Transoceanic Submarine Communication Cables

    Hello again, Habr.

    Yesterday, I published material regarding the laying by Google of its own fiber-optic communication cable across the bottom of the Pacific Ocean, which will connect the company's data centers in Oregon, USA, with Japan. It would seem that this is a huge project worth $ 300 million and a length of 10,000 km. However, if you dig a little deeper it will become clear that this project is outstanding only because it will be done by one media giant for personal use. The whole planet is already tightly entangled in communication cables and there are much more of them under water than it seems at first glance. Interested in this topic, I prepared a general educational material for the curious.



    The origins of intercontinental communication


    The practice of laying cables across the ocean dates back to the 19th century. According to Wikipedia, the first attempts to connect the two continents by wire were made back in 1847. It was possible to successfully connect Britain and the United States with a transatlantic telegraph cable only by August 5, 1858, but already in September the connection was lost. It is assumed that the reason was the violation of the waterproofing of the cable and its subsequent corrosion and breakage. A stable connection between the Old and New Worlds was established only in 1866. In 1870, a cable was laid to India, which made it possible to connect London and Bombay directly. Some of the best minds and industrialists of the time were involved in these projects: William Thomson (future great Lord Kelvin), Charles Wheatstone, the Siemens brothers. As you can see, almost 150 years ago, people were actively engaged in the creation of communication lines over the length of thousands of kilometers. And progress, of course, did not stop there. However, telephone communication with America was established only in 1956, and the work lasted almost 10 years. Details on the laying of the first transatlantic telegraph and telephone cable can be found in the book by Arthur Clark"Voice over the ocean . "

    Cable device


    Of direct interest is the direct cable arrangement, which will operate at a depth of 5-8 kilometers inclusive.
    It should be understood that a deep-sea cable should have the following number of basic characteristics:

    • Durability
    • Be waterproof (all of a sudden!)
    • To withstand the huge pressure of water masses above itself
    • Strong enough for installation and use
    • Cable materials must be selected so that during mechanical changes (stretching the cable during operation / laying, for example), its performance will not change


    The working part of the cable we are considering, in most cases, is no different from ordinary optics. The whole essence of deep-sea cables is to protect this very working part and maximize the life of its operation, as can be seen from the schematic drawing on the right. Let's analyze the purpose of all structural elements in order.

    Polyethylene is the outer traditional insulating layer of the cable. This material is an excellent choice for direct contact with water, as it has the following properties:
    Resistant to water, does not react with alkalis of any concentration, with solutions of neutral, acidic and basic salts, organic and inorganic acids, even with concentrated sulfuric acid.

    The oceans contain, in fact, all the elements of the periodic table, and water is a universal solvent. The use of such a common chemical. the material industry like polyethylene is logical and justified, since first of all the engineers had to exclude the reaction of the cable and water, thereby avoiding its destruction under the influence of the environment. Polyethylene was used as an insulating material during the laying of the first intercontinental telephone lines in the middle of the 20th century.
    However, due to its porous structure, polyethylene cannot provide complete waterproofing of the cable, so we move on to the next layer.

    Mylar film is a synthetic material based on polyethylene terephthalate . It has the following properties:
    It has no smell, no taste. Transparent, chemically inactive, with high barrier properties (including many aggressive media), resistant to tearing (10 times stronger than polyethylene), wear, shock. Mylar (or Lavsan in the USSR) is widely used in industry, packaging, textiles, and the space industry. They even sew tents from it. However, the use of this material is limited to multilayer films due to shrinkage during heat sealing.

    After a layer of mylar film, cable reinforcement can be seendifferent power, depending on the declared characteristics of the product and its intended purpose. Mostly, a powerful steel sheath is used to give the cable sufficient rigidity and strength, as well as to counter aggressive mechanical influences from the outside. According to some information, wandering around the network, the EMP coming from the cables can lure sharks that cut through the cables. Also, at great depths, the cable is simply laid to the bottom, without digging a trench, and fishing vessels can hook it with their gear. To protect against such influences, the cable is reinforced with a steel braid. The steel wire used in the reinforcement is pre-galvanized. Cable reinforcement can occur in several layers. The main task of the manufacturer during this operation is the uniformity of effort during the winding of steel wire. With double reinforcement, winding takes place in different directions. If the balance is not maintained during this operation, the cable may spontaneously twist into a spiral, forming loops.

    As a result of these measures, the mass of a running kilometer can reach several tons. “Why not light and strong aluminum?” - many will ask. The whole problem is that aluminum has a stable oxide film in air, but when it comes into contact with sea water, this metal can enter into an intense chemical reaction with the displacement of hydrogen ions, which have a detrimental effect on the part of the cable for which everything was conceived - optical fiber. Therefore, steel is used.

