization of light. Separate and complete control over different spin states, namely the orthogonal circular polarizations, has proven more challenging as compared to the control over orthogonal linear polarizations. Here, we present and experimentally demonstrate several spin-dependent wavefront control metasurfaces in the terahertz regime using all-silicon dielectric structures. Such spin-dependent all-silicon metasurfaces are easy to fabricate and have potential applications in spin-involved ultracompact and miniaturized terahertz optical systems as well as terahertz communication systems.

Ultra-Low-Profile Continuous Transverse Stub Array for SatCom Applications

Modern K-/Ka-band satellite communications have become increasingly demanding in recent years with regard to the performance of the terminal antenna used in the link. These terminals should be high gain and broadband, as well as guarantee polarization diversity over a large field of view. A low profile is also highly desired to integrate the antenna system into a variety of moving platforms, such as aircraft and trains. An ultra-low-profile continuous transverse stub array is proposed here to tackle these challenges. The antenna array is realized in printed circuit board technology by adopting a contactless transition between the stacked-up layers without resorting to blind or buried vias. The proposed antenna is wideband (impedance matched within the 19–31 GHz band, i.e., ~50%) and provides multibeam radiation for polar angles as far as ±22.5°. The peak value of the gain is 19.7 dBi, and the maximum radiation efficiency equals 50%. Furthermore, the antenna array is combined with a dual-band polarization converter. The latter provides orthogonal circular polarization (CP) in two non-adjacent bands. The overall antenna system performs right- and left-hand CPs within the SatCom downlink and uplink in the K-/Ka-band, respectively. For each polarization, the axial ratio is below 3 dB over 9.47% and 4.42% fractional bandwidths, respectively.

Broadband reflective dual-functional polarization convertor based on all-metal metasurface in visible region

In this paper, a broadband reflective dual-functional polarization convertor based on all-metal anisotropic metasurface was proposed and investigated numerically in visible region. The unit-cell of the all-metal anisotropic metasurface based polarization convertor is composed of the Au ellipse nanostructure adhered on an Au substrate. The proposed anisotropic metasurface can convert the incident linear polarization light into its orthogonal counterpart or circular polarization light by adjusting the geometric parameter of the ellipse nanostructure. When the all-metal anisotropic metasurface functioned as a linear-to-linear polarization convertor (LLPC), the conversion efficiency is over 90% operating from 356.5 THz to 536.5 THz. While the metasurface served as a linear-to-circular polarization convertor (LCPC), the absolute value of polarization extinction ratio (PER) is greater than 10 dB from 336.5 THz to 544.5 THz. The simulated electric field distributions on the unit-cell indicate that the higher polarization converion efficiency is mianly originated from the geometry anistropy and excitations of fundamental and higher-order dipolar plasmon resonance. Thus, our design can be found potential applications in many areas, such as remote nano-sensors, nano-antennas, and radiometers in visible region.

Flexible CP diversity antenna for 5G cellular Vehicle-to-Everything applications

A flexible circularly polarized (CP) MIMO antenna is evaluated for Sub-6 GHz 5G and cellular-vehicle-to-everything (C-V2X) applications. The design radiates CP waves with an L-shaped feed line and a modified ground plane embedded in the slot antenna. The MIMO design resonates in the band of frequencies 3.23–6.26 GHz and radiates CP waves in the 2.95 – 6.02 GHz frequency band. This antenna model is suitable for LTE-V2X/ 5G (3.3 to 4.2 GHz), WLAN 5.2 GHz, WiMAX 5.5 GHz, and IEEE 802.11p (5.85–5.925 GHz) vehicular application bands. Here both planar and antenna conformed on foam material and a car wing mirror are investigated. Improved lowest isolation of 18.2 dB is achieved in the entire working band using the orthogonal CP arrangement of elements. The diversity functionality is tested in terms of ECC, MEG, CCL, etc. Further, the antenna radiation characteristics are tested by positioning it on the vehicle roof-top and side mirror using the Ansys savant tool.

Pancharatnam–Berry phase reversal via opposite-chirality-coexisted superstructures

Recently discovered reflective Pancharatnam–Berry phase (PB phase) from chiral anisotropic media (e.g., cholesteric liquid crystal, CLC) has aroused great interest in the emerging frontier of planar optics. However, the single chirality of common CLCs results in the intrinsic limitation of the same spin-selective PB phase manipulation, which means the reversal of the input spin cannot realize the conjugated PB phase. In this work, an innovative scheme based on opposite-chirality-coexisted superstructures is proposed to simultaneously modulate orthogonal circular polarization and get PB phase reversal. Through refilling CLC into a washed-out polymer network with opposite chirality and delicate photo-patterned structures, reflective optical vortex (OV) with opposite topological charges and vector beams with conjugated spiral PB phases are efficiently generated depending on the incident polarization. Furthermore, OV holograms are encoded to reconstruct polarization-selective OV arrays, indicating the strong capability of such opposite-chirality-coexisted anisotropic media. This work provides a new compact platform for planar optics, and sheds light on the architectures and functionalities of chiral superstructures.

High-Efficiency Polarization Multiplexing Metalenses.

