Wavelengths in different bands
672 2023-08-10

With the rapid development of 5G networks, the demand for network data transmission is increasing exponentially. As the underlying bearer network, the transmission capacity of optical networks is crucial to the development of 5G networks. One of the magic weapons to expand the transmission capacity of optical networks is to continuously dig deep into the available band resources of optical fibers, that is, to continuously expand the transmission path width of optical networks. The wider the transmission road, the transmission capacity of the optical network will naturally increase. Next, I will talk to you about these bands of optical fiber.


Traditional band

As the name implies, optical fiber communication is the communication in which light is used as an information carrier and optical fiber is used as a transmission medium. However, not all light is suitable for fiber optic communication. Different wavelengths of light (which can be simply understood as light with different colors) have different transmission losses in optical fibers. Light with a large transmission loss cannot carry information in the optical fiber.

After long-term research by scientists, it was first discovered that the light with a wavelength of 850nm can be used as light for optical communication. This waveband is also directly called the 850nm waveband. However, the transmission loss in the wavelength region of the 850nm band is relatively large, and there is no suitable fiber amplifier. Therefore, the 850nm band is only suitable for short-range transmission.

Later, scientists explored the "low-loss wavelength region" optical band, that is, the light in the 1260nm~1625nm region, which is most suitable for transmission in optical fibers. See the figure below for the relationship between transmission loss and optical band.



What is an O-band?

O-band is the original band 1260-1360 nm. O-band is the first wavelength band historically used for optical communications, with minimal signal distortion (due to dispersion).

What is an E-band?

E-band (extended wavelength band: 1360-1460 nm) is the least common of these bands. E-band is mainly used as an extension of O-band, but there are few applications, mainly because many existing optical cables show high attenuation in E-band, and the manufacturing process is very energy-intensive, so its use in optical communication is limited.

What is an S-band?

The fiber loss in the S-band (Short-wavelength Band) (short-wavelength band: 1460-1530 nm) is lower than that in the O-band, and the S-band is used as many PON (passive optical network) systems.

What is C band?

The C-band (Conventional Band) ranges from 1530 nm to 1565 nm, representing the conventional band. Optical fiber exhibits the lowest loss in the C-band and has a greater advantage in long-distance transmission systems. It is usually used in many metropolitan, long-distance, ultra-long-distance and submarine optical transmission systems combined with WDM and EDFA technology. C-band becomes more and more important as transmission distances become longer and fiber amplifiers are used instead of optical-to-electron-to-optical repeaters. The use of C-band expanded with the advent of DWDM (Dense Wavelength Division Multiplexing), which enables multiple signals to share a single fiber.


What is L-band?

L-band (Long-wavelength Band) (long-wavelength band: 1565-1625 nm) is the second lowest-loss wavelength band and is often used when the C-band is not enough to meet the bandwidth requirements. With the widespread availability of b-doped fiber amplifiers (EDFAs), DWDM systems have been extended up to the L-band, and were initially used to extend the capacity of terrestrial DWDM optical networks. Now, it has been introduced to submarine cable operators to do the same thing - expand the total capacity of submarine cables.

Because the transmission attenuation loss of the two transmission windows of the C-band and the L-band is the smallest, the signal light in the DWDM system is usually selected in the C-band and the L-band. In addition to the O-band to the L-band, there are two other bands, the 850 nm band and the U-band (ultra-long band: 1625-1675 nm). The 850 nm band is the dominant wavelength for multimode fiber optic communication systems incorporating VCSELs (Vertical Cavity Surface Emitting Lasers). The U-band is mainly used for network monitoring.