Mode group multiplexing over graded-index multimode fiber

Data transmission over multi-mode fibers (MMF) has the potential to increase considerably the capacity limit of singlemode fibers (SMF) by exploiting the spatial dimension. Spatial multiplex using standard graded-index multimode fibers (GI-MMF) in combination with OOK modulation and direct detection might be advantageous for short haul transmission systems. The application of principal mode groups provides the possibility to eliminate the need for multiple-input multiple-output (MIMO) processing, especially if a fiber supporting a large number of modes is used for the transmission. Spatial multiplex using principal mode groups as individual transmission channels has been experimentally investigated at the example of a data transmission over OM4 graded-index multi-mode fiber. Eight principal mode groups have been identified being suitable for spatially separated transmission channels at a wavelength of 1550 nm for this fiber. Each mode group has been modulated with a 10 Gbit/s data signal showing the ability to transmit an overall bit rate of 80 Gbit/s over a 2 km long multi-mode fiber. Keywords: Multimode transmission, spatial multiplex, graded-index multimode fiber, principal mode groups, mode converter 1. INTRODUCTION From an information theoretical standpoint, multi-mode fibers (MMF) exhibit a higher transport capacity limit than single-mode fibers (SMF) by exploiting the various optical modes as independent communication channels. The utilization of different modes or mode groups of an MMF by different transmit signals and separation by optical mode filtering, partly in conjunction with multiple-input multiple-output (MIMO) processing at the receive side is under investigation for several years[1-6].