Fine and coarse servo system for access and tracking on an optical disk

摘要

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. Data writing is accomplished by fine tracking a previously recorded data track and maintaining the write beam a constant distance therefrom.