In the structured cabling system, optical fiber not only supports FDDI backbone, 1000Base-FX backbone, 100Base-FX to desktop, ATM backbone and ATM to desktop, but also supports CATV/CCTV and fiber to the desktop (FTTD), so it is compatible with copper cables Together they become the protagonists in structured wiring.
Today, there are mainly two popular international cabling standards, one is the North American standard EIA/TIA-568A; the other is the international standard ISO/IECIS11801. EIA/TIA-568A and ISO/IECIS11801 recommend using 62.5/125um multimode fiber optic cable, 50/125um multimode fiber optic cable and 8.3/125um multimode fiber optic cable.
Single-mode fiber and multi-mode fiber can be easily distinguished from the size of the core. The core of a single-mode fiber is very small, about 4-10um, and only transmits the main mode. In this way, modal dispersion can be completely avoided, so that the transmission frequency band is very wide and the transmission capacity is large. This kind of optical fiber is suitable for large-capacity, long-distance optical fiber communication. It is the inevitable trend of the future development of optical fiber communication and light wave technology.
Multimode fiber is divided into multimode mutation type fiber and multimode graded fiber. The former has a larger core diameter and more transmission modes, so the bandwidth is narrower, and the transmission capacity is smaller; the latter’s core refractive index decreases as the radius increases, and a relatively small modal dispersion can be obtained, so the frequency band is relatively small. Wide, large transmission capacity, the latter is generally used at present.
At present, the wavelength range of light waves used in optical communications is in the near-infrared region, with a wavelength of 0.8 to 1.8um. It can be divided into short wavelength range (0.85um) and long wavelength range (1.31um and 1.55um). Because optical fiber communication has a series of excellent characteristics, optical fiber communication technology has developed extremely rapidly in recent years. It can be said that this emerging technology is an important symbol of the world's new technological revolution, and it is also the main transmission tool for various information networks in the future information society.
Several bands of light waves are used in optical fiber wiring: 800nm～900nm short wave band; 1250nm～1350nm long wave band and 1500nm～1600nm long wave band.
In these bands, optical fiber transmission performance is the best, especially when operating in the center wavelength of the band. Therefore, the operating wavelength of multimode fiber is 850nm or 1300nm, while the operating wavelength of single-mode fiber is 1310nm or 1550nm. There is little difference between the two regulations, and both are very strict. Therefore, the longest distance for optical fiber as the backbone wiring is also stipulated. When the optical cable is applied to the backbone, at least 6-core optical cable should be used in the wiring closet of each floor, and 12-core optical cable is best used for advanced applications. This is considered from the three aspects of application, backup and expansion.
As for the optical fiber networking mode, it is also very flexible, which can realize:
(1) Point to point. A high-speed channel is established between the two computers. The transmission rate is several Mbps to several hundred Mbps, and the distance can reach 2 kilometers (multi-mode) to 5 kilometers (single-mode).
(2) Star network. Through optical fiber network equipment, a star-shaped network topology is established.
(3) Ring network. The signal regenerator is connected by optical fiber to form a loop.
