Sagnac interferometer-type fibre-optic current sensor using single-mode fibre down leads

A Sagnac interferometer-type fibre-optic current sensor using single-mode fibre down leads was proposed. To prevent non-reciprocal phase error, depolarizers are used in the Sagnac coil. This configuration makes the current sensor less costly and more accurate. We fabricated the current sensor for an electric power substation by using the proposed technique and confirmed its characteristics. The dynamic range of 80 dB and ratio error within +/-0.5% were satisfied. These results have demonstrated that the Sagnac interferometer-type current sensor using single-mode fibre down leads is suitable as an instrument for electric power plants.