Focus sensing apparatus using electrical AGC to enhance differential focus error signal
US5349175A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Oct 30, 1991 |
| Grant date | Sep 20, 1994 |
| Priority date | — |
| Expiry date | Oct 30, 2011 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B2007/0919
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A focus sensing apparatus for determining the focus of an illuminating beam relative to an optical disk is disclosed herein. In one preferred embodiment, a light source generates a linearly polarized beam which is collimated by a collimating lens. The collimated beam is then converged by an objective lens onto the surface of the optical disk. The disk reflects the illuminating beam focused thereon back through the objective lens to a polarization beam splitter. A portion of the optical energy incident on the beam splitter is then redirected to form a servo beam, wherein the degree of collimation of the servo beam is indicative of the focus position of the illuminating beam. A beam separation module having a reflectivity which varies in response to the angle of incidence of optical energy thereon is positioned to intercept the servo beam. The beam separation module is operative to separate the servo beam into two beams which could be transmitted and reflected beams of substantially similar shape and intensity. Electrical signals produced by photodetective elements in response to incidence of the transmitted and reflected beams thereon may then be used to differentially generate a fo…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.