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Line Singularities and Hopf Indices of Electromagnetic Multipoles.
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论文类型：期刊论文
发表刊物：Laser & Photonics Reviews
所属单位：光电学院，国家光电研究中心
刊物所在地：美国
学科门类：物理学
项目来源：自然科学基金
文献类型：J
卷号：14
期号：7
页面范围：2000049
关键字：无
DOI码：10.1002/lpor.202000049
发表时间：2020-06-08
教研室：c716
摘要：Electromagnetic multipoles serve as one of the most ubiquitous languages in photonics, forming a complete expansion basis for radiations of arbitrary types. Electromagnetic multipoles from the perspective of line fields and singularities are explored. It is then discovered that, for arbitrary finite sources in a homogeneous background, there have to be isolated directions along which the radiation is either zero or circularly polarized. For such singular directions, half-integer Hopf indices can be assigned and the index sum has to be a global invariant of 2. With this topological insight, the hidden dimensions of radiative circularly polarized Bloch modes of photonic crystal slabs are unveiled, revealing their topological origins of line singularities and indices. This work has established subtle connections between three seemingly unrelated but sweeping physical entities (line singularities of Hopf indices, electromagnetic multipoles, and Bloch modes), which can nourish new frames of visions and applications fertilizing many related fields.
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