Yasuyuki Miyaoka

New Inorganic Write-Once Disc Using Low-Cost and Environmentally Friendly Oxynitride Materials for Multilayer Disc System

We have developed a new inorganic write-once disc using low-cost and environmentally friendly recording materials of Si oxynitride and Al oxynitride with high transmittance. Data-to-clock jitters of 5.6% for Layer 1, 5.5% for Layer 2, and 6.3% for Layer 3 of the individual single-layer discs were obtained using a limit equalizer. This newly developed recording material is immensely promising for a multilayer disc system.

A New Inorganic Write-Once Disc using Hydrogen-Containing Dielectric Recording Material for Multi-Layered Blu-ray Disc System

We have developed a completely novel inorganic write-once disc using a hydrogen-containing dielectric recording material. We demonstrate the recording characteristics of a newly developed write-once disc on the basis of the Blu-ray disc format (dual-layered, 4? speed).

Anneal-less domain wall displacement detection of 27 Gbit/in2 land/groove recording using a deep groove substrate and a blue laser

We have studied an anneal-less domain wall displacement detection (DWDD) disk of a land/groove recording on a deep groove substrate using a numerical aperture (NA) 0.65 objective lens and a blue laser diode (LD). The substrates were prepared using a stamper formed by reactive ion etching (RIE) and O2 plasma treatment to realize both steep side-wall angles and smooth surfaces on the substrates. In designing the groove shape, we have clarified three key factors: the groove edge shape, the groove depth and the land width. These factors affected the magnetic film discontinuity at the groove edge and the recording power margin on the land. We have achieved a recording density of 27 Gbit/in2 by optimizing the groove shape.

Non-bias magneto-optical recording

Without applying an external magnetic field, high-density recording beyond the optical resolution limit was realized with light intensity modulation, using Domain Tail Erasing (DTE) and Domain Wall Displacement Detection (DWDD). In order to obtain a sufficiently strong bias field to perform recording with a bias layer introduced into the DTE medium, the stray field distribution during the recording process was studied by simulation. A stray field most effectively worked on the recording layer when the Curie temperature of the bias layer was designed at a certain level below the recording temperature. Furthermore, by replacing a part of the bias layer with a bias assist layer, which had a higher Curie temperature and lower coercive force, an even stronger stray field was generated. According to the simulation, non-bias DTE medium was designed, and as a result a sufficiently low jitter value and dropout rate were obtained without bias magnets at a bit length of 80 nm and a track pitch of 0.74 μm, using the same optical parameters of a current DVD.

15-Gbit/in2 recording on a DWDD disc using a land/groove substrate with a red laser enabled by a side-wall annealing process

We developed a side-wall-annealing technique for land/groove substrates. By applying this technique to our Domain Wall Displacement Detection (DWDD) Magneto-Optical (MO) recording stack formed on a land/groove substrate, even with an NA of 0.6 and a wavelength of 660 nm, we realized a density of 15 Gbit/in2 with a sufficiently wide recording tolerance. This density corresponds to a capacity of 4.7 GB mm disc like MiniDisc.

A New Data Detection Method for 35 Gbit/inch2 Multilevel Recording Using a Blue Laser and 0.85 Numerical Aperture Optics

In this study, a commercial Blu-ray disc was used for multilevel recording. The goal is to make its present capacity 2 times larger and data transfer rate 2 times faster. This technology is a promising candidate for improving extending the standard of the Blu-ray disc. To achieve this specification corresponding to an areal density of 36 Gbit/in.2, the bit length is reduced to 56 nm. The features of technology for 36 Gbit/in.2 are as follows: First, eight-level recording is adopted. Second, a new detection method named cell boundary data detection (CBDD) is developed to overcome severe intersymbol interference (ISI) from outer cells at a small cell length. Finally, we use the same optical pickup as that of the Blu-ray disc for doubling areal density. CBDD utilizes data sampled at the cell boundary, which is almost free of the influence of ISI without an equalizer. In addition, the popular error correction code of Bose–Chaudhuri–Hocquenghem (BCH) is applied to the part of the least-significant bit (LSB). As a result, CBDD with the BCH code achieved a bER of 1 ×10-5 at the effective bit length of 57.6 nm, which indicates an areal density of 35 Gbit/in.2 by computer simulation. Moreover, we experimentally obtained a bER of less than 1 ×10-5 using CBDD with the BCH code at a cell length of 200 nm.

An Advanced Data Detection Method for 34.6-Gbit/in2 Multilevel Recording using a Blue Laser and NA0.85 Optics

In this study, a commercial BD (Blu-ray disc) and BD optics (blue laser and NA0.85) were used for multilevel recording. The goal is to double both the present capacity and data transfer rate. To achieve this, it is necessary to overcome severe inter-symbol interference (ISI) from outer cells at a small cell length. In order to suppress ISI, we have developed an advanced data detection method that uses CBDD (Cell Boundary Data Detection) and TCM (Trellis-Coded-Modulation), and have achieved an areal density of 34.6-Gbit/in2 multilevel recording.

System tolerance of 64-mm-diameter magneto-optical disks with a 4.7-Gigabyte capacity

We observed sufficiently wide detection tolerances in a magneto-optical (MO) drive system based on the domain-wall-displacement detection (DWDD) method. Those DWDD disks had a capacity of 4.7 Giga-byte on 64 mm diameter substrates optimized for land and groove (L/G) recording. Addressing was performed with the assistance of a one-side-wobbled groove. We investigated two types of DWDD disks i.e. the anneal-less type and the sidewall-annealed type.

Turbo codes for a DWDD disc: bit length of 70nm recording with a red laser

Turbo codes, a partial turbo method and a serial turbo method, were experimentally applied to a Domain Wall Displacement Detection (DWDD) disk using a red laser. An effective bit length of 68nm recording was achieved by a partial turbo method with a parity bit rate of 1/17 at a bit error rate (bER) of 4x10-5 using a maximum a-posteriori probability (MAP) decoder, although a bit length of 80nm was the limit of the conventional partial response maximum-likelihood (PRML) method. It is presumable that the limit of the turbo decoding method for a DWDD disk depends on the number of consecutive 2-bit errors that occur with the disappearance of the 2T pattern. A max-log-MAP algorithm was introduced, instead of the usual MAP algorithm, to implement turbo codes in hardware, and an effective bit length of 69nm was achieved at a bER of 4x10-5.

More than 20 GB Capacity Rewritable Disk with the Same Physical Parameters as that of Digital Versatile Disc, Using a New Recording Method and Domain Wall Displacement Detection

We have developed a new light intensity modulation recording method called domain tail erasing method. This new recording method enables high-density recording far beyond the optical resolution limit with a medium combining the layer structure of domain wall displacement detection (DWDD) with that of light intensity modulation direct overwrite (LIMDOW). A recording performance nearly identical to that using magnetic field modulation (MFM) was confirmed with this method, using conventional optics with a wavelength of 660 nm and NA of 0.60.