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 fiber is mostly used only in the backbone of the network, that is, in the vertical backbone subsystem and the system wiring of the building subsystem to connect between buildings and between floors. Here is a brief understanding of the basic knowledge of optical fiber wiring, in the optical fiber wiring, first of all, to consider the requirements of optical cable laying. General optical cable to meet the following requirements.
The minimum allowable curvature radius of the optical cable shall not be less than 20 times of the outer diameter of the optical cable at the time of construction, and no less than 15 times of the outer diameter of the optical cable after construction. When laying the cable, the traction force of the cable should not exceed 80% of the allowable tension of the cable, and the instantaneous maximum traction force should not be greater than the allowable tension of the cable. The main traction force should be applied to the reinforced members of the cable, and the fiber should not directly bear the tension.
Indoor fiber optic cable is mainly applied to the laying of horizontal subsystem and vertical backbone subsystem. The horizontal subsystem cable is very similar to the twisted pair cable, except that the cable has worse tensile properties, so it should be pulled with more care and a larger radius of curvature. The vertical trunk subsystem cable is used to connect the equipment room to the wiring room of each floor, and is generally installed in the cable shaft or rising room. In order to prevent sagging or slip-off, the cable must be securely secured at the top, bottom, and middle of the slots on each floor. Usually, nylon cable ties or steel clips can be used for effective fixation. Finally, the oil and sesame sealing material is also applied to plug and seal all the slots and the gaps of the pipe holes that the optical fiber cable passes through in each floor of the building, and the fire prevention measures such as blocking fire prevention materials should be taken to achieve the effect of moisture-proof and fire prevention. When laying optical cable, the appropriate length should be reserved according to the design requirements. Generally, 5m-10m should be reserved at the equipment end, and it should be extended appropriately if there are special requirements.
The laying of outdoor optical cable can be divided into many kinds according to the different environment. In long-distance trunk line, city telephone relay, underwater and submarine communication and local area network, private network and other environments, the selection of optical fiber wiring is different, the main laying methods are overhead, directly buried, pipeline, underwater, indoor and so on.
1. Overhead optical cable
The overhead optical cable is mostly used on the telegraph pole. When laying the overhead optical cable, the original overhead pole road can be used, which can save the construction cost and shorten the construction period. However, the overhead fiber optic cable is located at a high position, which is vulnerable to typhoons, ice, floods and other natural disasters, and is also vulnerable to external forces and its own mechanical strength weakening. Therefore, the failure rate of overhead fiber optic cable is higher than that of directly buried and pipeline fiber optic cable. There are two main laying methods.
Cable type: first, the cable is fasten on the pole, and then the cable is suspended on the cable by the hook, and the load of the cable is carried by the cable. Self-supporting type: A self-supporting structure of the optical cable, the cable is "8" shape, the upper part of the self-supporting line, the load of the cable is carried by the self-supporting line.
2, Directly buried optical cable
Direct buried fiber optic cable Direct buried fiber optic cable is usually directly buried in the ground, which requires its resistance to external mechanical damage and soil corrosion performance. Depending on the soil and environment, the depth of the cable buried in the ground is generally between 0.8 and 1.2 meters. When laying, care must also be taken to keep the fiber strain within allowable limits.
The laying of the directly buried optical fiber cable needs to dig trenches, and the trenches should be dug 1.2 meters of ordinary soil, 1.0 meters of semi-stone, 0.8 meters of quicksand, and 1.2 meters when crossing the railway and highway. The bottom of the ditch should be added with 10CM fine soil or sandy soil, and the width of the ditch is generally 30CM. If two or more optical cables need to be laid, the distance between the optical cables should be 5CM. Steel pipe or rigid plastic pipe should be embedded in the road section where the surface layer is often pressurized. When laying fiber optic cable, it should be laid in "S" shape when it meets special areas such as slope, crossing railway and highway.
3. Pipeline optical cable
Pipelines are generally laid in urban areas, where the environment is not as bad as that of overhead fiber optic cables and directly buried fiber optic cables, so there is no special requirement for the cable sheath and no need for armor. The length of the laying section and the position of the connecting point must be selected before laying the pipeline. When laying, mechanical side guide or manual traction can be used. The traction force of a traction should not exceed the allowable tension of the cable. The material of making pipe can choose concrete, asbestos cement, steel pipe, plastic pipe and so on according to geography.
The size of the city standard pipe hole is generally 90MM, which can accommodate 3~4 inches of plastic pipe. 1 inch subtube is suitable for fiber optic cable with diameter less than 20MM. The subpipe is prone to distortion in the process of laying. When the twisted pitch is within 10 meters, the friction between the cable and the inner wall of the subpipe will increase, which will bring certain difficulties to the laying of the cable, so the distortion of the plastic subpipe should be avoided. The optical fiber cable laying of the pipeline should be equipped with a guidance device to reduce the friction of the optical fiber cable and reduce the traction tension of the optical fiber cable through the turning of the entrance and exit of the manhole, the curve and the height difference of the pipeline manhole. The special tool "nylon rod" should be selected in the cable traction tube, which can be pulled by the appropriate engineers and technicians according to the row. After the cable is pulled, the remaining cable in each manhole will be placed on the specified bracket manually. For future safety, the hose or PE hose is generally used for protection, and the tie is rolled for fixation. The end of the cable should be hung on the manhole wall after leaving the appropriate length of the coil, do not soak in water.
4. Underwater optical cable
Among these cable laying methods, the laying environment of underwater cable is the most severe, so the technology and measures to repair the fault are also much more difficult. Generally, the underwater optical fiber cable must adopt the structure of steel wire or steel tape armor, and the structure of the protective layer should be comprehensively considered according to the hydrogeological conditions of the river. For example, in the seasonal river bed with strong scour and rocky soil, the optical fiber cable is subjected to wear and tear and tensile force. Not only coarse steel wire is needed for armor, but also double armor is used. The method of construction should also be selected according to the width of the river, the depth of the water, the flow rate, the river bed, the flow rate, and the soil quality of the river bed.
