Standards and classification of optical cables and fibers

In 1966, the father of fiber optics, Gao Kun, proposed the concept of fiber optic communication. In 1977, the world’s first fiber optic communication system was put into commercial use in the United States. In 1982, China’s first practical fiber optic communication project, the Wuhan “82” Project, was successfully implemented. Until now, “fiber to the home” has brought optical communication into ordinary people’s homes.

However, in the development process of fiber optic cables, various standards coexist due to different research institutions, usage areas, application categories, and other factors. These standards each have their own characteristics and are interrelated. This article provides a simple classification and analysis of the current mainstream standards for fiber optic cables in China’s optical communication industry. While improving my understanding of standards, I hope it can also be helpful to colleagues who are interested in this information.

At present, the standards for fiber optic cables in China’s optical communication industry are mainly divided into two parts: international standards and domestic standards. The international standards mainly include the IEC series standards issued by the International Electrotechnical Commission and the ITU series standards issued by the International Telecommunication Union; The domestic standards mainly include the GB series standards jointly issued by the General Administration of Quality Supervision, Inspection and Quarantine of China and the National Standardization Administration of China, and the YD/T series standards issued by the Ministry of Information Industry of China.

A fiber optic cable itself has the function of independent optical signal transmission, which means that in an ideal environment, only one fiber optic cable, along with terminal devices at both ends, can form an optical communication system. So, the material and structure of optical fibers determine their optical transmission performance. However, due to the relatively poor mechanical and environmental properties of optical fibers, it is necessary to make them into optical cables through multiple processes to enhance their mechanical and environmental properties during actual use. In this process, the impact on the optical transmission performance of optical fibers must be minimized.

Part I Standards and Classification of Fibers

Fiber Standards

As shown in the table below, common international standards for optical fibers include IEC 60793 series and ITU G65x series, while domestic standards are GB series. The ITU series standards include both fiber optic and fiber optic cable standards.

In addition, in certain specific application fields, there are corresponding standards that specify the requirements for the fiber optic cables involved. A representative example is ISO 11801 Information technology Generic cabling for customer premises, which is a comprehensive cabling standard published by the International Committee for Standardization.

Due to the different formation systems of various standards, the focus is also different. For the same type of fiber optic products, different standards have different codes. Just like how we often see different fiber optic codes such as G652D, OS2, B1.3 in various industry news, manufacturer product information, and bidding documents, when in fact these codes refer to the same type of fiber optic product.

Fiber Classifications

We can compare the definitions of common optical fibers in various standards through the following table:

In terms of transmission performance, single-mode transmission systems are better than multi-mode transmission systems. But in current optical communication systems, not only performance but also system cost should be considered. From a cost perspective, single-mode optical cables are relatively cheaper than multi-mode optical cables, while for optical components such as light sources, receivers, connectors, etc., multi-mode cables are much cheaper than single-mode cables. Therefore, there are different focuses in different application fields. In long-distance trunk systems, fiber optic cables are used in large quantities and have high requirements for transmission performance, so single-mode transmission systems are often used. In areas close to user terminals, such as the comprehensive cabling system in buildings, the amount of optical devices used is often large, and the transmission performance of multi-mode transmission systems can also meet user needs, so single-mode transmission systems are often used.

From the perspective of standard usage, long-distance trunk systems often adopt the ITU-T G65x series standards. Integrated cabling systems often adopt the ISO 11801 standard. Therefore, we will use these two types of standards to understand the characteristics of various single-mode and multi-mode fibers in Table 1.

Single Mode Fiber (ITU/T G65x series)

G652 standard single-mode fiber

Standard single-mode fiber refers to a single-mode fiber with zero dispersion wavelength in the 1.3um (1310nm) window. The International Telecommunication Union (ITU-T) defines this fiber as G652 fiber. Its characteristic is that when the working wavelength is at 1.3um (1310nm), the dispersion of the optical fiber is very small, and the transmission distance of the system is only limited by the attenuation of the optical fiber. However, this type of fiber has significant losses in the 1.3um (1310nm) wavelength band, ranging from approximately 0.3dB/km to 0.4dB/km; The loss in the 1.55um band is relatively small, ranging from 0.2dB/km to 0.25dB/km. The dispersion is 3.5ps/nm · km in the 1.3um (1310nm) band and larger at around 20ps/nm · km in the 1.5um band. This type of fiber optic can support 2.5Gb/s trunk systems in the 1.55um band, but due to the large dispersion in this band, if a 10Gb/s signal is transmitted over a distance of more than 50 kilometers, an expensive dispersion compensation module is required.

