High-Density Recording with a Near-Field Optical Disk System Using a Medium with a Top Layer of High Refractive Index

Abstract

A near-field optical technology using a solid immersion lens (SIL) has been actively studied to expand the storage capacity higher than 100 Gbytes per layer in a 12-cm-sized optical disk. However, the working distance of an objective lens in a near-field optical disk system should only be 25 nm or less. Therefore, from the practical viewpoint, a topcoat layer is required to protect the recording layer when the SIL collides with a disk surface because of disturbances such as dust, shock and vibration. From a mechanical viewpoint, the topcoat should have the mechanical toughness to protect the disk surface. Moreover, from an optical viewpoint, it should have refractive index higher than the numerical aperture of an SIL to achieve a sufficient evanescent couple between the SIL and disk surface. In this study, we describe a topcoat for a near-field optical recording. First, we investigate the topcoat performance from the optical viewpoint. Second, we evaluate the topcoat performance from a mechanical viewpoint. Finally, we report the results of recording experiments for a disk with the topcoat and discuss its performance.

Short Trajectory Control between Focusing and Tracking Based on Two-Dimensional Equivalent-Perfect Tracking Control for Optical Disk

“…Therefore, at θ = 0 • , using the scaling factor, the output amplitude of the tracking control always has the same level as that of the focusing control. This scaling factor is a ratio of the numerator value of (1) and (2). As a result, at θ = 0 • , the twodimensional feedforward control is carried out smoothly and stably.…”

“…Near-field optical recording (NFR) using a solid immersion lens (SIL) was developed to meet these demands. NFR provides a high memory density using a numerical aperture (NA) of the SIL that is greater than 1 and a gap between the disk and lens that is less than 100 nm, which is narrower than the wavelength of the laser beam (1) (2) . It is necessary to have a narrow track pitch and gap to achieve a high memory density and large capacity for the optical disk.…”

Recording characteristics of high-density thin optical disk using near-field optical recording

“…[2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] It can exhibit a large capacity and a highdata transfer rate towards recording next-generation ultrahigh-definition television [i.e., Super Hi-Vision (SHV), 7320 Â 4320 pixels] video signals 17,18) for home-use. Fourfold higher density recording using NFR optical disks with 1.2-mm-thick disks has been reported, 12,14) and studies of larger capacity using multilayer recording using NFR have been reported.…”

Double Feedforward Control System Based on Precise Disturbance Modeling for Optical Disk

“…Research is being undertaken on the near-field recording (NFR) technology to increase their memory capacity. [1][2][3][4][5] Concurrently, work is underway in the development of flexible disks that can spin at 10000 rpm or higher to increase data transfer rate. [6][7][8] However, an increase in the memory capacity and transfer rate makes optical head control more difficult.…”