Options for Cost-effective Capacity Upgrades in Backbone Optical Networks

Upgrading the capacity of backbone optical networks while delivering contents to the end-users with a reduced cost per bit is a day-by-day challenge of network operators. In this paper, we first discuss several mid-term options for capacity upgrades including migration to multi-fibre and multi-band systems (utilizing amplification systems with bandwidth extending over the C+L or the S+C+L bands). The multi-band approach is shown to be more cost-effective than the multi-fibre approach under certain circumstances. We then focus on space-division multiplexing (SDM) based networks as the ultimate solution to address the "capacity crunch". We compare the performance and infrastructure cost of possible SDM switching options for a solution based on bundles of single-mode fibres as a first pragmatic generation of SDM networks. We show that the use of spatial-group switching reduces the switching-related infrastructure cost of the SDM network and can also lead to extra cost savings due to sharing of elements in other parts of the network.