Kenji Oishi

Single objective lens having numerical aperture of 0.85 for a high density optical disk system

For the optical disk systems in the next generation, a GaN laser and a high numerical aperture lens are key components. This paper describes the first single objective lens that have the numerical aperture of 0.85. The lens form, which is the most important factor in realizing the lens, is analyzed. The measured wavefront aberration was 0.027λ which is was well below the diffraction limit of 0.07λ. The lens was installed in an optical pickup and write/read characteristics of the pickup with phase-change disks were investigated on a drive. Data-to-clock jitter of a read back signal was 9.5% of channel clock at a disk capacity of 25 Gbytes per 120-mm-diameter disk. The direct overwrite (DOW) characteristic was also measured. The jitter remained stable up to 1×105 cycles. These results confirm the performance of the objective lens.

Super-Resolution Rewritable Optical Disk Having a Mask Layer Composed of Thermo-Chromic Organic Dye.

Super-resolution (SR) effects of a thermo-chromic organic dye mask layer are investigated for a rewritable disk with a Ag–In–Sb–Te phase-change recording layer. Clear SR effects were recognized in both linear and radial directions in the rewritable disk, corresponding to a capacity of 10.3 GB in a 120 mm disk. A carrier-to-noise ratio over 35 dB was obtained at a short mark length of 0.2 µm. Crescent-shaped marks, which are typically recognized in high-density magneto-optical (MO) media, were observed in the phase-change recording layer. The SR effects mainly operate on the reading process, resulting from a large non-linear transmittance change in the organic dye.

Super-Resolution Read-Only Memory Disk with Metal Nanoparticles or Small Aperture

We attempted to increase the signal intensity of small pits the sizes of which were smaller than the optical diffraction limit in read-only memory (ROM) disks. For this purpose we employed a granular film and a thermochromic film in this study. The reason for using these films was to apply the super-resolution near-field structure (super-RENS) model, which suggests that the signal intensity of very small marks is increased by metal nanoparticles or a small aperture in the disk, to super-ROM. We investigated the effect of adjoining these films to a reflective layer on readout signals. It was found that the signal intensity of very small pits was increased by both of these films, but the mechanisms of increase were different.

Holographic Data Storage Media Employing Phase-Change Reflector

We have proposed a novel structure of holographic data storage media, employing a phase-change (PC) reflector for optical disc applications. The PC layer, which is initially amorphous and has a low reflectivity in a write process, works as an absorber and inhibits reflected stray beam exposure. After the write process, the PC layer is crystallized and its reflectivity is switched to a high state, realizing a sufficient signal beam intensity in a read process. Experimental results show a low noise and a high signal-to-noise ratio, and a potential to have a large multiplexing number in the PC reflector.

Practical Properties of Thermochromically Induced Super-Resolution Read-Only Memory Disk (TSR-ROM)

Super-resolution effects and practical properties of a thermochromic mask layer for a read-only memory disk are evaluated using a conventional disk tester with a 635 nm light source and a 0.6 numerical aperture (NA) pickup. A carrier-to-noise ratio (C/N) of over 40 dB is obtained at a pit length of 0.20 µm which is far smaller than the resolution limit. Sufficient tilt margins and power margin are obtained at the capacity of 11 GB.

High-Density Rewritable Optical Disk Using Groove Recording

For an optical disk system using an objective lens of numerical aperture (NA) 0.7 and a GaN laser, the performances of the groove-recording scheme were investigated. A disk having 17 GB capacity showed the initial jitter of 11.9% with an equalizer for digital versatile disks (DVD). With an adaptive equalizer and a Viterbi decoder, sufficiently low bit error rates and wide tilt margins were obtained.

Thermochromic Super-Resolution in Phase-Change Rewritable Disk with Double Mask Layer

A new mask system for a thermochromically induced super-resolution (TSR) rewritable disk is proposed. In this system which consists of a high-sensitivity mask layer and a low-sensitivity mask layer, TSR effects are obtained in both read and write processes. At the high-density recording on a Ag–In–Sb–Te phase-change rewritable disk, cross-talk and cross-erase are improved.

Dual-Layer Recordable Digital Versatile Disc Having Protruded Land Pre Pit in L1 Layer Fabricated by Inverse Stack Method

The dual-layer recordable digital versatile disc (DVD-R DL) fabricated by an inverse stack method has not been released in the market because of unstable land pre pit (LPP) addressing in an L1 layer due to its peculiar disc structure. We have developed a DVD-R DL disc that has the novel shape of the protruded LPP in the L1 layer fabricated by an inverse stack method. The height of the protruded LPP is larger than the land height of the L1 substrate to restrain extensions in the radial direction of recording marks. We have confirmed that the protruded LPP disc satisfies the specifications of DVD-R DL and enables stable LPP addressing.