Apparatus and method for detecting a relative displacement between first and second diffraction gratings arranged close to each other wherein said gratings have different pitch sizes

摘要

A method and device for measuring the relative displacement between first and second diffraction gratings includes an interference optical system forming first and second interference rays of light from light diffracted from the first and second diffraction gratings and separating the first and second interference rays of light on the basis of the difference in their direction of polarization, a first detector for detecting the first interference ray of light to generate a first detection signal, a second detector for detecting the second interference ray of light to generate a second detection signal, and signal processing section for detecting the phase difference between the first and second detection signals and for determining the relative displacement between the first and second diffraction gratings on the basis of the phase difference.