AbstractTwo recent topics on high density recording are reviewed in this paper on conventionally structured MO disk by magnetic field modulation. One topic is the MO disk with a capacity of 650 MB/ φ 64 mm. Using a light wavelength of 650 nm and an numerical aperture of an objective lens of 0.52, a track pitch of 0.95 μm and a bit length of 0.34 μm for (1,7) RLL coding has been applied to achieve 650 MB within a size of a Mini Disc(MD). Groove conditions such as the depth and groove duty in a 1.2-mm thick polycarbonate substrate are optimized to reduce the cross-talk from adjacent tracks. As a result, the recording power margin of ± 20% is obtained. The disk tilt margin is ± 0.82 deg and ± 0.63 deg in the radial and tangential direction, respectively.The other topics is land/groove recording using an optical phase shifter. A maximum carrier level and a minimum cross-talk are achieved simultaneously when an optical phase shifter is inserted into the optical path before an analyzer. The optimum phase shift is 40 deg for recording on land and -40 deg for recording in groove. Recording on 0.5 μm land/0.5 μm groove with 1.2-mm thick substrate is investigated with a bit length of 0.35 μm for (1,7) RLL code using a light wavelength of 693 nm and a numerical aperture of 0.55. MO recording using an optical phase shifter is promising for an areal density of 3.7 Gb/in2. Furthermore, when an optical phase shifter is applied to recording on 0.36 jim land/0.36 μm groove with a bit length of 0.258 μm, light wavelength of 642 nm, and NA of 0.7, a capability of 7.0 Gb/in2 using conventionally structured MO disk is shown.
Realization of a High Density Magneto-Optical Disk through the Use of Magnetically Induced Super-Resolution with Magnetic Field Modulation Recording
