What Is Dark Fiber

For capacity expansionOne reason that dark fiber exists in well-planned networks is that much of the cost of installing cables is in the civil engineering work required. This includes planning and routing, obtaining permissions, creating ducts and channels for the cables, and finally installation and connection. This work usually accounts for more than 60% of the cost of developing fiber networks. For example, in Amsterdam's city-wide installation of a fiber network, roughly 80% of the costs involved were labor, with only 10% being fibre. It therefore makes sense to plan for, and install, significantly more fiber than is needed for current demand, to provide for future expansion and provide for network redundancy in case any of the cables fail.Many fiber optic cable owners such as railroads or power utilities have always added additional fibers for lease to other carriers.

In common vernacular, dark fiber may sometimes still be called "dark" if it has been lit by a fiber lessee and not the cable's owner.OvercapacityIn the dot-com bubble, a large number of telephone companies built optical fiber networks, each with the business plan of cornering the market in telecommunications by providing a network with sufficient capacity to take all existing and forecast traffic for the entire region served. This was based on the assumption that telecoms traffic, particularly data traffic, would continue to grow exponentially for the foreseeable future

The availability of wavelength-division multiplexing further reduced the demand for fiber by increasing the capacity that could be placed on a single fiber by a factor of as much as 100. As a result, the wholesale price of data traffic collapsed. A number of these companies filed for bankruptcy protection as a result. Global Crossing and Worldcom are two high profile examples.Just as with the Railway Mania, the misfortune of one market sector became the good fortune of another, and this overcapacity created a new telecommunications market sector.

MarketFor many years incumbent local exchange carriers would not sell dark fiber to end users, because they believed selling access to this core asset would cannibalize their other, more lucrative services. Incumbent carriers in the US were required to sell dark fiber to competitive local exchange carriers as Unbundled Network Elements (UNE), but they have successfully lobbied to reduce these provisions for existing fiber, and eliminated it completely for new fiber placed for fibre to the premises (FTTP) deploymentsCompetitive local carriers were not required to sell dark fiber, and many do not, although fiber swaps between competitive carriers are quite common. This increases the reach of their networks in places where their competitor has a presence, in exchange for provision of fiber capacity on places where that competitor has no presence. This is a practice known in the industry as "coopetition".

Meanwhile, other companies arose specializing as dark fiber providers. Dark fiber became more available when there was enormous overcapacity after the boom years of the late 1990s through 2001. The market for dark fiber tightened up with the return of capital investment to light up existing fiber, and with mergers and acquisitions resulting in consolidation of dark fiber providers.

Dark fiber capacity is typically used by network operators to build SONET and dense wavelength division multiplexing (DWDM) networks, usually involving meshes of self-healing rings. Now, it is also used by end-user enterprises to expand Ethernet local area networks, especially since the adoption of IEEE standards for Gigabit Ethernet and 10 Gigabit Ethernet over single-mode optical fiber. Running Ethernet networks between geographically separated buildings is a practice known as "WAN elimination".