Abstract: An optical disk servo system includes a coarse access and tracking system for optical head control and a fine access and tracking system for read/write beam control. Enlarged servo tracks are pre-recorded on the optical disk between bands of data track locations. The coarse system illuminates a relatively large area of the disk surface encompassing at least one of the servo tracks and detects light from the enlarged illuminated area. Suitable means including a photo-detector array identifies and controls the optical head position by means of the light returned from the illuminated servo track. Such photo-detection means are insensitive to light reflected from the data tracks. The fine access and tracking system uses a conventional, three spot tracking and read system, two spots for data track following and one spot for data track reading. The fine access and tracking system controls a galvanometer mirror or other suitable means steering the read spot beams.

Abstract: A system and method for optically measuring and maintaining track pitch in an optical storage system. A set of at least four calibration tracks, each having a prescribed track pitch or distance therebetween, are precisely placed on a recording medium of the optical storage system during the manufacture thereof. When this recording medium is subsequently inserted into the optical storage system, the track pitch of a select pair of the calibration tracks is optically measured by maximizing the amplitude of a data read radiation beam, and an offset signal is generated in response to this measurement. This offset signal is used within the optical storage system for controllably positioning a second radiation beam with respect to a first radiation beam, the first radiation beam being directed to follow a previously written data track on the recording medium.