Single Mode Fiber Optic Cable Standards
Comprehensive technical overview of ITU-T specifications for single mode fiber optic cable systems
Currently, the transmission of optical signals in long-haul trunk optical networks, metropolitan optical networks, and access optical networks in fiber optic communications mainly uses single mode fiber optic cable. The international standards for single mode fiber optic cable are primarily from the ITU-T series, which define the characteristics and performance requirements for various types of single mode fiber optic cable.
These standards ensure interoperability, performance, and reliability across different manufacturers and applications of single mode fiber optic cable. The main ITU-T recommendations include G.650 "Definitions and test methods for relevant parameters of single mode fiber," G.652 "Characteristics of single mode fiber and光缆," G.653 "Characteristics of dispersion-shifted single mode fiber and光缆," G.654 "Characteristics of cut-off wavelength shifted single mode fiber and光缆," G.655 "Characteristics of non-zero dispersion-shifted single mode fiber and光缆," G.656 "Characteristics of non-zero dispersion-shifted fiber and光缆 for wideband transmission," and G.657 "Characteristics of bending loss-insensitive single mode fiber and光缆 for access networks."
Importance of Single Mode Fiber Optic Cable Standards
The standardization of single mode fiber optic cable is crucial for the global telecommunications infrastructure. These standards ensure that single mode fiber optic cable from different manufacturers can work together seamlessly in complex network architectures. They define critical parameters such as attenuation, dispersion, and mechanical properties that determine the performance and reliability of single mode fiber optic cable in various applications.
1. G.652 Fiber
G.652 fiber is a standard specification single mode fiber optic cable, with zero dispersion near the 1.3μm wavelength, but relatively high loss of 0.3~0.4dB/km. At the 1.55μm wavelength, the loss is lower at 0.2~0.25dB/km, but the dispersion is higher at 18~20ps/(nm·km). ITU-T named this fiber G.652, which can operate in both the 1.31μm window and the 1.55μm window.
This single mode fiber optic cable can be used in 2.5Gb/s trunk systems operating in the 1.55μm band. However, due to its relatively high dispersion, when transmitting 10Gb/s signals over distances exceeding 50km, expensive dispersion compensation modules are required. ITU-T subdivides G.652 fiber into four subcategories: G.652A, G.652B, G.652C, and G.652D, with main differences in parameters such as macro-bending loss, attenuation coefficient, and PMD coefficient.
G.652A Performance
- Also known as Standard Single Mode Fiber (SSMF)
- Supports 10Gb/s systems up to 400km
- 10Gb/s Ethernet transmission up to 40km
- Supports 40Gb/s systems up to 2km
- Cost-effective solution for many applications
G.652B Performance
- Enhanced version of standard single mode fiber optic cable
- Supports 10Gb/s systems over 3000km
- Supports 40Gb/s systems up to 80km
- Improved PMD characteristics
- Wider application range for high-speed networks
G.652A and G.652B fibers are also known as Standard Single Mode Fiber (SSMF) or conventional single mode fiber optic cable. Due to their relatively low cost, they have been widely deployed and are among the most commonly used single mode fiber optic cable types currently. The G.652C and G.652D variants offer improved performance in terms of water peak attenuation, making them suitable for extended wavelength applications.
Key Parameters of G.652 Single Mode Fiber Optic Cable
| Parameter | 1310nm | 1550nm |
|---|---|---|
| Attenuation | 0.3-0.4 dB/km | 0.2-0.25 dB/km |
| Dispersion | 0 ps/(nm·km) | 18-20 ps/(nm·km) |
| Mode Field Diameter | 9.3 ± 0.5 μm | 10.5 ± 1.0 μm |
| Cut-off Wavelength | ≤ 1260 nm |
2. G.653 Fiber
While G.652 fiber has the lowest loss value at 1.55μm, its dispersion is relatively large, with a dispersion parameter of 18~20ps/(nm·km), which limits its engineering applications. If the dispersion parameter value of the single mode fiber optic cable can be further reduced, the performance of fiber optic communication systems can be further improved, and transmission capacity can be increased.
In fact, the reason why the dispersion parameter D of G.652 fiber shows a zero value near 1.31μm is due to the mutual cancellation of waveguide dispersion and material dispersion. Therefore, through the design of the fiber structure and control of the refractive index profile, zero dispersion (or minimum dispersion) can be achieved at any wavelength in the 1.3~1.7μm range. This is the principle of zero dispersion wavelength shifting.