The polarization multiplexing technique is a well-established method that improves the communication capacity of an optical system. In this paper, we designed orthogonal linear and circular polarization multiplexing metalens using a library of rectangle TiO2 nanostructures. The former can independently focus x- and y-linearly polarized incident lights to designed positions with a focusing efficiency of 53.81% and 51.56%, respectively, whereas the latter with two preset focal points can independently control left and right circularly polarized incident lights with a focusing efficiency of 42.45% and 42.46%, respectively. We also show that both metalenses can produce diffraction-limited focal spots for four polarization states with no obvious distortion, which opens up new applications in polarization imaging and polarization detection.

Single-Fed Dual-Circularly Polarized Stacked Dielectric Resonator Antenna for K/Ka-Band UAV Satellite Communications

A single-fed dual-band dielectric resonator antenna (DRA) with orthogonal circular polarizations (CPs) in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> - and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ka</i> -bands is proposed for satellite communications on unmanned aerial vehicle (UAV). The antenna overcomes the challenges of dual-band dual-CP operation, narrow axial-ratio bandwidth (ARBW) of single-fed antennas, and limited payload and space of UAVs. A shared-aperture merged-structure technique of DRA and slot-dipole antenna is proposed for dual-band dual-CP radiation, thus enabling full-duplex operation with compact size for high isolation systems. The orthogonal CPs in two frequency bands can be controlled independently by a phase compensation method. Besides, broadened ARBW and enhanced gain are attained from the stacked DR, from which high capacity and reliability communication can be achieved. A prototype operating at right-handed CP (RHCP) in the lower band, whereas left-handed CP (LHCP) in the upper band has been designed and measured. It features 10-dB impedance bandwidths of 6.4% and 12.8%, and 3-dB ARBW of 5.2% and 4.1% in the lower and upper bands, respectively. The antenna provides a low cost solution for high isolation, high throughput, and small payload full-duplex UAV satellite systems.

Stimulated Brillouin scattering in chiral photonic crystal fiber

Stimulated Brillouin scattering (SBS) has many applications; for example, in sensing, microwave photonics, and signal processing. Here, we report the first experimental study of SBS in chiral photonic crystal fiber (PCF), which displays optical activity and robustly maintains circular polarization states against external perturbations. As a result, circularly polarized pump light is cleanly backscattered into a Stokes signal with the orthogonal circular polarization state, as is required by angular momentum conservation. By comparison, untwisted PCF generates a Stokes signal with an unpredictable polarization state, owing to its high sensitivity to external perturbations. We use chiral PCF to realize a circularly polarized continuous-wave Brillouin laser. The results pave the way for a new generation of stable circularly polarized SBS systems with applications in quantum manipulation, optical tweezers, optical gyroscopes, and fiber sensors.

Near-infrared orthogonal polarized metalens

A metalens is a planar optical device that can accurately control the phase, polarization, and amplitude of light. Aiming at the application requirements of polarization imaging equipment for miniaturization, integration, and common field of view, we designed and fabricated two kinds of orthogonally polarized metalenses based on amorphous silicon and fused quartz. These metalenses can achieve orthogonal linear or circular polarization light imaging with a common field of view. The samples with a 2-mm diameter and 20-mm focal length were fabricated by electron beam exposure. The test results show that these metalenses can realize the imaging of orthogonal linearly or circularly polarized light simultaneously; the focusing efficiency is more than 50%, and the polarization contrast is >22 dB.

High-efficiency terahertz full-space metasurface for the transmission linear and reflection circular polarization wavefront manipulation

In this work, a high-efficiency full-space metasurface (MS) is demonstrated numerically, which can independently manipulate the transmitted linear polarization (LP) and the reflected circular polarization (CP) wavefront based on the transmission and geometric phase at terahertz (THz) range. The unit-cell of the full-space MS is composed of a C-shaped slot structure sandwiched with two twisted outer single-split-rings (SSRs) and parallel inner double-split-rings (DSRs). The proposed MS structure can achieve cross-polarization conversion of LP waves after transmission at the lower frequency (f1=0.55 THz), and CP waves after reflection at the higher frequency (f2=1.37 THz). The full 2π phase shifts of the transmitted cross-polarization wave and reflected orthogonal CP wave can be obtained independently by adjusting the opening direction and size of the C-shaped slot structure based on the transmission phase, and the orientation angle of the parallel inner DSRs structure based on geometric phase, respectively. In particular, anomalous refraction and reflection for LP and CP wave, focusing lens and vortex beam generation are also demonstrated numerically. These findings are beneficial in expanding the scope of full-space MS for wavefront manipulations, providing new possibilities to develop multifunctional THz device for both LP and CP waves.

A Millimeter-Wave Planar Dual-Band Array Antenna Having Individually LHCP and RHCP Radiation Characteristics

This article demonstrates a planar dual-band array antenna for millimeter-wave applications, which has a left-hand circular polarization and a right-hand circular polarization for two operating bands, respectively. By using aperture-fed stacked-curls, the proposed antenna can attain broad axial ratio (AR) bandwidths in both K-and Ka-bands through a single port. Meanwhile, two stacked-curls are designed to rotate in different directions for achieving orthogonal circular polarizations in two bands, respectively. An 8&#x00D7;8 stacked-curls array antenna is designed and manufactured for verifications. The measured 3 dB AR bandwidths are 11.59% (18.7-21 GHz) in the K-band and 9.93% (26.8-29.6 GHz) in the Ka-band, with reflection coefficient lower than -10 dB. The maximum gain in K-and Ka-bands are 18.59 dB and 18.13 dB, respectively. The proposed antenna can be used for developing compact satellite communication systems.