Polarisation and angular momentum of light in guided modes: theory and implementations of dipolar sources coupling

光具有许多自由度，其中最独特的是偏振，角动量，坡印廷矢量和螺旋度，在受限几何中，其表现与自由空间非常不同。在受限的几何结构中，这些自由度可以相互作用，产生诸如自旋到轨道角动量转移或自旋动量锁定的现象。在我的论文中，我们集中我们的注意力在偶极源的自由度和导模的自由度之间的交换。这允许实现感兴趣的导模激发，例如偏振相关耦合或单向激发。实现这些现象所需的偶极子是用一个非常简单的符号解析地找到的。通过数值分析两个现实的来源，通常是平面波照明下的纳米粒子，和波导结构的设计和优化。我们扩展的单向激发的导模，以前获得的圆极化电偶极子，圆极化磁偶极子和叠加的电和磁偶极子，如惠更斯偶极子。这是使用角谱的方法，我们证明它提供了相同的结果，将使用费米的黄金法则。我们还揭示了一个源的存在，Janus偶极子，其耦合到导模可以任意开关简单地反转其极化，其中我们显示了实验实现。此外，我们证明了电偶极子和磁偶极子的叠加足以控制幅度，相位和方向的单独高达五个不同的导模在同一波导。最后，我们提出了精确的计算，数值和分析的自旋，角动量和螺旋度的本征模式的纳米纤维和纳米线，显示，除其他属性外，总角动量的量化圆柱形导模。

Light possesses many degrees of freedom, the most distinctive of which are polarisation, angular momenta, Poynting vector and helicity, which, in confined geometries, behave very differently than in free space. In confined geometries, these degrees of freedom can interact with one-another giving rise to phenomena such as Spin-to-Orbit angular momentum transfer or Spin-momentum locking. In my thesis, we focus our attention on the exchange between the degrees of freedom of dipolar sources, and those of guided modes. This allows to achieve interesting excitations of guided modes, such as polarisation-dependent coupling, or unidirectional excitation. The dipoles needed to achieve these phenomena are found analytically, with a very simple notation. Via numerical analysis both realistic sources, usually being nanoparticles under plane wave illumination, and waveguiding structures are designed and optimised. We extend the unidirectional excitation of guided modes, previously obtained with circularly polarised electric dipoles, to circularly polarised magnetic dipoles and superpositions of electric and magnetic dipoles, such as the Huygens dipole. This is done using the angular spectrum approach, and we prove it provides the same results that would be obtained using Fermi's golden rule. We also reveal the existence of a source, the Janus dipole, whose coupling to guided modes can be arbitrarily switched on-and-off simply inverting its polarisation, of which we show an experimental realisation. Moreover, we demonstrate that a superposition of electric and magnetic dipoles is sufficient to control amplitude, phase and direction of individually up to five different guided modes in the same waveguide. Finally, we present accurate calculations, both numerical and analytical of spin, angular momenta and helicity for the eigenmodes of nanofibers and nanowires, showing, among other properties, the quantization of the total angular momenta of cylindrical guided modes.