| 摘要 |
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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