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Angular Momentum Spectrum of Electromagnetic Wave
Chao ZHANG Jin JIANG
Publication
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences
Vol.E103A
No.4
pp.715717 Publication Date: 2020/04/01 Online ISSN: 17451337
DOI: 10.1587/transfun.2019EAL2112 Type of Manuscript: LETTER Category: Analog Signal Processing Keyword: angular momentum, twisted radiation, spectrum, vortex, OAM,
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Summary:
Angular Momentum (AM) has been considered as a new dimension of wireless transmissions as well as the intrinsic property of ElectroMagnetic (EM) waves. So far, AM is utilized as a discrete mode not only in the quantum states, but also in the statistical beam forming. Traditionally, the continuous value of AM is ignored and only the quantized mode number is identified. However, the recent discovery on electrons in spiral motion producing twisted radiation with AM, including Spin Angular Momentum (SAM) and Orbital Angular Momentum (OAM), proves that the continuous value of AM is available in the statistical EM wave beam. This is also revealed by the socalled fractional OAM, which is reported in optical OAM beams. Then, as the new dimension with continuous real number field, AM should turn out to be a certain spectrum, similar to the frequency spectrum usually in the wireless signal processing. In this letter, we mathematically define the AM spectrum and show the applications in the information theory analysis, which is expected to be an efficient tool for the future wireless communications with AM.


