Byoung-ho Choi

A compact-disc-compatible digital versatile disc pickup using annular mask

An optical pickup has been developed for both digital versatile discs (DVD) and compact discs (CD) using an annular mask on an objective lens. A conventional lens without the annular mask has been optimized only for DVD disc with 0.6 mm-thickness. The intensity of the secondary peaks of the spot focused by the objective lens with an annular mask to a CD is reduced and the pickup is found to have large tolerance for disc tilt variation compared with a conventional objective lens without an annular mask.

Radial Tilt Detection Using One Beam and Its Compensation in a High-Density Read Only Memory

To increase the capacity of the optical disc, the shortening in the wavelength of the laser diode and the increase of the numerical aperture of the lens have been attempted for several years. Unfortunately, the efforts have generated adverse effects of comatic aberration caused by disc tilt. To solve this problem, a few detection and compensation methods of disc tilt have been proposed for random access memory (RAM) discs. However, no clear approach has been taken yet in the case of read only memory (ROM) disc. In this paper, we propose a method to detect the radial tilt in a high-density ROM disc using differential phase detection (DPD) signals generated by an 8 divided photodetector. The developed radial tilt servo with a 3-axis lens actuator compensates the detected radial tilt. Its effects on the tracking servo which arise when the actuator rotates are introduced. Finally, the feasibility of the proposed method is verified through experiments on a high-density ROM.