Optical disk for detesting and distinguishing servo tracks from data

Abstract

An improved coarse access and tracking servo system for use with an optical disk storage system is disclosed. Concentric servo tracks placed on the disk are readily distinguished from data tracks placed on the disk which may or may not be present on the disk depending upon the amount of information that has been written on the disk, i.e., how 'full' the disk is with respect to its maximum capacity for storing data. A predetermined signal is embedded within each of the plurality of concentric servo tracks found on the disk. A radial strip or line, sufficiently long to always include at least one servo track, but also long enough to include data tracks, if any, on either side of the illuminated servo track is projected on the surface of the disk in order to detect the servo tracks. Light returned from the illuminated servo tracks falls upon a detector and generates a frequency component that is readily distinguished from any frequency components associated with signals generated from light returned from any of the data tracks. The position of the servo track within the illuminated radial strip or line is then accurately determined, regardless of whether data tracks are present or not within the illuminated strip or line. This position of the servo track within the illuminated radial strip or line is then used by the coarse access and tracking servo system in order to accurately position an optical head at a desired position with respect to a selected coarse servo track on the disk.