Development of ultra-large capacity optical undersea cable system based on wavelength-division-multiplexing

Commercial optical undersea cables using the developed technologies

Fig.1 Commercial optical undersea cables using the developed technologies

  According as the worldwide spread of broadband services, the importance of optical undersea cable systems becomes significant as a basic international communication infrastructure to accommodate the rapidly growing traffic with ultra large capacity among the countries. In past two decades, there were three big technical breakthroughs in transoceanic undersea cable systems. The first is the introduction of the optical fiber in the trans-pacific undersea cable system, the second is the adoption of optical amplifier (EDFA)-based repeaters, and the last one is the introduction of the wavelength multiplexing (WDM) technologies with high-speed optical signals. With latest technologies, capacity per fiber pair was increased up to 1 Tera bit/s for undersea cable systems.

  The optical amplifier (EDFA)-based repeaters were first introduced in TPC-5 (Transpacific Cable No.5) in 1995, which enabled 8-fold increase in the system capacity compared to the previous systems using conventional repeaters based on the 3R-regenerator. Optical amplifier systems have many attractive features, such as the reduction of the size, power consumption and cost of the repeaters. On the other hand, the chromatic dispersion and nonlinear effects accumulate along the distance in optically-amplified repeater systems. Therefore, in the conventional undersea cable systems, relatively low-speed signals of 2.5G bit/s had to use to avoid the influence of these accumulated effects and total system capacity was limited to 20 Gbit/s. To increase the speed of the optical signals up to 10 Gbits/s, new system scheme mitigating these accumulated effects was required.

  Masatoshi Suzuki, Noboru Edagawa, and Yuichi Matsushima started the research on WDM undersea cable systems using high-speed optical signals since early ninetieth and have succeeded in the development of the world-first undersea cable system with high-speed optical signals of 10 Gbit/s. The newly developed scheme has been widely employed in recent large-capacity undersea cable systems. They greatly contributed the realization of 160 Gbit/s transpacific and transatlantic cable systems, and Asian cables with ultra-large capacity of 640 Gbit/s and 960 Gbit/s.

  Masatoshi Suzuki developed the 10 Gbit/s chirped Return-to-Zero (RZ) optical transmitter in order to alleviate increasing impact of fiber nonlinearity. Noboru Edagawa mainly contributed to the development of the hybrid fiber configuration within each repeater span, a fiber with large core fiber and non-zero dispersion-shifted fiber with reduced dispersion slope, which could minimize the accumulated chromatic dispersion and fiber nonlinear effects. Yuichi Matsushima realized the reliable 980 nm pumping laser diode for low-noise optical amplifiers.

  After developing the optical high-speed transmitter, the low-nonlinear fiber span, and the low-noise optical amplifiers, they confirmed the feasibility of 160 Gbiy/s (10 Gbit/s, 16WDM) over 10,000 km transmission and conducted long-term stability tests using a large-scale test-bed. Eventually, the developed transmission scheme was applied to many transoceanic undersea cable systems both in Pacific Ocean (>9000 km) and Atlantic Ocean (>7500 km), such as Japan-US cable, PC-1 cable and TAT-14 cable. For Asia cable systems with about 3000 km systems length, higher capacity up to 960 Gbit/s was applied since the accumulation of the dispersion and the nonlinear effect was relatively small.

  As described above, they developed totally new system design of ultra-large capacity undersea cable system and the scheme was adopted to many commercial undersea cable systems worldwide. They greatly contributed to the realization of recent global optical networks.

  For these contributions, IEICE gave the achievement Award to Masatoshi Suzuki, Noboru Edagawa, and Yuichi Matsushima in 2004.



Publications

[1] M. Suzuki et al.、170 Gb/s transmissin over 10,850 km using large core transmission fiber、1998、Proceedings of Optical Fiber Communication Conference OFC'98, San Jose, California, PD17, February 1998
[2] Shu Yamamoto and Masatoshi Suzuki、Research and development of international optical submarine cable system using optical amplifiers、1998、IEICE, Vol.81, No.12, pp.1195-1217, 1998
[3] Masatoshi Suzuki and Noburu Edagawa、Dispersion-managed high-capacity ultra-long-haul transmission、2003、IEEE Journal of Lightwave Technology, Vol.21, pp.916-929, April 2003

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