Diffractive security device on compact discs
US6226109A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Aug 9, 1999 |
| Grant date | May 1, 2001 |
| Priority date | — |
| Expiry date | Aug 9, 2019 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B23/281
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
This invention relates to marking the genuine CD in an easily detectable way while difficult to counterfeit. The improved CD has within its layers a second structured surface parallel to the flat surfaces of the CD. The second structured surface acts as a diffractive security device, that is to be read out from the same side of the CD, the verso side, as the data structure. In one example, the second structured surface is defined by a step of the refractive index or by a transparent reflective layer. Despite the diffractive rainbow colors observed on the verso side of the CD, the structure of the security device can be read out visually and/or with a CD-reader, even by a simple hand-held reader, and verified without the need of a bulky apparatus. A CD-reader prevents the playing of embodiments of the improved CDs.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.