An optical data processing apparatus reads and/or writes data from/on a data storage medium, in which first and second data storage layer are stacked, by radiating light from the second layer. The processor includes: a light detector including at least one photodetector for generating a light quantity...http://www.google.com.au/patents/US20040252612?utm_source=gb-gplus-sharePatent US20040252612 - Optical head and data processing apparatus including the same
