This part of IEC 60793 is applicable to optical fibre types D1, D2, D3, as described in Table 1. These fibres are polarization-maintaining fibre types, and are used or can be incorporated in information transmission equipment and optical fibre cable. These fibres are available for use in optical transport networks.Three types of requirements apply to these fibres: general requirements defined in IEC 60793-2; specific requirements common to the category D polarization-maintaining fibres covered in this standard and which are given in Clause 3; particular requirements applicable to individual fibre types or specific applications, which are defined in Annexes A to C.