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Dark fibre
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.
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. Many fibre-optic cable owners such as railroads and power utilities have always included additional fibres with the intention to lease these to other carriers. This is typically done using coarse wavelength division multiplexing CWDM because the wider 20 nm spacing of the wavebands makes these systems much less susceptible to interference.
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