Multilevel volumetric optical storage

Present optical storage devices use two-dimensional recording media which do not take advantage of the ability to focus light to a small spot at a large working distance throughout the volume of a storage media. In this report we propose an approach to volumetric optical storage where the optical had reads from and writes to distinct levels of a multilevel disk structure. This approach has been successfully applied to multilevel ROM and WORM optical disk memories. We detail the physical principles behind this technology, present detailed experimental data on two-level write-once media and briefly describe four-level recording. In companion papers we describe in detail results from four-level recording and readback and multilevel ROM based media and drives.