![]() ![]() However, germanium doping is not preferred due to purity concerns. In conventional optical fibers, germanium is doped to increase the refractive index of the core. For propagating light in the core, a refractive index difference between the core and cladding is necessary. Optical fiber has a double-layered structure, consisting of a core, which is the pathway for light, and the cladding around it. In the mid-1980s, low-loss, high-strength optical fiber was realized through the wholly-synthesized VAD method, and was introduced in the trans-Pacific submarine optical cable (TPC-3), which came into service in 1989.įor all optical fiber engineers, low transmission loss presented the ultimate challenge. With the wholly-synthesized VAD method, the preform size could be increased dramatically, leading to an expected improvement in productivity. Sumitomo Electric took on the wholly-synthesized VAD method, in which a glass layer is synthesized around the dehydrated and transparent preform by another cycle of the VAD process. The stage was now set for the unfolding of fierce competition among manufacturers. Sumitomo Electric’s World-class Technology and Know-how Light up the Seafloor The VAD method developed in Japan has today spread around the world and was even recognized as an internationally prestigious IEEE Milestone in 2015. In addition to Sumitomo Electric, nearly 60% of the world's optical fiber preforms are manufactured using the VAD method now. Sumitomo Electric engineers continued to take up new challenges in fiber optics after the expiration of the joint research agreement in 1983, and VAD technologies remain the foundation of Sumitomo Electric's optical fiber technology to this day. In 1981, when the commercialization of optical fibers and cables was first witnessed, Sumitomo Electric established the Fiber Optics Development Division, which was renamed the Fiber Optics Division in 1984. The culmination of the joint research’s achievements was the construction of a trans-Japan fiber optic trunk line connecting Asahikawa and Kagoshima from 1983. Although the technical challenge was significant due to having a thinner core than that of GI fiber, the VAD method came to surpass other methods in terms of both its properties and productivity as a SM fiber manufacturing method, thanks to the results of various innovations including the improved structure of a soot depositing burner for stable growth of the thin core. A transmission system using GI fiber* 1 developed as a result of this was then adopted in 1982 for actual use following commercial testing in 1980.ĭevelopment of SM fiber* 2 using the VAD method was then advanced in anticipation of the future need for high-capacity, long-distance transmissions. As such, the joint research team laid the foundation for fiber optic communications in Japan.Īfter 1978, improvements in dehydration techniques for the VAD method brought rapid progress to the development of low-loss optical fibers. The members of the joint research team worked day and night to solve these problems, leading to an important first step toward the completion of the VAD method. Many difficulties were encountered in the early days, including deformation or cracks in the porous preform during deposition and the formation of bubbles during the transparency process. The porous preform becomes a transparent glass preform through processes of high purification by heating in a dehydrating gaseous atmosphere, and then making transparent by heating at even higher temperatures. ![]() As the porous preform can be grown in the axial direction by lifting the starting material upward, large preforms are capable of being fabricated. VAD is a method in which gaseous glass material is fed into an oxyhydrogen burner, at which point the generated fine glass particles (soot) are deposited on the tip of the starting material to produce a porous preform. The key to the mass production of optical fibers was how best to manufacture a sufficiently large preform. To promote the widespread adoption of optical fibers, a manufacturing method suitable for mass production was necessary as well as for ensuring low transmission loss. Optical fiber is made by fabricating a preform consisting of a cylindrical block of glass, and then heating and melting it, to draw it out into thin threads. Through their research, they developed the VAD method, an original Japanese preform manufacturing technique. In 1975, Nippon Telegraph and Telephone Public Corporation (now NTT), Sumitomo Electric, and two other cable manufacturers established a joint optical fiber research team. Sumitomo Electric Begins Developing Optical Fibers in Earnestīirth of the Foundation of Optical Fiber Technology ![]()
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