Spatial multiplexing for high capacity transport

Spatial multiplexing provides a solution for fiber capacity increase beyond the limits foreseen for enhanced bandwidth efficiency by higher order modulation and more channels by additional wavelength bands in long haul optical transmission. Its adoption also offers potential for a reduction of the cost and energy per transmitted bit. Two fiber types have been identified as candidates for transmission of multiple signals at the same wavelength inside a single cladding: fibers with multiple single mode cores and single core multi-mode fibers. Major challenges arise from the coupling of signals along the transmission path. Multiple input/multiple output signal processing may provide a solution for the separation of signals at the end of the link. Concepts such as tapers in case of multi-core fibers and field transformation in case of single core multi-mode fibers exist to provide the spatial multiplexing and demultiplexing functions. The potential of spatial multiplexing for cost and energy efficiency can only be realized, if optical amplifiers are found which are capable of processing all channels simultaneously. Concepts for such amplifiers were analyzed with promising results. Direct pumping of the cores leads to acceptable power requirements of lumped erbium-doped as well as distributed Raman amplifiers.

► In this invited paper, we provide an overview on spatial multiplexing for high capacity transport.
► Requirements on technologies for capacity increase are discussed.
► We present solutions for transmission fibers, multiplexing and demultiplexing functions as well as optical amplification.
► Optical amplifier concepts suitable for spatial multiplexing with decent power efficiency could be identified.