The transmission distance of optical modules is divided into short distance, medium distance, and long distance. Short distance transmission usually refers to transmission distances below 2km, with a medium distance of 10-20km. Long distance transmission refers to distances greater than or equal to 30km. The commonly used wavelengths in optical fibers are 850nm, 1310nm, and 1550nm, which have longer waveforms and therefore have relatively less attenuation. Moreover, these three wavelengths have almost zero absorption and are most suitable for optical fiber transmission.
Generally, 850nm wavelength is used within 500m. The wavelength of 1310nm is commonly used from 500m to 20km. You can choose 1310nm or 1550nm for distances between 20-40km. 1550nm wavelength is usually used for distances greater than 40km.
Below are several commonly used wavelengths and their characteristics.
1. 850nm: It is a multi-mode communication method with relatively large attenuation, and the price of the light source transmitter and signal converter matched with the 850nm optical module is much lower than that of the 1310nm and 1550nm devices, making it a very economical communication method. So multimode optical fibers are mostly connected and transmitted using optical modules with a working wavelength of 850nm. At a wavelength of 850nm, a 100M optical module can transmit up to 2km, a 1G can transmit up to 550m, a 10G can transmit up to 300m, a 40G can transmit up to 400m, and 100G and 400G can transmit up to 100m.
2. 1310nm: The attenuation of optical fiber at 1310nm is approximately 0.35dB/km. When paired with multimode, the maximum transmission distance is 2km, and when paired with single-mode, the maximum transmission distance is 40km. At 1310nm wavelength, 100Mbps, 10G, 40G, and 100G optical modules can transmit up to 40km, and 400G can transmit up to 500m.
3. 1550nm: The attenuation of 1550nm by optical fiber is relatively small, about 0.19dB/km. Therefore, with the same power, the wavelength of 1550nm can transmit farther than the wavelength of 1310nm. At 1550 wavelength, the maximum transmission distance of 100M and 1G optical modules can reach 160km, and the maximum transmission distance of 10G optical modules can reach 80km. (For 40G and 100G optical modules with a distance of ≥ 40km, CWDM or DWDM is usually chosen for transmission.)
