Displacement measurement using grating images detected by CCD image sensor

Recently, the interference phenomenon known as grating imaging has been studied for some practical applications as well as for the theoretical interest. When the object grating, which is illuminated incoherently, is located in the vicinity of the transmission grating, the magnified image of the object grating is obtained at the image distances far from the gratings. Since the high magnification (approximately 10² to 10³) can be obtained, the image displacement is very sensitive to that of the object. We propose here a displacement sensing technique using the grating images detected by CCD image sensor. The images are processed with a computer by using a spatial phase detection method. The lateral displacement and the distance separating the two gratings can be obtained simultaneously and separately. The proposed technique will be useful as a compact two dimentional displacement sensing method in opto-mechanical systems.