Orthogonal Circular Polarizations Research Articles

A wideband dual-circularly polarized traveling wave dielectric resonator antenna array

ABSTRACT In order to meet the demand of high capacity and high speed transmission of satellite communication system, a wideband dual-circularly polarized dielectric resonator antenna (DRA) array is proposed based on the traveling wave principle. Four DRA elements with slot-coupling excitation are sequentially placed on the ground, and the feeding network is designed to realize the two orthogonal circular polarization radiation waves. A notched copper loop (NCL) around the antenna array is adopted to improve the radiation performance. Depending on the operation of the two ports, the NCL generates the induced currents which rotates clockwise/counterclockwise, increasing the axial ratio bandwidth. In order to further improve the gain stability, the copper sheets are embedded on the top surface of each radiation element, and the copper cylinders perturb the internal field distribution of the DRA to introduce higher-order modes. The measurement results show that the left-hand circular polarization and the right-hand circular polarization operating bandwidths are 11.8% (14.97–16.85 GHz) and 12% (14.91–16.82 GHz). The antenna gain achieves 9.0 dBic. This DRA array can be applied for the vehicle mounted RF terminals in satellite communication.

Customizable Generation of Arbitrary‐Order Polarization Vortices by Spin‐Decoupled Geometric Phases

AbstractDue to nontrivial field topologies, polarization vortices carrying polarization singularities have attracted increasing interest in the fields of optics and photonics. However, the conventional methods for generation of polarization vortcies still suffer from the complexity and the heavy bulk. In this work, taking advantage of spin‐decoupled geometric phase in metasurfaces, a novel method is proposed to generate polarization vortices with customizable topological charges. By tailoring spin‐decoupled geometric phases generated by the metasurface, distinct helical phase profiles can be imparted to left‐ and right‐handed circularly polarized components. Consequently, two scalar vortices with different topological charges can be simultaneously generated in the two orthogonal circular polarization components, leading to the generation of the polarization vortices with the needed topological charges and the diverse morphologies. Both simulation and experimental results well demonstrate the method. Owing to the nondispersive feature of geometric phases, the designed metasurface works well in a wide frequency band. The proposed method contributes a reliable and feasible solution for customizing the generation of polarization vortices, which can be further transposed to other frequencies and applied to information encoding and polarization detection etc.

Nonclassical Spin‐Multiplexing Metasurfaces Enabled Multifunctional Meta‐Scope

AbstractDielectric metasurfaces have emerged as attractive devices for advanced imaging systems because of their high efficiency, ability of wavefront manipulation, and lightweight. The classical spin‐multiplexing metasurfaces can only provide two orthogonal circular polarization channels and require high phase contrast which limits their applications. Here, metasurfaces with arbitrary three independent channels are demonstrated by proposing a nonclassical spin‐multiplexing approach exploring the low refractive index meta‐atoms. A zoom microscope with on‐axis tri‐foci and a synchronous achiral‐chiral microscope with in‐plane tri‐foci based on silicon nitride metasurfaces are experimentally demonstrated. Based on the on‐axis tri‐foci metasurface, singlet zoom imaging with three magnifications and a broadband response (blue to red) based on a single metasurface is first demonstrated. A compact microscope (meta‐scope) consisting of two metasurfaces with three magnifications of 9.5, 10, and 29X with diffraction‐limited resolutions is further constructed, respectively. Utilizing the in‐plane tri‐foci metasurface, a singlet microscope with three achiral‐chiral channels is demonstrated. It offers a magnification of 53X and a diffraction‐limited resolution, enabling simultaneous imaging of an object's achiral and chiral properties. Our multifunctional metasurfaces and meta‐scope approaches could boost the applications in biological imaging and machine vision.

Broadband multiple resonant metasurface for mixture surface-enhanced infrared absorption based on polarization-sensitive folded nanoantennas

Multiple resonant metasurfaces for mixture component detection by surface-enhanced infrared absorption in a broadband spectrum region are still highly desirable. This paper presents a polarization-sensitive multi-resonant broadband metasurface in the mid-infrared (MIR) region based on an odd symmetric folded antenna array. Six major resonant modes are effectively excited in 6–15 μm covering the absorption peak of multiple gases and biomolecules. In addition, the calculation indicates the maximum electric field intensity enhancement reaches 3607 and the average electric enhancement factors are dominantly amplified to a maximum of 75.08. The excited multiple hotspots provide more spatial overlap with analytes and would be beneficial for label-free detection. Moreover, owing to the contributions of the intrinsic phonons and polaritons in the ENZ material, the spectroscopy features are relatively stable when changing the geometry parameters and the incident angles, allowing more fabrication tolerance and experiment flexibility. Furthermore, the multiple resonant metasurface is also effectively enabled under orthogonal circular polarizations. Finally, the sensing abilities of the designed metasurface for polyethylene terephthalate and isopropanol molecules have been computationally validated. These results indicate the potential for nanophotonic detection and mixture spectroscopy analysis.

