Patent ID: 8064316
Filing Date: 2011-11-22
Classification: G11B

Abstract:
1. An optical system for extracting a plurality of signal beams from a bundle of rays reflected from a multilayer optical disc, the reflected bundle of rays including the plural signal beams and a plurality of stray beams, the optical system comprising: a polarizer situated on an optical path of the reflected bundle of rays for splitting the reflected bundle of rays; a condensing optical element situated in front or in back of the polarizer for condensing the reflected bundle of rays; a first polarization converting optical element situated between a first imaginary plane and a second imaginary plane, the first imaginary plane including condensing areas at which the plural signal beams are condensed by the condensing optical element, the second imaginary plane including condensing areas at which the plural stray beams are condensed by the condensing optical element, the first polarization converting optical element having a plurality of divided areas for dividing the plural signal beams and the plural stray beams into two bundles of rays and converting polarization of the divided bundles of rays so that one of the divided bundles of rays has a polarization different from the other divided bundle of rays; a second polarization converting optical element situated between the first imaginary plane and a third imaginary plane located farther from the condensing optical element than the first imaginary plane, the third imaginary plane including condensing areas at which the plural stray beams are condensed, the second polarization converting optical element having a plurality of divided areas facing the plural divided areas of the first polarization converting optical element for converting the polarization of the plural signal beams and the plural stray beams transmitted through the first polarization converting optical element so that the plural signal beams have a polarization different from the plural stray beams; and an analyzer for extracting the plural signal beams from the reflected bundle of rays transmitted through the second polarization converting optical element based on the difference of polarization; and wherein the first polarization converting optical element rotates polarization of one of the divided bundle of rays +45 degrees and rotates polarization of the other divided bundle of rays −45 degrees.