According to the transmission mode of light in the fiber, it can be divided into: single-mode fiber and multi-mode fiber. There is only one word difference between single-mode and multi-mode, is it just the difference in the number of modes? What are the differences? Let's take a look with ZR fiber.
Single-mode fiber: Only one mode of signal wave can be transmitted. Because single-mode fiber only propagates along a straight line without reflection, there is no modal dispersion, which makes the transmission band of single-mode fiber very wide, so it is suitable for backbone, large-capacity, and long-distance systems. The light-emitting diode or laser is used as the light source, and two bands of 1310nm and 1550nm are used. The central glass core of the single-mode fiber is very thin (the core diameter is generally 9 or 10 μm), which is much thinner than the multi-mode fiber in terms of appearance.
Multimode fiber: It can carry the transmission of multiple optical signals, that is, multiple optical paths can transmit multiple modes of light in one fiber at the same time. Since there are multiple modes of transmission, there is a large intermodal dispersion. The transmission performance is poor, the frequency band is narrow, and the capacity is small. Therefore, the distance of multimode fiber transmission is relatively short, generally only a few kilometers, and is often used in small-capacity, short-distance systems. The multimode fiber uses a laser as the light source and uses two bands of 850nm and 1300nm. The central glass core of the multimode fiber is thicker (50 or 62.5 μm).
In terms of price, under the same specifications, single-mode is more expensive than multi-mode. From a practical point of view, multi-mode is basically used in data access optical cables. The biggest disadvantage of multi-mode compared to single-mode is that Intermodal dispersion (due to different rates of the same light in different modes). In China, 62.5/125 multimode fiber is mainly used. As for the difference between the two, it seems that the use of the cable is different, and the 50 is mostly used for indoor optical cables.
Judging from the appearance and color, all single-mode fibers are yellow, gigabit multi-mode is orange-red, and 10-gigabit multi-mode is light blue.
The difference between multi-mode fiber and single-mode fiber is mainly in the transmission mode of light, and of course the bandwidth capacity is also different. The diameter of the multimode fiber is large, and the beams of different wavelengths and phases are continuously reflected and transmitted along the fiber wall, causing dispersion, which limits the transmission distance and bandwidth between the two repeaters. The bandwidth of the multimode fiber is about 2.5Gbps.
The diameter of the single-mode fiber is relatively small, and the light travels in a straight line and is rarely reflected, so the dispersion is reduced, the bandwidth is increased, and the transmission distance is also extended. However, the price of the supporting optical terminal equipment is relatively high, and the bandwidth of single-mode fiber exceeds 10Gbps.
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