Coherent optical detection: A thousand calls on one circuit: Dazzling applications for both long-distance and local networks are in the offing as experimental systems adapt long-successful radio techniques

Coherent detection of laser signals may well turn out to be the next great advance in optical communications. The technology is looking ever more promising. Just over a year ago experimental coherent-detection systems surpassed the performance of those based on conventional, direct-detection fiber-optic transmitters and receivers. Since then, laboratories around the world have been reporting coherent transmission at increasing bit rates over longer distances.