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Introduce in detail what is a submarine cable
Background
The Internet has become an indispensable part of our lives, and the submarine cable is the "central nerve" of the Internet. It carries more than 90% of the world's international voice and data transmission. Without it, the Internet is just a local area network.
At present, there are more than 400 submarine optical cables in the world, with a total length of about 1.2 million kilometers, which is three times the distance from the earth to the moon. Only 5% of the international data transmission on the Internet relies on land cables, and the remaining 95% all rely on submarine optical cables. The submarine optical cable is like the aorta in the human body, continuously transmitting the information sent from all over the world, connecting the world tightly.
Definition of submarine cable
Submarine (Undersea) Optical Fibre Cable, also known as submarine communication cable, is a wire wrapped with insulating material and laid on the seabed to establish telecommunication transmission between countries. The submarine optical cable system is mainly used to connect the optical cable and the Internet. It is divided into two parts: the shore equipment and the underwater equipment. The submarine optical cable is the most important and the most vulnerable part of the underwater equipment.
Submarine cable structure
The submarine optical cable is the same as the terrestrial optical cable, with a hair-sized core in the middle, but the submarine optical cable needs stronger armor protection. From the outside to the inside, it is divided into: polyethylene layer, polyester resin, steel strand layer, aluminum waterproof layer, carbonic acid resin layer, copper tube, paraffin, alkane layer, and finally to the optical fiber.
Structural analysis of a typical submarine cable:
- Polyethylene sheath Note: Polyethylene (polyethylene, abbreviation: PE) is one of the most commonly used plastics in daily life, and is widely used in the manufacture of plastic bags, films, barrels and other products. It has good corrosion resistance, so it is used for Making the outer skin of the submarine cable.
- Polyester resin or bitumen layer; Note: Polyester resin has good waterproof, weathering and anti-aging effects, and the price is low.
- Steel strand layer; Note: Steel strand is a wire made by twisting multiple steel wires, which is mainly used to improve the tensile strength of the cable.
- Aluminum waterproof layer
- Polycarbonate layer
- Copper or aluminum pipes
- Paraffin, alkane layer
- Fiber bundles
The protection of so many layers is to prevent the corrosion of seawater. The polymer layer of the outer layer is to prevent the reaction between seawater and the reinforced steel cable to generate hydrogen. Even if the outer layer is really corroded, the copper pipe, paraffin, and carbonate resin of the inner layer are also Will prevent hydrogen from harming the fiber. But no matter how well designed this mechanism is, with the accumulation of time and the destruction of external force, the optical fiber of the submarine cable will still be damaged.
Submarine | Underwater cable lifespan
Generally speaking, the life of the optical cable is 25 years.
Submarine cables are designed to have a shelf life of at least 25 years, and any risk less than that is unacceptable. During this time, changing tides, erosion, storms, and seawater can all wreak havoc on it. Debris, marine life clinging to the cable, and the occasional shark gnawing on the cable out of curiosity are all potential destroyers of submarine cables.
These non-malicious and naturally occurring incidents, such as earthquakes, gillnet equipment and shark bites, are just "extremely rare" causes of cable failures, according to Telegraphy, which monitors all undersea network outages and damage. The big threat is posed by humans: large vessels, such as fishing boats and cruise ships, sink their anchors to the depths of the ocean, which hits submarine cables, which account for about two-thirds of submarine cable failures.
Submarine cable packaging and transportation
According to the length of the plate, there are generally two ways: plate loading and wrapping
Drum package
Wrap Package
Submarine cable laying and installation
How are submarine cables laid?
Is it enough to just throw it into the sea? Obviously not.
The laying project of submarine optical cable is recognized as one of the most complex and difficult large-scale projects by countries all over the world.
The whole laying process can be divided into two parts, namely laying in shallow sea area and laying in deep sea area.
Let's look at the following picture, which is the laying process of submarine optical cables (including shallow sea and deep sea).
Shallow sea optical cable laying
Among them, in the shallow sea area, the fiber optic cable laying ship stays several kilometers away from the coast, and pulls the fiber optic cable placed on the floating bag to the shore through the traction of the onshore tractor, and then removes the floating bag, so that the fiber optic cable sinks to the seabed.