G.652 fiber optic

Single mode optical fiber, with a core diameter of generally 9 or 10 μ m, has a total dispersion of zero at a wavelength of 1310nm. From the perspective of the loss characteristics of optical fibers, 1310nm is exactly a low loss window for optical fibers, so the 1310nm wavelength range has become an ideal working window for optical fiber communication, with another window being 1550nm. The main parameters of 1310nm conventional single-mode fiber are determined by the International Telecommunication Union ITU-T in the G652 recommendation, therefore conventional single-mode fiber is also known as G652 fiber.  

ITU-T classifies G.652 fibers into four categories, namely G.652. A, G.652. B, G.652. C, and G.652. D. The classification of these four types of fibers is mainly based on the requirements of PMD (dispersion) and attenuation at 1383nm (revised G.652 fiber standard in January 2003).

*G.652. A fiber optic cable is used to support a transmission distance of up to 400km for 10Gbit/s systems; The transmission of 10Gbit/s Ethernet reaches 40km, and the distance supporting 40Gbit/s systems is 2km.  

*G.652. B fiber optic cable is used to support transmission distances of over 3000km for 10Gbit/s systems, and 80km for 40Gbit/s systems.  

*G.652. C has the same basic properties as G.652A, but has a lower attenuation coefficient at 1550nm and eliminates the water absorption peak near 1380nm, allowing the system to operate in the 1360-1530nm wavelength range. Similar to G.652. A, but the allowed wavelength range is extended from 1360 nm to 1530 nm.  

*The G.652. D properties are basically the same as those of G.652B fiber, while the attenuation coefficient is the same as that of G.652C fiber, which means the system can operate in the 1360-1530nm wavelength range. The PMDQ requirements for anhydrous absorption peak fiber G.652. D are stricter than those for G.652. C.  

Zero water peak fiber optic cable, also known as full wave fiber optic cable

In the manufacturing process of traditional single-mode optical fibers, a light absorption peak called the water peak appears in the 1400nm wavelength region, which originates from the absorption of hydroxide ions. The water peak increases the attenuation loss in this specific area. With the research and development of higher transmission rate applications such as 40Gb/s, multi-channel wavelength division multiplexing (WDM wavelength division multiplexing) is increasingly being adopted. Traditional single-mode fibers in the 1400nm water peak region render the four channels of the E-band unusable, thus failing to achieve optimal performance.  

In order to address the shortcomings of traditional single-mode fibers in multi-channel wavelength division multiplexing, a new single-mode fiber called “zero water peak” single-mode fiber is adopted. To use the entire spectral range, high attenuation in the water peak region must be eliminated. Zero water peak fiber has no hydroxide ions during manufacturing, thus achieving better attenuation control in the 1400nm region. By eliminating water peaks, not only can CWDM technology use the E-band, but it has also become an ideal single-mode fiber for high-speed communication.  

At present, the zero water peak single-mode fiber optic cable surpasses the latest indicator of G.652. D, eliminating the influence of 1400nm water peak and providing users with a wider range of transmission bandwidth. Users can freely use all bands from 1260nm to 1620nm. Therefore, the transmission channel has increased from 240 to 400, with 50% more available bandwidth than traditional single-mode fiber, laying a solid foundation for the future upgrade of CWDM coarse wavelength division multiplexing technology to 100G bandwidth. TeraSPEED solution is an ideal backbone fiber system for park/city level.  

Meanwhile, as G.652. D is the latest specification for single-mode fibers, it is the most stringent and fully backward compatible specification among all G.652 levels. If only indicating G.652 means the performance specification of G.652. A, this should be particularly noted.

G653 dispersion shifted fiber

A dispersion shifted fiber (DSF) has been developed to shift the zero dispersion wavelength from 1.3um to 1.55um in response to the characteristic of standard single-mode fiber attenuation and zero dispersion not being at the same operating wavelength. ITU defines this type of fiber as G653.

G654 minimum attenuation fiber

In order to meet the demand for long-distance communication of submarine optical cables, a pure quartz core single-mode fiber has been developed for the 1.55um band, which has the lowest attenuation in this band, only 0.185dB/km. ITU defines this type of fiber as G654 fiber. The dispersion of G654 fiber is zero in the 1.3um band, but the dispersion is relatively large in the 1.55um band, about 17-20ps/nm · km.

