| 摘要 |
<p>An optical disc comprises an optical recording area R and a clamping area C. In the optical recording area R, there is provided a recording section (2) where a magnetic layer, a magneto-optic recording layer, a recording layer having extrusions or recesses corresponding to information is formed. In the clamping area C, a hub (3) is provided. In this optical disc, the thickness of the part of the transparent substrate under the optical recording area R where a laser beam is actually transmitted in recording and reproducing is small. The thickness of the transparent substrate under the clamping area C where no laser beam is transmitted is greater than that of the part under the optical recording area R. In this way, it is possible to suppress the rate at which the aberration is increased due to the inclination of the optical disc. Even when the numerical aperture NA of an objective lens is large, the allowance of inclination of the optical disc can be within a practical range. The strength of the disc is great. The optical disc does not deform when the substrate is formed, the hub is attached, and the disc is chucked onto a disc table. High-density recording on the optical disc can be achieved.</p> |