In the mid-1980s, a type of dispersion-shifted fiber (DSF) was successfully developed that shifts the zero dispersion wavelength from 1.3μm to 1.55μm. ITU-T named this single mode fiber optic cable G.653, and its dispersion characteristics are shown in Figure 2-14.
Dispersion Characteristics of Various Single Mode Fiber Optic Cable Types
Advantages and Limitations of G.653 Single Mode Fiber Optic Cable
Advantages
- Zero dispersion at 1550nm wavelength
- Lowest attenuation in the 1550nm window
- Excellent performance for single-channel high-speed systems
- Optimized for long-distance communication
Limitations
- Severe four-wave mixing in WDM systems
- Smaller effective core area than G.652
- Limited application in dense WDM environments
- Not ideal for high-channel-count systems
The G.653 single mode fiber optic cable was a significant advancement when first introduced, allowing for higher speed transmission over longer distances without dispersion compensation in single-channel systems. However, with the development of wavelength-division multiplexing (WDM) technology, its limitations became apparent due to the increased nonlinear effects, particularly four-wave mixing, which occurs when multiple wavelengths propagate through the fiber simultaneously.
Despite these limitations, G.653 single mode fiber optic cable still finds application in certain scenarios where WDM is not utilized and the advantages of zero dispersion at 1550nm are beneficial. It represents an important step in the evolution of single mode fiber optic cable technology, paving the way for subsequent developments in fiber design.
3. G.654 Fiber
To enable transoceanic intercontinental submarine fiber optic communications, scientists developed cut-off wavelength shifted single mode fiber based on the G.652 single mode fiber optic cable. This fiber has a refractive index profile structure similar to that of G.652 single mode fiber optic cable.
It reduces fiber attenuation by using a pure silica (SiO₂) core and achieves the required refractive index difference by doping the cladding with fluorine (F). ITU-T recommendations define this cut-off wavelength shifted single mode fiber as G.654 fiber. Compared with G.652 fiber, the outstanding feature of G.654 single mode fiber optic cable performance is its extremely low attenuation coefficient at the 1550nm operating wavelength, only about 0.15dB/km, earning it the designation of low/ultra-low loss fiber.
Additionally, the bending additional loss of the fiber is significantly improved through the cut-off wavelength shifting method. G.654 single mode fiber optic cable has traditionally been used in submarine cables and is standardized into four subcategories: A, B, C, and D, with main differences in the fiber's mode field diameter (MFD) range and macro-bending performance.
G.654 Subcategories Comparison
| Subcategory | Mode Field Diameter | Application | Key Feature |
|---|---|---|---|
| G.654A | 8.0-11.0 μm | Submarine | Low loss |
| G.654B | 8.0-11.0 μm | Submarine | Improved bending |
| G.654C | 9.0-11.0 μm | Submarine | Large effective area |
| G.654D | 9.0-11.0 μm | Submarine | Enhanced characteristics |
| G.654E | 10.5-12.0 μm | Terrestrial | High speed, long haul |
Currently, mainstream 400Gb/s technology faces the challenge of limited unrepeatered distance. To address this issue, new fiber technologies with both large effective area and low loss characteristics have become the focus of industry research and application. For this reason, the industry has reached a consensus on the terrestrial use of G.654 single mode fiber optic cable to meet the deployment requirements of ultra-100Gb/s systems.
In the latest revised version of G.654 published in September 2016, a subclass E was added for application in terrestrial high-speed transmission systems. The G.654E single mode fiber optic cable specifies parameters such as mode field diameter, effective area, macro-bending loss, dispersion parameter, and attenuation coefficient, making it suitable for high-speed, long-distance terrestrial optical communication systems. This development expands the application range of G.654 single mode fiber optic cable beyond traditional submarine installations.
4. G.655 Fiber
Because the effective core area of G.653 fiber is smaller than that of G.652 fiber, and coupled with the fact that G.653 fiber has a zero dispersion coefficient at the 1550nm wavelength, the four-wave mixing efficiency is very high when applied in WDM systems, causing severe interference.
To overcome the problem of high dispersion in G.652 fiber at the 1550nm wavelength and severe four-wave mixing in G.653 fiber, scientists developed a type of fiber with small positive dispersion or negative dispersion at the 1550nm operating wavelength by designing the refractive index profile based on the dispersion-shifted single mode fiber. This is known as non-zero dispersion-shifted single mode fiber (NZ-DSF).
