Patent ID: 6618218
Filing Date: 2003-09-09
Classification: G11B

Abstract:
A displacement detecting apparatus for detecting displacement relative to a relatively moved portion to be detected, comprising:a polarizing separation element for dividing a condensed light beam to thereby produce two linearly polarized light beams of which the planes of polarization are orthogonal to each other, directing one of the linearly polarized light beams onto said portion to be detected, and combining a light beam reflected from said portion to be detected with the other linearly polarized light beam; a wavelength plate for producing a linearly polarized light beam of which the polarization azimuth changes in conformity with the phase difference of the wave front thereof, from the two linearly polarized light beams combined together by said polarizing separation element; an amplitude dividing element for amplitude-dividing the linearly polarized light beam from said wavelength plate into a plurality of light beams; a plurality of analyzers disposed at positions where corresponding one of the light beams amplitude-divided by said amplitude dividing element passes with their polarization azimuths deviated from one another; a group of light receiving elements each of which receives the light beam from corresponding one of said analyzers, bright and dark signals having their phases deviated from each other being obtained from each of the light receiving elements by said light reception, the relative displacement information of said portion to be detected being obtained from said bright and dark signals; an opening member for selectively passing therethrough part of the wave fronts of the two linearly polarized light beams combined together by said polarizing separation element, the light passed through said opening member travelling toward said group of light receiving elements; and a light detecting element for receiving the reflected light beam from said opening member, the focused state of said one linearly polarized light beam on said portion to be detected being detected by said light reception.