Four-mode multiplexing and manipulation technologies are reviewed in the context of space-division multiplexing (SDM) optical communication systems. These are multiplane light conversion (MPLC), fused fiber devices, such as photonic lanterns and tapered fiber bundles, 3-D waveguides fabricated using ultrafast laser inscription, and free-space imaging systems. Each device has its unique strengths and use cases. MPLC can create very complex transformations between two arbitrary sets of spatial modes and leverages mature gray-scale lithographic techniques. Photonic lanterns and tapered fiber bundles are all-fiber devices that can convert beams on single-mode fiber inputs into spatial modes. The all-fiber construction leads to very low losses and high-power handling. 3-D waveguides are inscribed into a glass block using ultrashort lasers and can arbitrarily route light in 3-D. Finally, free-space systems using lenses can also relay many multicore and multimode beams through a single free-space device, such as a thin film filter or an optical isolator. These four technologies have enabled hero transmission experiments in the multimode, multicore, and multimode fiber.

中文翻译：

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光子灯笼、3D 波导、多平面光转换和其他支持空分复用的组件


在空分复用（SDM）光通信系统的背景下回顾了四模复用和操纵技术。这些是多平面光转换 (MPLC)、熔融光纤设备（例如光子灯笼和锥形光纤束）、使用超快激光刻字制造的 3D 波导以及自由空间成像系统。每个设备都有其独特的优势和用例。 MPLC 可以在任意两组空间模式之间创建非常复杂的转换，并利用成熟的灰度光刻技术。光子灯笼和锥形光纤束是全光纤器件，可以将单模光纤输入上的光束转换为空间模式。全光纤结构可实现极低的损耗和高功率处理。使用超短激光将 3D 波导刻入玻璃块中，并可以在 3D 中任意路由光。最后，使用透镜的自由空间系统还可以通过单个自由空间设备（例如薄膜滤波器或光学隔离器）中继许多多芯和多模光束。这四项技术已经实现了多模、多芯和多模光纤的英雄传输实验。