Observation of the Sagnac effect in a ring resonant interferometer with a low-coherence light source

A fibre-optic resonant ring interferometer with a low-coherent light source was investigated experimentally. The feasibility of measuring the paramete rs of ring cavities characterised by very narrow lines (of the order of ten s of kilohertz) was demonstrated by using a broad-band light source and a r etroreflecting Doppler mirror. The Sagnac effect was first observed in a ri ng resonant interferometer with a low-coherence light source. Modulation an d compensation of the phase nonrecriprocity in a low-coherence resonant int erferometer with the aid of an optical frequency shifter located outside a sensing fibre loop were observed experimentally.