| 摘要 |
<P>PROBLEM TO BE SOLVED: To suppress interference light from an adjacent layer of a multilayer optical recording medium having a plurality of information recording surfaces by forming satisfactory spots on a plurality of optical recording media with different substrate thicknesses with a single objective lens. <P>SOLUTION: A diffraction optical element 106 includes two concentric split regions 106b, 106c of an aberration correction function and a region 106a of unnecessary light measure. The region 106b distributes an incident light beam of a wavelength of 405 nm to 0-th transmission light and +1st diffracted light by a diffraction structure of NA of 0.65. The region 106c limits the NA by a flat structure of NA 0.65 to NA 0.85, and diffraction for adjacent layer interference light measure is formed in the region 106a. The region 106b combined with the objective lens constitutes a bifocal lens structure, forms the spot on each optical recording medium, and corrects spherical aberration generated when that light is condensed on the information recording surface. The 0-th transmission light of the adjacent layer overlapped with the ±1st diffracted light reflected by an object layer is diffracted by the diffraction structure of the region 106a to suppress the reception of interference light from the adjacent player. <P>COPYRIGHT: (C)2009,JPO&INPIT |
