Electromagnetic Vortices. Группа авторов. Читать онлайн. Newlib. NEWLIB.NET

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Издательство: John Wiley & Sons Limited
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Жанр произведения: Физика
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isbn: 9781119662877
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of vortex waves for wireless communications in more sophisticated and realistic multipath environments, where strong inter‐channel and intra‐channel interference can take place. By combining with spatial equalization and orthogonal frequency division multiplexing techniques, it is shown that OAM communication can be useful in not only the line‐of‐sight environment but also in rich multipath environments. Chapter 12 presents the design consideration, application challenges, system implementation, and experimental characterization of free‐space OAM optical communication links. In particular, an inter‐channel crosstalk mitigation scheme is proposed and the application of optical OAM communications for unmanned aerial vehicles as well as in underwater environments is discussed and demonstrated. Chapter 13 focuses on two particular vector vortex beams, i.e., radially‐ and azimuthally‐polarized vortex beams, and provides the theoretical treatment for how they can be applied to chirality detection of subwavelength‐size particles and magnetic force microscopy. Chapter 14 investigates the usage of structured photons in quantum platforms and a method for generating/detecting single‐photons as well as entangled photon pairs carrying well‐defined OAM states. The chapter also includes illustrative examples showcasing their applications in quantum key distribution for quantum security and quantum simulation with quantum walks.

      We are indebted to all the coauthors of each of the 14 chapters for their excellent contributions to this book, which provides the readers with an invaluable resource documenting the cutting‐edge research outcomes in the field. The cooperation of the contributing authors during the course of this book preparation as well as their dedication to delivering a high‐quality product, especially under such globally difficult circumstances arising from the pandemic, is sincerely and deeply appreciated. Finally, we also gratefully acknowledge the editorial assistance provided by the highly professional staff of Wiley/IEEE Press. It has truly been a pleasure working with them on this book project.

      Zhi Hao Jiang

      Nanjing, P.R. China

      Douglas H. Werner

      University Park, PA, USA

Part I Fundamentals and Basics of Electromagnetic Vortices

       Anastasios Papathanasopoulos and Yahya Rahmat‐Samii

       Department of Electrical and Computer Engineering, University of California, Los Angeles, CA, USA

      The history of angular momentum dates back to the early twentieth century. The SAM of light was theoretically studied for the first time by Poynting in 1909 [1] and experimentally studied by Beth in 1936 [2]. SAM is intrinsic, since it does not depend on the choice of an axis, and it is only polarization dependent. If s is the SAM mode number, then s = ±1 corresponds to right‐ and left‐hand polarized waves, and s = 0 corresponds to linearly polarized waves. Although the experimental demonstration of the exchange of angular momentum between circularly polarized beams and matter was performed more than 80 years ago, the work associated with light’s angular momentum has been almost exclusively concerned with SAM.

      It was not until 1992 that Allen et al. [3] showed that helically phased beams with a phase term ejlϕ (where

is the imaginary unit, l is the OAM mode number, and ϕ is the azimuthal angle) carry OAM. The wavefront of an OAM beam is a spiral; the phase twists around the beam axis and changes 2πl after a full turn. Unlike SAM, OAM is linked to spatial distribution rather than polarization. OAM is extrinsic, since it depends on the choice of the calculation axis. The angular momentum is the composition of SAM and OAM, such that the angular momentum mode number is j = s + l.

      The first characteristic property of OAM beams is the orthogonality of distinct OAM modes. In general, the electric field of an OAM beam can be written as: