multimode fiber
Multimode fiber (MulTIModeFiber): The central glass core is thicker (50 or 62.5μm), which can transmit light in multiple modes. However, its intermodal dispersion is relatively large, which limits the frequency of digital signal transmission, and it will be more serious with the increase of distance. For example: 600MB/KM optical fiber has only 300MB bandwidth at 2KM. Therefore, the transmission distance of multimode fiber is relatively short, generally only a few kilometers.
single mode fiber
Single Mode Fiber (SingleModeFiber): The central glass core is very thin (core diameter is generally 9 or 10 μm), and only one mode of light can be transmitted. Therefore, its intermodal dispersion is very small, suitable for long-distance communication, but there are still material dispersion and waveguide dispersion, so 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 better. Later, it was found that at the wavelength of 1.31 μm, the material dispersion and the waveguide dispersion of the single-mode fiber are positive and negative, and their sizes are exactly equal.
At a wavelength of 1.31 μm, the total dispersion of single-mode fiber is zero. From the point of view of the loss characteristics of the optical fiber, 1.31 μm is just a low loss window of the optical fiber. In this way, the 1.31μm wavelength region has become an 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 fiber are determined by the International Telecommunication Union ITU-T in the G652 recommendation, so this fiber is also called G652 fiber
Single Mode Fiber and Multimode Fiber
Optical fiber colors are mainly divided into two categories:
Single-mode fiber (Single-mode Fiber): Generally, the fiber optic jumper is indicated by yellow, and the connector and protective sleeve are blue; the transmission distance is longer.
Multi-mode fiber (MulTI-mode Fiber): Generally, the optical fiber jumper is represented by orange, and some are represented by gray, and the connector and protective sleeve are beige or black; the transmission distance is short.
How to distinguish single mode fiber and multimode fiber
In the implementation of network engineering, there are often novices who do not know how to distinguish between single-mode fiber and multi-mode fiber
First of all, we need to understand that both single-mode fiber and multimode fiber are used for long-distance high-quality transmission of network signals. The reason why single-mode and multi-mode are distinguished is based on the way light propagates inside; light propagates along a straight line in a single-mode fiber without reflection, so its propagation distance is very long. The multimode fiber can carry the transmission of multiple optical signals.
Second, from the perspective of external light, the most conventional way to distinguish is; the yellow fiber optic cable is generally a single-mode fiber, and the orange or gray fiber optic cable is generally a multi-mode fiber. The difference between the two in the cable core is that the size of the multimode cable core is 50.0 μm and 62.5 μm; while the single mode is 9.0 μm.
Third, the optical fibers in the two pictures we saw above all have LC interfaces, so in addition, optical fibers also have a very rich interface selection.
