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Un '''câble sous-marin''' est un câble posé sur le fond marin, ou ensouillé à faible profondeur, destiné à acheminer des communications ou à transporter de l'énergie électrique.

Les câbles sous-marins sont mis en place et maintenus par des navires câbliers, après reconnaissance bathymétrique pour repérer le trajet idéal (le plus court, mais sans risque pour le câble) ; par faibles profondeurs, et lorsque la nature du fond le permet, les câbles sont généralement ensouillés à l'aide d'un système ressemblant à une charrue : ceci permet de minimiser les risques de dommages, notamment par les chalutiers.

== Transport d'énergie ==
Des câbles sous-marins peuvent relier des îles au continent, ou interconnecter des réseaux distincts ; ils sont aussi utilisés pour acheminer l'électricité produite dans les parcs éoliens en  mer (« parcs ''offshore'' »). Ces câbles permettent de transporter l'énergie (courant alternatif ou continu) sous des tensions comprises entre  et plus de  ; ils comportent généralement une ou plusieurs fibres optiques permettant la transmission simultanée d'informations d'exploitation (parcs éoliens) ou de télécommunications.

== Communications ==
thumb|Coupe d'un cable sous-marin de communication
Les câbles de communication sous-marins servent à acheminer des communications téléphoniques, ou à interconnecter des réseaux informatiques (internet) ; traditionnellement composés de câbles coaxiaux, ils contiennent désormais le plus souvent des fibres optiques,  Pour compenser l'atténuation progressive des signaux, des répéteurs peuvent être implantés à intervalles réguliers.

Les premiers câbles de communication sous-marins ont été des câbles destinés au fibres optiques pour transporter des charges utiles, qui sont ensuite utilisées pour transporter aussi bien le trafic téléphonique qu'informatique (internet) et des réseaux privés.

En câbles sous-marins relient tous les continents, à l'exception de l'Antarctique.

=== Les câbles transatlantiques ===

thumb|upright=2.0|Carte du câble télégraphique transatlantique de 1858

Un ''câble transatlantique'' est un câble de télécommunication reliant l'Europe à l'Amérique.

==== Caractéristiques du 1 câble transatlantique ====

* 3 200 km de distance
* 4 200 km de câble d’un poids de 7 000 tonnes.
 
* Une toron de sept fils de cuivre pur gainé de trois couches de gutta-percha (12,2 mm de diamètre)
* Une mince couche de toile goudronnée armée de 18 torons formés chacun de 7 fils de fer
* Départ en Europe : irlandaise de 11 km de long
* Départ en Amérique : Trinity Bay au Canada
* La maintenance s'effectue par relevage du câble
* Vitesse de transmission en morse : 2,75 mots par minute.

right|thumb|300px|A [[cross-section of a submarine communications cable.<br />
1. Polyethylene.<br />
2. "Mylar" tape.<br />
3. Stranded steel wires.<br />
4. Aluminum water barrier.<br />
5. Polycarbonate.<br />
6. Copper or aluminum tube.<br />
7. Petroleum jelly.<br />
8. Optical fibers.]]
thumb|250px|Submarine cables are laid using special [[cable layer ships, such as the modern ''René Descartes'', operated by France Télécom Marine.]]

A '''submarine communications cable''' is a cable laid beneath the sea to carry telecommunications between countries.

The first submarine communications cables carried telephony traffic, then fibre optic technology to carry digital payloads, which are then used to carry telephone traffic as well as Internet and private data traffic. They are typically 69 mm in diameter and weigh around 10 kg per meter, although thinner and lighter cables are used for deep water sections.<ref>http://image.guardian.co.uk/sys-images/Technology/Pix/pictures/2008/02/01/SeaCableHi.jpg</ref>

As of 2003, submarine cables link all the world's continents except Antarctica.

==History==
===Trials===
After telegraph in 1839, the idea of a submarine line across the insulator to cover the wire and prevent the electric current from leaking into the water was necessary for the success of a long submarine line. India rubber had been tried by Moritz von Jacobi, the Prussian electrical engineer, as far back as the early 1800s.

Another insulating gum which could be melted by heat and readily applied to wire made its appearance in 1842.  Scottish surgeon in the service of the Deutz and South Eastern Railway, submerged a wire coated with it, or, as it is technically called, a gutta-percha core, along the coast off Dover.

===The first commercial cables===
In August 1850, concession, and the next year, on hulk, the ''Blazer'', which was towed across the Channel. The next year, Great Britain and Ireland were linked together. In 1852, a cable laid by the Submarine Telegraph Company linked London to Paris for the first time. In May, 1853, England was joined to the Netherlands by a cable across the North Sea, from Orford Ness to The Hague. It was laid by the ''Monarch'', a paddle steamer which had been fitted for the work.

===Transatlantic telegraph cable===

The first attempt at laying a transatlantic telegraph cable was promoted by Cyrus West Field, who persuaded British industrialists to fund and lay one in 1858. However, the technology of the day was not capable of supporting the project, it was plagued with problems from the outset, and was in operation for only a month. Subsequent attempts in 1865 and 1866 with the world's largest steamship, the SS Great Eastern, used a more advanced technology and produced the first successful transatlantic cable. The Great Eastern later went on to lay the first cable to India in 1870.

