A multilayer optical recording medium comprises four recording layers including an L0 layer, an L1 layer, an L2 layer, and L3 layer laminated between a substrate and an optically transparent cover layer and optically transparent spacer layers each provided between the recording layers. The L2 layer has...http://www.google.de/patents/US7675838?utm_source=gb-gplus-sharePatent US7675838 - Optical recording medium
