School of Engineering and Technology and Science of Advanced Materials Program, Central Michigan University, Mount Pleasant, Michigan 48859, USA.
Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78712, USA.
Phys Rev Lett. 2018 Sep 7;121(10):103901. doi: 10.1103/PhysRevLett.121.103901.
Lasers and light emitters do not typically radiate fields with orbital angular momentum (OAM). Here we show that a suitable scheme of spatiotemporal modulation of a microring cavity laser can impart a synthetic angular momentum, resulting in beams with well-defined OAM. The phenomenon relies on a traveling wave modulation of the refractive index of the microring, which breaks the degeneracy of oppositely oriented whispering gallery modes. In parallel, a static structural grating on the periphery of the microring enables efficient vertical radiation. The proposed structure is inherently tunable and can also emit fields with zero net OAM while retaining toroidal energy distributions similar to the effect of an axicon lens.
激光器和发光器通常不会辐射具有轨道角动量（OAM）的场。在这里，我们展示了一种微环腔激光的时空调制的合适方案，可以赋予合成角动量，从而产生具有明确定义 OAM 的光束。该现象依赖于微环折射率的行波调制，该调制打破了相反方向的 whispering gallery 模式的简并。同时，微环外围的静态结构光栅可实现有效的垂直辐射。所提出的结构是固有可调谐的，并且在保留与轴棱锥透镜的效果类似的环形能量分布的同时，也可以发射具有零净 OAM 的场。