Simultaneous Dynamic Display of Meta‐Hologram and Meta‐Nanoprinting with High Frame Rate

AbstractDynamic holography can reconstruct realistic and highly interactive 3D scenes, offering a promising way for future display. Emerging metasurface with small pixel size and powerful light modulation capability demonstrates performance superior to traditional spatial light modulators, but dynamic meta‐holography with high information capacity and high frame rate remains a challenge. This paper presents a design scheme combining a preset polarization‐dependent metasurface with a high‐speed projection module to realize smooth dynamic display at multiple polarization states. With the projection module, the system can achieve dynamic meta‐holography at two orthogonal circular polarization states with 237 and 247 different holographic frames respectively, and grayscale meta‐nanoprinting at a linear polarization state with three different patterns. At the same time, the polarization multiplexed dynamic display scheme enables independent displays at three distinct polarization states with an extremely high frame rate (9523 frames per second). This advancement holds promise for applications in dynamic holographic display, optical encryption, virtual reality, and information storage.

Evolution of C-point singularities and polarization coverage of Poincaré–Bessel beam in self-healing process

As a vector version of scalar Bessel beams, Poincaré–Bessel beams (PBBs) have attracted a great deal of attention due to their non-diffracting and self-healing properties as well as the presence of polarization singularities. Previous studies of PBBs have focused on cases that consist of a superposition of Bessel beams in orthogonal circular polarization states; here, we present a theoretical and experimental study of PBBs for which the polarization states are taken to be linear, which we call a linear PBB. Using a mode transformation of a full Poincaré beam constructed from linear polarization states, we observe the linear PBB as providing an in-principle infinite number of covers of the Poincaré sphere in the transverse plane and with an infinite number of C-points with positive and negative topological indices. We also study the dynamics of C-point singularities in a linear PBB in the process of self-healing after being obstructed by an obstacle, providing insight into “Hilbert Hotel” style evolution of singularities in light beams. The present study can be useful for imaging in the presence of depolarizing surroundings, studying turbulent atmospheric channels, and exploring the rich mathematical concepts of transfinite numbers.

Polarization-multiplexed three-channel dielectric metasurfaces integrated with liquid crystals for holographic displays

Multi-channel metasurface holography based on polarization multiplexing has received close attention for its application in increasing information capacity. However, most of the existing spin-selective metasurfaces focus on the utilization of the cross-polarized channels while neglecting the co-polarized channels. Moreover, the real-time dynamic switching of the incident polarization of the metasurface remains a great challenge. This work presents a dielectric metasurface that combines geometric and propagation phase modulations. It allows phase control of a pair of orthogonal circular polarizations. A liquid crystal (LC) film is placed at the bottom layer of the metasurface to achieve dynamic switching of the incident polarization of the metasurface. As a proof-of-concept, we design and simulate a dielectric metasurface integrated with liquid crystals (LCs) for three-channel holographic displays. The LCs modulate the incident linear polarization into two orthogonal circular polarizations and illuminate the metasurface. The metasurface displays one holographic image in the vertical direction from the co-polarized channel and two holographic images at certain angles from the cross-polarized channel. It means that three holographic images can be displayed simultaneously without overlapping for linearly polarized (LP) light. Our design and simulations could provide a new, to our knowledge, scheme for multi-channel holography and active tunable metasurfaces.

One-shot self-calibrating phase-shifting interferometry by direct normalization of interferograms

Dynamic phase measurement is a valuable technique applied across various scientific and technological domains due to its high accuracy, non-contacting method, and numerous practical applications. In this manuscript, we present a phase retrieval method capable of measuring the object’s phase in real-time. Our proposal is based on a double aperture common-path interferometer adapted for polarization modulation in the input windows, enabling the superposition of two fields with orthogonal circular polarizations. Two interferograms and two intensities are captured in a single shot, showcasing the possibility of obtaining two normalized interferograms directly and straightforwardly. This allows for the derivation of expressions for phase recovery and, additionally, the determination of the arbitrary phase step. We demonstrate that this method is easy to implement, highly accurate, and sufficiently fast for real-time applications. To validate the effectiveness of the method, we conduct numerical error analysis and laboratory experiments.

