Tomoki Ushida

Recording Characteristics of 10-Layer Recordable Optical Disc and a Prospect for Over 500 Gbyte Recording

A 10-layer recordable optical disc with an inorganic recording material, Bi–Ge–O, was fabricated and the recording characteristics were measured using a Blu-ray Disc-based apparatus with a wavelength of 405 nm and a numerical aperture of 0.85. Practical signal quality was obtained from all the layers at densities of 25 and 32 Gbyte per layer. A 16-layer recordable optical disc was also fabricated and measured. Practical signal quality was also obtained from both the 1st layer and the 16th layer.

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.

High-Performance Hard Coat for Cartridge-Free Blu-ray Disc

A practical way of realizing cartridge-free Blu-ray disc using nanocomposite UV-curable resin as a hard coat on a laser incident surface of the disc is described. The hard coat is a composite material of UV-curable acrylic resin and nanoparticles of silica. A lubricant that exhibits oil repellency as well as low friction coefficient was added to the hard coat in order to facilitate the removal of fingerprints. It effectively prevents abrasions, scratches and problems of fingerprints on the disc surface. Abrasion and scratch resistances, and ease of fingerprint removal were evaluated and compared with those of a polycarbonate surface and a conventional UV-curable hard coat.

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.

Functional hard-coat for cartridge-free DVR-blue

Optical discs with larger storage capacity and higher data recording rates are required for the coming digital network society, for example, to realize non-linear editing and long term data archiving on broadcasting tasks. We have been developing a new phase change optical disc, which has much higher data recording rate of up to 140 Mbps (T. Kato et al, Tech. Dig. ISOM2001, pp. 200-201, 2001), based on the DVR system (/spl lambda/=405 nm, NA=0.85, cover layer thickness=100 /spl mu/m) (Y. Kuroda et al, 1999; M.J. Dekker et al, 2000; Y. Kasami et al, 2000). As a general rule, the smaller the laser spot size on the disc surface, the more sensitive the disc becomes to scratches or fingerprints on it. In such a system, the distance between the disc surface and objective lens (i.e. working distance) is very narrow due to a high NA. Therefore it is also feared that the objective lens hits the disc surface due to an external impact. To avoid these problems when the disc is taken out of a cartridge, we have developed a new hard-coat. The cartridge-free DVR-blue disc was expected to be accomplished by the following properties: (1) abrasion resistance; (2) scratch resistance; (3) water and oil repellency (low surface free energy). Among these properties, the abrasion resistance is considered to be the most important.

Spin-Coating Technology of the Cover Layer for Digital Video Recording-Blue Disc

We have achieved the cover layer thickness distribution of 100±1.5 µm on a disc by improving the spin-coating method and developing an original spin-coating machine. The small skew of the disc is achieved by using a newly developed UV-curable resin.