What is the relationship between optical module wavelength and transmission distance
2021-10-27
The transmission distance of the optical module refers to the distance over which the optical signal can be directly transmitted without relay amplification. It is divided into three types: short-distance, medium-distance, and long-distance. Generally speaking, 2km and below are short distances, 10-20km are medium distances, and 30km, 40km and above are long distances. Optical modules of different wavelengths with different optical fibers correspond to different transmission distances.
The working wavelength of the optical module is a range, and the unit is nanometer (nm). The commonly used center wavelengths of gray light modules are:
1. 850nm (with multi-mode MMF), low cost but short transmission distance, 100M rate can transmit 2km farthest; 1G rate can transmit 550m farthest; 10G rate can transmit 300m farthest; 40G rate can transmit 400m farthest; 25G /100G/200G/400G rate can transmit up to 100m.
2. 1310nm (with multi-mode MMF), the farthest transmission distance is 2km, such as 1000BASE-SX SFP.
3. 1310nm (usually with single-mode SMF), large loss during transmission but small dispersion, generally used for transmission within 40km.
4. At 1550nm (with single-mode SMF), the loss is small but the dispersion is large during transmission. It is generally used for long-distance transmission above 40km, and the farthest can be directly transmitted without relay for 120km.
The color light module carries light of several different central wavelengths, and is divided into two types: coarse-collected optical module (CWDM) and dense-wave optical module (DWDM). The wavelength of the CWDM module is 1270~1610nm; the wavelength of the DWDM module is 1525~1565nm (C band) or 1570~1610nm (L band). In the same waveband, there are more types of DWDM optical modules, so DWDM optical modules make fuller use of waveband resources. Lights with different central wavelengths can be transmitted without interference in the same fiber. Therefore, the light from the multiple color optical modules with different central wavelengths is combined through a passive combiner for transmission, and the far end is transmitted through a splitter according to Different central wavelengths split the light into multiple paths, effectively saving fiber optic lines. Colored optical modules are mainly used in long-distance transmission lines. The transmission distance of the optical module is mainly limited by loss and dispersion. Dispersion: In general, single-mode transmission does not produce inter-mode dispersion, while multi-mode transmission supports multiple transmission modes, and light will be refracted multiple times, which will produce inter-mode dispersion. The greater the dispersion, the longer the transmission distance of the optical module. short. Loss: The optical transmission loss of different wavebands is different, from largest to smallest, 850nm>1310nm>1550nm. The smaller the loss, the longer the optical module transmission distance. It can be seen that the wavelength of the optical module is not directly related to the transmission distance, but because the transmission characteristics of different wavelengths are different, it corresponds to the application of different transmission distances.
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