Abstract: The Verdet coefficient of fiber rings with different twisted turns has been measured with an interference method. The results basically agree with the reported values measured under 1.322 μm wavelength in a vertical annealed fiber and under 0.633 μm in vertical twisted fiber by measuring the deflection angles Δθ. The Sagnac interference method and a 1.31 μm light source, generally used in fiber-optics current sensor (FOCS), are used to measure the Verdet values. The measured results are useful in the research of FOCS.

Key words: Sagnac FOCS, Verdet coefficient, twisted fiber ring