Objective lens used with high density optical recording medium
US6353588B1 · kind B1 · utility
Assignee
Inventor
Key dates
| Filing date | Dec 15, 1999 |
| Grant date | Mar 5, 2002 |
| Priority date | — |
| Expiry date | Dec 15, 2019 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B11/10543
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
An objective lens having no more that two lens elements with refractive power is disclosed for reading or writing at high density on a recording medium. The first lens element, in order from a light source side, is biconvex and includes at least one aspheric surface so that it is individually well-corrected for spherical aberration. The second lens element is of a meniscus shape with its concave surface on the recording medium side of the objective lens. If the objective lens is used without a cover glass at the recording medium, the convex surface of the second lens element is made to have an aplanatic surface, which is a surface that is capable of changing the convergence or divergence of a cone of rays without introducing any spherical aberration, coma or astigmatism. Whether or not there is a cover glass at the recording medium, the following condition is satisfied0.8<R4/BF<1.2whereR4 is the radius of curvature of the surface on the optical recording side of the second lens element L2, andBF is the back focal length of objective lens.The surface of the second lens element on the optical recording medium side is preferably made to be normal to rays converging to/diverging from t…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.