Tetsuya Shihara

Lens Shift Correction in Tracking Servo System for Digital Versatile Rewritable Disc

In this paper the development of tracking offset correction for playback of a digital versatile rewritable disc (so called DVD-RAM), is described. The slim drive, having a small optical pick-up head with a small objective lens, is easily influenced by the deviation of the push-pull tracking error signal due to lens shift. The DVD-RAM disk format provides information not only on the amount of lens shift using the push-pull tracking error signal of address marks to correct tracking deviation, but also an opportunity to determine the optimum initial lens position using the differential phase tracking error signal.

Testing method to determine the influence of dust adhesion on digital versatile disk

We developed a testing method to determine the influence of dust adhesion on digital versatile disk (DVD). First, the dust testing system was developed. This system can control the dust density with an accuracy of ±20%. Second, the dust testing method was investigated. Reflectivity and jitter deteriorated gradually, making it easy to estimate the readability and lifetime of DVD. The system, testing procedure, and estimation indexes are adequate for the DVD dust test. Dust adhesion was observed. Dust particles adhere along the airflow direction and accumulate to 100 µm thickness. Third, in order to discuss the difference in readability between disks of 0.6 mm and 1.2 mm substrate thicknesses, the dust test was performed for DVD and compact disk (CD). It was found that the normalized reflectivity of DVD is 7% smaller than that of CD after 100 h exposure.