| 摘要 |
An apparatus for measuring the relative displacement information between it and scale means on which a diffraction grating is formed has light source means, separating means for separating a light beam from the light source means into a plurality of light beams, wave combining means for wave-combining the diffracted lights of the plurality of light beams separated by the separating means which are diffracted by the diffraction grating, light receiving means for receiving the interfering lights by the plurality of light beams wave-combined by the wave combining means, the relative displacement information between the apparatus and the scale means being measured by the light reception of the light receiving means, and optical means adapted to collimate the plurality of light beams or to form a spherical wave having so large a radius of curvature that it can be regarded as a plane wave of said plurality of light beams in the direction of light beam separation of the separating means and to condense the plurality of light beams in the optical path from the separating means to the wave combining means in a direction perpendicular to the direction of light beam separation. <IMAGE> |
