To establish a unified international standard for optical fibers, the ITU-T has developed a set of unified optical fiber standards. According to the ITU-T recommendations on optical fibers, fiber types are divided into seven main categories. Each main category also contains several subcategories.
I. Multimode Optical Fibers:
G.651 Fiber (Multimode Graded-Index Optical Fiber)
II. Single-Mode Optical Fibers:
G.652 (Dispersion Non-Shifted Single-Mode Fiber)
G.653 (Dispersion-Shifted Fiber)
G.654 (Cutoff Wavelength Shifted Fiber)
G.655 (Non-Zero Dispersion Shifted Fiber)
G.656 (Low-Slope Non-Zero Dispersion Shifted Fiber)
G.657 (Bend-Insensitive Fiber)
① G.651 Fiber (Multimode Graded-Index Optical Fiber)
G651 fiber is a multimode fiber. It is a 50/125μm multimode graded-index optical fiber, suitable for short-distance transmission at wavelengths of 850nm/1310nm. It is mainly used in local area networks and is not suitable for long-distance transmission, but for short-distance transmission networks of 300-500 meters, G651 is a cost-effective multimode transmission fiber. It is mainly used in multi-tenant and residential buildings in FTTH networks, as well as in enterprise networks. Its bending radius is half that of G652 fiber (approximately 15mm), which is its main advantage, making it suitable for indoor installation, and generally used in FTTH environments.
② G.652 (Dispersion Non-Shifted Single-Mode Fiber)
This is a conventional single-mode fiber, and also the most widely used fiber. It has the shortest cutoff wavelength and can be used at both 1550nm and 1310nm, but its optimal operating wavelength is in the 1310nm region. Its characteristics include zero dispersion near 1310nm, attenuation of 0.3-0.4 dB/km, and a dispersion coefficient of 0-3.5 ps/nm. km; the loss is minimal at a wavelength of 1550 nm, with attenuation between 0.19 and 0.25 dB/km, and a dispersion coefficient of 15-18 ps/nm·km. However, the dispersion coefficient is large in the 1550 nm band, at 17 ps/(nm·km), making it unsuitable for long-distance applications above 2.5 Gb/s.
G652 fiber can be further divided into G652A, G652B, G652C, and G652D, with the main difference being Polarization Mode Dispersion (PMD). A/B are basic single-mode fibers, while C/D are low-water-peak single-mode fibers. G652D is the most commonly used because its fiber dispersion is very small at the 1300 nm operating wavelength, and the system's transmission distance is only limited by loss.
The differences between these four types:
G652A fiber supports a transmission distance of 400 km in 10 Gbit/s systems, 40 km in 10 Gbit/s Ethernet systems, and 2 km in 40 Gbit/s systems. It can be used in the D, E, S, C, and L bands, and can operate across the entire 1260-1625 nm operating wavelength range. It has better bending performance and more precise geometric dimension requirements.
G652B fiber supports a transmission distance of 3000 km in 10 Gbit/s systems and 80 km in 40 Gbit/s systems.
The properties and application range of G652C fiber are similar to those of G652A fiber. However, G652C fiber has lower attenuation at the 1550nm wavelength. It can be used in the extended band (E-band) and short band (S-band) in the 1360-1530 nm range, in addition to the 1310nm and 1550nm wavelength regions, extending the usable wavelength range to 1360nm to 1530nm.
G652D fiber combines the advantages of G652B and G652C fibers. G652C is similar to G652A and has better performance at the 1550 nm wavelength. Therefore, G652D virtually encompasses G652A, G652B, and G652C. Currently, when referring to G652 fiber, most of the time it refers to G652D. G652D fiber is widely used in many applications.
③ G.653 (Dispersion-Shifted Fiber)
The dispersion is minimized around the 1550nm wavelength, thus minimizing optical loss, making it ideal for long-distance single-channel optical communication systems. Currently, G.653 fiber is rarely deployed and has been replaced by G.655 fiber for WDM applications, because the channels allocated near 1550nm in G653 fiber are severely affected by noise caused by nonlinear effects.
④ G.654 (Cutoff Wavelength Shifted Fiber)
It has the lowest attenuation coefficient at 1550nm (approximately 15% lower than G652, G653, and G655 fibers), hence it is called low-attenuation fiber. The dispersion coefficient is the same as G652, and it is one of the least used types of fiber in practice. It is mainly used for long-distance transmission in submarine or terrestrial applications, such as 400-kilometer routes without repeaters. It includes five revisions: G.654.A, G.654.B, G.654.C, G.654.D, and G.654. G654.A, G.654.B, G.654.C, and G.654.D fibers are suitable for extended long-distance submarine applications. G654.E fiber, on the other hand, is specifically designed for high-speed long-distance terrestrial optical networks.
⑤ G.655 (Non-Zero Dispersion Shifted Fiber)
Its main characteristic is that the dispersion at 1550nm is close to zero, but not exactly zero. It is an improved dispersion-shifted fiber designed to suppress four-wave mixing. G655 was initially used in WDM and long-distance cables, but is now largely replaced by G652.D fiber.
⑥ G.656 (Low-Slope Non-Zero Dispersion Shifted Fiber)
This is a type of non-zero dispersion-shifted fiber with strict requirements on the dispersion slope, ensuring transmission performance over a wider wavelength range in DWDM systems. G.655 fiber has low attenuation at 1460nm-1625nm, but the dispersion is too low for WDM systems when the wavelength is less than 1530nm. Therefore, G.656 fiber is not suitable for applications from 1460nm to 1530nm.
⑦ G.657 (Bend-Insensitive Fiber)
G657 is a bend-insensitive fiber with a minimum bending radius of 5-10mm, making it the most commonly used cable for FTTH (Fiber to the Home) applications. It is widely used due to its better performance, but its cost is slightly higher than G652D. The ITU-T standard divides G657 into two subclasses, A and B, which are further divided into four subcategories: A1, A2, B2, and B3. Class A supports O, E, S, C, and L bands, while Class B supports O, C, and L bands.
Dec 11th.