Patent ID: 7360228

Claim:
A multi-stack optical data storage medium for recording using a focused radiation beam having a wavelength λ and entering through an entrance face of the medium during recording, the multi-stack optical data storage medium comprising: a first substrate having, on a side thereof: a first L 0 guide groove formed therein, and a first recording stack L 0 comprising a recordable type L 0 recording layer, the L 0 recording layer having a thickness d L0G in the groove and a thickness d L0L adjacent the groove, and a first reflective layer present between the L 0 recording layer and the first substrate; a second substrate having, on a side thereof: a second L 1 guide groove formed therein, and a second recording stack L 1 comprising a recordable type L 1 recording layer, the L 1 recording layer having a thickness d L1G in the groove and a thickness d L1L adjacent the groove, said second recording stack being present at a position closer to the entrance face than the L 0 recording stack; and a transparent spacer layer sandwiched between the recording stacks, said transparent spacer layer having a thickness substantially larger than the depth of focus of the focused radiation beam, wherein the depth of the first L 0 guide groove is smaller than 0.15λ, the recordable type L 0 and L 1 recording layers comprise an organic dye, and the thickness d L0L of the L 0 recording layer adjacent the groove is substantially equal to or larger than the thickness d L1G of the L 1 recording layer in the groove, and wherein a reflectivity level of the first recording stack L 0 is more than 50%, and a modulation of recorded marks in the L 0 recording layer is more than 60%.