OPTICAL SCANNING DEVICE

摘要

An optical head for scanning a dual-layer disk includes a polarising beam splitter for splitting an input beam (7) from a single radiation source to form two separate, orthogonally polarised beams (9, 10). One of the beams is passed through a fixed collimator lens (13), whilst the other is passed through a movable collimator lens (21). The beams are directed along a common beam path through a common objective lens (17) which is itself movably mounted. Focusing and tracking error correction is provided separately for each layer when scanning the two layers by actuation of the objective (17) and movable collimator (21), respectively. The use of a single radiation source and a single objective provides a reduction in the number of components, and the complexity of components, required to read a dual-layer disk.