Telecommunication bands in the infrared
In optical communications, the part of the infrared spectrum that is used is divided into seven bands based on availability of light sources transmitting/absorbing materials (fibers) and detectors:[24]
| Band | Descriptor | Wavelength range |
|---|---|---|
| O band | Original | 1,260–1,360 nm |
| E band | Extended | 1,360–1,460 nm |
| S band | Short wavelength | 1,460–1,530 nm |
| C band | Conventional | 1,530–1,565 nm |
| L band | Long wavelength | 1,565–1,625 nm |
| U band | Ultralong wavelength | 1,625–1,675 nm |
The C-band is the dominant band for long-distance telecommunication networks. The S and L bands are based on less well established technology, and are not as widely deployed.
Among these five bands, the O-band (orignal band: 1260-1360 nm) was historically the
first wavelength bandused for optical communication, because signal distortion (due to chromatic dispersion) is minimum. It was also because optical fibers produced in the mid 1970s showed its lowest loss near the O-band.Today optical fibers show its lowest loss in the C-band (conventional band: 1530-1565 nm), and thus is commonly used in many metro, long-haul, ultra-long-haul, and submarine optical transmission systems combined with the WDM and EDFA technologies.
The L-band (long-wavelength band: 1565-1625 nm) is the second lowest-loss wavelength band, and is a popular choice when the use of the C-band is not sufficient to meet the bandwidth demand. The same WDM and EDFA technologies can be applied to the L-band.
The loss of optical fiber in the S-band (short-wavelength band: 1460-1530 nm) is lower than that of the O-band, and the S-band is used for many PON (Passive-Optical Network) systems as the downstream wavelength.
The E-band (extended-wavelength band: 1360-1460 nm) is the least common wavelength band among the five. This is because the attenuation of early optical fiber in the E-band was highest among the five bands, due to residual water (OH group) impurity remained in the glass. After the invention of dehydration technique during glass production, the attenuation of most commonly used optical fiber (ITU-T G.652.D) in the E-band has become lower than that in the O-band. The use of the E-band in optical communication is, nevertheless, still limited as many existing fiber optic cables installed before 2000 show high attenuation in the E-band.
In addition to the O- to L-bands, there are two more wavelength bands, namely the 850-nm-band and U-band (ultra-long-wavelength band: 1625-1675 nm). The 850-nm-band is the primary wavelength for multimode fiber optical communication systems, combined with VCSEL (Vertical-Cavity Surface Emitting Laser). The U-band is mainly used for network monitoring purposes.