| 摘要 |
PROBLEM TO BE SOLVED: To obtain a structure which suitably detects the tilt of a disk to an ideal plane by providing a data surface which has grooves and lands behind a transparent substrate and providing a radial tilt structure, which is short in the height of the grooves and lands and varies to circumferential length, on the data surface cyclically along radial line. SOLUTION: The radial tilt structure is provided in the data area from an internal diameter 302 to an external diameter 304 along many radius lines 306 varying the heights of the grooves and lands. In the area along the radius lines 306, the height of the part of a radial tilt measurement area is varied to the height of the lands 310 in the grooves 308 along the radius lines 306 and the height of the part of a radial tilt measurement area 314 is varied to the height of the grooves 308 in the lands 310 along the radius lines 306. The circumferential length of the center part of the area 312 is made shorter than the maximum length by which an optical system can resolve so as to minimize the influence of a tilt-directional detecting structure on a data signal. |
