LEADING SPOT TRACKING TECHNIQUE FOR OPTICAL DISK SYSTEMS
Original Publication Date: 1983-Oct-31
Included in the Prior Art Database: 2004-Apr-04
Xerox Disclosure Journal
One of the more promising focusing/tracking techniques for use in optical disk memories is based on having a central read or read/write beam straddled by radially offset outrigger beams. For example, to implement such a "three spot" focusing/tracking technique, a laser beam may be split by a diffraction grating, thereby providing + and - first order outrigger beams to straddle a centralized zero order read or read/write beam. Typically, however, such an implementation causes one of the outrigger beams to lead the read or read/write beam and the other to lag. In memories using a pregrooved disk, this might introduce an unwanted offset or instability into the tracking system while data is being written on the disk because the data alters the optical properties of the disk to the lagging beam but not the leading beam.