Mode group division multiplexing in graded-index multimode fibers

Data transmission over multimode fibers has the potential to considerably increase the capacity limit of single-mode fibers by exploiting the spatial dimension. For long-haul systems, mode division multiplexing using one mode per channel in a few-mode fiber requires coherent detection in conjunction with digital multiple input multiple output (MIMO) processing for signal separation. In the following we focus on spatial multiplexing using mode groups rather than spatial modes in standard graded-index multimode fibers. In combination with on-off keying (OOK) modulation and direct detection, these systems might be advantageous for access- and connection-related applications, e.g., for super computer interconnects or in the near metro region at link lengths shorter than about 10 km. In this paper we study the potential of mode groups for mode group division multiplexing (MGDM). Single-mode group transmission experiments at 10 Gb/s per mode group, experimental mode group launching by phase mask, and concepts for passive optical mode demultiplexers are discussed.