Electromagnetic Vortices. Группа авторов

on the cutting‐edge research area of electromagnetic vortices including fundamental theory, wave phenomena, and also the applications of vortex waves in a variety of disciplines. Akin to vortices that exist widely throughout nature, ranging from a fluid vortex with a central flow singularity to the countless spiral galaxies in the universe, vortices also exist in electromagnetic and optical fields which are manifested in what are called vortex waves. Such vortex waves refer to a class of electromagnetic waves carrying nonvanishing orbital angular momentum (OAM), which are characterized by their helical phase‐front and annular‐shaped intensity distribution, indicating a singularity at the beam center. This family of waves encompasses unconventional waveforms with complex structures such as vector vortex beams, higher‐order Bessel beams, etc. Their structured wavefronts endow them with unprecedented wave behavior that breaks conventional bounds enabling new physical properties, revealing a subtle connection between macroscopic physical optics and microscopic quantum optics. These unique properties have further led to the creation of revolutionary new ways of exploiting wave‐matter interactions, especially when coupled with interdisciplinary research areas such as nanophotonics, metamaterials, communications, nonlinear optics, quantum information, etc. Ever since the introduction of the concept of electromagnetic vortices in 1989 by Coullet et al. and the first demonstration of OAM in paraxially propagating vortex beams by Allen et al., there has been a dramatically increasing number of scientists and engineers enthusiastically devoting their efforts to this field of exploration. In particular, over the past few years, the field of electromagnetic vortices has witnessed tremendous advancements in many of its associated subareas, which have jointly enabled devices and even systems for a wide variety of applications including astrophysical observation, particle manipulation, nonlinear optics, microlasers, fiber optics, wireless communications, and even quantum cryptography, just to name a few. As such, electromagnetic vortices hold great promise for revolutionizing developments in many research areas and triggering key disruptive technologies that have the potential to change the daily lives of human beings.

The main goal of this book is to provide an all‐inclusive and in‐depth overview of many of the recent and important accomplishments regarding the various topics associated with the field of electromagnetic vortices. In this book, a comprehensive treatment of the field has been compiled from a group of leading researchers throughout the world on subjects ranging from the fundamental theoretical principles and discoveries of new physical wave behaviors to state‐of‐the‐art device designs and illustrative application examples encompassing a wide range of related sub‐areas. In particular, topics that will be covered include the basics of electromagnetic vortices, the generation and detection of various forms of vortex waves with homogeneous and inhomogeneous wavefronts from the microwave regime all the way down to optical wavelengths, the multiplexing and demultiplexing of vortex beams, nonlinear and active vortex beams, communication and sensing that exploits vortex beams, manipulation of structured photon states for quantum information, etc. Multidisciplinary research outcomes linking electromagnetic vortices to nanophotonics, quantum, wireless communications, astronomy, and optical forces are presented, which may serve to inspire interest from scientists and engineers currently outside this field. Throughout the book, a plethora of transformational application examples have also been included, encompassing OAM‐based wireless communication systems, radar detection, lasers, chirality detection, magnetic and chirality force microscopy, quantum security, as well as several others. Moreover, these examples were carefully selected for their transformational impact on pushing the research envelope in the field of electromagnetic vortices from investigations of physical phenomena to real‐world engineering applications. Importantly, each chapter is contributed by an internationally recognized author or group of authors covering the latest research results. We hope that this book will be an indispensable resource for researchers, faculty, and graduate students in academia as well as professionals working in the telecommunication, optical engineering, and even future quantum information industries.

This book contains 14 invited chapters contributed by the leading experts in the field of electromagnetic vortices, which are divided into four parts. Part I includes 2 chapters that are focused on providing an introduction to the fundamentals and basics of electromagnetic vortices, Part II contains a collection of 6 chapters emphasizing the physical wave phenomena associated with electromagnetic vortices, Part III has 4 chapters that highlight several of their disruptive engineering applications, and the last two chapters in Part IV cover some important multidisciplinary explorations in the field. A brief summary of each chapter is furnished as follows. Chapter 1 provides an introduction to the fundamentals of vortex beams and discusses their relationship with conventional pencil beams. It also includes a brief overview of the generation methods as well as potential applications of vortex waves in communications from the antenna standpoint. Chapter 2 presents a detailed step‐by‐step derivation of the physical foundations of OAM radios from the perspective of classical electrodynamic theory, followed by a short discussion regarding their physical implementation and astrophysics applications. Chapter 3 provides an overview of the generation of scalar vortex beams at microwave frequencies using coding metasurfaces, including both reflective and transmissive designs, and spoof surface plasmon polariton waveguiding circuits. Chapter 4 illustrates the design methodology and experimental characterization of vortex beam generators by utilizing a combination of transformation optics and additive manufacturing. By employing 3‐D printing enabled all‐dielectric platforms that are nearly non‐dispersive with respect to their frequency response, the resulting devices possess a very broad bandwidth. Chapter 5 considers the basic properties and generation methods for vector vortex beams, which represent a more generalized family of waveforms under the umbrella of electromagnetic vortices. By coupling various high‐efficiency transmit‐array cells with a globally coherent phase‐only synthesis strategy, high‐capacity generation and multiplexing of vector vortex beams are demonstrated (both numerically and experimentally) in the millimeter‐wave regime. Chapter 6 reviews the metamaterial approaches for achieving electromagnetic vortices at optical wavelengths using nanofabrication techniques and provides a brief overview of their optical applications, with a particular focus on active optical vortex emitters, i.e. OAM lasers. Chapter 7 continues the discussion of the generation of optical vortices, emphasizing the methodologies for achieving special types of vortices with intriguing physical properties, which are different from conventional scalar vortex beams, including perfect vortices, fractional vortices, anomalous vortices, and vortices with varying topological charges. Chapter 8 investigates both the generation and detection of electromagnetic vortices by employing metasurfaces and photonic crystals with defects. In addition, the nonlinear effects associated with vortex beams are also described, including the proposal of a precise numerical boundary element method and the formulation of a general angular momentum conservation law for studying the second harmonic generation of vortex waves. Chapter 9 introduces the application of vortex beams for radar detection, multiple‐in multiple‐out (MIMO) wireless systems, and spatial field digital modulation. In order to fulfill the system requirements with a simplified solution, several OAM antenna designs are proposed including a partial arc transmitting scheme for constructing higher‐order OAM modes. Chapter 10 focuses on the theoretical analysis of vortex beam multiplexing for short‐range microwave communications from the perspective of the antenna array, channel matrix, and beamforming circuits, arriving at an optimal solution for the array radius based on the geometric channel model. Chapter