A novel dual-band elliptical ring slot MIMO antenna with orthogonal circular polarization for 5G applications

This paper presents a dual-band 4-element multiple-input-multiple-output (MIMO) antenna featuring orthogonal circular polarization (CP) for Sub-6 GHz 5G applications. The single antenna combines a non-uniform width elliptical ring slot and a feed network, utilizing two L-shaped secondary feed lines to generate CP within the targeted frequency bands (3.55−3.80 GHz and 4.60−4.80 GHz). Using the single antenna as a unit antenna, a 4-element MIMO configuration is devised, employing a mirror technique for element placement to achieve orthogonal CP. This placement method effectively enhances coverage area and enlarges the 3-dB axial ratio bandwidth in the lower band (3.40–3.80 GHz). The common ground connections among elements are established via four strip lines. The antenna shows a good diversity performance considering the envelope correlation coefficient (ECC) result of less than 0.04 and isolation greater than 15 dB. The simulated gains of the MIMO antenna are 4 and 5 dBic in the respective bands. The single and MIMO antennas are fabricated, and the antennas’ performances are evaluated. A good agreement is observed between the measured and simulated results. The dual CP and diversity performances of the MIMO antenna make it more efficient for 5G wireless applications.

Antenna-waveguide devices with a single horn for satellite communication antenna systems

A technical and recommendations for their use in the development and practical implementation of devices as part of antenna-waveguide paths with a single horn are presented to increase efficiency in monitoring MPA satellite communication systems. The practical implementation of multi-band AVP for MPA is shown. Technical solutions for the construction of multi-band AVP for MPA satellite communication systems and remote sensing complexes, which differ from the known ones by the possibility of expanding the functionality of the AVT. Implementation of the monopulse auto-tracking mode using the H21 mode in dual-band auto-tracking machines using signals of specified polarizations in the required frequency ranges. When receiving signals of orthogonal linear and circular polarizations, the number of combined ranges increases to four.

Broadband spin-decoupled metasurface for independent wavefront manipulations of orthogonal circularly-polarized waves

Abstract Metasurfaces endowed with spin-decoupled functionalities offer the capability to meticulously customize the electromagnetic wavefronts of incident dual orthogonal circularly-polarized (CP) waves in a desirable manner, that holds immense potential for broadening their application fields. Nevertheless, a major lack that persists in most spin-decoupled metasurfaces is the limited bandwidth or the intricate design requirements. Herein, we propose a broadband spin-decoupled metasurface, consisted of weak-resonant mirror-symmetry unit structures, that enables independent and distinct wavefront manipulations under the incidence of orthogonal CP waves. As a demonstration, we present a dual-channel metasurface that integrates geometric and propagation phases to generate vortex waves with two distinct modes in a wide frequency range from 10 GHz to 16 GHz. Both simulated and experimental results are consistent and collectively confirm the validity of our proposed metasurface. The research provides a practical and efficient avenue for constructing spin-decoupled metasurface within a broad frequency band.

Interactions between fractional solitons in bimodal fiber cavities

AbstractWe introduce a system of fractional nonlinear Schrödinger equations (FNLSEs) which model the copropagation of optical waves carried by different wavelengths or mutually orthogonal circular polarizations in fiber‐laser cavities with the effective fractional group‐velocity dispersion (FGVD), which were recently made available to the experiment. In the FNLSE system, the FGVD terms are represented by the Riesz derivative, with the respective Lévy index (LI). The FNLSEs, which include the self‐phase‐modulation (SPM) nonlinearity, are coupled by the cross‐phase‐modulation (XPM) terms, and separated by a group‐velocity (GV) mismatch (rapidity). By means of systematic simulations, we analyze collisions and bound states of solitons in the XPM‐coupled system, varying the LI and GV mismatch. Outcomes of collisions between the solitons include rebound, conversion of the colliding single‐component solitons into a pair of two‐component ones, merger of the solitons into a breather, their mutual passage leading to excitation of intrinsic vibrations, and the elastic interaction. Families of stable two‐component soliton bound states are constructed too, featuring a rapidity which is intermediate between those of the two components.

