High-density recording systems using PRML with blue LD

Abstract

In advanced optical recording systems, a storage capacity of more than 20 Gbytes has been reached by adopting blue laser diodes, 0.85 numerical aperture (NA) objectives and 0.1 mm thin cover layer medium. This has been accompanied by a reduction of the optical and mechanical tolerance of the recording system. Among the parameters above, thickness error tolerance of the disc cover layer is said to be less than 3 /spl mu/m for mitigating the severe disc tilt tolerance. In order to mitigate such tolerances, an aberration compensation device is strongly required. The co-refractive index liquid crystal (LC) panel is one of the promising candidates as the aberration compensation device and has been extensively studied. The refractive index of an LC depends on the applied electric field; and thus the refractive index distribution can be controlled by the electrode configuration and the applied voltage. Although the direct measurement of spherical aberration is the best method for evaluating the performance, numerical estimation methods are also required for better device design. In this paper, we report on an optical simulation method for numerically evaluating the LC aberration compensation panel and show the performance and optical tolerance of the device. By using the optical simulation method, we numerically optimize the LC aberration compensation device and show the device can be applicable to the layer jump of 25 /spl mu/m for the dual layer optical recording, in next generation optical memory.