The “ITU-T G.657 Specifications of Twist-Loss Insensitive Single-Mode Optical Fiber and Cable” standard, developed by the International Telecommunication Union Telecommunications Standardization Sector (ITU-T), describes two categories of single-mode optical fiber cables suitable for use in access networks, including inside buildings at the ends of these networks.
This standard includes two subcategories, both categories A and B, that differ in macro bending loss. Category A fibers are suitable for use in the 1260 to 1625 nm band. Fibers and requirements in this category are a subset of ITU-T G.652.D fibers and have the same transmission and connection characteristics. Subcategory ITU-T G.657.A1 fibers are suitable for a minimum design radius of 10 mm. This subcategory completely covers ITU-T G.657 category A. ITU-T G.657.A2 fibers are suitable for a minimum design radius of 7,5 mm.
Category B fibers are suitable for transmission at 1310, 1550, and 1625 nm for limited distances. These fibers may have different splicing and connection characteristics than ITU-T G.652 fibers, but are capable of very low bend radius values. Subcategory ITU-T G.657.B2 fibers are suitable for a minimum design radius of 7,5 mm. This subcategory fully encompasses ITU-T G.657 Category B. ITU-T G.657.B3 fibers are suitable for a minimum design radius of 5 mm.
Worldwide, technologies for public transportation networks and broadband access networks are advancing rapidly. Among them, the technology applying single-mode fiber provides a high-capacity transmission medium that can meet the increasing demand for high-speed and broadband services.
Experience with the installation and operation of single-mode fiber and cable-based networks is vast and its specifications are described in the ITU-T G.652 standard. However, specific usage in optical access networks places different demands on fiber and cable, affecting their optimum performance characteristics. The differences in usage in public transport networks are mainly due to the high-density network of distribution and drop cables in the access network. Limited space and many manipulations require operator-friendly fiber performance and low bend sensitivity. Furthermore, cabling in crowded telecom offices, where space is a limiting factor, should be improved accordingly. Nevertheless, certain areas of public transport and data center networks can be identified as limited where bend-optimized cabling can be advantageous.
The aim of the ITU-T G.657 standard is to support this optimization by proposing significantly improved bending performance compared to ITU-T G.652 single-mode fiber and cables. One of these, Category A, is implemented via two categories of single-mode fiber that are fully compatible with ITU-T G.652 single-mode fibers and can be deployed across general transport and data center networks as well as access networks. The other, Category B, may not be compatible with ITU-T G.652 but has low macro bending loss values at very low bending radii and is designed for application in access networks inside or near buildings (e.g., off-building riser cabling). Category B fibers are system compatible with ITU - T G.657.A and ITU-T G.652.D fibers in access networks.
In the latest update of the ITU-T G.657 standard, among other things, the field of application for G.657 fiber was expanded and category B2 was merged with category A2.
The ITU-T G.657 standard is the latest version of the single-mode optical fiber standard and includes the specifications of bend-insensitive single-mode optical fibers. ITU-TG.657 fibers are mainly applied for broadband optical access networks in Telecom offices and customer premises in apartment buildings and single-family residences.
The ITU-T G.657 standard has two categories:
G.657.A and G.657.B fibers can be further divided into G.657.A1, G.657.A2, G.657.B2 and G.657.B3 according to their macrobending requirements. Among them, G.657.A2 and G.657.B3 fibers have better macrobending performance than G.657.A1 and G.657.B2 fibers.
Among the numerous testing, measurement, analysis and evaluation studies that our organization has carried out for businesses in various sectors, it also provides testing services defined in the “ITU-T G.657 Properties of single-mode optical fiber and cable insensitive to bending loss” standard with its trained and expert staff and advanced technological equipment.
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