Key Characteristics of G.655 Single Mode Fiber Optic Cable
This single mode fiber optic cable is characterized by non-zero dispersion in the 1530~1565nm operating window, maintaining an appropriate dispersion coefficient value that can suppress four-wave mixing, as shown in its dispersion characteristics in Figure 2-14. ITU-T named it G.655 fiber.
The NZ-DSF single mode fiber optic cable solves the dispersion limitation problem of G.652 fiber in the 1550nm window and reduces the limitation caused by four-wave mixing due to nonlinear effects. It is the preferred fiber type for dense wavelength division multiplexing fiber optic communication systems that实现 10Gb/s and above long-distance, large-capacity communication.
The G.655 single mode fiber optic cable was a significant innovation for WDM systems, providing a balance between dispersion and nonlinear effects. By maintaining a small but non-zero dispersion in the 1550nm window, it effectively suppresses four-wave mixing while still allowing for high-speed signal transmission over long distances without excessive dispersion compensation.
Different variants of G.655 single mode fiber optic cable offer varying dispersion values, typically in the range of 1-10 ps/(nm·km) in the C-band. This flexibility allows network designers to choose the appropriate fiber type based on specific system requirements, such as transmission distance, data rate, and channel spacing.
Low Dispersion
1-4 ps/(nm·km) suitable for very high-speed, moderate distance applications
Medium Dispersion
4-8 ps/(nm·km) balanced performance for most WDM systems
High Dispersion
8-12 ps/(nm·km) optimal for long-distance, high-channel-count systems
The introduction of G.655 single mode fiber optic cable significantly推动了 the development of dense wavelength division multiplexing (DWDM) technology, enabling the dramatic increase in fiber optic network capacity that we've witnessed over the past two decades. Its ability to support multiple high-speed channels simultaneously without significant crosstalk made it the foundation for modern high-capacity optical networks.
5. G.656 Fiber
To further expand the usable operating wavelength range of G.655 fiber, extending from the original C+L bands to the S+C+L bands, a broadband optical transmission non-zero dispersion-shifted fiber suitable for DWDM and CWDM systems was developed. ITU-T named it G.656 fiber, which is characterized by having an appropriate dispersion coefficient, moderate effective area, and relatively small dispersion slope within the operating wavelength range.
G.656 single mode fiber optic cable is essentially a type of broadband non-zero dispersion-flattened fiber, with a dispersion coefficient ranging from 2~14ps/(nm·km) in the S+C+L bands and a small dispersion slope. The effective area at the 1550nm wavelength is 52~64μm².
G.656 vs G.655C Fiber Parameter Comparison
| Parameter | G.655C | G.656 |
|---|---|---|
| Operating Wavelength | 1530-1565 nm (C-band) | 1460-1625 nm (S+C+L bands) |
| Dispersion Coefficient | 1-6 ps/(nm·km) | 2-14 ps/(nm·km) |
| Dispersion Slope | ≤ 0.10 ps/(nm²·km) | ≤ 0.12 ps/(nm²·km) |
| Effective Area | ≥ 55 μm² | 52-64 μm² |
| Attenuation (1550nm) | ≤ 0.25 dB/km | ≤ 0.25 dB/km |
The G.656 single mode fiber optic cable can significantly reduce the dispersion compensation cost of the system while further exploiting the potential huge bandwidth of silica glass fiber. It can ensure that a system with 100GHz channel spacing and 50Gb/s rate has a transmission distance of no less than 500km.
The extended wavelength range of G.656 single mode fiber optic cable provides network operators with additional bandwidth for future expansion, without the need for complete fiber replacement. This makes it an attractive option for networks that require long-term scalability. The S+C+L band coverage effectively increases the available spectrum by more than three times compared to the traditional C-band alone.
Another significant advantage of G.656 single mode fiber optic cable is its ability to support both dense wavelength division multiplexing (DWDM) and coarse wavelength division multiplexing (CWDM) systems. This versatility allows network designers to choose the most appropriate multiplexing technology based on specific application requirements, whether for high-density, long-haul links or lower-density, cost-sensitive applications.
As data rates continue to increase and network capacity demands grow, the G.656 single mode fiber optic cable represents an important advancement in single mode fiber technology. Its broadband characteristics, combined with good dispersion and loss properties, make it well-suited for next-generation optical communication systems that require both high performance and future-proofing.
Choosing the Right Single Mode Fiber Optic Cable
Each type of single mode fiber optic cable specified by ITU-T G.652 to G.656 offers unique characteristics optimized for specific applications. From standard installations to high-performance, long-haul systems, the evolution of single mode fiber optic cable technology continues to enable the ever-increasing demands of modern communication networks.
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