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 telecommunications transmission between countries.
The submarine fiber optic cable system is mainly used to connect the fiber optic cable and the Internet. It is divided into two parts: onshore equipment and underwater equipment. The submarine fiber optic cable is the most important and most vulnerable part of the underwater equipment.
Equipment structure
The submarine optical cable is laid on the seabed with a wire bundle wrapped in an insulating sheath. The seawater can prevent the interference of external light and magnetic waves, so the signal-to-noise ratio of the submarine cable is high; there is no time delay in the communication of the submarine optical cable. The design life of submarine optical cables is 25 years of continuous operation, while artificial satellites generally run out of fuel within 10 to 15 years.
The basic structure of the submarine optical cable is: polyethylene layer, polyester resin or asphalt layer, steel strand layer, aluminum waterproof layer, polycarbonate layer, copper or aluminum tube, paraffin, alkane layer, optical fiber bundle, etc.
The submarine optical cable system is mainly used to connect optical cables and the Internet. It is divided into two parts: onshore equipment and underwater equipment. The shore-based equipment packs and transmits communication services such as voice, image, and data. The underwater equipment is responsible for the processing, sending and receiving of communication signals. Underwater equipment is divided into three parts: submarine fiber optic cable, repeater and "branch unit": the submarine fiber optic cable is the most important and most vulnerable part.
The structure of the deep-sea optical cable is more complicated: the optical fiber is set in the U-shaped groove plastic skeleton, and the groove is filled with grease or elastic plastic to form the core. The core is wrapped with high-strength steel wire. During the wrapping process, all gaps should be filled with waterproof material. Then a layer of copper tape is wrapped around the steel wire and the seam is welded to make the steel wire and the copper tube form a resistance Combination of compression and tension. A layer of polyethylene sheath should be added on the outside of the steel wire and copper pipe. Such a tight multi-layer structure is to protect the optical fiber, prevent breakage and prevent the intrusion of sea water. In areas where sharks are infested, an additional layer of polyethylene sheath is added to the outside of the submarine cable.
The structure of the submarine optical cable is required to be strong and light in material, but light metal aluminum cannot be used, because aluminum and seawater will electrochemically react to produce hydrogen, and hydrogen molecules will diffuse into the glass material of the optical fiber, which will increase the loss of the optical fiber. Therefore, the submarine optical cable must not only prevent hydrogen from being generated inside, but also prevent hydrogen from penetrating into the optical cable from the outside. For this reason, in the early 1990s, a carbon- or titanium-coated optical fiber was developed to prevent hydrogen penetration and chemical corrosion. The optical fiber connector is also required to be high-strength, requiring the connection to maintain the strength of the original optical fiber and the surface of the original optical fiber from damage.
Main species
According to different marine environments and water depths, it can be divided into deep-sea optical cables and shallow-sea optical cables. Correspondingly, the optical cable structure is represented by a single-layer armor layer and a double-layer armor layer. In the product model representation method, DK is used for single-layer armor, and SK is used for double-layer armor. The specifications are expressed by the number and type of fibers.
According to the role and function can be divided into
Submarine communication cable and submarine optical power cable. The former is mainly used for communication services, and the latter is mainly used for underwater transmission of high-power light energy
Technical Principle
The networks of various countries in the world can be regarded as a large local area network. The submarine and land optical cables connect them to form the Internet. The optical cable is the "central nerve" of the Internet, and the United States is almost the "brain" of the Internet. As the birthplace of the Internet, the United States stores a lot of Web and IM (such as MSN) servers. Of the 13 root servers that resolve domain names globally, 10 are in the United States. Log in to most .com and .net websites or send e-mails, data Almost all have to go around the United States to reach the destination.
Submarine cables are now maintained separately, and for safety purposes, submarine cables also need to be maintained at ordinary times. If someone fished out the submarine cable and added optical fiber, the information could be stolen. If there is a war, someone may damage the fiber optic cable. Submarine cables are the best solution for communication today. Other methods such as satellites and microwaves can be used as supplements, but it seems that they cannot replace submarine cables because their channels are limited. It is a way that allows the majority of users to communicate in a cheap way.
