We propose the study and the design of an ultra sensitive polarimetric torque sensor. The principle is based on the measurement of the torsion angle (theta) induced on the shaft when a torque T is applied on it. This optical torque sensor has been tested for aluminum, steel and Plexiglas shafts with different geometries. The torsion angle has been measured with 0,001 degree(s) accuracy. The torsion angle is then studied as a function of the applied torque. The comparison between the theoretical and the experimental results give us respectively 4,33%, 1,30% and 1,24% for the Plexiglas, the aluminum and the steel shafts. These results permit us good perspectives for our applications.