| 摘要 |
PROBLEM TO BE SOLVED: To provide a recording and reproducing device which is compatible with optical disks differing in thickness. SOLUTION: A lens system which has double focuses, i.e., the bifocal lens 4 is constituted by forming a hologram 3 which generates lights 20 and 21 of (±1)st order and arranging the hologram 3 nearby an objective 2. Further, a hologram area which is higher in diffraction efficiency or a refraction type optical element is formed at the outer peripheral position of the hologram 3 to give the bifocal lens 4 different numerical apertures with the degrees of diffraction. Further, to record and reproduce an optical disk 1 which is different in the thickness up to its information recording surface 12, the bifocal lens 4 consisting of the hologram 3 and objective 2 is used for an optical pickup 90. |
