Radial Tilt Detection for Blue DVD-ROM/R/Rewritable Disks

An optical disk system which employs a 405nm-wavelength laser diode, a 0.65-numerical- aperture (NA) objective lens and a 0.6mm-thick-substrate disk has been proposed as a next generation DVD (blue DVD) standard. In this system, it is indispensable to detect and correct the radial tilt of the disk, because the coma aberration caused by the radial tilt which deteriorates the read/write characteristics is larger compared with the conventional DVD system. For this purpose, the authors have previously proposed a radial tilt detection method using a 5-beam optical head[1]. This paper further proposes an improved 5-beam method which is applicable to the blue DVD read-only (ROM) disks, recordable (R) disks and rewritable disks.