An optical head is provided, which suppresses the offset in the tracking error signal. This head comprises (a) a light source for emitting a light beam to be irradiated to an optical recording medium as an incident light beam; (b) a hologram element for receiving a reflected light beam generated by reflection...http://www.google.de/patents/US7120107?utm_source=gb-gplus-sharePatent US7120107 - Optical head for optical recording having a hologram element that generates multiple diffracted light beams of different orders
