Multi-level recording in erasable phase-change media by light intensity modulation

Multi-level recording has advantage of increasing the recording density without extensively altering the current optic configuration. In this paper, a new four-level recording phase-change disk using three-recording layers was demonstrated. By modulating the intensity of the laser pulse, marks were chosen to record in any of recording layers, to form four recording regions. Utilizing the property of the phase change media whose amorphous and crystalline states differ largely in refractive indices, each recording region corresponds to different reflectance. For the four-level recording disk, each recording region represents two-bit data, then the recording density of the four-level disk is a factor of two higher than that of a conventional disk recorded by adopting the pulse position modulation (PPM).