Views: 260 Author: Site Editor Publish Time: 2020-11-07 Origin: Site
The fiber optic cable is a structure made of multiple optical fibers or fiber bundles that conforms to optical, mechanical, and environmental characteristics. The structure of the fiber optic cable directly affects the transmission quality of the communication system. Optical cables with different structures and performances are operated in different ways in engineering construction and maintenance. Therefore, it is necessary to understand the structure and performance of optical cables, which can ensure the normal service life of optical cables.
Multimode fiber patch cable: The central glass core is thicker (50 or 62.5μm), and it can transmit multiple modes of light. However, the inter-mode dispersion is large, which limits the frequency of the transmission of digital signals, and it will be more serious with the increase of distance. For example: 600MB/KM fiber has only 300MB bandwidth at 2KM. Therefore, the transmission distance of multimode fiber optic cables is relatively short, generally only a few kilometers.
Single mode fiber patch cord: The central glass core is relatively thin (the core diameter is generally 9 or 10 μm), and it can only transmit light in one mode. Therefore, its inter-mode dispersion is very small, which is suitable for long-distance communication, but its chromatic dispersion plays a major role. In this way, single mode fiber optic cables have 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 better.
Conventional type: The optical fiber manufacturer optimizes the optical fiber transmission frequency to a single wavelength, such as 1310nm.
Dispersion-shifted type: The optical fiber manufacturer optimizes the optical fiber transmission frequency to two wavelengths, such as: 1310nm and 1550nm.
We know that single-mode fiber has no modal dispersion and has a very high bandwidth. If single-mode fiber is operated in the 1.55μm wavelength region, can't it achieve high bandwidth and low-loss transmission? But it's actually not so simple. The dispersion of conventional single-mode fiber at 1.31μm is much smaller than the dispersion at 1.55μm. If this kind of optical fibers works in the 1.55μm wavelength region, although the loss is low, it will still have a serious impact on the high-speed optical communication system due to large dispersion. Therefore, this optical fiber is still not an ideal transmission medium.
In order to make the fiber work well at 1.55μm, a new kind of fibers was designed, called dispersion-shifted fibers (DSF). This kind of fibers can compensate for the dispersion and move the zero dispersion point of the fiber from 1.31μm to around 1.55μm. This kind of fibers is also called 1.55μm zero-dispersion single-mode fiber, its code-named is G653.
Abrupt type: The refractive index from the central core of the fiber to the glass cladding is abrupt. The cost is low and the inter-mode dispersion is high. It is suitable for short-distance and low-speed communication.
Graded type: The refractive index from the center core of the optical fiber to the glass cladding is gradually reduced, which can make the high-mode light propagate in a sinusoidal form. It can reduce the inter-mode dispersion, increase the fiber bandwidth, and increase the transmission distance, but the cost is higher.
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