A new technique for the relative measurement of scatter levels in single mode fibres

Introduction

The ability to measure relative scatter levels in single-mode fibres is essential for minimising fibre losses in telecommunications fibres operating in the 2nd and 3rd window for optical communications. In this way fabrication processes can be optimised in response to small improvements in measured scatter levels. Surprisingly, there is no simple way in which this can be done with sufficient accuracy to suit current very-low fibre scatter losses.

We therefore describe a new sensitive technique to separate the Rayleigh scatter loss from the total loss in a single mode fibre. In this, a reference fibre, the scatter loss of which may, if required, be determined by calorimetric techniques, is spliced to the fibre under investigation. The splice loss is then probed using OTDR. The backscattered light powers from each side of the splice are compared by using the test and reference fibres in turn as the launch fibre. The technique is particularly suited to determining very small changes in scatter from fibre to fibre and is therefore ideal for process control and optimisation.

Presented at IEE Colloquium Test Equipment for Optical Communications Systems London 28-May (1986)

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