Method of and apparatus for writing and reading a magneto-optical record carrier with an information density greater than that corresponding to the size of the scanning spot
US5065377A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Dec 20, 1989 |
| Grant date | Nov 12, 1991 |
| Priority date | — |
| Expiry date | Dec 20, 2009 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B11/10528
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A method and apparatus for optically writing and reading information as a pattern of magnetic domains in the information recording layer of a record carrier. An optical scanning beam is focused to a diffraction-limited radiation spot for scanning the recording layer, and the region under the spot is subjected to a magnetic field generated by a magnetizing coil energized with a square-wave energizing current having a duty cycle which is modulated in accordance with the information signal. The frequency and amplitude of the energizing current are independent of the information signal, and the frequency thereof exceeds the optical cut-off frequency determined by the size of the radiation spot. Several different values of the information signal can therefore be recorded within a distance equal to the width of the radiation spot in the scanning direction at each position thereof, so that the recorded information density exceeds that corresponding the width of the scanning spot. Read-out is based on the "grey" level produced by the recorded information areas under the scanning spot at each position thereof, so that the same size scanning spot can be used for both writing and reading the …
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.