用空间光调制器模拟叉形光栅的方式产生高阶和分数阶涡旋光束，分离各阶涡旋光束并探究单级特性，探测其拓扑荷数以验证实验方法的正确性。设计了涡旋光束生成光路，编写了产生叉形光栅全息图的计算机程序，利用透射式空间光调制器模拟叉形光栅，以全息图的方式加载到空间光调制器上。调节参数改变全息光栅图样，得到拓扑荷数从1.0到100.0的整数阶与间隔为0.1的分数阶涡旋光束。利用孔径光阑分离出一级衍射，分析其特性并利用干涉法测量其拓扑荷数。实验发现，整数与分数阶光场分布与拓扑荷数为单调关系，拓扑荷数接近100时光束质量显著下降的特性，利用干涉法测得的拓扑荷数与计算全息图设置的参数完全相同。干涉测量结果验证了计算全息方法的正确性。该方法装置简易、参数可调，可为高阶和分数阶涡旋光的产生和应用提供一定的参考。

Multi-band signal propagation and processing play an important role in quantum communications and quantum computing. In recent years, optical nonreciprocal devices such as an optical isolator and circulator are proposed via various configurations of atoms, metamaterials, nonlinear waveguides, etc. In this work, we investigate all-optical controlled nonreciprocity of multi-band optical signals in thermal atomic systems. Via introducing multiple strong coupling fields, nonreciprocal propagation of the probe field can happen at some separated frequency bands, which results from combination of the electromagnetically induced transparency (EIT) effect and atomic thermal motion. In the proposed configuration, the frequency shift resulting from atomic thermal motion takes converse effect on the probe field in the two opposite directions. In this way, the probe field can propagate almost transparently within some frequency bands of EIT windows in the opposite direction of the coupling fields. However, it is well blocked within the considered frequency region in the same direction of the coupling fields because of destruction of the EIT. Such selectable optical nonreciprocity and isolation for discrete signals may be greatly useful in controlling signal transmission and realizing selective optical isolation functions.

A terahertz (THz) waveguide using a metallic nanoslit whose width is much smaller than the skin depth is analytically investigated. By taking some important physical properties into account, we derive a simple, yet accurate, expression for the effective index. We also study the changes in modal field and the attenuation coefficient in the whole THz region, and find some interesting physical properties. Finally, we verify that these theoretical analyses coincide with the rigorous numerical simulations. This research can be useful for various applications of THz waveguides made of metallic nanoslits.