High-density magneto-optical (MO) recording using a land/groove structured domain wall displacement detection (DWDD) medium has been achieved with a digital versatile disc (DVD) dimensional optical head including a 664-nm wavelength laser diode and a 0.60-NA objective lens. Due to the deep groove depth, easy domain wall displacement is obtained without the use of a track boundary postannealing process. Sufficient readout performance is obtained in experiments at an areal recording density of 11 Gbit/inch2, which is obtained using a 0.13-µm bit length and a 0.45-µm track pitch. This areal density corresponds to a capacity of 15 GB per one 120-mm-diameter disk.

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 landlgroove 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 of4.7 GB on a 64 mm disc like MiniDisc.

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Tripled areal density optical recording was realized with the combination of a high power laser-diode pumped intracavity frequency-doubled Nd:YAG laser (SHG green laser), a low noise GdFeCo/TbFeCo double-layered magneto-optical (MO) disk, and high sensitivity photodetectors optimized for the wavelength of the light source. A high carrier-to-noise (C/N) ratio of more than 48 dB and a bit error rate of less than 3×10-6 by (2, 7) run-length-limited (RLL) mark position recording was obtained at a mark length of 0.45 µm (0.6 µm/bit) for a disk with a 0.9 µm track pitch.

An ordinary structured magneto-optical disk was improved and optimized to achieve high areal recording density using the magnetic field modulation recording technique. After studying film material/thickness, groove geometry, and birefringence in a poly-carbonate substrate, a track pitch of 0.85 µm with a linear recording density of 0.31 µm/bit is determined to be a good combination for a wavelength of 690 nm and an objective lens with a numerical aperture of 0.55, which results in an areal density of 3.8 bit/µm2 or 2.4 Gbit/inch2.