Fumihiko Yokogawa

The Path from a Digital Versatile Disc (DVD) using a Red Laser to a DVD using a Blue Laser

The next generation digital versatile disc(DVD) using a blue laser is required to have 15 Gbytes capacity so that it can reproduce motion picture expert group 2(MPEG2) video stream with a main profile at a high level format for a maximum of 133 min. To achieve this goal, further improvements are necessary in both the recording and the reproducing systems. For the recording system the authors developed a super resolution recording material and an electron beam recording system. For the reproducing system the authors devised four technologies: a Viterbi decoder, a liquid crystal tilt servo system, a cross talk cancel system and a tangential adaptive equalizer. By combining these with a pick up head of 430 nm vavelength/0.6 NA lens and a 0.6-mm-thick substrate, the authors confirmed sufficient tilt margins in the case of 12.7 Gbytes (radial tilt margin: ±1.61°, tangential tilt margin: ±0.48°). Our next target is to work on the 15 Gbytes capacity.

Organic Dye 25 GB Write-Once Disk with In-Groove Structure

We have developed a new write-once disk technology, which is applicable to the Blu-ray disc system. An organic dye was adopted for the recording layer, which was optimized for the recording of the laser diode wavelength of 405 nm. We adopted a concave in-groove for the recording tracks to avoid thermal interference with adjacent recording tracks due to undesired and uneven dye pooling between adjacent tracks, considering the advantage of fabrication by spin-coating. We optimized the in-groove structure for low-to-high modulated recording. A sample disk, which was made by the conventional spin-coat process, showed good recording and readout characteristics with remarkably low cross-talk and cross-writing.

25 Gbyte Read-Only Memory Disk by Injection-Compression Molding Process

We studied the feasibility of fabricating a disk replica at a recording capacity of 25 Gbytes by a conventional injection molding process. This work is the first attempt at fabricating a disk replica using a stamper recorded by an electron beam recorder. The bottom jitter value of the injection-molded disk was 9.3% when using a conventional equalizer and 6.5% when using an additional limit equalizer. These values were highly similar to those of the photo-polymer (2P) disk. The residual error on the axial tracking of the injection-molded disks was smaller than that of the 2P disk, and the residual error on the radial tracking was almost the same as that of the 2P disk.

Inorganic Recordable Disk with More Eco-Friendly Material for Blue

We realized an inorganic write-once disk using a high numerical aperture (NA) objective lens and a blue-violet laser diode. Its recording layer was Bi?Ge nitride alloy which was more environmentally friendly than that of the rewritable disk. The data-to-clock jitter of 5.7% was obtained at 25 GB capacity, using the limit equalizer. In addition, we confirmed that this disk had potential for application as a 1X-2X recordable disk.

25 GB Read-Only Disk System using the Two-Dimensional Equalizer

In order to achieve a higher density disk system, we applied a two-dimensional equalizer along with a limit equalizer to an optical disk drive system which has an objective lens with a numerical aperture of 0.85 and a thin transparent cover layer of 0.1 mm thickness. Consequently we realized the 25 GB read-only disk system with sufficient margins against disk tilt and defocus. The two-dimensional equalizer is composed of a cross-talk cancel system and a tangential adaptive equalizer, and could prevent deterioration due to inter-symbol interference and cross-talk from adjacent tracks. Using the limit equalizer could prevent deterioration due to disk noise. By measuring the jitter with the limit equalizer, which has an ability to expand the system margin almost equivalent to that of the Viterbi decoder, we could evaluate the disk quality for standardization and verification.

Signal Processing for 15/27 GB Read-Only Disk System

In order to realize 15/27 GB read-only disk systems using blue laser, new signal processing is required. The technology of large-scale integrated circuits has advanced considerably. Hence we can use a complicated circuit with a big gate size without increasing the system cost significantly when we fabricate the blue laser disk system. We have realized the 15/27 GB system using the two-dimensional equalizer and the limit equalizer. The two-dimensional equalizer was composed of the cross-talk cancel system and the asymmetry compensation type tangential adaptive equalizer. And could improve the deterioration due to the inter symbol interference and the cross-talk from the adjacent tracks. The limit equalizer could improve the deterioration due to the disk noise. Using these signal-processing systems, we could reduce the bottom jitter by more than 3% and expand the tilt margin.

Practical electron beam recorder for high-density optical and magnetic disk mastering

Electron beam mastering is a promising technique to realize next-generation disk media. We have been developing electron beam recorders since 1993 and have proved their effectiveness for high-density disk fabrication. To introduce electron beam mastering technology into practical application in next-generation disk mastering, we developed a new electron beam recorder as a commercial prototype. The electron beam recorder was improved in terms of recording resolution, beam-blanking characteristic and recording stability. For production use, a load-lock system was adopted to improve throughput, and the recording and substrate exchange operations were automated through computer control. The recording stability was proved experimentally by fabricating 100-GB-capacity stampers recorded on the whole recording area of 22 to 58 mm radius with a good pattern size uniformity. A superhigh-density patterning of 350 Gbit/in.2 density (510 GB capacity/layer) was realized for the next-generation optical disk, and a 35 nm line and space pattern could be fabricated for the next-generation magnetic disk.

Signal Simulation of 25 Gbytes Read-Only Optical Disk System using a High Numerical Aperture Objective Lens

We have already developed and reported the high-definition digital-versatile-disk read-only-memory system of capacity 15 Gbytes using a blue laser and new signal processing technique. On the other hand, a high numerical-aperture system has been reported of numerical-aperture 0.85 and cover layer thickness 0.1 mm. In this paper, we examined the increase in capacity on application of our signal processing technique to the high numerical-aperture system using computer simulation. As a result, we found that a 25 Gbytes read-only-memory disk system had sufficient system margins on applying the limit equalizer and the adaptive tangential equalizer. Furthermore, if the crosstalk canceler is applied, we may achieve a system of capacity larger than 25 Gbytes.

Near-Field Readout of 75 Gbyte Disc Made with Conventional Optical Disc Manufacturing Equipment

In this report, the results of the study of a 75 Gbyte (GB) disc for the solid immersion lens (SIL) system are presented. We used conventional mastering and molding equipment except for the recording process for the SIL disc. The electron beam recorder (EBR) was used as a signal recording machine for small pits. From the results of the experiments, we confirmed that conventional equipment could be used for high-density disc manufacture. The jitter value of the 75 GB disc was 9.5%.

Bd-type write-once disk with pollutant-free material and starch substrate

We realized an inorganic write-once disk for an optical recording system of the Blu-ray disk format. We developed a new Al alloy for the reflective layer and a Nb-compound oxide nitride material for the dielectric layer. By adopting these materials for the reflective layer and the dielectric layer of our write-once disk, we achieved complete exclusion of toxic substances specified in the pollutant release and transfer register (PRTR) law. That is, this disk did not contain any substances specified in the PRTR law. We confirmed this disk to be compatible with 1× to 2× recording at the user capacity of 25.0 GB. The bottom jitter values of both 1× and 2× were less than 6.0%. In addition, we developed another kind of substrate, which was made of a natural polymer derived from corn starch. The bottom jitter value was 6.0% at the user capacity of 25.0 GB with the limit equalizer.