Patent ID: 7443774

Claim:
An optical data processing apparatus for reading and/or writing data from/on a data storage medium, in which storage layers are stacked, the apparatus comprising: a light source for radiating light; a focusing optical system for forming a focal spot by condensing the light that has been emitted from the light source; a light detector, which includes at least one photodetector for receiving the light and generating a light quantity signal representing quantity of the light received; a detecting optical system for guiding reflected light beams, which have been reflected from the storage layers, respectively, to the light detector; and a signal processor for generating a layer sensing signal from the light quantity signal and, by the layer sensing signal, determining which of the storage layers of the loaded data storage medium the focal spot is located near, wherein the light detector includes, as the at least one photodetector, a layer sensing photodetector arranged in view of an area of the light detector where a reflected light beam from a storage layer other than the determined storage layer, near which the focal spot is located, is incident, and wherein the light detector further includes a photodetector which receives the reflected light beam to generate a focus error signal and which is different from the layer sensing photodetector.