High-Track-Density Flattened Magnetooptical Disks with Low Crosstalk

Abstract

The carrier-to-noise ratio (CNR), crosstalk and noise levels have been investigated for flattened and semiflattened magnetooptical disks with narrow track pitches of 1.2 and 1.0 µm. The track pitch of the flattened and semiflattened disks can be reduced to less than the laser spot size under the condition that the laser spots irradiated on the adjacent recording regions overlap each other only on the spiral guiding band. The CNR of 48.3 dB and low crosstalk of less than -36 dB were achieved for the track pitch of 1.2 µm when the domains of 0.76 µm length were recorded. Crosstalk of less than -30 dB was obtained for the track pitch of 1.0 µm with the conventional optical head having an objective lens of 0.53 NA and a 780-nm laser.

THE CHARACTERIZATION OF TRACKING SERVO SIGNAL AND CROSS-TALK OF MAGNETO-OPTICAL DISKS WITH Cr GUIDING LAYERS

“…This result reveals that the disk noise which arises at the edges of the spiral Cr bands is very small. Since the conventional mastering technique for optical disks is used for the formation of a Cr guiding layer, recording region width Wa becomes wide as cutting power Pcutrises [7], where cutting power Pcutits exposure power for photoresist on the Cr film.…”

“…We have proposed that the magneto-optical disks with Ta guiding layers are useful for reduction of track pitch (7] [8]. However, tracking servo signal, that is divided push-pull signal, is too small to achieve stable tracking for a track pitch of less than 1.0 J..lI1l.…”