"100km VAD Single-Mode Optical Fiber" that contributed to the realization of the optical communication era
Registered in the National Museum of Nature and Science
[MIRAI Technology Heritage]

Nippon Telegraph and Telephone Corporation (Headquarters: Chiyoda-ku, Tokyo, President: Jun Sawada, hereinafter "NTT") that its"100km VAD Single-Mode Optical Fiber," a star entry in "NTT History Center of Technologies," has as, of September 1st 2021, has been designated by National Museum of Nature and Science as an "Essential Historical Materials for Science and Technology (short form: MIRAI Technology Heritage)."^*1 As the first technology to demonstrate the validity of the industrial-scale production of long, low-loss single-mode optical fiber, the vapor-phase axial deposition (VAD) method^*2 is of critical importance in terms of realizing the optical communication era.
※ Registration certificate and commemorative plaque award ceremony will be held at the National Science Museum on September 14, 2021.

1．Details of 100km VAD Single-Mode Optical Fiber

Current optical fibers that support most optical fiber communication, have a two-layer structure consisting of a core in the center through, which light passes, surrounded by a cladding.
　The most common approach to producing optical fiber starts with quartz glass as the raw material.
　Very fine particles of core and cladding are produced by flame hydrolysis. A columnar porous two-layer structure (base material) is formed continuously and fused at high temperature to make it transparent.
　Optical fiber is created by heating and stretching this base material.
　In the early 1970s, NTT began researching optical fiber manufacturing technology, as research and development activities began around the world in the latter half of the 1960s had shown the feasibility of glass optical fibers as a transmission medium for communications.
　Concurrently with the MCVD method and OVD method^*3 devised in the United States, NTT launched a joint research project with Furukawa Electric Co., Ltd., Sumitomo Electric Industries, Ltd., and Fujikura Ltd. to improve the MCVD method so that is was suitable for mass production and unique to Japan.
　In 1977, at the international conference "IOOC'77"^*4, the VAD method was announced as a truly innovative optical fiber manufacturing method unique to Japan with excellent mass productivity; it was evaluated very highly.
　Further research and development activities conducted after 1977 yielded the establishment of an optical fiber mass production process based on the VAD method.
　The result was a practical manufacturing method for ultra-low loss optical fiber^*5.
　The VAD method has several additional benefits such as easy enhancement and low loss of the optical fiber base material.
　It has become possible to manufacture optical fibers with extremely low transmission loss in long continuous lengths of 100 km or more without connection or seams.
　VAD has greatly contributed to the mass production of optical fibers with the attendant economy of scale.

100km long VAD single mode optical fiber

Reference: What is NTT History Center of Technologies?

The NTT HISTORY CENTER OF TECHNOLOGIES exhibits in timeline fashion a collection of historical assets of the NTT group, accumulated as the result of the group's development of telecommunications technologies with particular focus on the half-century since the foundation of the Nippon Telegraph and Telephone Public Corporation.
　It introduces more than 1,500 technical historical materials in two parts: "Tracing the History" and "Exploring the technologies".
　So far, the following technical historical materials have been registered with the "MIRAI technology Heritage".
　The NTT History Center of Technologies is open to the public for free visits. For details, please check the NTT History Center of Technologies website（http://www.hct.ecl.ntt.co.jp/）.

Glossary / Supplement