To confirm the feasibility of realizing subterabyte or terabyte optical memories, we evaluated a multilayer read-only disk having 20 information layers. We propose a new disk structure, which is an alternative structure to reduce interlayer crosstalk, optimized by computer simulations. We fabricated multilayer read-only optical disks using a conventional manufacturing process for Blu-ray disk (BD) dual-layer media. Moreover, we improved the reproduction system to compensate for the large spherical aberration. From the experimental results, we obtained sufficiently low jitter values reproduced from a 20-layer disk. We confirmed the feasibility of the multilayer read-only disk with a capacity of 500 Gbytes.

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.

No abstract

A numerical code has been developed to calculate the loading of a cavity loop antenna in threedimensional geometry. The loading of the cavity is calculated for fast wave and ion Bernstein wave coupling and compared with the loading of a conventional loop antenna. For fast waves, the cavity loading increases with increasing edge density, while the conventional loop loading is less sensitive to the edge density but shows a slight decrease of loading because of a steeper density gradient. For ion Bernstein waves, the two types of antenna behave similarly; however, in contrast to the loading for fast waves, the loading for ion Bernstein waves increases with decreased edge density and a steeper density gradient.

We have developed a new coaxial interference method for the next-generation storage system. A signal beam and a reference beam are coaxially arranged and focused into a holographic medium using a bifocal lens. We can easily downsize the system because the optics is very simple. The reference beam is focused on the mirror surface of the medium, and the signal beam is defocused on this surface. A semicircular reference pattern is used to select normal playback or phase conjugate playback in a reproducing process. We have recorded a single hologram and a multiplexed hologram in a photopolymer medium with this method. These holograms are reconstructed successfully. We have found that our interference method has a 4 mm shift selectivity and excellent characteristics for the next-generation high-capacity optical memory.