Residual stress diagnosis in jacketed optical fibres by a pulse delay technique

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Description/Abstract

The application of a secondary jacketing material such as nylon and subsequent incorporation of a fibre into a cable produces a level of residual stress within the fibre which depends upon the materials, cable structure and manufacturing method. The remaining tension or compression in the cabled fibre is of some importance to cable designers since ideally the fibre should be neutrally stressed if static fatigue and microbending effects are to be avoided. We have found that the precise measurement of the transit time of a pulse within the fibre provides a powerful diagnostic tool for residual longitudinal stress assessment, being capable of detecting a tension as low as a few g.wt in a km length of fibre. We report here the development of the technique, its calibration and the results of stress tests on jacketed fibres