Broadband Optical Access Technologies and FTTH Deployment in NTT

The NTT access network encompasses NTT central offices and customer terminals and networks, and consists of transmission devices for individual customers in each NTT central office, transmission lines, and corresponding devices on the customers’ premises. Unlike trunk relay lines between NTT central offices, access networks are not designed to carry concentrated communication traffic. Since cost reduction strategies such as multiplexing and task splitting cannot be employed, it is important that the component parts are as inexpensive as possible. Providing an access network for ordinary customers that covers the length and breadth of the nation represents an enormous undertaking. For instance, the process of upgrading facilities to alleviate congestion in telephone services necessitated a substantial 20-year investment program that started in the 1950s, when NTT was known as the Nippon Telegraph and Telephone Public Corporation. Given the scale of the task, it is especially important to develop simple, well-designed technologies and systems for the construction, operation, and maintenance of the access network. The transmission characteristics of the access network have a direct bearing on service provision. Equipment and system designs must strike an appropriate balance between the need to keep costs down at the initial stage and the need for the scalability and flexibility to accommodate the future diversification and modernization of the services. Thus, the access network is governed by a wide range of conditions and a different level of requirements. Much is expected from NTT’s optical technology research program, which began with the trunk network. In particular, it is hoped that the optical