The ship needs to carry a large amount of fiber optic cables to be laid. The state-of-the-art fiber optic cable laying vessel can carry 2,000 kilometers of fiber optic cable and lay it at a speed of 200 kilometers per day.
Deep sea optical cable laying
In the deep sea area, the laying vessel first uses an underwater detector and an underwater remote control vehicle to conduct underwater monitoring and adjustment to avoid uneven and rocky areas on the seabed.
After completing the route survey, it is necessary to lay the optical cable.
At this time, the excavator came into play. It will initially be placed on the shore and attached to the fixed end of the fiber optic cable. Its function is a bit like a plough for ploughing a field. For optical cables, it is a counterweight that sinks the optical cables into the seabed.
The excavator is towed forward by the laying vessel. In addition to serving as a counterweight for the fiber optic cable to sink to the ocean floor, it works in three steps:
- The first step is to use high-pressure flushing water to create a trench about 2 meters deep on the seabed;
- The second step is to put the optical cable into the groove through the optical cable hole;
- The third step is to cover the optical cable with the help of the sand next to it.
Simply put, the fiber optic cable laying ship is the cable laying, and the excavator is the real fiber optic cable laying. However, the transoceanic optical cable is relatively thick and has poor flexibility, so the forward speed of the ship must be strictly controlled.
In addition, on the seabed with rough terrain, the robot needs to constantly detect the best path to prevent rocks from damaging the optical cable.
Therefore, in general, the process of burying optical cables is exploration and cleaning, submarine cable laying and burial protection.
During this process, the cable laying ship should pay special attention to the sailing speed and the release speed of the optical cable to control the water entry angle of the optical cable and the laying tension, so as to avoid damage to the fragile optical fibers in the optical cable due to too small bending radius or excessive tension.
Damaged submarine cable
Cables are often vulnerable to accidental damage from fishing boat trawls, anchors or marine life, and sometimes by enemy forces in wartime. The 1929 Newfoundland earthquake caused a massive collapse of the seafloor, which damaged multiple submarine cables at the same time. Damage to submarine cables may lead to the interruption of regional Internet and long-distance telephone services, causing incalculable losses. For example, the 2006 Hengchun earthquake was an example. This submarine landslide is located near the Luzon Strait. The submarine cable landing station in Fangshan is not far away, and the submarine cables passing by are also affected.
Submarine Underwater Cable repairing
Repairing these fiber optic cables is not an easy task, as even the smallest damage can cause the cable to fail. It takes a lot of manpower and material resources to find a small gap in the tens of thousands of kilometers of optical cable.
To repair the deep sea cable, the damaged position must be located first, and the damaged part will be brought to the surface for repair. The cable of the deep water belt must be cut off the damaged part, and then brought to the surface to connect with the other end, and the repaired part will be longer than the original one.
Schematic diagram of the principle of submarine cable repair
Repair specific steps
The repair process of submarine optical cable can be roughly divided into the following five steps:
The first step is to use an optical time domain reflectometer (OTDR) to locate the approximate fault location, and then use an underwater robot to scan and detect the exact location of the damaged submarine cable.
The OTDR uses the principle of time domain reflection to send and receive a whole set of signals first. The broken position will reflect the signal. The recovered reflected signal is compared with the signal shape and time calculated by the mathematical algorithm, so as to locate the specific position of the fiber breakage. .
In the second step, the robot digs out the fiber optic cable buried on the seabed, then cuts it off, ties the cut ends to the ropes put down on the ship, and pulls it out of the sea.
The third step is to complete the repair welding on the ship. This splicing process is quite complicated, because the fibers of the thickness of a hair in the optical cable must be spliced one by one.
In the fourth step, after the connection of the new submarine optical cable is completed, repeated tests are required to ensure normal communication and data transmission.
The fifth step is to re-throw the repaired submarine optical cable into the sea, and then use the robot to bury and cover it with sand.
In this case, the damaged submarine optical cable is completely repaired.
