Dual-layer Blu-ray Disc based on fast-growth phase-change materials

A dual-layer disc is developed for blue-laser phase-change recording. The two recording stacks are based on fast-growth phase-change materials (FGMs). Both layers show good recording performance at a total disc capacity of 46.6 GB and with a slightly high jitter at 50 GB. The thicknesses of both the cover and spacer layers are controlled such that the deviations from the reference thicknesses of both recording layers are less than 2 mum. This eliminates the need for dynamical spherical aberration correction in the drive. The absolute difference in transmission between the written and unwritten states of the upper layer is only 2%. It is shown that this transmission difference causes no problem for readout and writing of the lower layer.