Fiber optic sensor for high precision angular displacements

The paper presents two configurations of a fiber optic sensor built to detect accurate angular displacements. In the first configuration, the sensor is made of a light emitting diode (LED), a fiber optic bundle (five fibers) and a two-quadrant photodiode. In the second configuration, an additional microlens is fixed on the bundle tip. To avoid signal variations coming from potential axial displacements during the rotation of the mirror placed in front of the bundle, a video alignment technique was used. The first configuration, without a GRIN microlens, provides an angular displacement range of 157 mrad (9°) with a limit of resolution of 53 μrad (3×10^-3°) and a root mean square accuracy of 355 μrad (1.2×10^-2°). The second configuration, with a microlens, gives an angular displacement range of 70 mrad (4°), a 9 μrad (4.9×10^-4°) limit of resolution and a root mean square accuracy of 195 μrad (1.1×10^-2°).