Amplification technology for spatial division multiplexing signals transmitted using multicore fibres

Abstract

Amplification technologies needed for spatial division multiplexing (SDM) signal transmission have been reported, especially focusing on submarine systems, which have stricter requirements than terrestrial ones. As the first step of a large-scale commercialisation, 2-core un-coupled (UC) fibre production has already been announced. However, optical amplifiers for SDM signals are still under investigation because SDM amplifiers have various architectural possibilities, depending on the requirements to be considered in designing systems. The multicore erbium-doped fibre amplifier (MC-EDFA) architecture is classified from the viewpoint of the number of erbium-doped fibre (EDF) cores and its pumping method. Core pumped MC-EDFA is more compatible with the conventional single-core fibre (SCF)- based system and more mature than cladding pumped MC-EDFA. However, cladding pumped MC-EDFA has a unique feature of collective amplification of all cores in a single multicore fibre (MCF) and the potential of large-scale integration of amplification cores in a single package. For a feasibility study, a C-band 19-core cladding pumped MC-EDFA prototype is fabricated using a 19-core isolator. A half volume of the equivalent conventional single-core (SC-) EDFA is successfully demonstrated. One unique feature of UC-MCF is bidirectional (BD-) transmission using a single UC-MCF. Signal transmission direction can differ from core to core. This feature is useful for efficiently accommodating traffic of asymmetric communication data and expanding transmission capacity at a constant transmission distance. A C-band 7-core cladding pumped BD-MC-EDFA prototype is fabricated for the bidirectional MCF transmission line. Experimental results show transmission capacity was expanded by 17% using the prototype when bidirectional signal assignment was adapted. Towards practical use, optical components suitable for MC-EDFA need to be developed to draw out potential advantages of SDM technologies.