Dark fiber

Dark fiber is installed but unused (unlit) optical fiber that a customer leases and lights with its own transmission equipment, rather than buying a managed bandwidth service. The lessee controls the technology and capacity entirely: with modern DWDM equipment, a single fiber pair can carry tens of terabits per second, and capacity upgrades require only new optics, not new contracts. Dark fiber is sold as long-term leases or IRUs (indefeasible rights of use) running 10-25 years, with pricing per fiber pair per route-kilometer. Hyperscalers and large enterprises use dark fiber to link data center campuses and reach carrier hotels; it is essential for high-bandwidth, low-latency data-center-to-data-center links, including metro rings connecting availability zones. The trade-off is operational responsibility for the optical layer.