Optical pickup device
US4897828A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jul 15, 1988 |
| Grant date | Jan 30, 1990 |
| Priority date | — |
| Expiry date | Jul 15, 2008 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B7/13
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A focusing error detecting apparatus having a first photo-detector of which the light receiving portion is halved to provide first and second light receiving portions asymmetrical with respect to the center of a beam spot of a bundle of incident laser beams, the first photo-detector being located in the optical path ahead of the focusing point of the bundle of the incident laser beams, a second photo-detector of which the light receiving portion is halved to provide first and second light receiving portions asymmetrical with respect to the center of a beam spot of a bundle of incident laser beams, the second photo-detector being located in the optical path behind a focussing point of the bundle of the incident laser beams and a calculating circuit for calculating a difference between a difference of detected outputs from the first and second light receiving portions of the first photo-detector and a difference of detected outputs from the first and second light receiving portions of the second photo-detector, thereby to derive a focusing error signal from the output of the calculating circuit.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.