Singlemode fiber and multimode fiber


Multimode fiber

Multimode fiber (MulTIModeFiber): The central glass core is thicker (50 or 62.5μm), which can transmit light in multiple modes. But its intermodal dispersion is large, which limits the frequency of transmitting 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 distance of multimode fiber transmission is relatively short, generally only a few kilometers.


single mode fiber

Single Mode Fiber: The central glass core is very thin (the core diameter is generally 9 or 10 μm) and can only transmit light in one mode. Therefore, its intermodal dispersion is very small, which is suitable for long-distance communication, but there are also material dispersion and waveguide dispersion, 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 narrow and stable. Be good. 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 the magnitudes are exactly the same.


This means that at a wavelength of 1.31 μm, the total dispersion of a single-mode fiber is zero. From the loss characteristics of the fiber, 1.31μm is just a low-loss window of the 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.

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Singlemode fiber and multimode fiber

Fiber colors are mainly divided into two categories:

Single-mode fiber (Single-mode Fiber): Generally, the fiber jumper is shown in yellow, and the connector and protective sleeve are in blue; the transmission distance is longer.


Multi-mode fiber (MulTI-mode Fiber): Generally, the fiber patch cord is indicated in orange, and some are indicated in gray, and the connector and protective sleeve are in beige or black; the transmission distance is short.


The blue one is not 10000000000000000!!! That's just an unconventional color


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 must understand that both single-mode fiber and multi-mode fiber are used to transmit high-quality network signals over long distances. The reason for distinguishing single-mode and multi-mode is based on the way light propagates inside it; 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 method of distinguishing is: the yellow optical fiber is generally a single-mode fiber, and the orange-red or gray optical fiber is generally a multi-mode fiber. The difference between the two in the cable core is that the multimode cable core size is 50.0μm and 62.5μm; while the single mode is 9.0μm.


Third, the two optical fibers we saw above all have LC interfaces, so in addition, the optical fibers have a very rich selection of interfaces.


There are many FC interfaces used in fiber distribution panels in operators. And the ST interface commonly used by FTTB.


The most commonly used is the LC interface, which is much smaller than all other interfaces. More ports are accommodated in the fixed unit area of ​​the box switch. Two LC light jumpers together, called DLC.


Another small interface is the same as LC, but it is more used in fiber to the desktop - MTRJ, which integrates the common dual fiber into one port.


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