Fiber that carries no light because nothing is connected to it, either spare capacity built in for growth or strands leased as raw glass to a customer who installs their own optics. Leasing dark fiber gives the customer full control of speed and protocol, limited only by distance and the glass. Because cable costs little next to digging, routes are built with many more fibers than needed and the extras sit dark.
We lease a dark fiber pair between the two campuses and run our own DWDM on it, so upgrading is just a shelf swap.
Also heard as
- dark
- unlit fiber
Do not mix it up with
- Lit: Lit fiber already carries traffic from installed equipment; dark fiber is bare glass waiting for someone to light it.
Related terms
Lit
Describes a fiber that is carrying live traffic from active equipment, as opposed to dark.
Lambda
A single wavelength channel on a fiber, named after the Greek letter used for wavelength.
Cable plant
All the passive fiber infrastructure of a network: cable, splices, connectors, panels and closures.
WDM
Wavelength Division Multiplexing: sending several signals on different wavelengths over the same fiber.