Present and future of one of the largest Grid infrastructures in Europe

An optical head comprising two light sources, a beam splitter, and two photodetectors. The first light source emits a first light beam to be applied to the recording surface of a first-type optical disk. The second light source emits a second light beam to be applied to the recording surface of a second-type optical disk. The first light beam and the second light beam intersect with each other at an angle other than 90 DEG . The beam splitter is provided at the intersection of the first and second light beams. The beam splitter guides both light beams in a common optical path which extends to the recording surface of either optical disk. The beam splitter guides the first light beam reflected from the first-type optical disk toward the first light source, and the second light beam reflected from the second-type optical disk toward the second light source. The first photodetector detests the first beam reflected from the first-type optical disk. The second photodetector detests the second beam reflected from the second-type optical disk.