Disclosed is a Sagnac interferometer with a looped or an in-line optical fiber. The interferometer includes an hybrid integrated optical circuit having at least a first, electro-optic, substrate and a second, transparent, substrate with a common interface, the first substrate including a first optical waveguide, a second optical waveguide, the first optical waveguide and the second optical waveguide being connected to at least one end of the fiber-optic coil, and an input-output optical waveguide connected to a light source and to a detection system, the second substrate including at least one U-shaped optical waveguide and the hybrid integrated optical circuit including a planar waveguide Y-junction with a common branch and two secondary branches.