Installed but unused optical fibre capacity, reserved for future use or leased to a third-party operator.
Dark fibre designates optical fibre capacity that is installed but not yet lit, that is, without the transmission equipment that makes it active. It forms a capacity reserve that operators and data centre managers can activate later or lease to third parties, who then deploy their own equipment and control the link end to end. For artificial intelligence infrastructure, the availability of dark fibre conditions the ability to interconnect compute sites at very high bandwidth, a critical issue for distributed training. From the insurance standpoint, dark fibre is part of a centre's connectivity risk: dependence on single physical links creates network points of failure, while redundancy through dual grid and multiple paths mitigates isolation risk. The physical security of the routes, exposed to civil works, sabotage and disasters, completes the exposure analysis.
An operator leasing dark fibre to interconnect two compute sites controls its own link, but remains exposed to physical severance of the route during civil works or sabotage.
dark fiber, fibre noire, fibre optique inactive