Simulation studies on media jitter in phase change optical recording at high data rates

One of the most critical sources of noise in PC recording is the irregularity in the definition of the recorded marks, leading to timing jitter. The maximum linear bit density that can be achieved at a given wavelength and lens numerical aperture is often limited by jitter. Jitter is largely determined by a combination of the optical, thermal and crystallization properties of the media and the recording strategy of the laser beam. In this thesis, the issue of reducing jitter arising from the PC media is addressed.;A model was developed that incorporates thermal diffusion and crystallization kinetics to simulate mark formation and read-back signals from the written marks. The statistical nature of nucleation process was included in the model. The mark evolution process and the origin of mark edge jitter from nucleation was studied. Mark edge jitter arising from nucleation was estimated. It was found that by an appropriate choice of the metal reflection layer thickness and the erase power, the mark edge jitter can be minimized. Overwrite jitter, which is a major cause for concern at high disk rotation velocities due to interference between old and new data, was investigated. Even with a disk that was designed to compensate for the difference in properties of the amorphous and crystalline phases, it was seen that overwrite jitter increased with velocity. A modified multipulse scheme was proposed to reduce overwrite jitter and increase erasability. In practice, it is necessary to change the multipulse strategy with a change in the linear velocity. Multipulse strategies suitable for high data rates in the red wavelength were analyzed for two different velocities. We estimated the maximum velocity in the blue and made a comparative study of the multipulse strategies with the red wavelength at two velocities. The model was extended to study mark shapes, thermal cross erase and overwrite jitter in growth-dominant PC media. A disk structure with an additional Au heat sink layer and a new multipulse strategy that utilizes power more efficiently were proposed to reduce thermal cross erase and overwrite jitter in growth-dominated phase change materials.