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 bl ue 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 leng th of light beams making it possible to cancel out wavefront aberrations. F irst, 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 c ompact and reliable. We also developed a system for sensing the amount of d isk tilt by comparing the signal levels of crosstalk from adjacent tracks. Consequently a tilt servo without any extra sensors was achieved. Another a pplication of the LC panel is for the compensation of spherical aberrations . It was confirmed, by simulations and experiments, that the LC panel was p ractically useful for correcting disk thickness error which has been determ ined to become more serious when a blue laser was used.