The prospect of increasing the carrying capacity of under sea fibre optic cables 100-fold is held out by work being done at AT&T Co’s Bell Laboratories. According to the Wall Street Journal, scientists at the Murray Hill, New Jersey lab are using a new filtering technique to achieve the large gains in capacity, and say they have succeeded in transmitting signals error-free over 8,125 miles at 20 Gbps, double the previous record for long-distance transmission. The transmissions use those soliton waves we told you about way back in summer 1990 (CI No 1,459), which are electronically induced and never lose their shape as they whiz through optical glass fibre, so that signalling errors are all but non-existent, obviating the need for costly error-correction equipment, which also slows down transmission. The highest-capacity undersea system now in use is capable of carrying 80,000 concurrent phone conversations where a 20Gbps system could carry 8m concurrent calls. The test was done using a 16-mile loop of glass fibre, lasers, amplifiers and filters to prove that solitons can provide the key to future ultra-high capacity transmission. The team started with an existing 2.5Gbps and used time-division multiplexing to up the capacity of 10Gbps, and then used wavelength division multiplexing to double capacity again to the full 20Gbps speed. The system uses a sliding frequency guiding filter to regulate the speed of the soliton waves. Bell Labs acknowledges that it is in competition with the likes of British Telecommunications Plc and Nippon Telegraph & Telephone Corp to perfect the technology.
