Patent ID: 7054095

Claim:
A displacement detection apparatus comprising: a light beam illuminating system that converts a linearly polarized light beam emitted from a light emitting element into a substantially parallel light beam; a light beam splitting optical system that splits the parallel light beam emerging from said light beam illuminating system into a plurality of polarized light beams having different polarized states; a focusing optical system that focuses the plurality of split light beams to different positions which are spatially separated from one another on a surface of a relatively moving object; a polarizing prism that splits reflected light beams from the relatively moving object on the basis of a difference between the plurality of directions of polarization, wherein said reflected light beams are matched by said light beam splitting optical system; a plurality of light receiving optical systems that individually detect the different polarized light beams split by said polarizing prism and output light receiving signals of the respective light beams; and a comparator that compares light receiving signal levels of the respective light beams to detect a relative displacement of the relatively moving object.