Orbital angular momentum (OAM) beams with topological charge ℓ are commonly generated and detected by modulating an incoming field with an azimuthal phase profile of the form exp(iℓϕ) by a variety of approaches. This results in unwanted radial modes and reduced power in the desired OAM mode. Here, we show how to enhance the modal purity in the creation and detection of classical OAM beams and in the quantum detection of OAM photons. Classically, we combine holographic and metasurface control to produce high purity OAM modes and show how to detect them with high efficiency, extending the demonstration to the quantum realm with spatial light modulators. We demonstrate ultra-high purity OAM modes in orders as high as ℓ = 100 and a doubling of dimensionality in the quantum OAM spectrum from a spontaneous parametric downconversion source. Our work offers a simple route to increase the channel capacity in classical and quantum communication using OAM modes as a basis.

中文翻译：

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增强轨道角动量光子的模态纯度

轨道角动量（OAM）梁与拓扑电荷ℓ通常产生，并通过与形式EXP（的方位角相位分布调制传入场检测iℓφ）通过各种方法。这导致不需要的径向模式，并降低了所需OAM模式下的功率。在这里，我们展示了如何在创建和检测经典OAM光束以及在OAM光子的量子检测中提高模态纯度。经典地，我们将全息和超表面控制相结合，以产生高纯度的OAM模式，并展示如何高效地检测它们，并通过空间光调制器将演示扩展到量子领域。我们证明在订单超高纯度OAM模式高达ℓ= 100，并且自发的参数下转换源的量子OAM谱中的维数加倍。我们的工作提供了一条简单的途径，可以使用OAM模式作为基础来增加经典和量子通信中的信道容量。