| 摘要 |
A local track pitch measuring apparatus is disclosed for an optical disk of the type that stores optically readable information in the form of a spiral or annular pattern defining a plurality of essentially concentric tracks (3). The apparatus has a laser light source (27) and a drive mechanism (20), which projects a laser beam spot from the laser light source onto a surface of the optical disk and moves the projected laser beam spot radially over a portion of the disk surface across at least some of the tracks. A light detector (24a-b) detects a diffraction (23a-b) or reflection from the projected laser beam spot during its movement (54). The light detector produces a time variant measurement signal (RE) having a periodicity associated with passages of the moving laser beam spot across respective tracks. A processing device (36) determines a local deviation in the periodicity of the measurement signal and provides an output (&Dgr;TRP) indicative of a local track pitch for the spiral or annular pattern (2). |
