In an optical head, a laser beam L emitted from a semiconductor laser is collimated by a collimator lens and is incident on a beam splitter. The laser beam passing through the beam splitter is and a quarter wave plate converged by an objective lens onto an optical disk and reflected by the optical disk....http://www.google.fr/patents/US4783589?utm_source=gb-gplus-shareBrevet US4783589 - Focus and tracking detection apparatus for optical head employing light guide means having different radii of curvature
Focus and tracking detection apparatus for optical head employing light ...
