A pick-up device which includes a light source and a condenser lens for effecting recording and reproduction of information by projecting a light beam as collected by the condenser lens onto a recording medium. A diffraction grating is provided between the light source and the condenser lens for dividing...http://www.google.de/patents/US5050155?utm_source=gb-gplus-sharePatent US5050155 - Pick-up device for use in an optical information recording system utilizing a diffraction grating with blaze characteristics
