In order to minimize the loss and ensure the transmission effect, scientific researchers have been working to find the most suitable light.

 850 band

  In the early 1970s, optical fiber communication started the process of practical implementation. At that time, the main research and development object was multimode fiber. The core diameter of multimode fiber is larger, allowing different modes of light to be transmitted on one fiber. The first light used is the light with a wavelength of 850 nm. This band is also directly called the 850 nm band.

   The wavelength range of O band is 1260nm~1360nm. The signal distortion caused by light dispersion in this band is the smallest, and the loss is the lowest, which is the early optical communication band. Therefore, it is named O-band, where O refers to "Original"

  E-band

  The wavelength range of E-band is 1360nm~1460nm, and E-band is the least common of the five bands. E refers to "extended". From the above diagram of transmission loss and optical band, we can see that there is an obvious irregular transmission loss bump in E-band. This transmission loss bump is caused by the absorption of light at the wavelength of 1370nm~1410nm by hydroxide ion (OH -), which leads to a sharp increase in transmission loss. This bump is also called water peak.

 Due to the limitation of early optical fiber technology, water (OH base) impurities are often left in the optical fiber glass fiber, resulting in the highest attenuation of E-band light transmission in the optical fiber, which cannot be normally used for transmission and communication. With the improvement of optical fiber processing technology, ITU-T G.652. D optical fiber appears, which makes the transmission attenuation of E-band light lower than that of O-band light, and solves the water peak problem of E-band light. ITU-T G.652. D optical fiber is a low water peak optical fiber.

  S-band

 S-band wavelength range: 1460nm~1530nm. S refers to "short wavelength". The transmission loss of S-band light is lower than that of O-band light, and it is often used for the downlink wavelength of PON (passive optical network) system.

  C-band

 C-band wavelength range: 1530nm~1565nm. C means "conventional". C-band light has the lowest transmission loss and is widely used in metropolitan area networks, long-distance, ultra-long-distance and submarine optical cable systems. C-band is also often used in wavelength division networks.

 L-band

L-band wavelength range: 1565nm~1625nm. L refers to "long wavelength". The transmission loss of L-band light is the second lowest. When C-band light is not enough to meet the bandwidth requirements, L-band light will be used as a supplement for optical networks.

 U-band

In addition to the above five bands, there is actually another band that will be used, that is, the U band. The wavelength range of U-band is 1625 nm~1675 nm. U refers to "ultra long wavelength". U-band is mainly used for network monitoring.