Abstract
A current sensor based on a stabilised fibre-optic Sagnac interferometer has been constructed and preliminary tests have been carried out. Measurements made with this system are independent of variations in the following parameters: laser intensity, light intensity injected into the optical fibre and birefringence within the fibre. The stabilised output is obtained by electronically combining the output signal from the interferometer with samples of the signal which have traversed the optical fibre in opposite directions. The mathematical basis for the stabilisation technique and construction details for the instrument are given.