Low-Loss 25.3 km Few-Mode Ring-Core Fiber for Mode-Division Multiplexed Transmission

We report the design, fabrication, and characterization of a few-mode ring-core fiber supporting four mode groups (i.e., seven spatial modes including spatial degeneracies). By carefully designing the ring-core parameters, the fiber can support only single-radial-order modes, which enables weak intermodal coupling between higher order modes and has potential to reduce the complexity of mode-division multiplexed digital signal processing. The low loss (~0.3 dB/km) and long length (25.3 km) RCF is successfully fabricated and they are both records for a ring-core fiber.