Basic knowledge of optical fiber to know for weak current engineering
1. Optical fibers can be divided into quartz optical fibers and plastic optical fibers according to their manufacturing materials. Silica optical fibers are commonly used optical fibers. Silica optical fibers are divided into single-mode optical fibers and multi-mode optical fibers according to their different transmission modes. Plastic optical fibers are all composed of plastics and are usually used for multimode short-distance applications. They are still in their infancy and have not been applied on a large scale.
2. Structure of silica fiber: Silica fiber consists of core, cladding and coating. The transmission of light in the fiber is carried out in the core. Due to the different refractive indices of the cladding and the core quartz, the light is totally reflected on the surface of the core and the cladding, so that the light is always transmitted in the core, while the plastic coating layer It plays the role of protecting the silica fiber and increasing the strength of the fiber. Because the silica is very brittle, it cannot be applied in practice without the protection of plastic. Because of the structure of the fiber, the fiber is easy to break, but has a certain tensile force.
3. Classification of silica fiber
single mode fiber
G.652A (B1.1 referred to as B1) G.652B (B1.1 referred to as B1) G.652C (B1.3) G.652D (B1.3) G.655A fiber (B4) (for long-distance trunk lines) G. 655B optical fiber (B4) (for long-distance trunk lines) G.657A2 (indoor butterfly cable)
50/125 (A1a referred to as A1) 62.5/125 (A1b)
Second, the structure of the optical cable
1. Outdoor optical cables mainly have three structures: central tube optical cable, layered optical cable and skeleton optical cable. According to the use of optical fiber bundles and optical fiber ribbons, they can be divided into 6 types, such as ordinary optical cable and optical fiber ribbon cable. Structural features of each type of optical cable: ① Central tube type optical cable (Executive standard: YD/T769-2003): the optical cable structure type in which the center of the optical cable is a loose tube, and the reinforcing member is located around the loose tube, such as the common GYXTW optical cable and GYXTW53 Type optical cable, the number of cores is small, usually less than 12 cores. ② Layer stranded optical cable (Executive standard: YD/T901-2009): The reinforcing member is located in the center of the optical cable, and 5~12 loose tubes are stranded on the central core strength member in a twisted manner, and the twisting is usually SZ twist. combine. Such optical cables, such as GYTS, can obtain optical cables with a larger number of cores by combining loose tubes. The color separation of the stranded loose tube is usually separated by the red and green color spectrum, which is used to distinguish different loose tubes and different optical fibers. The number of cores of the stranded optical cable can be larger. At present, the number of cores of the stranded optical cable of our company can reach 216 cores or higher. ③ Skeleton optical cable: The reinforcing member is located in the center of the optical cable, and the reinforcing member is composed of a plastic skeleton groove. The optical fiber or optical fiber ribbon is located in the skeleton groove. This kind of structure optical cable is rare in China and accounts for a small proportion. ④ Figure 8 self-supporting structure, this kind of structure optical cable can be incorporated into the central tube type and layer twisted optical cable, it is listed separately mainly because the optical cable structure is quite different from other optical cables. There are usually central tube type and layer stranded type 8 self-supporting optical cable. 5 Flame retardant optical cable for coal mine (Executive standard: Q/M01-2004 enterprise standard): Compared with ordinary optical cable, the requirements for the flame retardant performance of optical cable are improved, and the optical cable is specially designed to be suitable for use in mine environment. The color of the sheath is blue to facilitate the identification of the optical cable in the mine. According to the structure, it can be divided into two types of structure: central tube type optical cable and layered optical cable.
2. Indoor optical cables Indoor optical cables are classified according to the number of optical fiber cores, mainly including single-core, double-core and multi-core optical cables. Indoor optical cable is mainly composed of tight-buffered optical fiber, spun fiber and PVC outer sheath. According to the type of optical fiber, it can be divided into two categories: single-mode and multi-mode. The color of the outer sheath of the single-mode indoor cable is usually yellow, the color of the outer sheath of the multi-mode indoor cable is usually orange, and the color of the outer sheath of some indoor cables is grey.