Any fiber-optic cabling or fiber device such as a repeater that is installed but not currently in use. Since no light is being transmitted through the cabling, it is called “dark.” The term “dark fiber” is not generally used to refer to a problem in the fiber-optic cabling system; it simply means that the fiber media and components are waiting to be used.
However, various problems can occur in a fiber-optic cabling system that can cause it to remain dark once the system is turned on. These can include the following:
Before dark fiber is activated, the system is usually tested using an optical time domain reflectometer (which measures and analyzes a fiber link) and other measuring devices to determine whether the system has integrity, and to measure its bandwidth and attenuation parameters.