| 摘要 |
The present invention provides a method and apparatus for robust tracking at narrow track-pitches on optical discs, enabling higher densities on Blu-ray Discs (5) as well as near-field discs. Increasing radial density results in loss of radial diffraction within the numerical aperture of the lens. Due to this loss in diffraction, current tracking methods, such as Push-Pull and Differential Phase Detection (DPD), will stop working. The invention provides a method and apparatus that relies on cross-correlating the central aperture (CA) signals of 3 optical spots (22, 24, 26) that are positioned such that there are a central spot (24) and spots (22, 26) positioned to the left (22) and right (26) of the central spot (4) . By using CA signals, the tangential diffraction is used, which is hardly affected by a track-pitch reduction. |
