Photonic Lanterns, 3D Waveguides, Multiplane Light Conversion and other Components that enable Space Division Multiplexing

Four mode multiplexing and manipulation technologies are reviewed in the context of space division multiplexed optical communication systems. These are multiplane light conversion, fused fiber devices such as photonic lanterns and tapered fiber bundles, 3D waveguides fabricated using ultrafast laser inscription, and free-space imaging systems. Each device has its unique strengths and use cases. Multiplane light conversion 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. 3D waveguides are inscribed into a glass block using ultra short lasers and can arbitrarily route light in 3D. Finally, freespace systems using lenses can also relay many multicore and multimode beams through a single freespace device such as a thin film filter or optical isolator. These four technologies have enabled hero transmission experiments in multimode, multi-core and multimode fiber.