Long distance transmission experiments using the WDM technology

The wavelength division multiplexed (WDM) technology is useful to utilize the vast bandwidth of the optical fiber, and it should be one key to overcome the transmission capacity problems of the future broadband communications such as multimedia services. Until the optical amplifiers were developed, only the short distance (up to a few tens kilometers) WDM system was in focus, because the optical repeaters for the WDM transmission were considered to be not practical. The advent of the optical amplifiers made it possible to construct the long distance (more than several hundreds kilometers) WDM systems, and many demonstrations of the long distance WDM transmission have been reported up to today. This paper describes the recent results of the long distance transmission experiments using the WDM technology. A few examples of the long distance transmission experiments using WDM technology is presented. As the four-wave mixing (FWM) is the substantial limiting factor of the WDM transmission, these system demonstrations adopt the method to reduce the FWM effect. The stability of the performance is another significant concern to design a practical system. Therefore, the experimental study of the WDM system stability is also discussed.