Telecommunications – Receiver or analog modulated signal frequency converter – Signal selection based on frequency
Patent
1977-01-21
1980-08-12
Griffin, Robert L.
Telecommunications
Receiver or analog modulated signal frequency converter
Signal selection based on frequency
350 9633, 455608, H04B 900
Patent
active
042174880
ABSTRACT:
A transmitter of information to be communicated in secure form is optically coupled to a composite optical fiber at one end, the fiber being connected to a receiver of the secure information at the other end. The composite optical fiber has cores including a central core for carrying the secure information, one or more guard signal cores, a cladding matrix surrounding all the cores, and a metallic or other nontransmissive film surrounding the central core but not the guard cores. A guard signal optical transmitter section is coupled to the guard cores for jamming any leakage of secure information through the film, and a guard signal receiver section is provided at the other end of the fiber for monitoring purposes. The optical transmitter apparatus employs pulse code modulation (PCM) and sends related security bits in the guard and secure signals. The optical receiver apparatus features amplitude monitoring and a comparison of the related security bits and provides a warning when unexpected changes indicative of tampering are observed.
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Mayo--A Bipolar Repeater for PCM Signals--Bell Syst. Tech. Jour., _Jan. 1962, pp. 25, 66, 67, 84-87.
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Bell Telephone Laboratories Incorporated
Dubosky Daniel D.
Griffin Robert L.
Orsino Jr. Joseph A.
Sherman Sylvan
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