Atsuko Kosuda

Sixteen-Layer Write Once Disc with a Separated Guide Layer

We proposed a new recordable multilayer optical disc and its recording system. The new optical disc has multiple-plane-recordable layers and a separated guide layer, and we fabricated 16 recording layers made of high-transmittance inorganic recording materials stacked on the separated guide layer. The recorded signals were evaluated on all recording layers by using jitter and i-MLSE as the evaluation indicators. As a result, the technical feasibility of our proposal was confirmed to achieve the total capacities of 400 and 512 Gbytes, respectively, by the continuous recording of all 16 recording layers with a track pitch of 0.32 µm and two bit lengths. We believe that our multilayer optical disc and recording system are the most practical solutions for realizing huge-capacity data storage.

Proposal of a Design Principle of Multilayer Media

We propose a design principle of stacking-type super-multilayer media in this paper. By the use of an original high-transmittance and high-recording-sensitivity recording material, bismuth–germanium–oxide, the recording layers of a 10-layer super-multilayer disc can be designed using only two types of recording layer. This leads the conventional super-multilayer media structure to a much simpler structure with only two thicknesses of spacer layers while maintaining a satisfactory signal quality on the farthest layer from the incident laser beam, where signal fluctuation due to coherent crosstalk is the strongest. The above design principle will greatly contribute to the reduction of the cost of super-multilayer media.

512 GB recording on 16-layer optical disc with Blu-ray Disc based optics

We confirmed the feasibility of a 16-layer write once disc based on Blu-ray Disc optics that was fabricated with inorganic recording material Bi-Ge-O. The total capacity of the disc achieved 400 GB and 512 GB per single disc side with BD 1x recording speed utilizing conventional BD technique.

A New Class of Photopolymer for Holographic Data Storage Media Based on Organometallic Matrix

New photopolymer materials were prepared with a view to achieving holographic data storage media of large dynamic range. For this purpose, organometallic compounds of high refractive index were used as a matrix, and organic compounds as photosensitive monomers. The organometallic matrix was obtained from transition metal– and silicon–alkoxides by modifying the sol–gel process. The matrix was combined with low refractive index monomers, and then the mixture was filled between glass substrates to fabricate recording media. These media showed M-number (M/#) of about 42 to 64 (per 1 mm thickness) when evaluated by a plane-wave tester equipped with a 407 nm laser diode. As for the sample which gave M/# of approximately 42, a raw data density of 76 Gbit/in.2 was achievable upon multiplex page-data recording by a coaxial optical system, in which a page-data volume was 56.8 kbit/page. In another experimental result, optimization of monomer structures brought about a shrinkage ratio of 0.08% as a mechanical volume change.