An improved optical head which eliminates the need for a biprism or cylindrical lens for focus detection and allows the placement of a photodetector immediately adjacent to the semiconductor laser to reduce alignment problems and vibrational errors. A semiconductor laser is provided which produces a...http://www.google.de/patents/US4731772?utm_source=gb-gplus-sharePatent US4731772 - Optical head using hologram lens for both beam splitting and focus error detection functions
