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What is the major advantage of a single mode optical fiber

Uploaded2021/2/17 22:42:12     Hits    Sourcebaudcom

What is the major advantage of a single mode optical fiber

Single Mode Fiber is an optical fiber that can only transmit one mode at a specified wavelength. The central glass core is very thin (the core diameter is generally 9 or 10 μm), so its inter-mode dispersion is small, suitable for remote communication, but it still exists due to material dispersion and waveguide dispersion, single-mode fibers 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. Later, it was discovered that at the wavelength of 1.31μm, the material dispersion and waveguide dispersion of the single-mode fiber were positive and negative, and the magnitudes were exactly the same. In this way, the 1.31μm wavelength region has become a very ideal working window for optical fiber communication, and it is also the main working band of practical optical fiber communication systems. The main parameters of 1.31μm conventional single-mode optical fiber are recommended by the International Telecommunication Union ITU-T in G652. Certainly, so this fiber is also called G652 fiber. Single-mode fiber can be divided into 652 single-mode fiber, 653 single-mode fiber and 655 single-mode fiber.

Interpretation of "single-mode fiber" in academic literature: Generally, when V is less than 2.405, only one wave peak passes through the fiber, so it is called single-mode fiber. Its core is very thin, about 8-10 microns, and the mode dispersion is very small. The main factors affecting the width of the optical fiber transmission band are various dispersions, and the modal dispersion is the most important. The dispersion of single-mode fibers is small, so it can transmit light in a wide frequency band for a long distance.

Single-mode fiber has a core diameter of 10 micron, which can allow single-mode beam transmission, and can reduce the bandwidth and modal dispersion limitations. However, because the core diameter of single-mode fiber is too small, it is difficult to control the beam transmission, so it is necessary expensive lasers are used as the light source. The main limitation of single-mode optical cables is material dispersion. Single-mode optical cables mainly use lasers to obtain high-frequency bandwidth. Since LEDs emit a large number of light sources with different bandwidths, material dispersion requirements are very important. Compared with multi-mode fiber, single-mode fiber can support longer transmission distance. From 100Mbps Ethernet to 1G Gigabit network, single-mode fiber can support transmission distance of more than 5000m from a cost perspective. From the perspective of cost, since the optical transceiver is very expensive, the cost of using single-mode fiber will be higher than that of multi-mode fiber optic cable.

The refractive index distribution is similar to that of abrupt fiber, the core diameter is only 8~10μm, and the light propagates in the direction of the core axis in a straight line. Because this fiber can only transmit one mode (the two polarization states are degenerate), it is called a single-mode fiber, and its signal distortion is very small.

Summary

The equipment for single-mode fiber is relatively expensive, and the coupling loss is large. The bending loss is large. But the advantage is that the transmission distance is long.

Multimode fiber has short transmission distance and low price of supporting equipment. The coupling is relatively lossless. The bending loss is small.

So in the end, the choice must be made according to the specific purpose. In the long-distance backbone network, single-mode must be used.

However, if it is in a local area network or a small metropolitan area network, multi-mode is almost always used. Especially fiber to the home now also uses multi-mode fiber.


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