arXiv subjects

Bing-Zhong Wang

Publications and source records attributed to Bing-Zhong Wang.

15 recordsLinked to original sources

arXiv2026

Observation of helical pulses

Ultrafast spatiotemporal vortex pulses constitute a category within spatiotemporal topological waves. Nevertheless, the experimental realization of helical pulses single or few cycle short vortex pulses characterized by space time nonseparability remains elusive to date. Here, we introduce two complementary methods for experimentally generating such space time nonseparable helical pulses (SNHPs) in the optical and microwave spectral regimes. We achieve few cycle quasi linearly polarized SNHPs by decomposing the optical toroidal pulses into their polarization components. We also generated single cycle nontransverse SNHPs directly from a microwave ultrawideband spiral emitter. These approaches enable the experimental realization of SNHPs and provide a platform for further investigation into their properties and applications, such as nontrivial light-matter interactions and optical communications.

physics.optics↗

arXiv2026

Toroidal helical pulses

Toroidal topologies and helicity are pervasive in nature and hold basic importance in scientific research. In particular, the interplay between these features gives rise to fascinating toroidal helical electromagnetic excitations. Here, we present a theoretical framework and experimental realization to introduce a family of toroidal helical pulses, exploring the intersection of the helicity and propagating toroidal modes. For this purpose, we propose a configuration combining a coaxial horn emitter and an equiangular spiral grating to directly generate such single-cycle pulses. In addition to their inherent non-transverse toroidal topology and space-time nonseparability, such pulses also possess controllable helicity. This work gives rise to a helical version of propagating toroidal electrodynamics, thereby paving the way for advanced applications, such as nontrivial light-matter interactions and data transfer.

physics.optics↗

arXiv2024

Double-Helix Singularity and Vortex-Antivortex Annihilation in Space-Time Helical Pulses

Topological structures reveal the hidden secrets and beauty in nature, such as the double helix in DNA, whilst, the manipula-tion of which in physical fields, especially in ultrafast struc-tured light, draw booming attention. Here we introduce a new family of spatiotemporal light fields, i.e. helical pulses, carry-ing sophisticated double-helix singularities in its electromag-netic topological structures. The helical pulses were solved from Maxwell's equation as chiral extensions of toroidal light pulses but with controlled angular momentum dependence. We unveil that the double helix singularities can maintain their topological invariance during propagation and the field exhibits paired generation and annihilation of vortices and antivortices in ultrafast space-time, so as to be potential information carriers beating previous conventional vortex structured light.

physics.optics↗

arXiv2024

Hybrid electromagnetic toroidal vortices

The ubiquitous occurrence of toroidal vortices or vortex rings in fluid-dynamic scenarios in nature has garnered significant attention of scientific frontier, whilst, the electromagnetic counterparts of which were only proposed recently with two distinct manifestations: vector toroidal pulses [Nat. Photon. 16, 523 (2022)] and scalar phase toroidal vortices [Nat. Photon. 16, 519 (2022)]. This dichotomy in the understanding of toroidal vortex phenomena has prompted a reassessment of their fundamental nature. Herein, we theoretically propose a novel form of electromagnetic toroidal vortex solutions, that uniquely integrate both scalar and vector characteristics, challenging the prevailing notion of their mutual exclusivity. We also present the experimental generation of the hybrid toroidal vortex pulses by a compact coaxial horn emitter augmented with a metasurface. This methodology not only demonstrates the feasibility of creating such complex vortex structures but also endows the resulting pulses with unique properties, including the coexistence of transverse orbital angular momentum, electromagnetic vortex streets, and topological skyrmion textures. These attributes introduce new dimensions in topologically complex structured waves, opening avenues for enhanced free-space information transmission, topologically nontrivial light-matter interaction and microscopy techniques.

physics.optics↗

arXiv2024

Single-antenna super-resolution positioning with nonseparable toroidal pulses

The fundamental principle of satellite or node-based positioning involves triangulating the receiver's coordinates through the intersection of spatial distances. Recent advancements in hybrid wireless networks have yielded high-precision positioning at decimetre-level (wavelength-level) (Nature 611, 473-478 (2022)), approaching the resolution limits in free space. Here, we present a three-dimensional (3D) super-resolution positioning paradigm in free space by utilizing a novel kind of topologically structured pulses, toroidal electromagnetic pulses (Nat. Photonics 16(7), 523-528 (2022); Sci. Adv. 10(2), eadl1803 (2024)). Excited by the recent compact generator of toroidal pulses and their sophisticated topological and nonseparable structures, we demonstrate that the space-time nonseparability and skyrmion topology inherent in toroidal pulses can be harnessed to achieve freespace microwave 3D positioning with super-resolution accuracy, reaching the centimeter level, using a single emitting antenna. This work opens up new avenues for exploring the potential applications of topological electromagnetic pulses including but not limited to positioning, imaging, and sensing technologies.

