Orbital angular momentum (OAM) of light provides a new dimension to increase the communication capacity. The compact and miniaturized devices are preferred because of the advantages in reliability and easy integration. In this work, a quarter-ring-shaped phase-gradient metasurface (QR-PGM) is proposed to sort various propagating waves into fully separated waveguide channels according to their OAM states. The principle is based on focal spot shifting arising from the constructive interference of surface plasmon polaritons with azimuthal phase modulated by the vortex beam. A thorough analysis of the SPP focusing properties was also carried out, which suggests the superiority of quarter-circular arc in OAM sorting (compared with half-circular arc). Focusing efficiency of the QR-PGM reaches to 25%, owing to dense sampling of incident light and unidirectional excitation of SPPs. By coupling spots to waveguides, the wide band on-chip sorting was demonstrated. In the broad wavelength band from 1.3 to 1.6 μm, the extinction ratio of each waveguide port keeps above 3 dB. The proposed structure is compact, efficient, wavelength-division-multiplexing-compatible, and easy to integrate with other on-chip devices. It will be a promising element for high capacity optical communication systems.

中文翻译：

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表面等离激元极化透镜的片上轨道角动量排序

光的轨道角动量（OAM）为增加通信容量提供了新的维度。紧凑和小型化的设备是优选的，因为其具有可靠性和易于集成的优点。在这项工作中，提出了一种四分之一环形的相位梯度超表面（QR-PGM），用于根据其OAM状态将各种传播波分类到完全分离的波导通道中。该原理基于焦点偏移，该焦点偏移是由表面等离振子极化子与涡旋光束调制的方位角相位的相长干涉引起的。还对SPP聚焦特性进行了彻底的分析，这表明四分之一圆弧在OAM分选中的优势（与半圆弧相比）。QR-PGM的聚焦效率达到25％，由于入射光的密集采样和SPP的单向激发。通过将斑点耦合到波导，展示了宽带片上分类。在1.3至1.6μm的宽波段中，每个波导端口的消光比均保持在3 dB以上。所提出的结构是紧凑的，高效的，波分复用兼容的，并且易于与其他片上器件集成。对于大容量光通信系统来说，它将是一个有前途的元素。