In an optical information recording medium having at least two information layer, guide grooves for tracking or sample pits or information pits corresponding to information signals are formed on a surface of a first substrate. A first information layer formed by a thin line for reflecting a portion of...http://www.google.de/patents/US6226239?utm_source=gb-gplus-sharePatent US6226239 - Optical information recording and reproducing apparatus for multiple layer recording medium
