Optical fibre backscatter-loss signatures: identification of features and correlation with known defects using the two-channel technique

Abstract

A pulse propagating in an optical fibre returns scattered light to the source as an exponentially decaying waveform, the instantaneous slope of which yields the local attenuation at a corresponding point in the fibre. However, plots of local attenuation with length (the backscatter-loss signature) frequently exhibit severe fluctuations and anomalies such as negative values. We report here a study based on the newly-developed two-channel technique, aimed at verifying the accuracy of the average loss determined by backscatter measurements and correlating features in the signature with known fibre defects. In particular, a complete spectral backscatter attenuation measurement performed over a wide spectral range has been obtained, thus allowing an effective comparison to be made with that obtained by the conventional cutback technique.
Furthermore, backscatter-loss signatures are presented which clearly show correlation with programmed fibre defects and indicate that, in contrast to the conclusions of ref. 2, in many cases diameter fluctuations are the cause of unidentified features in the backscatter waveform. Moreover, it is possible to infer the nature of the diameter variation from its loss signature.

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