Polarization evolution on higher and hybrid-order Poincaré spheres with coaxial polarization holograms

Based on the tensor polarization holography theory, we propose a simple and convenient method in the recording material, phenanthrenequinone-doped polymethylmethacrylate, to generate beams on higher and hybrid-order Poincaré spheres, and realize their polarization evolution on the spheres by combining the recorded phase with the Pancharatnam–Berry phase. By simultaneously adjusting the polarization azimuth angle and relative phase of the recorded waves, independent phase-shifts can be imparted onto two orthogonal circular polarization states in reconstruction process of polarization holography. The beams on basic Poincaré sphere are transformed into that on arbitrary higher or hybrid-order Poincaré spheres. We get the Poincaré spheres’ type and polarization distribution of the reconstructed wave by interferometry and polarizer, and the results match well with the theoretical predictions.

Polarization Diffraction Gratings in PAZO Polymer Thin Films Recorded with Digital Polarization Holography: Polarization Properties and Surface Relief Formation

In this work, we study the polarization properties of diffraction gratings recorded in thin films of the azopolymer PAZO (poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzene sulfonamido]-1,2-ethanediyl, sodium salt]) using digital polarization holography. Using two quarter-wave plates, the phase retardation of each pixel of the SLM is converted into the azimuth rotation of linearly polarized light. When recording from the azopolymer side of the sample, significant surface relief amplitude is observed with atomic force microscopy. In contrast, recording from the substrate side of the sample allows the reduction of the surface relief modulation and the obtaining of polarization gratings with characteristics close to an ideal grating, recorded with two orthogonal circular polarizations. This can be achieved even with a four-pixel period of grating, as demonstrated by our results.

Spatiotemporal modulation of ultrafast plasmonic vortices with spin–orbit coupling

The vortex field of surface plasmon polariton with orbital angular momentum (OAM), called plasmonic vortex, has played an important role in various research fields. However, the spatiotemporal properties of plasmonic vortex pulses excited by ultrafast laser, especially the dynamics of spin‒orbit coupling in the ultrafast plasmonic vortex field, have yet to be investigated deeply. Here, we study the spatiotemporal modulation of ultrafast plasmonic vortices with spin‒orbit coupling, using both analytical and simulation methods. The ultrafast plasmonic vortices are excited by a ring-shaped plasmonic lens, with an incident light composed of two time-delayed femtosecond sub-pulses carrying the same OAM but orthogonal circular polarizations. The dynamics of time-varying electric field, energy flow and angular momentum distributions of the plasmonic vortices are demonstrated, revealing details of the spin‒orbit coupling in spatiotemporal domain, such as the merging of multiple phase singularities with energy flow loops, and the variation of spin/orbital angular momentum per photon over time. This work could deepen the understanding of spin‒orbit coupling in plasmonic field and provide new ideas for ultrafast on-chip optical information processing.

Tempering Multichannel Photon Emission from Emitter-Coupled Holographic Metasurfaces.

On-chip manipulation of photon emission from quantum emitters (QEs) is crucial for quantum nanophotonics and advanced optical applications. At the same time, the general design strategy is still elusive, especially for fully exploring the degrees of freedom of multiple channels. Here, the vectorial scattering holography (VSH) approach developed recently for flexibly designing QE-coupled metasurfaces is extended to tempering the strength of QE emission into a particular channel. The VSH power is demonstrated by designing, fabricating, and optically characterizing on-chip QE sources emitted into six differently oriented propagation channels, each representing the entangled state of orthogonal circular polarizations with different topological charges and characterized with a specific relative strength. We postulate that the demonstration of tempered multichannel photon emission from QE-coupled metasurfaces significantly broadens the possibilities provided by the holographic metasurface platform, especially those relevant for high-dimensional quantum information processing.

All-silicon metasurface-enabled non-coaxial superposition of vector vortex beams

Vector vortex beams (VVBs) possess great applications in fundamental science, from particle trapping to quantum communication. Recently, the complex system for evaluating VVBs has been simplified by implementing metasurfaces and demonstrating the evolutionary trends of its coaxial polarization states. Nevertheless, it is quite challenging to obtain the polarization singularities generated in the terahertz (THz) band when non-coaxial superposition is performed by two multiplexed VVBs. Herein, a minimalist all-silicon metasurface platform is proposed, capable of being implemented to evaluate the non-coaxial superposition states of two identical VVBs. The employment of spin-polarization multiplexing techniques gives higher encoding degrees of freedom within the orthogonal circular polarization channel, enabling the superposition behavior of inhomogeneous polarization states to be performed at predefined focal planes. A systematic analysis of the newly generated polarization singularities in the interaction region is performed by applying the full Stokes polarization vector. With the ultra-compact configuration, the experimental results obtained by the proposed strategy under THz wave illumination exhibit good agreement with the numerical simulations. Thus, such mechanisms offer potential applications for multiple particle capture based on non-coaxial superimposition of VVB and provide efficient meta-platform in data encryption, high-resolution imaging, and quantum communications.