physics.app-ph↗

arXiv2024

Propagation-invariant strongly longitudinally polarized toroidal pulses

Recent advancements in optical, terahertz, and microwave systems have unveiled non-transverse optical toroidal pulses characterized by skyrmionic topologies, fractal-like singularities, space-time nonseparability, and anapole-exciting ability. Despite this, the longitudinally polarized fields of canonical toroidal pulses notably lag behind their transverse counterparts in magnitude. Interestingly, although mushroom-cloud-like toroidal vortices with strong longitudinal fields are common in nature, they remain unexplored in the realm of electromagnetics. Here, we present strongly longitudinally polarized toroidal pulses (SLPTPs) which boast a longitudinal component amplitude exceeding that of the transverse component by over tenfold. This unique polarization property endows SLPTPs with robust propagation characteristics, showcasing nondiffracting behavior. The propagation-invariant strongly longitudinally polarized field holds promise for pioneering light-matter interactions, far-field superresolution microscopy, and high-capacity wireless communication utilizing three polarizations.

physics.optics↗

arXiv2024

Simultaneous Localization and Recognition of Subwavelength Non-Cooperative Entities Based on SISO Time Reversal and Neural Networks

The simultaneous localization and recognition of subwavelength non-cooperative entities within complex multi-scattering environments using a simplified system continues to pose a substantial challenge. This letter addresses this challenge by synergistically integrating time reversal time-frequency phase prints (TRTFPPs) and neural networks. Initially, a time reversal (TR) single-input single-output (SISO) framework is employed to generate TRTFPPs. To enhance the models' adaptability, particularly in the presence of noise, data augmentation techniques are applied. Subsequently, neural networks are employed to comprehend the TRTFPPs. Specifically, a cascaded neural network structure is embraced, encompassing both a recognition neural network and distinct neural networks for localizing different entities. Through the devised approach, two types of subwavelength entities are successfully identified and precisely localized through numerical simulations and experimental verification in laboratory environment. The proposed methodology holds applicability across various electromagnetic systems, including but not limited to detection, imaging, human-computer interaction, and the Internet of Things (IoT).

physics.app-ph↗

arXiv2024

Time-varying k-domain modulation around a point sink in time reversal cavity

This paper derives and investigates a time-varying k-domain modulation in vector form using a time-reversal (TR) field decomposition theory proposed for the first time. First, the proposed theory illustrates that the TR field can exhibit super-resolution property from the perspective of spatial focusing pattern if a point sink is set at the initial source point. Afterward, the instantaneous TR fields with and without the point sink, as well as their k-domain patterns are compared to illustrate the time-varying k-domain modulation, which accounts for the superresolution property. The phenomenon observed and derived in this paper shows great potential in the applications empowered by super-resolution focusing, such as wireless communication carrying the subwavelength information and high spatial resolution wireless power transfer.

physics.optics↗

arXiv2024

Inverse Design of Frequency Selective Surface Using Physics-Informed Neural Networks

This paper uses Physics-Informed Neural Network (PINN) to design Frequency Selective Surface (FSS). PINN integrates physical information into the loss function, so training PINN does not require a dataset, which will be faster than traditional neural networks for inverse design. The specific implementation process of this paper is to construct a PINN using field solutions of mode matching method, and given the design goal, the PINN can train the shape of the diaphragms. The single frequency FSS that meets the design goal was designed using the inverse design method proposed in this paper without a dataset, verifying the rationality of using PINN to design metasurface. Using PINN for inverse design is not limited to single frequency FSS, but can also be used for more complex metasurface.

physics.app-ph↗

arXiv2023

Determining Aperture Field for Arbitrary Phaseless Far-Field Utilizing Inverse Design Method Based on Spectral Analysis

Existing electromagnetic inverse design methods are often established in the spacial domain. This communication presents an inverse design method, which can design aperture field for the desired phaseless radiation pattern, from the spectral domain perspective. In addition, it naturally adapts to the polarization constraint. Specifically, the inverse design can be converted into solving the first kind of Fredholm integral equation, using the spectral domain method. To deal with the ill-posedness of such integral equation, we apply modal expansion to the integrand. To cope with the non-linearity introduced by phaseless, we use a multi-objective optimization algorithm to obtain the coefficients in the modal expansion. Finally, we use this method to break the cosine rule that the directivity of 2D arrays drops as cosine of the angle, which is a puzzle in wide-angle scanning. The numerical simulation results meet expectations and illustrate the feasibility of the method.

