Noriaki Murao

The Applications of a Liquid Crystal Panel for the 15 Gbyte Optical Disk Systems

We have studied the next-generation digital versatile disk (DVD) using a blue laser and investigated the application of a liquid crystal (LC) panel to the high-density disk. The LC panel can easily shift the optical path length of light beams making it possible to cancel out wavefront aberrations. First, the authors applied an LC panel to a tilt servo system. Compared with a mechanical tilt servo system, the LC tilt servo is expected to be more compact and reliable. We also developed a system for sensing the amount of disk tilt by comparing the signal levels of crosstalk from adjacent tracks. Consequently a tilt servo without any extra sensors was achieved. Another application of the LC panel is for the compensation of spherical aberrations. It was confirmed, by simulations and experiments, that the LC panel was practically useful for correcting disk thickness error which has been determined to become more serious when a blue laser was used.

Photo-Polymer Objective Lens for Red Blue Lasers

The authors designed a photo-polymer objective lens which can be used for both red and blue lasers. The following two conditions were set to facilitate this lens production process. 1) We chose photo-polymer resin as one of the doublet lens materials. 2) One surface of the photo-polymer lens was designed to be flat. We installed this lens in pickup heads and played back some disks. Its performance was almost as good as that of a noncompatible glass lens.

High-Numerical-Aperture Objective Lens for Blue Laser Disk System

The authors have developed and prototyped an adjustment-free two-component objective lens for a blue laser disk system (numerical aperture = 0.85, disk thickness = 0.1 mm). The lens is designed to be sufficiently tolerant to the relative position, i.e., the decentering, tilt and spacing inaccuracy between the two lenses, and does not require adjustment of the two lenses. We have carried out some experiments and the tolerance of our newly developed objective lens has been experimentally verified.