| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to accurately access all of a CD, CD-R and DVD, by advancing two light beams having different wavelengths, which are emitted from two laser diodes, in the same advancing direction with different flux diameters. SOLUTION: The 1st light beam from the 1st laser diode 32 advances to the side of an objective lens passing through a hologram pattern 38B or a prism 38A around it. The 1st light beam, with which the hologram pattern 38B is irradiated, is separated into 0-order diffracted beam and 1st-order diffracted beam, and the 0-order diffracted beam advances along a center axis of the hologram pattern 38B together with the 1st light beam passed through the prism 38A. Whole area of the prism 38A including the hologram pattern 38B is irradiated with the 2nd light beam from the 2nd laser diode 34, but a luminous flux, with which the hologram pattern 38B is irradiated, is only diffracted and advances along the same direction as that of the 1st light beam. |
