A Novel Micro-Displacement Measuring Method Based on Optical Path Modulation

According to the interference theory of double-grating interferometers, the feature of Moire fringe imaging in each region is investigated and a novel micro-displacement measuring method based on optical path modulation is proposed. The basic measurement principle is that the displacement is measured through Moire fringe shifting, which is caused by the whole phased object thickness variation, in the case of non-relative movement of gratings. The object displacement measured can be changed into the phased object variation inserted in region II using a mechanical arrangement. The principle of the micro-displacement measurement is analyzed theoretically. The light intensity of the distributing image in each interference region is given no matter whether we insert the phased object or not. The effect on the Moire fringe of the whole thickness variation of the phased object is also discussed. It is confirmed that the Moire fringe shifts with phased object variation by calculation with MATLAB. The experimental result proves that the resolution of this method is 2.1093 mu m, and the resolution of the system is 0.5273 mu m after a four-subdivision circuit.