Factors to consider when choosing fiber optic cables
According to the performance requirements, the suitable application fiber is selected, and the optical fiber can be divided into single mode (SMF) and multimode (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, which is 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, which is expressed as 8.3/125 μm. A multimode fiber has a thicker core and can transmit light in multiple modes. However, its modal dispersion is large, which limits the frequency of transmitting digital signals, and it will become more serious with the increase of distance. Therefore, the distance of multimode fiber transmission is relatively short, generally only a few kilometers.
The central glass core of the single-mode fiber is relatively thin, the core diameter is generally 9 or 10 μm, and the outer diameter of the cladding is 125 μm, which is 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 narrower and the stability should be better. .
Select high-quality optical fibers according to standard grades. Because traditional multimode optical fibers can only support 10 Gigabit transmission for several tens of meters, ISO/IEC 11801 has formulated a new multimode optical fiber standard grade for new optical transceivers used in 10 Gigabit applications. , the OM3 category.
OM3 fiber is optimized for both LED and laser bandwidth modes and is subject to rigorous DMD testing and certification. The optical fiber cabling system using 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 wavelengths of the optical fiber are short-wave 850nm, long-wave 13l0nm and 1550nm. The 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 for 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 index of single-mode fiber, the most stringent index among all G.652 levels, and is 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.
The selection of optical fiber is not only based on the number of fiber cores and the type of optical fiber, but also according to the use environment of the optical cable. If the transmission distance is within 2km, multi-mode fiber can be selected, and if the transmission distance exceeds 2km, relay or single-mode fiber can be selected.
Optical fibers used in buildings should pay attention to their flame retardant, toxic and smoke characteristics when selecting them. Generally, the type of flame retardant but smoke can be used in the pipeline or forced ventilation; if it is in an exposed environment, the type of flame retardant, non-toxic and smoke-free should be used. When the outdoor optical cable is directly buried, the armored optical cable should be selected. When overhead, an optical fiber with a black plastic outer jacket with two or more reinforcing ribs can be used.
Based on the above analysis, regardless of single-mode or multi-mode, users should invest in the best performance at the lowest price by considering various factors from the perspective of application, transmission distance, forward-looking, and cost.