Alberucci Alessandro, Jisha Chandroth P, Marrucci Lorenzo, Assanto Gaetano
Optics Laboratory, Tampere University of Technology, FI-33101 Tampere, Finland; NooEL - Nonlinear Optics and OptoElectronics Lab, University "Roma Tre", IT-00146 Rome, Italy.
Centro de Física do Porto, Faculdade de Ciências, Universidade do Porto , PT-4169-007 Porto, Portugal.
ACS Photonics. 2016 Dec 21;3(12):2249-2254. doi: 10.1021/acsphotonics.6b00700. Epub 2016 Nov 11.
We investigate electromagnetic propagation in uniaxial dielectrics with a transversely varying orientation of the optic axis, the latter staying orthogonal everywhere in the propagation direction. In such a geometry, the field experiences no refractive index gradients, yet it acquires a transversely modulated Pancharatnam-Berry phase, that is, a geometric phase originating from a spin-orbit interaction. We show that the periodic evolution of the geometric phase versus propagation gives rise to a longitudinally invariant effective potential. In certain configurations, this geometric phase can provide transverse confinement and waveguiding. The theoretical findings are tested and validated against numerical simulations of the complete Maxwell's equations. Our results introduce and illustrate the role of geometric phases on electromagnetic propagation over distances well exceeding the diffraction length, paving the way to a whole new family of guided waves and waveguides that do not rely on refractive index tailoring.
我们研究了光轴方向横向变化的单轴介质中的电磁传播，光轴在传播方向上处处保持正交。在这种几何结构中，场没有折射率梯度，但它获得了横向调制的潘查拉特纳姆 - 贝里相位，即一种源于自旋 - 轨道相互作用的几何相位。我们表明，几何相位相对于传播的周期性演化会产生纵向不变的有效势。在某些配置中，这种几何相位可以提供横向限制和波导作用。我们将理论结果与完整麦克斯韦方程组的数值模拟进行了对比测试和验证。我们的结果引入并阐明了几何相位在远超衍射长度的距离上对电磁传播的作用，为全新的一类不依赖于折射率定制的导波和波导铺平了道路。
