Displacement information measuring apparatus with hyperbolic diffraction grating

摘要

An apparatus for detecting the displacement information of an object has a light source, a diffraction grating for diffracting a light beam from the light source so that the light beam diffracted by the diffraction grating is incident on the object, and a photodetector for detecting the light from the object caused upon the incidence of the light beam thereon by the diffraction grating. Information regarding the relative displacement to the object along a predetermined direction is detected on the basis of a light detection signal from the photodetector. The diffraction grating is formed so that the light beam applied to the object may be condensed on the object in a direction in which the relative displacement to the object cannot be detected by the signal from the photodetector.