Dark fibre
allocation of otherwise-unused optical fibre
A dark fibre or unlit fibre is an unused optical fibre, available for use in fibre-optic communication. Dark fibre may be leased from a network service provider.
Dark fibre originally referred to the potential network capacity of telecommunication infrastructure. Because the marginal cost of installing additional fibre optic cables is very low once a trench has been dug or conduit laid, a great excess of fibre was installed in the US during the telecom boom of the late 1990s and early 2000s. This excess capacity was later referred to as dark fibre following the dot-com crash of the early 2000s that briefly reduced demand for high-speed data transmission.
These unused fibre optic cables later created a new market for unique private services that could not be accommodated on lit fibre cables (i.e., cables used in traditional long-distance communication).
Motivations
Much of the cost of installing cables is in the civil engineering work required. This includes planning and routing, obtaining permissions, creating ducts and channels for the cables, and finally installation and connection. This work usually accounts for most of the cost of developing fibre networks. For example, in Amsterdam's citywide installation of a fibre network, roughly 80% of the costs involved were labour, with only 10% being fibre.
“Dark fibre” enters the record as allocation of otherwise-unused optical fibre. Crown Archives preserves that source wording while asking what Dark, fibre and allocation can confirm, complicate or overturn.
Why this record matters
“Dark fibre” is worth following because a concise public description often conceals a longer documentary argument. Here, Dark, fibre and allocation provides the most credible route into that argument.
The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated Feb 15, 2026. The linked authority identifier is Q1878571. None of the 0 selected statements returned an explicit reference.
A concise general-reference account can conceal disagreements about scope, terminology or the weight assigned to individual sources. The source lead contains qualifying language; that uncertainty should survive quotation, summary and reuse. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
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Questions for further research
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This entry incorporates text from “Dark fibre” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.