US Patent 7362692 Method and system of mass producing double-sided optical discs

Double-sided optical discs, such as a DVD-18 disc, are mass produced with data tracks on each layer. The tracks on one side of the discs are oriented along one spiral while the tracks on the other side are oriented along a different spiral, the two spirals being oriented in opposite directions as viewed from the respective sides, so that they are mirror images of each other. This allows data to be read by a player seamlessly from either side of the disc without changing the direction of rotation of the disc while normal data reading is proceeding. The process for making the discs includes forming master discs corresponding to the data layers and using these master discs to produce molded optical discs.