Multiple focus lens, an optical head apparatus and an optical information recording-reproducing apparatus
US5986779A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Aug 12, 1996 |
| Grant date | Nov 16, 1999 |
| Priority date | — |
| Expiry date | Aug 12, 2016 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B2007/0006
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
Coma of an objective lens occurs depending on the lens-forming condition when plural disks of different substrate thickness are recorded and reproduced. An objective lens according to this invention is not influenced by the coma even if the thickness of the substrates is changed. For this purpose, a diffraction grating whose aberration is corrected is formed on the first side of an aspheric objective lens. Due to this correction, light beams having different diffraction orders, e.g. 0th order diffracted light and +1st order diffracted light, are focused respectively on two kinds of substrates of different thickness. The whole objective lens is tilted to correct its axial coma, and the tilt angle is predetermined to be substantially identical with respect to plural substrates which are different in thickness.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.