Multimode Fiber Raman Amplifier for Unrepeatered Optical Communications

Introduction

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.

Objectives

MULTIBRIDGE will permit crossing 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.

Expected Outcomes

This will lead to a breakthrough distance increase of high-capacity, mode-division multiplexed, unrepeatered optical systems.

Current Limitations

Today, fiber optic links based on singlemode fibers need the periodic insertion of devices for:

• Lumped optical amplification (erbium-doped fiber amplifiers, EDFA)
• Distributed optical amplification (Raman pump)

Amplifiers dramatically limit the number of fibers that can be inserted into a single submarine or terrestrial cable. Unrepeatered optical systems based on singlemode fibers cannot extend their reach over more than 300 km due to the limited amount of optical power that can be coupled into the fiber ends.

MULTIBRIDGE Approach

In the MULTIBRIDGE approach:

• Both individual signals and pump radiation are coupled into separate modes of a multimode fiber using mode-division multiplexers.
• Raman amplification of signals is obtained by inter-modal stimulated Raman scattering, allowing multiple processes of Raman amplification to act simultaneously, thus increasing the amplification efficiency.

Compatibility and Advantages

Mode-division multiplexing is naturally compatible with the proposed technology, permitting the simultaneous transmission of multiple high-speed optical tributaries.

Conclusion

Multimode optical fibers may carry several tens of Watts 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.