An fiber-optic interferometric rotation sensor device has a laser source combined with an optical fiber. These are configured to cause interference between a beam from the laser source and a beam coming from the optical fiber. The laser source includes an optical cavity having a gain lasing medium. The sensor device includes, along the path of the beam output by the laser cavity, a beam splitter device associated with a mirror, wherein the beam split off from the beam output by the laser cavity is sent into one of the ends of the optical fiber and directed from the other end toward the gain lasing medium to form a nonlinear mirror. The splitter device is followed by a detector.