近场方向性的Janus和Huygens偶极源
Janus and Huygens' dipolar sources for near-field directionality
摘要：
控制发射、散射和波导的方向性是量子光学技术、集成光子学和新超颖表面设计以及无线电和微波工程中的重要要求。最近，已经开发了几种方法来实现依赖于惠更斯偶极源的远场中的单向散射，以及基于涉及圆极化电或磁偶极的自旋霍尔效应的波导光学器件中的单向散射，所有这些都可以用等离子体或介电纳米颗粒来实现。在这里，我们表明，存在一个偶极源互补惠更斯偶极子，称为Janus偶极子，这是不是在远场方向，但其耦合到波导模式的拓扑保护，使它被允许在一侧的偶极子，但不是在相反的一侧。惠更斯偶极子的近场方向性也被揭示，并介绍了一个广义的Kerker的远场和近场方向性的条件。圆形电偶极和磁偶极，与惠更斯和Janus偶极源一起，形成了一套完整的远场和近场定向偶极源，为有前途的应用铺平了道路。
英文摘要：
Controlling directionality of emission, scattering and waveguiding is an important requirement in quantum optical technology, integrated photonics and new metasurface designs, as well as radio and microwave engineering. Recently, several approaches have been developed to achieve unidirectional scattering in the far-field relying on Huygens' dipolar sources, and in waveguided optics based on spin-Hall effects involving circularly polarised electric or magnetic dipoles, all of which can be realised with plasmonic or dielectric nanoparticles. Here we show that there exists a dipolar source complimentary to Huygens' dipole, termed Janus dipole, which is not directional in the far-field, but its coupling to waveguided modes is topologically protected so that it is allowed on one side of the dipole but not on the opposite side. The near field directionality of the Huygens' dipole is also revealed and a generalised Kerker's condition for far- and near-field directionality is introduced. Circular electric and magnetic dipoles, together with Huygens' and Janus dipolar sources, form a complete set of directional dipolar sources in far- and near-field, paving the way for promising applications.
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