A dual interferometer implemented in parallel on a single birefringent monomode optical fibre

Abstract

An interferometric optical fibre sensor has been constructed employing a highly birefringent monomode optical fibre sensing element. The sensing element is configured such that two separate division-of-amplitude interferometers are effectively realised within a single fibre, each corresponding to one of the orthogonal polarisation eigenmodes. Both the optical phase change of each interferometer and the differential optical phase change induced by a physical change within the fibre may be separately recovered. The high resolution of the conventional interferometric sensor is therefore maintained with a greatly increased unambiguous dynamic range corresponding to the period of the differential phase change. The system has been demonstrated as a temperature sensor.