Optical head and data processing apparatus including the same

摘要

An optical data processing apparatus reads and/or writes data from/on a data storage medium (1), in which first and second data storage layer are stacked, by radiating light from the second layer. The processor includes: a light detector (10) including at least one photodetector for generating a light quantity signal; a detecting optical system for guiding first and second reflected light beams from the first and second layers to the light detector; and a signal processor (20) for generating a layer sensing signal from the light quantity signal and determining, by the layer sensing signal, whether the focal spot is now located near the first layer or the second layer. The detecting optical system includes an optical element (9) that produces astigmatism to the first and second reflected beams. The light detector includes, as the at least one photodetector, a layer sensing photodetector arranged so as to include respective areas of the light detector where the second reflected beam is incident when the focal spot is located near the first layer and where the first reflected beam is incident when the focal spot is located near the second layer.