High density recording with a visible laser diode in direct overwrite MO disk

To achieve a higher storage density on an overwritable exchange-coupled quadrilayer magnetooptic (MO) disk, the overwrite recording characteristics using the optical head with 680-nm laser diode were investigated. High recording sensitivity was obtained and the write power was estimated to be about 10 mW at 22-m/s linear velocity. Carrier-to-noise ratio (CNR) of more than 46 dB was obtained at the 0.66-μm mark length, and 0.5-μm/b recording with a bit error rate less than 1×10^-5 was obtained at 1.2-μm track pitch. The authors conclude that 130-mm double-sided direct overwrite MO disk could have 2.5 Gbyte storage capacity. If 1.0-μm track pitch disk can be used, a storage capacity of 3.5 Gbyte might be expected