According to ITU-T standards, communication optical fibers are divided into 7 categories: G.651 to G.657. What is the difference between them?
1、G.651 fiber
G.651 is Multi-mode fiber, and G.652 to G.657 all are single-mode fibers.
The optical fiber is composed of core, cladding and coating, as shown in Figure 1.
Generally the diameter of the cladding is 125um, coating layer (after coloring) is 250um; and the core diameter no have a fixed value, because the difference of core diameter will change the optical fiber transmission performance in huge.
Figure 1. Fiber structure
Normally the core diameter of multimode fiber from 50um to 100um. The transmission performance of the fiber is significantly improved when the core diameter becomes smaller. As shown in Figure 2.
Figure 2. Multi mode transmission
Only one transmission mode when the core diameter of the fiber is smaller than a certain value, as shown in Figure 3, which becomes a single-mode fiber.
Figure 3. Single mode transmission
2、G.652 Fiber
G.652 optical fiber is the most widely used optical fiber.At present, in addition to fiber to the home (FTTH) home optical cable, the optical fiber used in long distance and metropolitan area is almost all G.652 optical fiber.Also customers order this type most from Honwy.
Attenuation is one of the most important factor which affect the transmission distance of optical fiber. The attenuation coefficient of an optical fiber is related to the wavelength. As shown in Figure 4. It can be seen from the figure that the attenuation of the fiber at 1310nm and 1550nm is relatively small, so 1310nm and 1550nm have become the most commonly used wavelength windows for single-mode fibers.
Figure 4. Attenuation coefficient of single mode fiber
3、G.653 Fiber
After the speed of optical communication systems is further increased, signal transmission begins to be affected by fiber dispersion. Dispersion refers to the signal distortion (pulse broadening) caused by different frequency components or different mode components of a signal (pulse) propagating at different speeds and reaching a certain distance, as shown in Figure 5.
Figure 5. Fiber dispersion
The dispersion coefficient of the optical fiber is also related to the wavelength, as shown in Figure 6. Single-mode fiber has the smallest attenuation coefficient at 1550 nm, but the dispersion coefficient at this wavelength is larger. So people developed a single-mode fiber with a dispersion coefficient of 0 at 1550nm. This seemingly perfect fiber is G.653.
Figure 6. The dispersion coefficient of G.652 and G.653
However, the dispersion of optical fiber is 0 but it is not suitable for the use of wavelength division (WDM) systems, so G.653 optical fiber was quickly eliminated.
4、G.654 Fiber
G.654 optical fiber is mainly used in submarine cable communication systems. In order to meet the long-distance and large-capacity requirements of submarine cable communication.
5、G.655 Fiber
G.653 fiber has zero dispersion at 1550nm wavelength and does not use the WDM system, so a fiber with small but not zero dispersion at 1550nm wavelength was developed. This is G.655 fiber. G.655 fiber with the smallest attenuation near the 1550nm wavelength, small dispersion and not zero, and can be used in WDM systems; Therefore, G.655 fiber has been the first choice for long-distance trunk lines for more than 20 years around 2000. The attenuation coefficient and dispersion coefficient of G.655 fiber are shown in Figure 7.
Figure 7. The dispersion coefficient of G.652/G.653/G.655
However, such a good optical fiber is also facing a day of elimination. With the maturity of dispersion compensation technology, G.655 fiber has been replaced by G.652 fiber. Starting from about 2005, long-distance trunk lines began to use G.652 optical fiber on a large scale. At present, G.655 optical fiber is almost only used for the maintenance of the original long-distance line.
There is another important reason why G.655 fiber is eliminated:
The mode field diameter standard of G.655 fiber is 8～11μm (1550nm). The mode field diameter of fibers produced by different fiber manufacturers may have a large difference, but there is no difference in the type of fiber, and the fiber with large difference in mode field diameter is connected Sometimes there is a large attenuation, which brings great inconvenience to maintenance; Therefore, in the trunk system, users will choose G.652 fiber rather than G.655, even if requires greater dispersion compensation costs.
6、G.656 Fiber
Before introducing G.656 optical fiber, let’s go back to the era when G.655 dominated long-distance trunk lines.
From the perspective of attenuation characteristics, G.655 fiber can be used for communication in the wavelength range from 1460nm to 1625nm (S+C+L band), but because the dispersion coefficient of the fiber below 1530nm is too small, it is not suitable for wavelength division (WDM). ) system used, so the usable wavelength range of G.655 fiber is 1530nm～1525nm (C+L band).
In order to make the 1460nm-1530nm wavelength range (S-band) of the optical fiber also can be used for communication, try to reduce the dispersion slope of the G.655 optical fiber, which becomes the G.656 optical fiber. The attenuation coefficient and dispersion coefficient of G.656 fiber are shown in Figure 8.
Figure 8
Due to the non-linear effects of optical fiber, the number of channels in long-distance WDM systems will not increase significantly, while the construction cost of metropolitan area optical fibers is relatively low. It is not meaningful to increase the number of channels in WDM systems. Therefore, the current dense wavelength division (DWDM) ) Mainly still 80/160 wave, the C+L wave band of the optical fiber is enough to meet the demand. Unless high-speed systems have greater requirements for channel spacing, G.656 fiber will never have a large-scale use.
6、G.657 Fiber
G.657 optical fiber is the most used optical fiber except G.652. The optical cable used for FTTH home which thinner than the telephone line, it is with G.657 fiber inside.If you need more details about it,pls find https://www.gl-fiber.com/bare-optical-fiber/ or email to [email protected], Thanks!