Multimode Fiber Raman Amplifier for Unrepeatered Optical Communications

The project aims at a proof-of-concept demonstration of a novel technology, enabling a substantial extension of the reach of unrepeatered fiber optic communication links. MULTIBRIDGE will permit to cross the ultimate frontier of high-capacity transmission systems, by introducing a new method for the amplification of multiple optical signals, that simultaneously propagate in long-haul, unrepeatered transmission systems based on multimode optical fibers. This will lead to a breakthrough distance increase of high capacity, mode-division multiplexed, unrepeatered optical systems. Today, fiber optics links based on singlemode fibers need the periodic insertion of devices for lumped (erbium-doped fiber amplifiers, EDFA) or distributed (Raman pump) optical amplification. Amplifiers dramatically limit the number of fibers that it is possible to insert into a single submarine or terrestrial cable. Unrepeatered optical systems based on singlemode fibers cannot extend their reach over more than 300 km, because of the limited amount of optical power that can be coupled into the fiber ends. In the MULTIBRIDGE approach, both individual signals and pump radiation are coupled into separate modes of a multimode fiber by using mode-division multiplexers. Raman amplification of signals is obtained by inter-modal stimulated Raman scattering, so that multiple processes of Raman amplification act simultaneously, thus increasing the amplification efficiency. Mode-division multiplexing is naturally compatible with the proposed technology, permitting the simultaneous transmission of multiple high-speed optical tributaries. Multimode optical fibers may carry several tens of Watt of optical pump and signal power, thus permitting the extension of unrepeatered fiber links well above the 300 km limit of single-mode systems, as well as the deployment of long-haul systems with hundreds of fibers into a single submarine/terrestrial cable.