The remote power supply of the submarine cable system is very important, and the repeaters along the submarine cable rely on the remote power supply of the landing station. The digital repeater used in the submarine optical cable has many functions, and the power consumption is several times larger than that of the analog repeater of the submarine cable. The power supply requires high reliability and cannot be interrupted. Therefore, in areas where sharks are infested, two layers of steel tape and a layer of polyethylene outer sheath should be added to the outside of the submarine optical cable. Even with such tight protection, there were instances where the polyethylene insulators of deep-sea optical cables were bitten by sharks and caused power failures in the late 1980s.
Main features
Compared with terrestrial fiber optic cables, submarine fiber optic cables have many advantages: First, they do not need to dig tunnels or support by brackets, so the investment is low, and the construction speed is fast; Due to the destruction of the natural environment such as wind and waves and the interference of human production activities, the cable is safe and stable, with strong anti-interference ability and good confidentiality performance.
Construction method
The design of the submarine optical cable must ensure that the optical fiber is not affected by external forces and the environment. The basic requirements are: it can adapt to the environment of submarine pressure, abrasion, corrosion, biology, etc.; have a suitable armor layer to prevent damage from fishing boat trawls, anchors and sharks; fiber optic cable breaks At the same time, minimize the length of seawater penetrating into the optical cable; it can prevent the hydrogen permeating into the optical cable from the outside and the hydrogen generated inside; it has a low-resistance remote power supply circuit; it can withstand the tension during laying and recycling; the service life is average The requirement is more than 25 years.
The deep-sea (above 1,000 meters) submarine optical cable adopts a steel-free armored structure, but the structure of the cable core and the reinforcing member (usually the central steel wire) must be able to protect the optical fiber to prevent the high pressure of seawater and the high pressure during laying and recycling. tension. In order to prevent shark damage, two layers of steel tape should be spirally wrapped on the sheath of the deep-sea optical cable in the sea area where the sharks are infested, and a layer of polyethylene outer sheath should be squeezed.
The core structure of the shallow sea (within 1000 meters of water) submarine optical cable is the same as that of the deep sea optical cable, but the shallow sea optical cable must have a single layer or double-layer steel wire armor. The number of armor layers and the outer diameter of the steel wire are determined according to the submarine environment, water depth, whether it can be buried, fishing, etc. of the submarine cable route.
Laying process
The submarine cable project is recognized as a complex and difficult large-scale project by countries all over the world. In shallow seas, if the water depth is less than 200 meters, cables are buried, while in deep seas, they are laid. Hydraulic jet burying is the main burying method. There are several rows of water spray holes at the bottom of the buried equipment, which are distributed in parallel on both sides. During operation, each hole sprays high-pressure water jets to the seabed at the same time to wash away the seabed sediment and form a submarine cable trench; the upper part of the equipment has a fairlead, It is used to guide the cable (optical cable) to the bottom of the submarine cable trench, and the trench is automatically filled in by the tide. The buried equipment is towed forward by the construction ship, and various instructions are given through the working cable. Cable laying machines generally do not have underwater burying equipment, and are laid on the surface of the seabed by the weight of the submarine cable.
The boat keeps driving forward, and then flushes a trench with the underwater robot, puts the optical cable in, and then flushes the sand back with the underwater robot, covers the optical cable, and then keeps moving forward. When the docking is needed, the connection is completed on the boat, and then Seal, and then continue to lay. At present, all submarine optical cables are optical fibers, and there are very few cables, and all the cables currently laid are buried in the soil, that is, an underwater robot is used to flush a trench and put it in and then bury the soil.
The underwater robot actually uses a high-pressure water pump to pressurize the water to a high pressure and spray it out, thereby rushing out of the trench. As for maintenance, there is no maintenance at all. Normally, there is no need for maintenance. You only need to check whether the optical cable is exposed on a regular basis with an underwater robot, and if there is, cover the mud. In addition, if it breaks, use the attenuation detector to measure it to get the specific position, and then go there to fish it, connect it or other methods, usually cut off all the damaged section and replace it with a new one.
