Abstract: An optical-fiber polarimetric sensor for measuring the displacement of an object relative to a frame, the sensor comprising a measurement optical fiber secured, over a fraction of its length, both to a central point of the object and to first and second fixed points of the frame, means disposed at one end of the measurement fiber and serving to emit a light beam of determined polarization into said measurement fiber, means for exerting twist on the measurement fiber so as to modify the polarization of the light beam, and means disposed at another end of the measurement fiber and serving firstly to detect the resulting light beam and secondly to determine the displacement of the object by analyzing the polarization modified in this way, wherein said measurement fiber is stripped, over said fraction of its length, of the covering that imparts mechanical strength thereto, and it is slid into a deformable guide sheath fixed both to the rotary object and also to the frame.