Secure fiber optic data transmission system
AssigneeInternational Telephone and Telegraph Corporation
InventorsJames H. Bowen, David L. Baldwin, Philip R. Couch
Life of this patent
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Abstract
A fiber optic data transmission system is protected against external physical intrusion by obscuring the data in the natural quantum noise and then limiting access to the intruder by means of an optical power alarm. This is accomplished by modulating the data on a very large predetermined average optical power with a very small modulation index and then providing an alarm arrangement which is responsive to the received optical energy to activate an alarm means and to deactivate its associated transmitting arrangement when the received optical energy has an amplitude outside of a given amplitude region.
Claims14
A secure fiber optic data transmission system comprising:
- an optical fiber means to provide two way optical communication between two spaced terminals;
- each of said two terminals including
- first means coupled to an adjacent end of said optical fiber means to receive optical energy modulated by data transmitted from the other of said two terminals;
- second means coupled to said adjacent end of said optical fiber means to transmit modulated optical energy to said other of said two terminals, said transmitted optical energy having a predetermined average optical power and data modulated thereon with a modulation index;
- and
- third means coupled to said first and second means resonsive to said received optical energy to activate an alarm means and to deactivate said second means when said received optical energy has an amplitude outside of a given amplitude region,
- said third means including
- a threshold comparator coupled to said first and second means having two spaced threshold values to define said given amplitude region.
Dependencies are inferred from the claim text.