Incident handling
fracture
There are generally two main reasons for submarine cable breaks. One is force majeure such as earthquakes and tsunamis, and the other is man-made causes. Once the cable is disconnected, it will not only have a huge impact on international communications, but the loss caused is even more incalculable.
damage
Cables are often susceptible to damage by fishing trawlers, anchors, and even sharks. Cables are sometimes destroyed by enemy troops during wartime. The Great Newfoundland earthquake in 1929 caused a large-scale submarine collapse that caused damage to the transatlantic cable.
Once multiple submarine cables are damaged at the same time (for example, damaged by an earthquake), it may cause the interruption of regional Internet and long-distance telephone services, resulting in incalculable losses. For example, the Hengchun earthquake in 2006 is an example.
Repair the deep cable, and the damaged part is brought to the surface for repair. The damaged part of the deep-water cable must be cut off and brought to the surface for repair. The repaired part will be longer than the original one.
Some important cables near ports have been set up to repair ships dedicated to repairing cables. Several restoration companies such as CS Cyrus West Field have been established near Halifax, Nova Scotia. Some large telecom operators, such as France Telecom and Japan Telecom, have their own submarine cable ships.
repair
Submarine optical cables are usually buried at a depth of 1-2 meters below the seabed. Because the seabed is not very regular, the optical cables will inevitably be exposed sometimes. The fiber optic cable may be destroyed when the fishing boat is anchored or using a trawl to fish. Therefore, the place where the fiber optic cable passes on the seabed is designated as a no-anchor zone and no ships are allowed to dock. This principle is the same as that of optical cables on land. We often see signs like "There are optical cables underground and construction is forbidden" on the road. Submarine optical cables need to be protected, and technology needs to be strengthened to improve the tensile strength of the submarine cable itself.
The first step in the repair work is to find the breakpoint. Submarine cable engineers can find the approximate location of the breakpoint through telephone and Internet outages. The shore terminal can emit light pulses, and the normal optical fiber can always transmit these pulses in the sea, but if the fiber is broken, the pulse will bounce back from that point, and the shore terminal can find the break point in this way. After that, new optical cables need to be brought in by ships for repair, but the first step is to retrieve the broken optical fibers.
If the optical cable is less than 2,000 meters deep underwater, you can use a robot to salvage the optical cable. Generally, it is located in the sea with a water depth of about 3,000 to 4,000 meters. Only one type of grappling hook can be used. It takes more than 12 hours to retract the grapple once. It is necessary to add the cable in the middle after fishing the broken optical cable on the ship. This work is done by a highly professional technician.
1. After the robot dives into the water, it scans and detects the precise location of the damaged submarine optical cable.
2. The robot digs out the submarine optical cable buried in mud and cuts it with cable scissors. The rope was put down on the boat, and the robot was tied to one end of the optical cable, and then it was pulled out of the sea. At the same time, the robot installs a wireless transponder at the cut.
3. Use the same method to pull another section of optical cable out of the sea. As with the maintenance of telephone lines, the instruments on the ship are connected to both ends of the optical fiber cable, and the submarine optical cable landing station in two directions is used to detect which end of the optical cable is blocked. After that, take back the longer part of the submarine cable with the blocked part and cut it off. The other section was fitted with a buoy and left to float on the sea temporarily.
4. Next, manually connect the spare submarine optical cable to the two breakpoints of the submarine optical cable. Connecting fiber optic cable connectors is a job with extremely high "technical content", which is not competent for ordinary people. It must be a person who has been specially trained and obtained a license from an international organization before it can be operated.
5. After the spare submarine optical cable is connected, after repeated tests, after the communication is normal, it will be thrown into the sea water. At this time, the underwater robot is about to "fight" again: "flush" the repaired submarine optical cable, that is, use a high-pressure water gun to flush the silt on the seabed out of a trench, and "lay" the repaired submarine optical cable into it.
At the same time, severe weather such as strong winds and waves at sea may slow down the restoration work.
