Tsutomu Shiratori

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.

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.