Back Reflection Images courtesy of Atlantic-Cable.com
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From Coaxial to Fibre Cables: Japanese Submarine Cables Part 2 Trans-Pacific Cable – 1 (TPC-1), the first transpacific submarine telephone cable, installed in 1964, provided 138 x 3kHz voice channels, which significantly improved the quality of telephone circuits between the US and Japan, and was a major contributory factor in the economic development of Japan at that time. However, the second transpacific submarine cable, TPC-2, connecting Hawaii, Guam and Okinawa, was not laid until over a decade later, in 1975. This added another 845 x 3kHz voice circuits to the existing Japan to US traffic. Over the next few years, in order to deal with the rapidly growing demand for international communications, an enormous amount of effort was expended by the Japanese industry as a whole in enhancing the bandwidth and voice circuit carrying capacity of coaxial cable systems. In the domestic market, Fujitsu and NEC Corp developed viable 36Mhz systems for NTT which provided 2,700 x 4kHz voice channels. This technology was first deployed in a shallow water system between Kure and Marsuyama, in 1971. The first deep water application was the Okinawa – Miyakojima system, installed in 1975. 36MHz technology was even commissioned by KDD for the Japan – Korea international system, which went into service in 1981. However, to achieve this transmission performance, repeater spacing was reduced to 2nm and so the power feed demands for such systems made the technology impracticable for transoceanic systems. In 1979, NTT commissioned from Fujitsu and NEC an experimental coaxial system (Sagami Bay No.4). This 15km cable loop contained 4 repeaters operating at 43.2MHz. It was able to provide 10,800 x 4kHz voice circuits but repeater spacing was reduced to 1.8nm. After this trail, in Japan as elsewhere, it was finally accepted
by Stewart Ash & Kaori Shikinaka
that for both domestic and international applications the technical and economic limits of submarine coaxial cables had been reached and an alternative technology was required. Building on the pioneering work of Dr Charles Kao and Dr George Hockham at STL, Harlow UK. Corning Inc., in 1970, succeeded in producing the first “lowloss” optical fibre that surpassed the less-than-20dB/km benchmark by achieving a transmission loss of just over 16dB/km. This milestone was the catalyst for the start of research and development into the use of optical fibre for telecommunications systems. Use of the technology for land applications advanced rapidly and by the late 1970’s serious consideration was being given to applying it to the more challenging environment of submarine cable systems. Development work started in France, Japan, UK and USA at almost the same time, so, for the first time, the Japanese industry was on a level playing field relative to its international competitors. The first experimental fibre optic submarine cable system deployed in Japan was a 50km cable loop between Inatori and Kawazu. The cable was supplied by OCC and contained 5 graded-index multimode fibres. There were no submerged repeaters and the system was laid for NTT by the cableship Tsugaru Maru. Terminal Transmission equipment was provided by both Fujitsu and NEC Corp. The system operated at 1,310nm and tests were carried out at bit rates of 6.3, 32 and 100 Mb/s. In 1981, NTT conducted the first sea trail of an optical regenerator using the cableship Tsugaru Maru; the trail system included a single regenerator repeater supplied jointly by Fujitsu and the NEC Corp. The first Japanese experimental systems containing repeaters were deployed in 1982 by both KDD and NTT. The KDD system comprised a 50km loop from
a single landing at Ninomiya, the loop contained two regenerating repeaters (one supplied by Fujitsu the other by NEC Corp). The system cable was supplied by OCC and contained 6 single-mode fibres. The cable was laid by the cableship KDD Maru. Terminal equipment was once again supplied by Fujitsu and NEC. The system operated at 1,310nm and a line rate of 300Mb/s providing the equivalent of 4,000 voice circuits. The repeaters were power by a 1.0A PFE on a double end feed basis. The NTT system comprised a 50km loop from a single landing at Yahatano, the loop contained two regenerating repeaters (one supplied by Fujitsu the other by NEC Corp). The system cable was supplied by OCC and contained 6 single-mode fibres. The cable was laid by the cableship Kuroshio Maru. Terminal equipment was once again supplied by Fujitsu and NEC. The system operated at 1,310nm and a line rate of 400Mb/s providing the equivalent of 2 x 5,760 voice circuits. The repeaters were power by a 1.0A PFE on a double end feed basis. In 1984, KDD conducted a deep water trail using the cableship KDD Maru. A 50km length of OCC cable containing 6 single mode fibres also included two regenerating repeaters. This mini-system was deployed and recovered from a water depth of 7,000m. The Fujitsu and NEC Corp supplied repeater designs were 280Mb/s operating at 1,310nm with a transmission speed of 295.6mBaud and a Line Code of 24B1P. The system was powered by a 1.6A PFE on a single end basis. This design was to form the basis of the first generation of international commercial fibre optic submarine systems. With this final trail the Japanese industry was perfectly placed to address what would effectively be a brand new market for submarine cable systems that would emerge in the next few years.