ABSTRACT
In the relatively short history of optical communication, only a little over two decades, we appear to have made impressive progress. Even today, higher data rates and longer repeaterless transmission distances continue to set new records. In the current digital trends, digital communication has become the dominant mode for information exchange, even though optical fiber communication (OFC) continues to experience technical difficulties and technological immaturity. Some of the difficulties are inherent and something that we may have to live with for many years or forever. Nevertheless, in the digital world and in comparison with electronic cable systems, OFC’s progress is indeed impressive. The electronic cable’s economical transmission speed is around 10 Mb/s (or MHz) and transmission distance is around 10 km. Therefore, the bandwidth distance product is 0.1 GHz·km. On the other hand, OFC’s speed has exceeded 10 Gb/s, and repeaterless distances over 100 km have been achieved. The bandwidth distance product is thus 1000 GHz·km or 1 THz·km, a very impressive improvement of four orders of magnitude. OFC’s strength is high speed and low media loss. Its weaknesses are its inherent optical nonlinear modulation, large frequency shift (FM) associated with AM (more accurately IM, intensity modulation), and the fiber’s dispersion, which to a large extent is inherent. Also, until recently, because of lack of suitable optical amplifiers, all-optical long-distance communications and multiple-port data distributions have been difficult and not 378economical. OFC’s reputation and success have thus been in point-to-point high-speed transmission, such as telephone and computer network trunk lines and transoceanic undersea telephone lines. The mode of operation is still similar to that of the cable system. At a predetermined distance, the data stream is regenerated electronically at a repeater station. The data management, such as congregating 64-kb phone calls into a high-speed data stream and switching each call to the right destination, is done by computers at the exchange stations. Therefore, the success of OFC is the result of the indispensable and sophisticated electronic computer support. OFC itself has been playing only a passive and supporting, albeit important role in the complex communication system. The current computer network is basically formed by connecting many computers (servers, bridges, or gateways) at different locations into a mesh with most data links still operating at relatively low speed. Some high-speed trunks have been and/or are now being deployed. The success of current computer networks is again due to the computer’s role in intelligently routing data packets to the right destinations. At a steady 1 Gb/s, only supercomputers can handle and route the data. Clearly, replacing all copper cables with high-speed fiber link will not improve a computer network’s throughput proportionally. This is known as the electronic bottleneck. Apparently, OFC’s success has pushed the power of electronic computers to their limits. The speed mismatch between OFC and the computer will continue to widen. One possible solution is to use an all-optical computer network.
