Feedback compensation method for angular displacement measurement based on a Fabry-Perot interferometer

In this paper, we describe a new method for wide range and high-precision angular displacement measurement. In this method, the system real-time detects the testing object rotation, obtains the wide range angular displacement through accumulating its micro angular displacement. By adjusting the reflector, the beams reflected from the testing object normal incidence to the FP plate, before it is rotated. When the testing object is rotated, the system real-time gives the testing object micro angular displacement and the rotated angle of the Fabry-Perot (FP) plate. The testing object micro angular displacement is used for accumulating. The FP plate is real-time rotated under the control of the feedback system to compensate the initial angle's loss of incidence on the FP plate, and makes the beams reflected from the testing object normal incidence to the FP plate all the time. Each measurement accuracy of 10(-8) is abstained by use of the sinusoidal phase-modulating interferometry([1, 2]). So that, the wide range and high-precision angular displacement measurement is obtained.