physics.app-ph↗

arXiv2023

Free-Space Propagation and Skyrmion Topology of Toroidal Electromagnetic Pulses

Toroidal electromagnetic pulses have been recently reported as nontransverse, space-time nonseparable topological excitations of free space [Nat. Photon. 16, 523-528 (2022)]. However, their propagation dynamics and topological configurations have not been comprehensively experimentally characterized. Here, we report that microwave toroidal pulses can be launched by a broadband conical horn antenna. We experimentally map their skyrmionic textures and demonstrate how that during propagation the pulses evolves towards stronger space-time nonseparability and closer proximity to the canonical Hellwarth and Nouchi toroidal pulses.

physics.class-ph↗

arXiv2023

Block definition design for stretchable metamaterials: enabling configurable sensitivity to deformation

The sensitivity to deformation plays a key role in determining the applicability of stretchable metamaterials (MMs) to be used for conformal integration or mechanical reconfiguration. Typically, different unit designs are required to achieve the desired sensitivity, but this article proposes a block definition design for stretchable MMs that enables regulation of the MMs' response to deformation by defining various block arrangements with the same precursor structure. The article demonstrates a stretchable MM that employs the block definition design to show the mechanical reconfigurability of resonant frequency. Different block definitions result in modulation ranges of resonant frequency ranging from 39\% to 85\% when applying a 20\% tensile strain. Additionally, the proposed design is also used to realize another MM with contradictory sensitivity to the deformation and electromagnetically induced transparency (EIT) MMs with configurable transmission bandwidth to the deformation, indicating its potential for broader applications.

physics.app-ph↗

arXiv2023

Dynamic Modulation of Electromagnetically Induced Transparency Metamaterials through Mode Coupling and Stretchable Design

The active control of electromagnetically induced transparency (EIT) metamaterials (MM) has the potential to revolutionize communication networks without relying on quantum technology. However, current reconfigurable systems offer limited flexibility and have high fabrication costs and difficulties. In this study, we examine a classical EIT metamaterial and discover a novel modulation mechanism that leverages mode coupling to dynamically adjust the bandwidth and group delay of the EIT MM. This mechanism is verified through analyses of the electric field and surface charge density distributions. Additionally, a robust coupled Lorentz oscillator model is used to explain the coupling mechanism, with results that are in good agreement with simulations and experiments. To capitalize on this mechanism, we propose a block-definition approach where the MM is divided into stretchable sections, allowing for dynamic modulation of the bandwidth and group delay by stretching the EIT MM. Furthermore, the fabrication process is highly compatible with traditional flexible printed circuit board techniques. Our block-definition EIT MM offers unprecedented tunability and flexibility, requiring no complex components or specialized materials, making it a promising candidate for tunable slow-wave devices and other reconfigurable microwave applications.

physics.app-ph↗

arXiv2022

Space Time Nonseparable Electromagnetic Vortices

In structured light with controllable degrees of freedom (DoFs), the vortex beams carrying orbital angular momentum (OAM) give access to provide additional degrees of freedom for information transfer, and in classic field, the propagation invariant space time electromagnetic pulses are the possible approach to high dimensional states. This paper arose an idea that coupling the space polarization nonseparable states of vortex beams and space time nonseparable states of spatiotemporal pulse can generate numerous unique and beneficial effects. Here, we introduce an family of space time nonseparable electromagnetic vortices (STNEV). The pulses exhibit complex and robust spatiotemporal topological structure of the electromagnetic fields, multiple singularities in the Poynting vector maps and distributions of energy backflow. We apply a quantum-mechanics methodology for quantitatively characterizing space time nonseparability of the pulse. Our findings facilitate their applications in fields of information transfer, toroidal electrodynamics and inducing transient excitations in matter.

physics.optics↗

arXiv2014

Enhancement of Time Reversal Sub-wavelength Wireless Transmission Using Pulse Shaping Technique (submit/1139227)

A novel time-reversal subwavelength transmission technique, based on pulse shaping circuits (PSCs), is proposed. This technique removes the need for complex or electrically large electromagnetic structures by generating channel diversity via pulse shaping instead of angular spectrum transformation. It is shown that, compared to our previous time-reversal system based on chirped delay lines, the PSC approach offers greater flexibility and larger possible numbers of channels, i.e. ultimately higher transmission throughput. The PSC based time-reversal system is also demonstrated experimentally.

physics.optics↗