As a high-bandwidth and high-security transmission medium, optical fiber has been widely used in major transmission networks. Due to the high cost of cables and equipment, optical fibers are mostly only used in the backbone of the network, that is, used in the system wiring of the vertical backbone subsystem and the building group subsystem to realize the connection between buildings and between floors. Let us briefly understand the basic knowledge of optical fiber wiring.
Before proceeding with optical fiber wiring, first consider the requirements of optical cable laying. Generally, optical cables must meet the following requirements:
The minimum allowable radius of curvature of the optical cable shall not be less than 20 times the outer diameter of the optical cable during construction, and shall not be less than 15 times the outer diameter of the optical cable after construction. When laying the optical cable, it is required that the pulling force of the optical cable should not exceed 80% of the allowable tension of the optical cable, and the instantaneous maximum pulling force shall not be greater than the allowable tension of the optical cable. The main traction should be added to the strength member of the optical cable, and the optical fiber cannot directly bear the tension.
After understanding the basic requirements of optical fiber laying, the next step is to carry out optical fiber wiring. Light wiring is usually divided into indoor wiring and outdoor wiring. Below we will analyze them in detail.
1. Optical cable classification and wiring knowledge
Indoor optical cables are mainly used in the laying of horizontal subsystems and vertical backbone subsystems. The laying of the horizontal subsystem optical cable is very similar to the twisted pair, but because the tensile performance of the optical cable is worse, you should be more careful when towing and have a larger radius of curvature. The vertical backbone subsystem optical cable is used to connect the equipment room to the wiring room on each floor, and is generally installed in the cable shaft or riser room. In order to prevent sagging or slipping, the optical cable must be firmly fixed on the upper, lower end and middle of the channel on each floor. Under normal circumstances, nylon cable ties or steel clips can be used for effective fixation. Finally, oil-seed plugging materials are used to block and seal all the gaps of the optical cables on each floor of the building, and the gaps of the pipe holes should be blocked, and fire-proof measures such as blocking fire-proof materials should be taken to achieve the effect of moisture and fire prevention. When laying the optical cable, an appropriate length should be reserved in accordance with the design requirements. Generally, 5m-10m should be reserved at the equipment end, and if there are special requirements, the appropriate length should be extended.
The laying of outdoor optical cables can be divided into many types according to different environments. In environments such as long-distance trunk lines, intra-city telephone relays, underwater and submarine communications, local area networks, and private networks, the selection of optical fiber cabling is different. The main laying methods are overhead, direct buried, pipeline, underwater, indoor, etc.
1. Overhead optical cable
Overhead optical cables are mostly used on telegraph poles. When laying overhead optical cables, the original overhead open wire poles can be used, which can save construction costs and shorten the construction period. However, overhead optical cables are located in high places and are vulnerable to natural disasters such as typhoons, ice and floods, as well as external forces and weakening of their own mechanical strength. Therefore, the failure rate of overhead optical cables is higher than that of direct-buried and ducted optical fiber and optical cables. There are two main laying methods:
Hanging wire type: first fasten the cable on the pole with a hanging wire, and then hang the optical cable on the hanging wire with a hook, and the load of the optical cable is carried by the hanging wire. Self-supporting type: use a self-supporting structure of the optical cable, the optical cable is in the shape of "8", the upper part is a self-supporting line, and the load of the optical cable is carried by the self-supporting line.
2. Directly buried optical cable
Directly buried optical cables Directly buried optical cables are usually directly buried in the ground, which requires the performance of resisting external mechanical damage and soil corrosion. Depending on the soil quality and the environment, the depth of the fiber optic cable buried in the ground is generally between 0.8 meters and 1.2 meters. During laying, care must be taken to keep the strain of the optical fiber within the allowable limit.
The laying of directly buried optical cables requires trenching. The trenching standard is generally 1.2m of ordinary soil, 1.0m of semi-rock, 0.8m of quicksand, and 1.2m of digging when crossing railways and highways. The bottom of the above-mentioned trench should be filled with 10cm fine soil or For sandy soil, the width of the trench bottom is generally 30cm. When it is necessary to lay two or more optical cables, the distance between the optical cables should be 5cm. Steel pipes or hard plastic pipes should be pre-embedded in sections where the surface of the pavement is often compressed. The laying of optical fiber cable should be laid in an "S" shape when it encounters a slope, crosses railways, highways and other special sections.
3. Pipe fiber optic cable
Pipe laying is generally in urban areas, and the environment is not as harsh as overhead optical cables and direct buried optical cables. Therefore, there are no special requirements for the optical cable sheath and no armoring is required. Before laying the pipeline, the length of the laying section and the location of the connection point must be selected. When laying, mechanical bypass or manual traction can be used. The traction force of one haul should not exceed the allowable tension of the optical cable. The materials for the pipes can be selected from concrete, asbestos cement, steel pipes, plastic pipes, etc. according to geography.
The city standard pipe hole size is generally ф90MM, which can accommodate 3 3-4 inch plastic sub-pipes. The 1-inch sub-tube is suitable for optical cables with a diameter less than 20MM. The sub-tube is easy to be twisted during the laying process. When the twist pitch is less than 10 meters, the friction between the optical cable and the inner wall of the sub-tube will increase. This will bring certain difficulties to the installation of the optical cable. Therefore, the laying of plastic sub-tubes should be avoided. distortion. When laying optical cables in ducts, there are bends in the entrance and exit routes of the manholes, as well as the curve and the height difference of the manholes in the ducts. Guiding devices should be arranged in a timely manner to reduce the friction of the optical cable and reduce the traction tension of the optical cable. A special tool "nylon rod" should be used in the optical cable traction sub-pipe, which can be towed by a row of appropriate engineers and technicians. After the optical cable is towed, the remaining cables in each manhole will be manually placed on the specified bracket. For future safety, hoses or PE hoses are generally used for protection, and fixed with cable ties. The end of the optical cable should be left with a proper length of coil and hung on the wall of the manhole, and should not be immersed in water.
Pipe fiber optic cable
4. Underwater optical cable
Among these kinds of optical cable laying methods, the laying environment of underwater optical cables is the most severe, so it is much more difficult to repair fault technologies and measures. Generally, the underwater optical cable must adopt a steel wire or steel tape armored structure, and the structure of the sheath must be considered comprehensively according to the hydrogeological conditions of the river. For example, in stony soils and seasonal riverbeds with strong scouring properties, where the optical cable suffers from abrasion and high tension, not only thick steel wires are required for armoring, but even double-layered armoring is required. The construction method should also be selected according to the river width, water depth, flow rate, river bed, flow rate, and river bed soil quality.
Underwater optical cable
