Chong Sam Chung

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.

High Response Twin-Objective Actuator with Radial Tilt Function for Blu-ray Disc Recorder

We have developed Blu-ray Disc (BD) optical pick-up with a twin-objective lens actuator which is compatible with compact disc (CD) and digital versatile disc (DVD) in the high-speed BD-read only memory (ROM) and BD Recorder. In order to readout CD and DVD in BD Recorder, we adopted twin-objective lens actuator in consideration of optical utilization efficiency, optical performance and insurance of sufficient working distance (WD). This twin-objective lens actuator has two objectives in radial direction, one is for CD/DVD and the other is for BD. Through our careful investigation in design process, this actuator has extremely high AC sensitivities and good 2nd resonance characteristics in consideration of twin-objective actuator. Also, this actuator has linearity in wide focus range, that is to say, more than ±1.0 mm and has radial tilt function which is tilt range more than 7 deg.

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.

Blu-ray Disc Pickup Head for Dual Layer

For dual-layer Blu-ray disc (BD) recording systems, the compensation of thickness differences is required. In addition the influence from the other layer should be considered. As a spherical compensation method, we have adopted a liquid crystal panel to fabricate a compact pickup head. Furthermore we have inserted a polarization diffractive optical element to reduce the influence from the other layer. In this paper, we report the readout test results of a dual-layer disc using a compact optical head.

One Beam Optical Head for High-Density Optical System with Eight Segment Photodiode.

We propose a one-beam optical head for groove-only high-density optical system. Using an eight-segment photodiode with a new detection method, the cross-talk in the wobble signal and the offset of track error signal can be reduced.

A Compact Disc-Recordable Compatible Digital Versatile Disc Pickup with a Lens for 780 nm and 650 nm Wavelengths.

Two types of compact disc-recordable(CD-R) compatible digital versatile disc (DVD) pickups have been developed. One has separate conjugate points for DVD and compact disc(CD) readouts. The other has a common conjugate point for DVD and CD readouts. Optical and signal properties are considered for both types. Both types have been shown to exhibit good qualities for practical use.

Optical Pickup for Compact Disc Player Using Computer-Generated Hologram and Reflection-Type Grating

A functional prototype of an optical pickup using a Computer-generated hologram (CGH) has been developed for compact disc player (CDP). A 780 nm-wavelength laser diode, a finite conjugated objective lens, and a reflection-type grating are used in the pickup. The fringe pattern of the CGH functions as cylindrical and negative power lenses, and produces astigmatism for focusing signal to the objective lens. Also, the effect of chromatic aberration of the CGH on the pickup is estimated.

Three-Element Objective Lens with Numerical Aperture of 0.85

We have developed a three-element objective lens with a numerical aperture of 0.85 at 405 nm, which can correct chromatic aberration caused by mode hopping and wavelength change of the laser diode.

New method of the readout signal generation to reduce the adjacent track crosstalk

To realize more than 15GB data capacity using blue laser diode, suppression of the adjacent track crosstalk may be one of the key technology. Several methods have been proposed for the adjacent track crosstalk cancellation using 2 beams or 3 beams. Kasazumi et.al. have proposed one method with coaxial dual beams. Although they can reduce the adjacent track crosstalk, it is not easy to get enough optical power from the objective lens for recording. In this paper, we propose new method of the readout signal generation to reduce the adjacent track crosstalk.