ABSTRACT
Recordable optical disk drive technology provides a well-matched solution to the increasing demands for removable storage. An optical disk drive provides, in a sense, infinite storage capabilities: extra storage space is easily acquired by using additional media cartridges. The purposes of the optical head are to transmit the laser beam to the optical disk, focus the laser beam to a diffraction limited spot, and to transmit readout signal information from the optical disk to the data and servo-detectors. The servo-system is what enables the focused laser spot to be positioned with accuracy onto any of the tracks on the disk and ensure that it can be moved to any track on the disk as required. The focus control system requires a feedback signal that accurately indicates the degree and direction of focus error. Phase-change recording takes advantage of the fact that certain materials can exist in multiple metastable crystalline phases, each of which have differing optical properties.