===Cable to India, Singapore, Far East and Australasia===
An 1863 cable to  Frontpage | Third cable cut, but India’s safe<!-- Bot generated title -->]</ref> In 1870 Bombay was linked to London via submarine cable in a combined operation by four cable companies, at the behest of the British Government. In 1872 these four companies were combined to form the mammoth globespanning [[Cable & Wireless#History|Eastern Telegraph Company, owned by John Pender. A spin-off from Eastern Telegraph Company was a second sister company, the Eastern Extension, China and Australasia Telegraph Company, commonly known simply as "the Extension".

===Submarine cable across the Pacific===
This was completed in 1902&ndash;03, linking the US mainland to Hawaii in 1902 and Guam to the Philippines in 1903.<ref>[http://www.brainyhistory.com/events/1903/july_4_1903_69271.html Pacific Cable (SF, Hawaii, Guam, Phil) opens, President TR sends message July 4 in History<!-- Bot generated title -->]</ref> Canada, Australia, New Zealand and Fiji were also linked in 1902.<ref>[http://geo.international.gc.ca/asia/australia/relations/history-en.asp Australia :: Canada-Australia Relations :: History<!-- Bot generated title -->]</ref>

The North Pacific Cable system was the first laser regenerative (repeatered) system to completely cross the Pacific from the US mainland to Japan. The US portion of NPC was manufactured in Portland Oregon in 1990 at STC Submarine Systems, and later Alcatel Submarine Networks (the plant was shutdown in 2001). The system was laid by Cable & Wireless Marine on the CS Cable Venture in 1991.

===Construction===
Transatlantic cables of the 19th century consisted of an outer layer of iron and later steel wire, wrapping India rubber, wrapping gutta-percha, which surrounded a multi-stranded copper wire at the core. The portions closest to each shore landing had additional protective armor wires. Gutta-percha, a natural polymer similar to rubber, had nearly ideal properties for insulating submarine cables, with the exception of a rather high dielectric constant which made cable capacitance high. Gutta-percha was not replaced as a cable insulation until polyethylene was introduced in the 1930s.  In the 1920s, the American military experimented with rubber-insulated cables as an alternative to gutta-percha, since American interests controlled significant supplies of rubber but no gutta-percha manufacturers.

===Bandwidth problems===
Early long-distance submarine telegraph cables exhibited formidable electrical problems. Unlike modern cables, the technology of the 19th century did not allow for in-line bandwidth<!-- this is not quite right, because 'bandwidth' in this context means bit rate. -->.

As early as 1823, earth (or water) surrounding it. Faraday had noted that when a wire is charged from a battery (for example when pressing a telegraph key), the signal travels through the conductor of the cable. 

Early cable designs failed to analyze these effects correctly. Famously, E.O.W. Whitehouse had dismissed the problems and insisted that a transatlantic cable was feasible. When he subsequently became electrician of the Atlantic Telegraph Company he became involved in a public dispute with William Thomson. Whitehouse believed that, with enough voltage, any cable could be driven. Because of the excessive voltages recommended by Whitehouse, Cyrus West Field's first transatlantic cable never worked reliably, and eventually short circuited to the ocean when Whitehouse increased the voltage beyond the cable design limit.

Thomson designed a complex electric-field generator that minimized current by resonating the cable, and a sensitive light-beam early polar expeditions.
 	
Thomson had produced a mathematical analysis of propagation of electrical signals into telegraph cables based on their capacitance and resistance, but since long submarine cables operated at slow rates, he did not include the effects of inductance. By the 1890s, Oliver Heaviside had produced the modern general form of the telegrapher's equations which included the effects of inductance and which were essential to extending the theory of transmission lines to higher frequencies required for high-speed data and voice.

===Transatlantic telephony===
thumb|left|Five submarine communication cables crossing the Scottish shore at Scad Head on [[Hoy, Orkney.]]
While laying a transatlantic telephone cable was seriously considered from the 1920s, a number of technological advances were required for cost-efficient telecommunications that did not arrive until the 1940s. A first attempt to lay a pupinized telephone cable failed in the early 1930s due to the Great Depression.

In 1942, Siemens Brothers of Charlton, London in conjunction with the National Physical Laboratory, adapted submarine communications cable technology to create the world's first submarine oil pipeline in Operation Pluto during World War II.

TAT-1 (Transatlantic No. 1) was the first transatlantic telephone cable system. Between 1955 and 1956, cable was laid between Gallanach Bay, near Oban, Scotland and Clarenville, Newfoundland and Labrador. It was inaugurated on September 25, 1956, initially carrying 36 telephone channels.

In the 1960s, transoceanic cables were frequency-multiplexed voiceband signals. A high voltage direct current on the inner conductor powered the repeaters. The first-generation repeaters are among the most reliable vacuum tube amplifiers ever designed.<ref>. From this page: In 1966, after ten years of service, the 1608 tubes in the repeaters had not suffered a single failure. In fact, more than 100 million tube hours over all AT&T undersea repeaters were without failure.</ref> Later ones were transistorized. Many of these cables are still usable, but abandoned because their capacity is too small to be commercially viable. Some have been used as scientific instruments to measure earthquake waves and other geomagnetic events.<ref></ref>

===Optical telephone cables===
right|250px|thumb|Diagram of an optical submarine cable repeater.
In the 1980s, fibre optic cables were developed. The first transatlantic telephone cable to use optical fibre was TAT-8, which went into operation in 1988. 