The use of CD-ROM has become widespread. PC users have generally been satisfied with the performance CD-ROM's, however, there is also a demand for larger-capacity removable rewritable media for “Multimedia” applications. The “PD” system offers users an optical disk which is easily handled such as floppy disks presently in use. In addition, “PD” can also read CD-ROM at fourtimes of the speed using a single common slot for both CD-ROM and PD media. The PD system (name of the new optical disk system prososed by Matsushita Electric Industrial. Co., Ltd.) has good compatibility for pit and groove recording. We calculated the reflectivity, tracking error, and ROM modulation, and varied the groove depth and width to maximize performance. A signal was written on various pregroove depths, and the reproduced signal ratio was measured. We obtained good results by using a phase-change material with the PD optical disk.
A phase-change optical disk that has an optical phase-shift signal reproducing structure and the same physical specifications as the 4.7 GB read-only digital
versatile disc (DVD) was developed. A minimum jitter of 9% and a wide tilt tolerance for the jitter were obtained under DVD reproducing conditions of λ=650 nm and N
A=0.60. This new medium can be used
as an inspection tool for DVD authoring. It was also confirmed that this optical disk had a potential for use as a rewritable 4.7 GB DVD medium that has compatibility with the read-only DVD.
A polarizing holographic optical element (HOE) with compensating grooves on the surface of a LiNbO3 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. Wth 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 ±1 st 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.
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