Read and write unit for different types of optical disc - has detector facility to determine focussing error, which is used to control focussing servo

摘要

The read-write system for optical discs [AT] has a laser diode [LD] output directed through an optical splitter [PBS] and a lens system [CL,WL,OL], and onto the disc. The optical signals are reflected back from tracks on the disc. The nature of the reflected signals will depend upon the depth of the tracks [F1,F2], which are dependent upon the type of recording. The optical signals are reflected through the prism and onto the photo detectors [PD]. A detection unit [AE] indicates an error, and a controller [SE] adjusts the focus to suit the disc. -