Apparatus for optically scanning a radiation-reflective information plane
US4835378A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Dec 21, 1987 |
| Grant date | May 30, 1989 |
| Priority date | — |
| Expiry date | Dec 21, 2007 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B7/094
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
Apparatus for scanning a radiation-reflective information plane (2). A scanning beam of radiation (b) from a diode laser (4) is focused by an objective lens (6) on the information plane and the beam reflected therefrom is deflected by a composite diffraction grating (9) so as to form two asymmetrical radiation spots (V.sub.1, V.sub.2) respectively focused on respective pairs of photodiodes (18, 19; 20, 21). The relative outputs of the photodiodes in each pair control focusing of the scanning beam on the information plane. The photodiodes in each pair are separated by a strip (22',23') positioned so that it is at an acute angle to the line (22, 23) along which the asymmetrical reflected radiation spot formed on the relevant diode pair becomes displaced as a result of variations in the wavelength of the scanning beam. Such angle is set so the separating strip is on the line along which the center of the intensity distribution of such radiation spot becomes displaced as a result of such variations. Consequently, such variations do not affect the relative outputs of the photodiode pairs and so are prevented from affecting focusing of the scanning beam on the information plane.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.