Focus error detection apparatus utilizing focusing an front and rear sides of focal planes
US4742218A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Feb 11, 1986 |
| Grant date | May 3, 1988 |
| Priority date | — |
| Expiry date | Feb 11, 2006 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B11/10576
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A focus error detection apparatus and an optical disk apparatus comprising a focusing lens for focusing reflected light coming from a light reflecting surface which is to be adjusted at the focal point of a projected light beam; a beam splitter means for dividing the output light of said focusing lens into a first and a second focused light beam; a first and a second photo-detector disposed respectively on the optical paths of said first and said second focused light beam, one of which is located behind the convergence point of said first focused light beam and the other of which is located before the convergence point of said second focused light beam, each of them generating outputs proportional to the amount of light within a predetermined region of the received light image, when it varies so that it is enlarged; and a circuit generating a focus error signal by using the difference between the outputs of said two photo-detectors.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.