Fibre-optic current sensor exploiting Sagnac interferometer with Lyot-type fibre depolarizers

A Sagnac interferometer-type fibre-optic current sensor using single-mode fibre was proposed. To prevent non-reciprocal phase error, depolarizers are used in the Sagnac coil. This configuration makes the current sensor less costly and rather accurate. We fabricated the current sensor for an electric power substation by using the proposed technique and confirmed its characteristics. The dynamic range of 50 dB and ratio error within ±0.2% were satisfied. These results have demonstrated that the Sagnac interferometer-type current sensor using a single-mode fibre is suitable as an instrument for electric power plants.