G655 non-zero dispersion fiber

The dispersion shifted fiber mentioned earlier has zero dispersion in the 1.55um band, which is not conducive to multi-channel WDM transmission. When a large number of channels are used and the spacing between channels is small, four wave mixing (FWM) occurs, leading to crosstalk between channels. People’s research has found that if the dispersion of fiber optic lines is zero, the interference of FWM will be very serious; If there is trace dispersion, FWM interference will actually decrease, so a new type of optical fiber, namely non-zero dispersion optical fiber, has been born. ITU defines it as G655 fiber optic. Non zero dispersion optical fiber is actually an improved dispersion shifted fiber, with a zero dispersion wavelength not at 1.55um, but at 1.525um or 1.585um. Therefore, non zero dispersion optical fiber reduces both dispersion effect and four wave mixing effect, while standard fiber and dispersion shifted fiber can only overcome one of these two defects. Therefore, non zero dispersion optical fiber combines the best transmission characteristics of standard fiber and dispersion shifted fiber, and is particularly suitable for transmission in high-density DWM systems.

G656 non-zero dispersion fiber

G656 fiber, also known as non-zero dispersion fiber for broadband optical transmission, is an improved version of G655 fiber. It expands the band range of non-zero dispersion from 1.525um or 1.585um of G655 fiber to 1.460-1.625, which will greatly improve the application range of WDM systems. G656 fiber can significantly reduce the dispersion compensation cost of the system and further explore the potential huge bandwidth of quartz glass fiber. G656 fiber optic can ensure a channel spacing of 100GHz and a 40Gbit/s system transmission of at least 400km.

G657 bending insensitive fiber

Due to the widespread use of optical transmission systems in access networks, installation environments have raised higher requirements for the bending performance of optical fibers, resulting in the emergence of bend insensitive single-mode optical fibers. ITU defines it as G657 fiber optic. Compared to ordinary single-mode fibers, it has a smaller bending radius and macro bending loss.

Multimode Fiber

Multimode fiber is currently widely used in access networks

In September 2002, ISO/IEC 11801 officially issued a new standard grade for multimode optical fibers, which reclassified multimode optical fibers into three categories: OM1, OM2, and OM3. Among them, OM1 and OM2 refer to the traditional 50 μ m and 62.5 μ m multimode optical fibers, while OM3 refers to 10 Gigabit multimode optical fibers. In 2009, a new type of OM4 10G multimode fiber was added.

The differences between several multimode fibers are shown in the table below:

Note: In ISO/IEC 11801, only bandwidth is required for OM1 and OM2. However, in the actual selection and application of optical fibers, certain rules have been formed: OM1 refers to traditional 62.5/125 optical fibers, OM2 refers to traditional 50/125 optical fibers, and 10 Gigabit multimode OM3 and OM4 are both new generation 50/125 optical fibers.

Part II Standards And Classification Of Fiber Optic Cable

Due to the fact that optical cables are mainly used to enhance the physical and mechanical properties of optical fibers, the standards related to optical cables are relatively simpler compared to optical fibers

Let’s take a look at the standards related to optical cables:

Cable standard is generally divided into two parts in terms of content: one is some general guidelines and testing methods for all optical cables involved in this standard, such as IEC 60794-1, GB/T 7424.1, GB/T 7424.2, etc. The other part is a separate specification developed for different application areas or usage environments, such as IEC 60794-2, GB/T 13993.2, YD/T 1258.3, etc.

Let’s take the fiber optic cable testing project as a starting point to understand the differences and connections between various fiber optic cable standards.

The above table shows common testing items for communication optical cables, and the selection of specific testing items varies for different types of optical cables. As outdoor optical cables are used in outdoor environments, more attention is paid to their tensile strength, impact resistance, compression resistance, water resistance, and other properties. Indoor optical cables pay more attention to their winding, bending, flame retardant and other properties. So, outdoor optical cables often do not have aging, burning, and other test items, and indoor optical cables generally do not have water resistance, low-temperature impact, low-temperature bending, and other test items. Moreover, in testing projects such as stretching, flattening, and impact, the specific parameter requirements for indoor optical cables are much lower than those for outdoor optical cables. Indoor and outdoor universal optical cables combine the characteristics of both indoor and outdoor optical cables, including flame retardancy, water resistance, tensile strength, impact resistance, and compression resistance. They also meet the needs of different indoor and outdoor application environments, using relatively balanced parameter values.

Since optical cables have different classifications, how can we quickly identify a particular cable?

There is no relevant standard in international standards to define the naming of optical cables. In China, it is usually defined according to the<YD/T 908 Optical Cable Model Naming Method>standard.