According to the performance requirements, select the suitable optical fiber for the application, and the optical fiber can be divided into single-mode (SMF) and multi-mode (MMF) according to the transmission mode of light in it. The core diameter of the multimode fiber is 50 or 62.5 μm, and the outer diameter of the cladding is 125 μm, expressed as 50/125 μm or 62.5/125 μm. The core diameter of the single-mode fiber is 8.3 μm, and the outer diameter of the cladding is 125 μm, expressed as 8.3/125 μm. Multimode fiber has a thicker core and can transmit light in multiple modes.
The central glass core of the single-mode optical fiber is relatively thin, the core diameter is generally 9 or 10 μm, and the outer diameter of the cladding is 125 μm, expressed as 8/125 μm, 9/125 μm, 10/125 μm, and can only transmit light of one mode. Therefore, its intermodal dispersion is very small, which is suitable for long-distance communication, but its chromatic dispersion plays a major role, so the single-mode fiber has higher requirements on the spectral width and stability of the light source, that is, the spectral width should be narrow and the stability should be good. .
Choose high-quality optical fiber according to the standard grade. Because the traditional multimode fiber can only support tens of meters of 10G transmission, ISO/IEC 11801 has formulated a new multimode fiber standard grade for the new type of optical transceiver used in 10G applications. , the OM3 category. OM3 fiber is optimized for both LED and laser bandwidth modes, and must be certified by strict DMD testing. The optical fiber cabling system adopting the new standard can support at least 10 Gigabit transmission to 300 meters in multimode mode, and can reach more than 10 kilometers in single mode mode (1550nm can support 40 kilometers transmission).
Select the most economical transmission frequency window from the perspective of cost performance. The working wavelength of the optical fiber is short-wave 850nm, long-wave 13l0nm and 1550nm. Optical fiber loss generally decreases with the increase of wavelength. The loss of 850nm is generally 2.5dB/km, the loss of 1.31μm is generally 0.35dB/km, and the loss of 1.55μm is generally 0.20dB/km, which is the lowest loss of optical fiber. The loss tends to increase at wavelengths above 1.65 μm. The main parameters of the 1310nm conventional single-mode fiber are determined by the International Telecommunication Union ITU-T in the G652 recommendation, and l310nm is just a low loss window of the fiber.
Therefore, this fiber is also called G652 fiber. G.652.D is the latest specification for single-mode fiber, the strictest specification among all G.652 levels, and fully backward compatible. If only G.652 is specified, it generally means the performance specification of G.652.A, which should be paid special attention to.
The selection of optical fiber is not only based on the number of optical fiber cores and the type of optical fiber, but also based on the environment in which the optical cable is used. If the transmission distance is within 2km, you can choose multi-mode fiber, and if it exceeds 2km, you can use relay or choose single-mode fiber. The optical fiber used in the building should pay attention to its characteristics of flame retardancy, poison and smoke. Generally, the flame retardant but smoke type can be selected in the duct or forced ventilation; if it is exposed to the environment, the flame retardant, non-toxic and smoke-free type should be selected. When the optical cable is directly buried outdoors, armored optical cable should be selected. When overhead, you can choose an optical fiber with a black plastic outer sheath with two or more ribs.
Based on the above analysis, regardless of single-mode or multi-mode, users should invest in the best performance at the lowest price from the perspectives of application, transmission distance, forward-looking, cost, etc., and integrate various factors.
