Duplicating light beams in fiber optics allows clearer signal

BBC : Signals sent over fiber-optic cables collect noise as they travel: The farther a signal travels, the noisier it becomes. Now, Xiang Liu of Bell Laboratories and his colleagues have demonstrated a way to increase both the speed and the distance that a fiber-optic signal can travel and still maintain its clarity. They duplicated a signal and sent the pair of light beams down a cable. At the end of the cable, when the two signals were recombined, the parts of one of the signals that were disrupted by noise were overwritten by the unchanged parts of the other signal. The overwriting technique allows for the removal of signal repeaters, which are used in fiber optics to extend the distance a signal can travel but which tend to limit the power and speed of the data transmission. Liu’s test setup used a 12 800-km-long fiber-optic cableâmdash;longer than the longest transoceanic cableâmdash;and reached speeds of 400 Gb/s, four times the speed of the best commercial cable systems.