Remote Absolute Roll-Angle Measurement in Range of 180° Based on Polarization Modulation

Remote measurement of object orientation is often required in many applications. Out of the six degrees of freedom (DoF) that determine object orientation in space, the roll angle is the most difficult to measure using optical methods. In this letter, we propose a remote Stokes roll-angle sensor that measures roll angles from the detected Stokes vectors of modulated polarized light retroreflected from a sensing unit comprised simply of a retarder and a planar reflection mirror. Experimental results have shown that the proposed sensor can realize absolute roll angle measurement in an unprecedented range of 180° with a maximum absolute error of less than 0.25° and a measurement resolution of better than 0.01°. The proposed sensor adopts a coaxial design and takes the advantages of compactness, simplicity and low cost, and moreover, can be further expanded to a three-DoF angle sensor due to the sensitivity of the sensing unit to other two kinds of angles (pitch and yaw).