Dark Fiber

In fiber-optic communications, dark fiber or unlit fiber (or fibre) is the name given to individual fibers that have yet to be used within cables that have been already laid. They are hence not yet connected to any device, and are only there for future usage.

The term was originally used when talking about the potential network capacity of telecommunication infrastructure, but now also refers to the increasingly common practice of leasing fiber optic cables from a network service provider.