| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an objective optical element condensing a luminous flux having the same wavelength on information recording surfaces of a BD and an HD by using a common objective lens, recording or reproducing information, being compatible with BD or HD, and suppressing the occurrence of an error signal, and to provide an optical element unit. <P>SOLUTION: In the optical path difference giving structure of the objective optical element, m-th diffraction light and n-th diffraction light (m and n each denotes an integer) are generated when a luminous flux passes therethrough, m and n satisfy the following expression (1): ¾m-n¾=1, the m-th diffraction light is condensed on the information recording surface of a first optical disk, n-th diffraction light is condensed on the information recording surface of a second optical disk, a luminous flux having passed through a second region is condensed on the information recording surface of the first optical disk and a luminous flux having passed through a second region is not condensed on the information recording surface of the second optical disk. The optical path difference imparting structure has a plurality of circular rings whose cross sections including an optical axis has a blazed shape and the level difference of at least one circular ring is larger than that of a circular ring separated from the optical axis. <P>COPYRIGHT: (C)2009,JPO&INPIT |
