This part of IEC 60793 establishes uniform requirements for the mechanical characteristic: fibre curl or latent curvature in uncoated optical fibres, i.e. a specified length of the fibre has been stripped from coating. 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 are recognized for the measurement of fibre curl, in uncoated optical fibres:
method A: side view microscopy;
method B: laser beam scattering.
Both methods measure 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. Method A uses visual or digital video methods to determine the deflection of the fibre while method B uses a line sensor to measure the maximum deflection of one laser beam relative to a reference laser beam.
By measuring the deflection behaviour of the fibre as it is rotated about its axis and understanding the geometry of the measuring device, the fibre’s radius of curvature can be calculated from simple circular models, the derivation of which are given in Annex C.
Both methods are applicable to type B optical fibres as described in IEC 60793 (all parts).
Method A is the reference test method, used to resolve disputes.
