Hidenori Wada

Application of a Polarizing Holographic Optical Element to a Recordable Optical Head

A polarizing holographic optical element (HOE) with compensating grooves on the surface of a LiNbO 3 substrate has good polarizing beam-splitter characteristics. This polarizing HOE was applied to a recordable optical head with an integrated laser and photodetector unit. In the optical head, a correct far-field tracking method is constructed by setting the polarizing HOE and a quarter-wave plate right under the objective lens, which can be moved with the objective lens. A holographic pattern of the polarizing HOE is divided into 20 portions along a disc track direction for spot size focus error detection and far field tracking detection. With this optical head, conventional CD play-back and recording signals on phase change discs were performed. Then the tracking offset caused by objective lens shift was measured and determined to be markedly decreased. Signal degradation by the ±1st light diffracted by a polarizing HOE was not observed. Good characteristics of recording and play-back for phase change discs were also obtained. This recordable optical head was found to have desirable characteristics and high productivity.

Optical Pickup for Recording to Dual-Layer 2x-Speed Blu-Ray Disc, DVD and Compact Disc

An ordinary half-height size optical pickup with high light-use efficiency for Blu-ray Discs (BDs) has been realized. It has two objective lenses arranged tangentially. Although one of the objective lenses, BD objective lens, does not follow the line that passes thorough the center of the spindle motor, stable tracking-error detection has been achieved by enhancing a one-beam method. This pickup has a beam shaper which changes a divergent angle of light with high magnification. Although beam shapers are sensitive to a positional error, our pickup accomplished stable positioning by introducing a new structure.