    Aluminum water barrier, or a layer of aluminum-polyethylene is used as another layer of waterproofing and shielding the cable. Aluminum polyethylene is a combination of aluminum foil and a plastic film, interconnected by an adhesive layer. Sizing can be either one-sided or double-sided. Throughout the entire structure, alumina polyethylene looks almost invisible. The film thickness can vary from manufacturer to manufacturer, but, for example, one of the manufacturers in the Russian Federation has a thickness of the final product of 0.15-0.2 mm with single-sided gluing.

    The polycarbonate layer is again used to reinforce the structure.Lightweight, durable and resistant to pressure and shock, the material is widely used in everyday products, for example, in bicycle and motorcycle helmets, is also used as a material in the manufacture of lenses, CDs and lighting products, the sheet version is used in construction as a light-transmitting material. It has a high coefficient of thermal expansion . Application to him was found in the manufacture of cables.

    Copper or aluminum tubeIt is part of the core of the cable and serves to shield it. Directly in this design fit other copper tubes with optical fiber inside. Depending on the cable design, there can be several tubes and they can be intertwined in different ways. Below are four examples of cable core organization:



    Laying the optical fiber in copper tubes that are filled with a hydrophobic thixotropic gel, and metal structural elements are used to organize remote power supply of intermediate regenerators - devices that restore the shape of the optical pulse, which, propagating through the fiber, undergoes distortion.

    The cut turns out to be something similar to this:



    Cable manufacturing


    A feature of the production of optical deep-sea cables is that most often it is located near ports, as close as possible to the sea. One of the main reasons for this arrangement is that the linear kilometer of the cable can reach a mass of several tons, and to reduce the required number of splices during installation, the manufacturer strives to make the cable as long as possible. Nowadays, 4 km is considered to be usual now long for such a cable, which can result in approximately 15 tons of mass. As can be understood from the above, the transportation of such a bay deep-sea OK is not the easiest logistics task for land transport. Conventional wooden reels for cable winding do not withstand the previously described masses and for transporting OK on land, for example,

    Cable management


    It would seem that having such a product that is so powerful in appearance can be loaded onto ships and dumped into the deep sea. The reality is a little different. Routing a cable is a long and laborious process. The route should be, of course, cost-effective and safe, since the use of various methods of cable protection leads to an increase in the cost of the project and increases its payback period. In the case of cable laying between different countries, it is necessary to obtain a permit for the use of coastal waters of a country, it is necessary to obtain all the necessary permits and licenses for cable laying. After that, geological exploration is carried out, seismic activity in the region, volcanism, the likelihood of underwater landslides and other natural disasters in the region where the work will be carried out and, subsequently, the cable are laid, are assessed. The forecasts of meteorologists also play an important role, so that the deadlines are not disrupted. During geological exploration of the route, a wide range of parameters is taken into account: depth, bottom topology, soil density, the presence of foreign objects, such as boulders, or wrecks. A possible deviation from the original route, i.e. possible extension of cable and increase in cost and duration of work. Only after carrying out all the necessary preparatory work can the cable be loaded onto the ships and begin laying. A possible deviation from the original route, i.e. possible extension of cable and increase in cost and duration of work. Only after carrying out all the necessary preparatory work can the cable be loaded onto the ships and begin laying. A possible deviation from the original route, i.e. possible extension of cable and increase in cost and duration of work. Only after carrying out all the necessary preparatory work can the cable be loaded onto the ships and begin laying.



    Actually, from the gif, the styling process becomes extremely clear.

    The fiber-optic cable laying along the seabed / ocean floor runs continuously from point A to point B. The cable is laid in bays on ships and transported to the place of descent to the bottom. These bays look, for example, like this:


    If it seems to you that it is not enough, then pay attention to this photo:


    After the ship enters the sea, only the technical side of the process remains. The team of stackers using special machines unwinds the cable at a certain speed and, while maintaining the necessary cable tension due to the movement of the ship, advances along a previously laid route.

    It looks like this:



    In case of any problems, breaks, or damage, special anchors are provided on the cable, which allow you to raise it to the surface and repair the problem section of the line.

    And, in the end, thanks to all this, we can comfortably and at high speed watch photos and videos with cats from around the world on the Internet.

    In the comments on the article about the Google project, Lux_In_Tenebris provided a list of interesting literature on this topic , maybe someone will come in handy.

    Also, the user YoMan provided a link to the video about the cable-laying ship Tyco Resolute, thanks.

    http://youtu.be/GAmSfd01_6I

    Dear Readers. The article is exclusively general educational. If you have something to say on this topic, supplement or fix - I will only be glad. Report in PM or comments.

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