This Recommendation describes two categories of single-mode optical fibre cable with improved bending loss performance compared with that of ITU-T G.652 fibres. ITU-T G.657 fibre was originally developed for use in access networks, including inside buildings at the end of these networks. Both categories A and B contain two subcategories which differ in macrobending loss.

Category A fibres are optimized for reduced macrobending loss compared to ITU-T G.652.D fibres and can be deployed throughout the access network. These fibres are suitable for use in the O-, E-, S-, C- and L-band (i.e., throughout the 1 260 nm to 1 625 nm range). Fibres and requirements in this category are a subset of ITU-T G.652.D and are therefore compliant¹ with ITU-T G.652.D fibres and have the same transmission and interconnection properties. Thus, ITU-T G.657.A fibres can be used for all networks where ITU-T G.652.D fibres are specified.

Subcategory ITU-T G.657.A1 fibres are appropriate for a minimum design radius of 10 mm.

Subcategory ITU-T G.657.A2 fibres are appropriate for a minimum design radius of 7.5 mm.

Category B fibres are optimized for further reduced macrobending loss and therefore are capable of being used at very low values of bend radius. These fibres are intended for short reach distances (less than 1 000 m) at the end of access networks, in particular inside buildings or near buildings (e.g., outside building riser cabling). The application length of ITU-T G.657.B fibre depends on the deployment strategy of each network operator. These fibres are suitable for use in the O-, E-, S-, Cand L-band (i.e., throughout the 1 260 nm to 1 625 nm range). Category B fibres are not necessarily compliant with ITU-T G.652.D]in terms of chromatic dispersion coefficient and polarization mode dispersion (PMD) specifications. These fibres, however, are system compatible² with ITU-T G.657.A (and ITU-T G.652.D) fibres in access networks.

Subcategory ITU-T G.657.B2 fibres are appropriate for a minimum design radius of 7.5 mm.

Subcategory ITU-T G.657.B3 fibres are appropriate for a minimum design radius of 5 mm.

This Recommendation and the different performance categories found in Tables 1 and 2 in clause 8 are intended to support the following related system Recommendations:

The meaning of the terms used in this Recommendation and the guidelines to be followed in the measurement to verify the various characteristics are given in [ITU-T G.650.1] and [ITU-T G.650.2].

The characteristics of these fibre categories, including the definitions of the relevant parameters, their test methods and relevant values, will be refined as studies and experience progress.

1 Compliance here means adherence to the referenced Recommendation ([ITU-T G.652], category D) meeting or exceeding the values of the specified attributes.

2 Compatibility means here that the product in this category will introduce negligible system impairment or deployment issues but may not be compliant with the referenced Recommendation ([ITU-T G.652], category D).