G.652 fiber is the earliest type of single-mode optical fiber used and is currently the most widely used optical fiber in communication networks. Whether it is a long-distance network, local network, or access network, it is the absolute protagonist, accounting for more than 95% of its overall usage. Often referred to as standard single-mode fiber (SSMF), G.652 fiber has undergone several advancements and subcategories that cater to specific applications. In this blog post, we will explore the differences and applications of each subcategory of G.652 fiber, shedding light on the critical role it plays in modern communication networks.

What is G.652 Fiber?

G.652 is a type of optical fiber designed for carrying a single mode of light, which means it is ideal for long-distance, high-capacity communication networks. It is designed to have a zero dispersion wavelength of around 1310 nm, so it is optimized for operation in the 1310 nm band and can also operate in the 1550 nm band. It offers several advantages that make it a popular choice for a wide range of applications. The first version of G.652 fiber was standardized in 1984 and now has four subcategories: G.652.A, G.652.B, G.652.C, and G.652.D. All four variants have the same G.652 core size, which is 8-10 microns. Today’s OS2 optical fiber is generally G.652.C or G.652.D, and categories A and B are rarely used.

Differences Between Various Subcategories of G.652 Fiber

(1) Attenuation Characteristics of Optical Fiber

The loss coefficient of conventional single-mode fiber changes with wavelength, as shown in the figure below. Due to the influence of hydroxyl ions in the optical fiber material, the attenuation of the optical fiber at the wavelength of 1383nm is relatively large, and a wave peak will be displayed in the figure, which is usually called the “water peak”. Therefore, communication systems generally avoid the 1383nm wavelength area.

Conventional single-mode optical fiber has good attenuation characteristics in the wavelength range from 1260nm to 1675nm (excluding the 1380nm region). Therefore, ITU-T divides the single-mode optical fiber communication system into several optical bands: O, E, S, C, L, and U. The wavelength range of each band is shown in the figure below.

Among the above bands, except E band, several other bands can be used for communication. A company called Lucent couldn’t stand it anymore. In 1998, they invented an optical fiber. The attenuation curve of this fiber in the E-band is flat, as shown in the figure below. This kind of optical fiber can be used for communication in the O, E, S, C, L, and U light bands. Therefore, this kind of optical fiber is also called full-wave optical fiber, or low water peak optical fiber.

(2) PMD Coefficient of Optical Fiber

The optical fiber is pulled out through a drawing pulley, just like ramen noodles, and the cross-section of the optical fiber is not a completely regular circle. This results in that when an optical signal is transmitted in a single-mode fiber, the two mutually perpendicular polarization modes contained in the fundamental mode will propagate at different rates, resulting in a time difference when reaching the other end of the fiber. This is Polarization Mode Dispersion, or PMD for short, as shown in the figure below. The time difference per unit length of the optical fiber is called the PMD coefficient.

When the communication rate is low, PMD is not enough to affect system transmission. As the transmission rate increases, PMD becomes an important factor affecting the transmission distance. The relationship between PMD coefficient, transmission rate and transmission distance is shown in the table below.

Obviously, the smaller the PMD coefficient of optical fiber, the better. The current national standard recommends that the PMD coefficient not exceed 0.2ps/√km, and the PMD coefficient of actual optical fiber products generally does not exceed 0.1ps/√km.

Application of G.652 Fiber

Optical fiber types with larger PMD coefficients show that they cannot meet the transmission requirements of increasingly higher speeds. Therefore, with the improvement of optical fiber manufacturing technology, G.652A and G.652C have gradually been eliminated by the market.

There is current market demand for both G.652B and G.652D optical fibers because the prices of G.652D and G.652B optical fibers are almost the same. Therefore, the sales proportion of G.652B optical fiber is very low (less than 5% of the total sales of G.652 optical fiber).

Although G.652D optical fiber is a full-wave optical fiber, it seems that there is not much need to use so many bands for optical communication. For example, the current DWDM mainly operates 80 waves in the C band. For many years, the S and L bands have not been used. Moreover, due to the limitation of the nonlinear effect of optical fiber, the number of channels that can be carried in the wavelength division system is limited. For DWDM applications, full-wave optical fiber is completely unnecessary.

In order to cooperate with the use of full-wave optical fiber, ITU-T released the CWDM standard in 2002, which divided the full band of single-mode optical fiber into 18 wavelengths, and the channel spacing of each wavelength is 20nm, as shown in the figure below.

However, since CWDM has no advantages over DWDM, nearly 20 years after the release of the G.652D optical fiber and CWDM standards, there are few practical applications in the E-band. Until the past two years, passive wavelength division using CWDM technology has been widely used in C-RAN (centralized radio access network) bearers. The advantages of G.652D optical fiber are fully reflected.

Conclusion

G.652 fiber, in its various subcategories, has evolved over the years to meet the ever-increasing demands of modern communication networks. Understanding the differences and applications of each subcategory is essential for designing and maintaining efficient and high-performance optical networks. Whether you’re working on long-haul connections, metropolitan networks, or cutting-edge data centers, there’s a G.652 fiber subcategory that’s perfectly suited to your needs. As technology continues to advance, G.652 fiber will remain a fundamental component of our global communication infrastructure, facilitating the flow of data and information across the world. If you want to know more about fiber optic products, please feel free to contact HOLIGHT at sales@holightoptic.com!