Secure communications system
US5223967A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jun 11, 1986 |
| Grant date | Jun 29, 1993 |
| Priority date | — |
| Expiry date | Jun 11, 2006 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04B10/85
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
There is provided by this invention a secure fiber optic communication system based on the Sagnac interferometer that allows multiple authorized users to communicate on the system by modulation and detection of two counterpropagating light beams. The security of the system is based on a combination of the information being modulated on the relative phase difference between the counterpropagating light beams and the low coherence length of the light source. In order for an intruder to intercept the signal, both counterpropagating beams must be accessed and the pathlength of the two beams matched to within a few coherence lengths of the light source so that an amplitude modulated output signal may be constructed. The system is further comprised of a random pathlength generator used to randomly vary the relative pathlength of the two counterpropagating beams. A light level alarm is provided that detects changes in the light level within the system. If the signal level changes sufficiently, the light level alarm shuts down the system.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.