| 摘要 |
PROBLEM TO BE SOLVED: To unnecessitate a lens switch mechanism by arranging a diffraction grating so that O-order light is focused on an optical disk with small substrate thickness, and +1st-order diffracted light is focused on the optical disk with large substrate thickness. SOLUTION: When the optical disk 20 with the substrate thickness (t) of 0.6mm is loaded on an optical drive, the O-order light 111 transmitting through a double focus hologram 40 is focused on the optical disk, and its reflection light is used as return back light of an optical head. The +1st-order diffracted light 112 is reflected without focusing. On the other hand, when the optical disk 21 with the substrate thickness (t) of 1.2mm is loaded, the +1st-order diffracted light 112 is focused on the optical disk, and its reflection light is used as the return back light of the optical head. Then, the O-order light is reflected without focusing. |
