US Patent 7106525 Objective lens for optical pick-up

There is provided an objective lens for an optical pick-up used for different types of optical discs. The objective lens has at least one surface on which a plurality of annular zones are formed. The at least one surface is divided into an inner area having a low NA and an outer area having high NA outside the inner area. Further, with regard to a light beam used for a second optical disc (e.g., a DVD), an optical path difference generated between at least one of steps formed between adjacent annular zones of the plurality of annular zones within the outer area is lower by a predetermined amount than an integral multiple of a wavelength of the light beam used for the second optical disc.