Asymmetric Full-Color Vectorial Meta-holograms Empowered by Pairs of Exceptional Points.

Holography holds tremendous promise in applications such as immersive virtual reality and optical communications. With the emergence of optical metasurfaces, planar optical components that have the remarkable ability to precisely manipulate the amplitude, phase, and polarization of light on the subwavelength scale have expanded the potential applications of holography. However, the realization of metasurface-based full-color vectorial holography remains particularly challenging. Here, we report a general approach utilizing a modified Gerchberg-Saxton algorithm to achieve spatially aligned full-color display and incorporating wavelength information with an image compensation strategy. We combine the Pancharatnam-Berry phase and pairs of exceptional points to address the issue of redundant twin images that generally appear for the two orthogonal circular polarizations and to enable full polarization control of the vectorial field. Our results enable the realization of an asymmetric full-color vectorial meta-hologram, paving the way for the development of full-color display, complex beam generation, and secure data storage applications.

Dual-band terahertz reflective-mode metasurface for the wavefront manipulation of independent linear and circular polarization waves

Metasurfaces (MSs) are being extensively researched owing to their ability to modulate the polarization and wavefront of electromagnetic (EM) waves in a flexible manner, which usually offer significant advantages including ultra-thinness, low losses, and easy fabrication. However, conventional MSs typically operate well only with a single polarization. Here, we propose a novel design strategy for a terahertz (THz) reflective-mode MS that relies on a single unit-cell arrangement combining propagation phase and geometric phase. Our designed MS can achieve multiple wavefront manipulations in reflection mode, not limited to circular polarization (CP) transformation, but also enabling linear polarization (LP) conversion. The MS we propose consists of a periodic array of bilayered metal patterned resonator structures sandwiched by a dielectric substrate. The metallic resonator is made of the outer single-split-ring (SSR) and C-shaped slot (CSS), inner double-split-ring (DSR), and its complementary structure. With this design, the MS is capable of converting a LP wave to its orthogonal counterpart at lower frequency (f1=0.7THz) after reflection. Additionally, at higher frequency (f2=1.4THz), the proposed MS can also convert the right-handed CP (RCP) to left-handed CP (LCP) upon reflection or vice versa. The 2π phase full coverage of the orthogonal LP and CP waves can be achieved independently and simultaneously by adjusting the opening and orientation angles of the SSR based on propagation phase, and orientation angle of the DSR based on geometric phase. We numerically demonstrate beam deflection, planar focusing, and the vortex beam for both reflected orthogonal LP and CP waves with three representative MSs to provide proof of concept. These findings reveal the great potential for multifunctional devices for dual-polarization in imaging and communication systems.

Polarization conversion filter based on electromagnetically induced transparency-like effect

Owing to the large losses in the conversion process of traditional polarization converters, there is an increasing demand for metasurfaces with excellent transmission performance. In this work, an efficient polarization conversion metasurface is proposed based on electromagnetically induced transparency-like (EIT-like) effect in the terahertz band. The multi-level bright mode paths are excited by an asymmetric structure to obtain orthogonal circular polarization conversion windows. The transmission window is generated by the mutual interference of two sets of bright modes with similar resonant frequencies. Then an asymmetric structure is constructed to achieve transmission window shift under TE polarization and TM polarization, thereby realizing dual-frequency polarization conversion. The metamaterial unit structure consists of four open metal resonant rings and four metal resonant strips. The working mechanism is explored by analyzing the surface current distribution, frequency response, and incident angle characteristics. The results show that electromagnetically induced transparency can be achieved under different polarizations. Furthermore, based on the EIT resonance between the two incident polarizations, the conversion from linear polarization to right-hand circular polarization is achieved at 0.692 THz, and the conversion from linear polarization to left-hand circular polarization is realized at 0.782 THz, transmission coefficients are 0.7 and 0.68 respectively. According to the Stokes parameters, the corresponding ellipticity <i>η</i> values are 96% and 98%, respectively. This EIT-based polarization conversion metasurface with low loss and ultra-thin characteristics has great potential applications in compact antennas, derived radar phased arrays, and military detectors.