Chul Woo Lee

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.

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.

AN OPTICAL HEAD WITH SPECIAL ANNULAR LENS FOR LASER DISC-COMPATIBLE DIGITAL VERSATILE DISC PICKUP

A compact and inexpensive design for a laser disc(LD)-compatible digital versatile disc(DVD) pickup that uses a special annular lens is presented and the measurement technique of the lens is described. One objective lens having a special annular area functions as an aberration-corrected lens for reading LD, compact disc recordable(CDR) and DVD regardless of differences in substrate thickness. The special area has an aspherical surface optimized for a thick substrate. This lens can also be used for compact disc rewritable(CDRW).

Signal characteristics from a catadioptric system for near field application

Technologies related to optical memory using near field optical phenomena have been developed.

Investigation of certain diffraction effects in a double-layer optical disk

We study, both by computer simulation and experimentally, the diffraction of the incident beam from the grooved structure of the first layer onto the second layer of a double layer optical disk. We also examine the cross-talk between the focused-error signal curve obtained from the two layers. Good qualitative agreement is obtained between simulations and measurement. It is hoped that these and similar studies will enable us to estimate the magnitude of the noise caused by diffraction from one layer on the signal obtained from the other layer.

New stable servo method for optical disk systems

In an optical pick-up for high areal density recording using Nd:YAG SHG (second harmonic generation) green laser, the stability of a servo mechanism may be deteriorated easily due to many optical elements and long optical path. We propose a new stable servo method employing a differential critical-angle prism. This method showed one order of higher stability than conventional astigmatic servo method to the chief ray tilt. We obtained more than a CNR of 48dB even in case of the large chief ray tilt with 0.5 micrometers mark length on MO recording layer, which is close to the case of no chief ray tilt.

Analysis on read-out signal in magnetooptical disc drive system

Waveforms of read-out signals are calculated for a magnetooptical disc drive system by using diffraction theories on slits. Also, using a Yttrium aluminum garnet; second-harmonic generation (YAG;SHG) laser (λ=532 nm) as a light source, the read-out signals are measured from a magnetooptical disc drive system. Jitter is investigated with the theoretical and experimental results. Good agreement is found between the results.