This part of IEC 60793 establishes uniform requirements for the mechanical characteristic fibre curl or latent curvature, in uncoated optical fibres. Fibre curl has been identified as an important parameter for minimizing the splice loss of optical fibres when using passive alignment fusion splicers or active alignment mass fusion splicers.

Two methods, presented in Annexes A and B respectively, are recognized for the measurement of fibre curl, in uncoated optical fibres:

• method A: side view microscopy;
• method B: laser beam scattering.

The side view microscopy procedure measures the radius of curvature of an uncoated fibre by determining the amount of deflection that occurs as an unsupported fibre end is rotated about the fibre's axis.

The laser beam scattering procedure measures fibre curl in an optical fibre by laser beam scattering. By knowing the maximum deflection of the fibre and the overhang distance from the fibre fixture to the measurement point, the fibre's radius of curvature can be calculated from a simple circular model, the derivation of which is given in annex C.

Both methods are applicable to types A1, A2, A3 and B optical fibres.

Method A is the reference test method, used to resolve disputes.