Site: Nippon Telegraph and Telephone Corporation
Optical Network Systems Laboratory
Y-808A 1-2356 Take Yokosuka
Kanagawa 238-03 Japan
Date Visited: November 17, 1994

Report Author: S. Esener



S. Esener
D. Keck


Dr. T. Matsumoto
Executive Research Engineer, Project Leader, Optical Network Systems Lab
T. Sakano
Research Engineer, Photonics Signal Processing Research Group
K. Inoue
Senior Research Engineer, Photonics Signal Processing Research Group
Hisao Yoshinaga
Research Engineer, Broadband Transmission Research Group


In 1944, there were 1 million telephone subscribers in Japan. By the end of the war, that number had been reduced to 400,000. NTT was established to reconstruct the Japanese telecommunication facilities and to develop the required technology for domestic use and production. Between 1966 and 1980, NTT went through an age of growth, introducing new communication services, and the number of subscribers exceeded 10 million by 1968. From 1981 to 1990, NTT became a world class competitor, with many of its technologies, including its optical communication technologies, being used throughout the world. In 1985, NTT was converted into a private corporation. Its R&D activities strengthened in the areas of original software development and LSI. The results constitute the technical base for a network reform for the coming information communication age. Since 1991, NTT has entered an era of cooperation, with R&D results that lead the world and are used throughout the world. For example, in 1991, NTT succeeded in demonstrating optical transmission over 1,260 km at 10 Gbit/s under actual field conditions. [See NTT/Atsugi site report starting on p. 285 for further general background information on NTT.] NTT R&D centers are grouped in one department and 3 lab groups where a total of 3,000 researchers are involved:

These groups consist of a total of 13 labs distributed in seven locations near Tokyo and one additional in Kyoto. The Yokosuka facility that this JTEC team visited employs 1,250 researchers. The facility hosts, in addition to NTT, subsidiaries such as NTT DoCoMo, which specializes in wireless communication.

The team visited the Optical Network Systems Laboratory, one of the 5 labs of the Telecommunication Network Laboratory group. It has 230 researchers, of whom 10% have PhD degrees, 75% have MS degrees, 10% have BS degrees, and 5% are high school graduates. The Optical Network Systems Laboratory, headed by Dr. T. Miki, consists of 4 labs: the Lightwave Communication Lab, the Transport Processing Lab, the Optical Subscriber Network Lab, and the Kanaya Research Lab, in addition to the Project Team 1 lead by Dr. T. Matsumoto, our host. Project Team 1 is subdivided into three groups: the Photonic Networks, Photonic Transmission, and Photonic Signal Processing Groups.


The role of NTT's Optical Network Systems Laboratory is to research and develop communication systems and related fundamental and application technologies. Some technologies developed are supplied to manufacturing companies. Competition among the companies brings cost reductions in components and systems.

Joint work between system and device labs within NTT is put in place with a proposal of a new system or device. Demonstration of the system is carried out under the cooperation with the labs. The system labs use devices from NTT labs as well as those bought from other companies.

Originally, NTT was not set up to manufacture; it used to buy from other Japanese companies. In 1985, NTT became a private company. It now has several subsidiaries, such as NEL, which fabricates LSIs, active OE components, and passive couplers. Competition between the subsidiaries is possible. There are several Japanese competitors in the area of communications.

In general, telecom companies in Japan expand their business independently of funding from the government. Electric companies supply systems and components to the telecom companies. In order to get feedback from its clients, NTT establishes pilot projects. For example, in Kansai an experiment involving 250 homes is being carried out that provides them with an optical access network. The official goal is to provide every home in Japan access to such a network by 2015. The network will provide broadband services such as high-speed data, multimedia, and video, in addition to conventional telephone services by employing optical cable via service nodes.

The main difference between Japan and the United States in this respect is that the United States has already a well-developed coaxial cable TV distribution network; it may be cheaper for the United States to use this network in a hybrid form with analog fiber optics. In Japan, the coax network is not extensive, and it may be as economical to adopt a fully digital system, with the fiber reaching all the way through the home.

In terms of the evolution of such a network, NTT sees the role of analog networks decreasing as the network size increases beyond 50 million users, and it sees an evolution in digital networks from N-ISDN to ATM to B-ISDN as the number of users approaches 80 million by the year 2010. Presently, B-ISDN is simply too costly to deploy. However, in the Transport Processing Lab several kinds of key technologies for B-ISDN are an advanced stage of R&D, including ATM transmission and cross-connect, circuits for network interfaces, massively parallel signal processing for super high-definition images, and advanced software for network operation.


The JTEC panel saw several accomplishments in the area of free-space optical interconnects, optical transmission experiments, and a demonstration room describing how optical access networks may affect homes. The demonstration was similar to the Kansai experiment.

On the free-space interconnects, T. Sakano demonstrated three systems: the COSINE-1 system dating from 1990 with a manually reconfigurable free space optical switch operating with LEDs, where optical alignment requirements were carefully analyzed; the COSINE-2 multiprocessor system that uses an automatically rearrangeable free space switch dating from 1992; and the more recent COSINE-3, 3-D mesh multiprocessor system using board-to-board free-space interconnects. In addition the JTEC team saw a rearrangeable 128 x 128 multistage network optical switch based on a liquid crystal light modulator array. In all cases, major emphasis was put on the packaging aspect of the prototypes.

On the transmission experiment, K. Inoue showed a 20 Gbit/s experiment with multimedia capability.

Finally, in the demonstration room H. Yoshinaga demonstrated and discussed further the benefits of an optical access network by showing a piano lesson where the student and the teacher are in visual contact via a high-definition TV remote link.

Published: February 1996; WTEC Hyper-Librarian