Eiichi Fujii

Physical Characteristics and Format of a Two-Inch-Diameter Magneto-Optical Disk System with 3 GB Capacity

Recording at a high density four times that of a current digital versatile disk random access memory (DVD-RAM) has been achieved by applying the domain wall displacement detection (DWDD) technology using a conventional optical head with the same wavelength of 660 nm and numerical aperture (NA) of 0.60 as those the DVD head. It has been confirmed by using an alternating sampled servo, laser annealing of the inter track area and partial response maximum likelihood (PRML) that a recording density of 15 Gbit/inch2 with a track pitch of 540 nm and bit length of 80 nm has sufficient system margins. A newly developed 1-bit-distributed address format has achieved a redundancy of 23%. Furthermore, the edge shift compensation technique has reduced the recording magnetic field. These indicate that a capacity of 3 GB on a two-inch-diameter disk is now available for mobile use. If applied to a digital video camera, one hour or more of moving-picture-experts-group-2 (MPEG2) video contents can be recorded at a bit rate of 6 Mbps.

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.