An optical head device includes: a light source for emitting a light beam; an objective lens for converging the light beam on an information storage medium; a hologram for receiving the light beam reflected by the information storage medium and generating diffracted light from the light beam,...http://www.google.com/patents/US5687153?utm_source=gb-gplus-sharePatent US5687153 - Optical head device and optical information apparatus using a lithium niobate hologram with divisional areas to diffract light to corresponding photo detector areas 
