Hidehiko Kando

Simulations of Marks Formed on Phase-change, Land/Groove Disks*

Finite-difference time-domain (FDTD) simulation was used to determine the amount of absorption of light propagating inside a land/groove optical disk. The results showed that three-dimensional geometry influenced absorption. Furthermore, heat conduction inside the disk depended on its geometry, so the temperature profiles of land and groove tracks were not equal. Therefore, the spatial and historic profiles of temperature must be investigated in three dimensions. These temperature profiles can then be input into a phase-change simulator in order to carry out a simulation of the process of writing marks in land and groove tracks. To predict the optical and thermal effects of a land/groove structure on the writing process, we integrated an FDTD and phase-change simulation. The integrated simulation effectively evaluated the differences between the marks formed in land and groove tracks. As well, we applied the FDTD simulation to a blue-laser recording and found that groove-track recording showed higher light convergence than land-track recording. This inclination was explained the convex/concave effect of the structure of the disk surface.

Simulations of heat generation and conduction on a land/groove disc

We applied the finite-difference time-domain (FDTD) method to an optical disc to estimate the energy absorption inside a multi-layered disc with land-and-groove structure. The FDTD method was developed to measure the electromagnetic fields generated by diffraction in a near-field. Afterwards we analyzed the heat conduction. We found that temperature transition depended not only on conductivity but on the initial distribution of the heat and on disc geometry.

Mark-forming simulations of phase-change land/groove disks

The track pitches of optical discs have become so narrow that it is comparable to the wavelength of laser beam. Finite-difference time-domain (FDTD) simulation, based on vector diffraction analysis, can predict the propagation of light more accurately than scalar analysis, when the size of media texture becomes sub-micron order. The authors applied FDTD simulation to land-and-groove optical disc models, and found out that the effects of 3D geometry is not negligible in analyzing the energy absorption of light inside the land- and-groove multi-layered media. The electromagnetic field in the media does not have the same intensity distribution as the incident beam. Furthermore, the heat conduction inside the media depends on the disc geometry, so the beam spots centered on land and groove makes different effects in heating the recording layers. That is, the spatial and historical profile of temperature requires 3D analysis for both incident light absorption and heat conduction. The difference in temperature profiles is applied to the phase change simulator to see the writing process of the marks in land and groove. We have integrated three simulators: FDTD analysis, heat conduction and phase change simulation. These simulators enabled to evaluate the differences in mark forming process between land and groove.