Optical disk recording using a GaN blue-violet laser diode

The combination of a GaN laser diode and a 0.85 numerical aperture objective has achieved an optical storage capacity of over 22 GB. Owing to sufficient modulation ability and low-noise characteristics, GaN semiconductor lasers possess adequate quality to be light sources in optical recording systems. A bit size of 130 nm x 300 nm, corresponding to the areal recording density of 16.5 Gbit/in.(2), was realized on a six-layered thin-cover phase-change disk with a crystallization-promoting structure. Each active layer was inversely stacked and was thermally as well as optically optimized for the blue-violet light sources. A new small electromagnetic actuator with a lightweight phi 3 mm two-element lens has extended its servo-bandwidth up to 8 kHz and enabled precise focusing control at the data transfer rate of 35 Mbps.