On-line tension measurement in an optical fibre

A process of contactless monitoring the tension in an optical fibre and a tension meter which enables contactless measurement of the tension in a bare and in a coated optical fibre. By measuring the retardation induced by the birefringence of an optical fibre by means of a polarised light beam incident to the fibre at an angle between about 10° and 25° to the detection optical axis, it is possible to accurately measure tensions over a wide range, i.e., from less than about 10 g to about 450 g. The method enables monitoring the tension during the ramp-up of the drawing process and is particularly advantageous for the control of the drawing tension in manufacturing of NZD, multimode or special fibres. Accurate monitoring of the tension both on a bare and on a coated fibre can also be achieved.