Focusing and tracking servo system for controlling the projection of an optical beam on an optical disk
US4888752A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jul 28, 1988 |
| Grant date | Dec 19, 1989 |
| Priority date | — |
| Expiry date | Jul 28, 2008 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B7/0908
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A focusing and tracking servo system for generating focusing and tracking error signals for use in driving a servo system which focuses and tracks an optical beam, such as a laser beam on an optical disk. The system includes a photosensor having two sub-photosensors arranged to be adjacent to each other and to have a common boundary, and the laser beam has a circular cross-section and an optical axis. The laser beam reflected by the optical disk is incident on the photosensor so that the optical axis is offset from the boundary between the sub-photosensors. Consequently, the optical spot formed on each sub-photosensor has a different area and the sub-photosensors generate different photoelectric currents. The output currents from the sub-photosensors are individually amplified by amplifiers having adjustable amplification factors, and the amplification factors are set so that they are inversely proportional to the output current of the sub-photosensors when the laser beam incident on the optical disk is in an in-focus state. When the laser beam incident on the optical disk is in an out-of-focus state the optical spot changes, and thus the relative output currents of the sub-photose…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.