DUAL-STACK OPTICAL DATA STORAGE MEDIUM AND USE OF SUCH MEDIUM

摘要

A dual-stack optical data storage medium (10) for recording using a focused radiation beam (9) having a wavelength lambda is described The beam enters through an entrance face (8) of the medium (10) during recording. The medium comprises at least one substrate (1, 7) with present on a side thereof a first recording stack (2) named L0, comprising a recordable type L0 recording layer (3), said first recording stack L0 having an optical reflection value RL0 and an optical absorption value AL0 at the wavelength lambda, and a second recording stack (5) named L1 comprising a recordable type L1 recording layer (6), said second recording stack L1 having an optical reflection value RL1 and an optical absorption value AL1 at the wavelength lambda, and a transparent spacer layer (4) sandwiched between the recording stacks (2, 5). The second recording stack is present closer to the entrance face than the first recording stack. By fulfilling the formula AL1 <= 1 - Rmin -√(Rmin/RL0) in which formula Rmin is the minimum required effective optical reflection value for each recording stack full compatibility is achieved with a read only (ROM) version of the medium.