The transmission distance of optical module is divided into short distance, medium distance and long distance. Usually short distance transmission is the transmission distance below 2km, medium distance is 10-20km. ≥30km is long distance transmission. Light commonly used in optical fiber is 850nm, 1310nm, 1550nm, these three light wavelengths are longer, so relatively less attenuation of optical fiber, and these three wavelengths have almost zero absorption, the most suitable for fiber optic transmission. From the analysis of commonly used wavelengths of optical modules, it is easy to conclude that generally short distance transmission, within 500m is generally used 850nm wavelength. 500m to 20km commonly used 1310nm wavelength. 20-40km can choose 1310nm, 1550nm. ≥ 40 usually use 1550nm wavelength. Here are a few common wavelengths and their characteristics.

1) 850nm: multimode communication mode, attenuation is relatively large, and 850nm optical module with the light source transmitter and signal converter price is much lower than the price of 1310nm and 1550nm devices, is a very economical way of communication. So most of the multimode optical fiber with the working wavelength of 850nm optical module for connection transmission. 850nm wavelength 100 megabit optical module can transmit up to 2km, gigabit can transmit up to 550m, 10 gigabit can transmit up to 300m, 40G can transmit up to 400m, 100G, 400G can transmit up to 100m.

2) 1310nm: fiber to 1310nm attenuation of about 0.35dB/km, with multimode, the farthest transmission distance distance of 2km, with single-mode farthest transmission distance of 40km. 1310nm wavelength, 100 megabit, gigabit, 10 megabit, 40G, 100G optical modules can transmit up to 40km, 400G farthest transmission distance of up to 500m.

3) 1550nm: fiber attenuation of 1550nm is relatively small, about 0.19dB/km. so the same power, 1550nm wavelength than 1310nm wavelength to send farther. 1550 wavelength under the 100 megabit, gigabit optical modules up to 160km transmission distance, 10 gigabit optical modules up to 80km transmission distance. (40G, 100G optical modules ≥) 40km distance transmission will usually choose to use CWDM or DWDM)

Why is defined in these three bands? This is related to the optical signal transmission medium fiber loss. Through continuous research experiments, people found that fiber loss usually decreases with the wavelength lengthening, 850nm loss less, 900 ~ 1300nm loss and become higher; and 1310nm and become lower, 1550nm loss the lowest, 1650nm loss tends to increase. So 850nm is the so-called short wavelength window, 1310nm and 1550nm is the long wavelength window.