Method and apparatus for detecting focussing error signal of objective lens
US4505584A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jan 15, 1982 |
| Grant date | Mar 19, 1985 |
| Priority date | — |
| Expiry date | Jan 15, 2002 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B2007/0919
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
In order to derive a focussing error signal of an objective lens with respect to a video disc on which a light beam is focussed by the objective lens, the P-polarized light beam is made incident upon a prism and then upon a thin film which is applied to the prism and has a refractive index higher than that of the prism, and the light beam reflected by a boundary surface between the thin film and the air is detected by a photo-detector having two light receiving regions. The thin film is made of material having a higher refractive index than that of the prism. Between the prism and the thin film there may be interposed at least one additional thin film in such a manner that the lower and higher refractive index thin films are alternately arranged.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.