Displacement metrology based on grating imaging with a cylindrical lens array and a phase grating

A novel sensor for use in displacement metrology is proposed. The proposed displacement sensor is based on the grating imaging, which conventionally uses two amplitude gratings with rectangular apertures of fifty percent width of the period. In the conventional way, signal to noise ratio of displacement output is one of issues to be overcome for precise measurement because about seventy five percent of the illumination light is trapped by two amplitude gratings. On the other hand, in the proposed sensor a cylindrical lens array and a phase grating are applied as the first and the second grating, respectively. Therefore, the illumination light is trapped neither by the first grating nor the second grating except absorption. In our experiments, the cylindrical lens array with 200 μm period and the reflective sine phase grating with 100 μm period are used. Experimental results demonstrate that higher position resolution and higher accuracy of the displacement measurement is feasible by our proposal.