Method and apparatus for detecting focussing error signal of objective lens
US4390781A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Oct 8, 1980 |
| Grant date | Jun 28, 1983 |
| Priority date | — |
| Expiry date | Oct 8, 2000 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B2007/0924
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
In a method 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 a central light ray in the reflected light flux, and two light fluxes which situate on respective sides of a boundary plane including the central light ray and perpendicular to a plane of incidence, and are reflected by the reflection surface are separately received by two light receiving regions which are divided along a boundary plane including the central light ray reflected by the reflection surface and perpendicular to the plane of incidence. 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.