Optical Fiber Telecommunication Submarine Cables

The first major submarine cables using optical amplification technology, TAT 12 and TAT 13, were deployed in 1995 and 1996 between Europe and the United States, transmitting a modulated wavelength of 5 Gb/s per fiber. In 20 years, transmission capacity has increased 2,000-fold, reaching 10 Tb/s per fiber in 2015, thanks to the following successive technological developments:

• the introduction of wavelength multiplexing. In 1999, the Columbus 3 cable linking Portugal to the United States over a distance of 7,340 km was commissioned; it transmits 8 wavelengths modulated at 2.5 Gb/s, offering a capacity of 20 Gb/s per fiber on an 8 nm optical band;

• increased throughput (10 Gb/s) per wavelength and extension of the optical repeater band to 32 nm. The Apollo transatlantic link (6,600 km), commissioned in February 2003, is designed to transmit 80 wavelengths modulated at 10 Gb/s, giving a total capacity of 800 Gb/s per fiber;

• polarization multiplexing combined with coherent detection and digital signal processing, starting in 2012. The America Movil AMX-1 cable (6,670 km) linking Brazil to the United States is designed to transmit 100 wavelengths modulated at 100 Gb/s, giving a total capacity of 10 Tb/s per fiber pair; it will be commissioned in 2014.

Although similar to terrestrial links in terms of transmission capacity, the design of submarine links must take into account very specific constraints such as :

• transmission distances of up to 12,000 km;

• repeater reliability, with a failure rate of less than 1% over the lifetime of the link, i.e. 25 years;

• compatibility with very high voltages: repeaters are supplied with direct current (~ 1 A) from terrestrial end stations, which means that, for long links, voltages of up to 15 kV must be carried, since cable resistivity varies between 1 and 1.6 Ω ;

• watertightness, but also to gases such as hydrogen;

• pressure resistance up to 800 bar;

• resistance to stress, particularly when repairing cables at a depth of 8,000 m.

We'll also look at marine operations such as route marking, silo installation and subsea link repair.

The last section is dedicated to transponderless submarine links, whose design calls on specific amplification technologies such as remote erbium amplification or distributed Raman amplification.