Tae-yong Doh

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.

Optical Storage System for 0.4 mm Substrate Media Using 405 nm Laser Diode and Numerical Aperture 0.60/0.65 Objective Lens

The most important application of the blue-laser optical storage system is the recording high-definition digital broadcasting. For this application, the next-generation blue laser optical storage system requires a data capacity of at least 2 h of a digital broadcasting data stream with a data transfer rate of 23.5 megabits per second (Mbps). In addition to the capacity goal, system compatibility with the conventional digital versatile disc (DVD) system as well as the compact disc (CD) system is important. In order to satisfy the requirements of blue-laser optical storage, a system for media with a substrates thickness of 0.4 mm was proposed, and improved molding technology, crosstalk cancellation technology, dynamic tilt compensation technology and quadrature phase shift keying (QPSK) modulated wobble addressing method were developed for the system. We confirm the feasibility of the proposed system for media with a 0.4 mm substrate using a 405 nm blue laser diode and objective lens with a numerical aperture (NA) of 0.6 (0.65 for rewritable system).