The rapid development of optical communication is inseparable from the development of optical fibers. Since the first optical fiber was born, the types of optical fibers have become increasingly diverse, supporting optical communication systems in various fields. Today, let's talk about a new type of optical fiber - G.654E optical fiber, and its advantages over the traditional G.652D optical fiber.
First, let's give the basic concept. What is G.654E optical fiber? G.654E optical fiber is a new type of optical fiber specifically designed for long-distance terrestrial trunk transmission systems. It maintains low attenuation while having a larger effective area, thus being better able to cope with the challenges brought by high-speed and long-distance transmission.
Those who are familiar with the naming of optical fibers will notice that since it is named G.654E, there must be G.654A, G.654B, G.654C, and G.654D before it. So, let's summarize the background of the emergence of G.654E.
How did G.654E optical fiber come into being? To understand G.654E optical fiber, we have to mention its predecessor (or it's more appropriate to call it its family) - G.654 optical fiber. In the mid-1980s, to meet the needs of long-distance communication in submarine optical cables, G.654 optical fiber was developed. This type of optical fiber has an attenuation of more than 10% lower than that of the traditional G.652 optical fiber at the 1550nm wavelength and is known as the "single-mode optical fiber with the lowest attenuation at 1550nm wavelength".
In the 1990s, WDM technology began to be applied in submarine optical communication systems. This technology enables multiple optical channels to be transmitted simultaneously in a single optical fiber, greatly increasing the transmission capacity of the optical fiber. However, with the use of optical amplifiers, high-power multi-wavelength optical signals are coupled into a single optical fiber, causing the optical fiber to exhibit nonlinear characteristics. We also know that the nonlinear effect of optical fibers is related to the optical power density in the fiber core. If the input optical power remains unchanged, increasing the effective area of the optical fiber can reduce the optical power density in the fiber core, thereby reducing the nonlinear effect. Therefore, people began to try to increase the effective area of G.654 optical fiber.
There is another small problem, that is, the increase in the effective area of the optical fiber will lead to an increase in the cut-off wavelength. An increase in the cut-off wavelength will limit the use of the optical fiber, so the cut-off wavelength must be controlled. Specifically, to not affect the use of the optical fiber in the conventional C-band (1530nm~1565nm), the cut-off wavelength of G.654 optical fiber was set at 1530nm.
In 2000, when ITU revised the G.654 optical fiber standard, it was renamed "cut-off wavelength shifted single-mode optical fiber". Since then, G.654 optical fiber has mainly been optimized for attenuation and large effective area, and gradually developed into four subcategories: A/B/C/D. So far, we have learned that G.654A/B/C/D optical fibers are mainly used for submarine cables.
Next, let's talk about the emergence of G.654E optical fiber (this is the main topic). Unlike submarine cable systems, G.652D optical fiber is mainly used in terrestrial trunk transmission lines. However, as the single-carrier rate in WDM systems exceeds 100Gbps, the nonlinear effect becomes more obvious, affecting the transmission performance of the system. Therefore, researchers thought of introducing G.654 optical fiber and applying it to terrestrial long-distance trunk transmission systems.
However, there are still differences between land transmission systems and submarine transmission systems. Therefore, the characteristics of G.654 optical fiber were improved, and G.654E optical fiber was thus produced. What improvements were made specifically? The macro-bend loss requirements for G.654 optical fiber used on land are much stricter (consistent with G.652D), while the requirements for effective area and attenuation of the optical fiber are more lenient than those for submarine use. The main transmission indicators of each subclass of G.654 optical fiber are shown in the table below.
The application scenarios of G.654E are mainly on land, while those of G.654A/B/C/D are mainly in the sea. What are the advantages of G.654E optical fiber? Since G.652D optical fiber was mainly used in land cables before, we will use it for comparison. Compared with the traditional G.652D optical fiber, G.654E optical fiber has the following significant advantages:
1. Large effective area
The effective area of G.654E optical fiber mainly includes two types: A110 (110 um²) and A130 (130 um²). Since 2018, all newly built trunk lines have uniformly chosen A130 optical fiber, so A130 is the main type. Compared with G.652D (A80) optical fiber, the effective area of G.654E optical fiber has increased by approximately 47%. Under the premise that the nonlinear effect remains unchanged, this increase has raised the optimal input fiber power by about 1.7 dB. Thus, it can support higher transmission rates and longer transmission distances.
2. Low attenuation
The typical attenuation value of G.654E optical fiber is also about 0.02 dB/km lower than that of G.652D optical fiber. Although this may seem insignificant within a single optical amplification section, in long-distance transmission, this advantage is magnified, significantly reducing the overall system attenuation.
3. Better OSNR performance
Due to the large effective area and low attenuation characteristics of G.654E optical fiber, its OSNR (optical signal-to-noise ratio) performance is also significantly improved. This is crucial for high-rate, long-distance transmission systems.
Application of G.654E optical fiber?
Currently, G.654E optical fiber has been widely applied in multiple inter-provincial and intra-provincial trunk line constructions. The actual application results show that G.654E optical fiber has significant advantages in improving transmission performance and reducing system attenuation.
Especially in WDM systems with single-carrier rates exceeding 100G, G.654E optical fiber has demonstrated its unique charm.
Of course, G.654E optical fiber is not without flaws.
Due to its cut-off wavelength of 1530nm, it cannot be used in the wavelength range below 1530nm. For example, in metropolitan area networks, single-module transmission systems exceeding 100G often operate around the 1310nm wavelength, and G.654E optical fiber is not suitable for this.
In addition, the application scale of G.654E optical fiber cannot be compared with that of G.652D, so its production volume is not high, and the price is relatively high.
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