High-resolution fibre-optic sensor for angular displacement measurements

Abstract

The design of a fibre-optic sensor able to measure high-precision angular displacements is presented. The sensor has a small size which allows easy integration in miniature mechanical systems. Two configurations are designed: lens-free configuration and GRIN micro-lens configuration for which the micro-lens is fixed on the tip of the probe. The experimental results obtained by the angular displacement sensor based on the lens-free configuration are compared with the simulation results based on the modelling of the system and a good agreement is found. Then, a long-range measurement technique is described. In the ‘lens-free and long-range configuration’, the limit of resolution is measured (2 × 10−3°) or calculated (4.8 × 10−4°) over a range of [−23.4°, +23.4°]. In the ‘GRIN lens and long-range configuration’, the best limit of resolution is decreased to 2.2 × 10−4° but over a smaller range of [–14.5°, +14.5°]. Finally, the sensor in its ‘lens-free configuration’ design is integrated into a miniature electromagnetic actuator to determine its stroke by a comparison of the output signal obtained between this unknown-stroke actuator and a rotating stage for which the stroke was precisely known.