With the rapid development of 5G networks, the demand for network data transmission is increasing exponentially. As the underlying carrier network, the transmission capacity of optical networks is crucial for the development of 5G networks.
A major magic weapon for expanding the transmission capacity of optical networks is to continuously explore the available band resources of optical fibers, which means continuously expanding the transmission path width of optical networks. As the transmission path widens, the transmission capacity of optical networks naturally improves.
Recently, optical networks have emerged in the CE, Cpp, and C+L bands, adding bricks and tiles to expand the transmission capacity of optical networks.
Fiber optic communication, as the name suggests, refers to communication where light serves as an information carrier and fiber optic serves as a transmission medium. However, not all light is suitable for fiber optic communication. The different wavelengths of light (which can be simply understood as light of different colors) result in different transmission losses in optical fibers. Light with high transmission loss cannot carry information through optical fibers.
After long-term research by scientists, it was first discovered that light with a wavelength of 850nm can be used as light for optical communication, which is also directly referred to as the 850nm band. However, the transmission loss in the wavelength range of 850nm is relatively high, and there is no suitable fiber amplifier available. Therefore, the 850nm band is only suitable for short range transmission.
Subsequently, scientists explored the "low loss wavelength region" optical band, which is the region between 1260nm and 1625nm, which is most suitable for transmission in optical fibers. The relationship between transmission loss and optical band is shown in the following figure.
The 1260nm~1625nm region is further divided into five bands: O-band, E-band, S-band, C-band, and L-band.
O-band
The wavelength range of the O-band is 1260nm~1360nm. The signal distortion caused by the dispersion of light in this band is the smallest and the loss is the lowest, making it the early optical communication band. Therefore, it is named O-band, where O refers to "Original".
E-band
The wavelength range of the E-band is 1360nm~1460nm, and the E-band is the least common of the five bands. E refers to 'extended'. From the graph of transmission loss and optical band relationship above, it can be seen that there is a clear irregular transmission loss bump in the E-band. This transmission loss bump is caused by the absorption of light at wavelengths of 1370nm to 1410nm by hydroxide ions (OH -), resulting in a sharp increase in transmission loss. This bump is also known as the water peak.
Due to early limitations in fiber optic technology, water (OH based) impurities often remain in the fiber optic glass fibers, resulting in the highest attenuation of E-band light transmission in the fiber and inability to be used for normal transmission and communication purposes.
With the improvement of fiber processing technology, ITU-T G.652. D fiber has emerged, making the transmission attenuation of E-band light lower than that of O-band light, solving the water peak problem of E-band light.
S-band
The wavelength range of the S-band is 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) systems.
C-band
The wavelength range of the C-band is 1530nm~1565nm. C refers to '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. The C-band is also frequently used in wavelength division networks.
L-band
The wavelength range of the L-band is 1565nm~1625nm. L refers to "long wavelength". The transmission loss of L-band light is the second lowest. When C-band light is insufficient to meet 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, which is the U-band. The wavelength range of the U-band is 1625nm~1675nm. U refers to "ultra long wavelength". The U-band is mainly used for network monitoring.
Let's summarize these traditional bands below.
CE/Cpp/C+L-band
The commonly used wavelength range for optical communication is 1529.16nm~1560.61nm in the traditional C-band. The emerging band CE/Cpp/C+L mentioned here refers to the new band resources introduced by current optical communication to expand traditional C-band transmission resources.
From the previous traditional band analysis, it can be seen that to expand the C-band used in optical communication, support can be sought from nearby short wavelength bands (S-band) and long wavelength bands (L-band). This is like, if you want to expand an existing road, you can only see if the wasteland on both sides of the road is available, and if there is wasteland, you can expand the road.
Next, let's take a look at the emerging band CE/Cpp/C+L, and what resources have been borrowed from the S and L bands?
CE band
The CE (C Extended) band is also known as the C+band. What wavelength range does the CE band have compared to the C band? We can divide the C-band resources into 80 channels for transmitting information, with each channel occupying a band range of 0.4 nm. Therefore, the C-band is also known as the C80 band. The CE band borrows some wavelength resources from the L-band (i.e. long wavelength band), and the wavelength range is expanded to 1529.16nm~1567.14nm. The CE band resources can be divided into 96 channels to transmit information, namely the C96 band. The transmission capacity of the CE band has increased by 20% compared to the C band.
CPP band
The Cpp (C plus plus) band is also known as the C++band. The Cpp band not only borrows wavelength resources from the L-band like the CE band, but also from the S-band, expanding the wavelength range to 1524.30nm~1572.27nm. According to the resource allocation of each channel occupying a band range of 0.4 nm, the band resources can be divided into 120 channels for transmitting information. Therefore, the Cpp band is also known as the C120 band. The transmission capacity of the Cpp band has increased by 50% compared to the C band.
C+L band
The C+L band literally indicates that both the C and L band resources are used for optical communication. Similarly, according to the resource allocation of each channel occupying a 0.4 nm band range, there are three common transmission schemes for the C+L band.
- C120+L80: Cpp band (120 channels)+L-band (80 channels), achieving a 200 wave system. The L-band is actually the L+band, with a wavelength range of 1575.16nm~1617.66nm. The transmission capacity of the C120+L80 transmission scheme has increased by 1.5 times compared to the C-band.
- C96+L96: CE band (96 channels)+L band (96 channels), achieving a 192 wave system. The L-band is actually the L++band, with a wavelength range of 1575.16nm~1626.43nm. The transmission capacity of the C96+L96 transmission scheme has increased by more than twice compared to the C-band.
- C120+L96: Cpp band (120 channels)+L-band (96 channels), achieving a 216 wave system. The L-band is actually the L++band, with a wavelength range of 1575.16nm~1626.43nm. The transmission capacity of the C120+L96 transmission scheme has increased by about twice compared to the C-band.
Finally, a picture shows these three emerging bands.
Summary
In short, scientists have expanded the available wavelength resources of optical fibers to a very large range. However, these band resources can be truly applied to communication systems such as 5G, and are also affected by the following factors.
Due to the limitations of optical devices, for example, the following optical devices cannot directly support the newly expanded band range and need to be upgraded.
- Erbium doped fiber amplifier (EDFA)
- Active devices such as modulators
- Wavelength selective switch (WSS) passive device
For the L-band, the degradation of transmission performance will increase the complexity of operation and maintenance, thereby increasing cost investment.
It is gratifying that operators have fully utilized existing fiber optic resources, expanded available fiber optic band resources, and improved transmission capacity. As a goal for the development of future optical communication networks, some operators have also begun to deploy Cpp band optical networks.
With the rapid development of technology, we will definitely see optical communication networks using C+L band solutions in the future.
This article refer to: https://baijiahao.baidu.com/s?id=1745178232708444597&wfr=spider&for=pc