NEW YORK, Aug. 9 -- Metromedia Fiber Network Inc. has launched intracity dark fiber networks in the metropolitan areas of Chicago, Dallas and Washington, D.C. Dark fiber networks are comprised of fiber-optic cable that has no signal or light passing through it. Metromedia Fiber leases individual dark fiber strands to organizations that attach their own transmissions and receiving equipment to the fibers, providing these customers with the flexibility to deploy a wide range of telecommunications technologies.With these three networks joining the company's existing networks in New York and Philadelphia, Metromedia Fiber now provides dark fiber infrastructure in five of the nation's 15 largest cities. The company is in the process of constructing networks in six additional US metropolitan areas as well as in Canada and Europe.