Osamu Nagatsuka

A Study of Near Field Recording Optics for Cover-Layer Incident Dual-Layer Disc with an NA=1.45 Hemispherical Solid Immersion Lens

Practical optics for a cover-layer incident dual-layer disc with an NA=1.45 hemispherical solid immersion lens are designed, using a spherical aberration compensating liquid crystal cell. A hybrid servo system, gap servo for NA >1 and focus servo for NA < 1, is proposed.

Domain wall displacement detection magnetooptical drive for mobile use, with 15 Gbit/inch2 recording density and 24 Mbps data transfer rate

We have developed a domain wall displacement detection (DWDD) magnetooptical drive for the 2-inch-diameter disc with 3 GB capacity. The newly developed magnetic head and the drive circuit realize the high efficiency of 1.84 Oe/mA and the high speed switching of 13.5 ns. An optical pickup (OPU) with wavelength of 660 nm and numerical aperture (NA) of 0.6 is sufficiently compact to approach the innermost disc radius of 11 mm, and the overall weight is 3.2 g. The volume and power consumption of the entire drive system are 35.5 cc and 0.78 W respectively, and they are adequate for use in mobile storage devices. Furthermore, we have confirmed a complete read/write performance with 15 Gbit/inch2 recording density and 24 Mbps data transfer rate.