The meaning of Dark Fiber refers to unused or dark network infrastructure that is a mixture of cabling, switches and repeaters. Data is transported over optical fibre networks by passing light through the cables. If there is no data being transported, there is no light – this means that the fibre is ‘dark’. Dark Fiber is essentially optical fibre infrastructure that is not in use.

When fibre optic cables are laid down, many companies will, in order to future-proof their networks from exponential data growth, overestimate the amount of infrastructure and cabling required. This overestimation coupled with technical advances in the way in which data is packaged means that many optical dark fiber network have extra capacity that is not being used. As a result, Dark Fiber networks have developed to take advantage of this extra capacity.

The term Dark Fiber has now evolved to encompass the practice of leasing dark fiber optic cables from network providers and operators. A client will lease unused strands of dark fiber optic cable to create their own privately-operated optical fibre network rather than just leasing bandwidth. The dark fiber network is separate from the main network and is controlled by the client rather than the network provider.