Method and apparatus for detecting a focussing condition of an objective lens
US4422168A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Aug 14, 1981 |
| Grant date | Dec 20, 1983 |
| Priority date | — |
| Expiry date | Aug 14, 2001 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B2007/0919
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A method and apparatus for detecting a focussing error signal of an objective lens with respect to a video disc on which a light beam emitted from a laser light source is to be focussed as a light spot by the objective lens. A light flux reflected by the video disc is made incident upon a detection prism surface which is set substantially at a critical angle with respect to peripheral light fluxes reflected by the video disc, and the peripheral light fluxes reflected by the reflection surface are separately received by two light receiving regions which are spaced apart from each other. The focussing error signal is derived as a difference between output signals from the two light receiving regions.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.