A fiber that supports only one propagation mode for each polarization direction at a given wavelength is called a single-mode fiber. According to the ITU-T recommendation, single-mode fibers can be divided into six types: G.652 (non-dispersion 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), and G.657 (bend resistant fiber). Among them, G.652 and G.655 single-mode fibers are the most common types of fibers. This article will explain the classification and differences of these two single-mode fibers in detail.

G.652 Single-mode Fiber Type In 1984, the International Telecommunication Union ITU-T formulated the first version of the G.652 single-mode fiber. After five revisions in 1988, 1992, 1996, 2000, and 2003, it was revised for the sixth time in 2005 to form the current latest version (the seventh version). In the sixth version, G.652 single-mode fiber is divided into four types: G.652A, G.652B, G.652C, and G.652D, with a core diameter range of 8-10μm. Among them, G.652A and G.652B single-mode fibers have zero dispersion wavelengths near 1310nm, which are very suitable for application environments in the 1310nm band. Due to their water absorption peak characteristics, G.652A and G.652B single-mode fibers are not suitable for wavelength division multiplexing (WDM) application environments. G.652C and G.652D single-mode fibers have a lower attenuation coefficient at 1550nm, and they eliminate the water absorption peak near 1380nm. They can work in the 1360nm~1530nm band to support Wavelength Division Multiplexing (WDM) transmission. Among them, G.652D single-mode fiber is the most stringent single-mode fiber among all G.652 levels and can be fully backward compatible. It has no structural difference from ordinary G.652 fiber and is currently the most advanced non-dispersion shifted single-mode fiber used in metropolitan area networks. The following figure lists the basic parameters of the four types of G.652 single-mode fibers.

Explanation:

E band: Wavelength range is 1360nm~1460nm

S band: Wavelength range is 1460nm~1530nm

C band: Wavelength range is 1530nm~1565nm

L band: Wavelength range is 1565nm~1625nm

G.655 Single-mode Fiber Type G.655 single-mode fiber was specially designed for the new generation of optical amplifier dense wavelength division multiplexing transmission systems in 1994. It is divided into G.655A, G.655B, G.655C, G.655D, and G.655E single-mode fibers. Among them, G.655C, G.655D, and G.655E single-mode fibers are the three most commonly used single-mode fibers at present. Because the dispersion of G.655 single-mode fiber is close to zero (not equal to zero) at a wavelength of 1550nm, it is also called non-zero dispersion shifted fiber or NZDSF (NonZero Dispersion Shifted Fiber). NZDSF can be divided into (-D) NZDSF and (+D) NZDSF, which represent the negative slope and positive slope of the wavelength, respectively, as shown in the figure below:

Compared with G.652 single-mode fiber, G.655 single-mode fiber has lower dispersion in the C band (1530nm~1565nm), so the function of the optical amplifier can be maximized in this band, and the core area of the fiber is larger. As an improved dispersion-shifted single-mode fiber, G.655 single-mode fiber can suppress nonlinear effects such as four-wave mixing with lower dispersion, suitable for longer-distance and larger-capacity application transmission, fully meeting the needs of DWDM networks.

The following table lists the basic parameters of three common types of G.655 single-mode fibers.

How to Choose Between G.652 and G.655 Single-mode Fibers?

G.652 single-mode fiber is commonly used in local area networks, metropolitan area networks, access networks, and coarse wavelength division multiplexing transmissions. Among them, coarse wavelength division multiplexing transmission is an economical and efficient choice, generally using G.652 single-mode fiber that does not need to amplify the optical signal for short-distance transmission, while G.655 single-mode fiber is the second most common type of fiber in terrestrial networks, its main feature is low dispersion (including dispersion and polarization mode dispersion), generally deployed in long-distance transmission networks and dense wavelength division multiplexing transmission networks.

Both G.652 single-mode fiber and its upgraded version G.657 single-mode fiber are low-cost standard single-mode fibers, very suitable for short-distance transmission with a transmission rate of less than 10Gbps. If your network transmission rate is higher than 10Gbps or needs to be transmitted over a long distance, without considering the cost, G.655 single-mode fiber is a good choice. The following table lists the application of G.652 and G.655 single-mode fibers in coarse wavelength division multiplexing or dense wavelength division multiplexing transmission:

Conclusion As can be seen from the above, different types of single-mode fibers have different application fields. For long-distance transmission, choosing the right single-mode fiber is crucial. In actual applications, performance, cost, reliability, and safety and other factors need to be considered comprehensively. For example, in a network with medium to long distance transmission (such as 2km) and not high transmission rate (such as 10Gbps), considering the cost, you can preferentially choose G.652 single-mode fiber. If it is a higher transmission rate (more than 10Gbps) and a longer transmission distance (more than 40km), G.655 single-mode fiber is a good solution.