Radial tilt detection using 3-beam optical head

An optical disk system which uses a high numerical aperture (NA) objective lens is effective for achieving high recording density. However, in such a system, it is necessary to detect and compensate for the radial tilt of the disk, because the coma aberration which deteriorates the read/write characteristics increases and the radial tilt margin becomes narrower. For this purpose, a radial tilt detection method for DVD-RAM disks using the CAPA (Complementary Allocated Pit Address) was reported. This paper proposes a new radial tilt detection method for rewritable optical disks using a 3-beam optical head. This method features high-sensitivity characteristics and is suitable for high-frequency servo operation, because the radial tilt signal is obtained from push-pull signals instead of header signals.