| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an objective optical element compatible with BD and HD, securing a light amount at a condensed spot, effectively suppressing sidelobe, overcoming a flare problem, and securing a working distance. <P>SOLUTION: In the objective optical element, one optical surface is divided into a plurality of areas including a first optical disc area, a second optical disc area, and a common area, which are concentric. The common area has an optical path difference giving structure. A first luminous flux which has passed through the first optical disc area is condensed only on an information recording surface of a first disc. The first luminous flux which has passed through the second optical disc area is condensed only on an information recording surface of a second optical disc. When the first luminous flux has passed through the optical path difference giving structure of the common area, n-th order diffracted light and m-th order diffracted light are generated more than the other order diffracted light. The n-th diffracted light is condensed on the information recording surface of the first disc, while the m-th diffracted light is condensed on the information recording surface of the second disc, where n and m are different integers (including zero). <P>COPYRIGHT: (C)2009,JPO&INPIT |
