MORRISTOWN, N.J., March 4 -- Researchers from Tyco Telecommunications have investigated the potential transmission capacity from an undersea transmission system by increasing the repeater spacing threefold from typical values of 40-50 km up to 120 km, which the company said substantially reduces costs.
   Tyco announced at OFC 2004 that is has used well-established techniques for sending and receiving wavelength division multiplexing (WDM) data channels to demonstrate that sixty-four 10 Gbit/s WDM channels can be supported over a distance of 4800 km. The company said this result shows that a transmission capacity of 640 Gbit/s on a single fiber can be achieved.
   "Recently, the priorities for system suppliers and purchasers in the undersea telecommunication industry have changed dramatically," Tyco said in a statement. "Emphasis has shifted away from the cost per bit when the system is equipped with its maximum transmission capacity toward lowest possible cost when the system is initially installed. The resulting design tradeoff is lower initial cost vs. higher ultimate capacity."
   One of the most practical ways to reduce the initial cost of an undersea cable system is to minimize the cost and number of the undersea repeaters that are used to periodically compensate for the loss of the transmission fiber as the data signals propagate through the cable, Tyco said. The distance between repeaters has typically been in the 40-50 km range for long transoceanic systems.