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Intrusion detection system for secure fiber optics

  • US 6,819,849 B1
  • Filed: 07/29/1988
  • Issued: 11/16/2004
  • Est. Priority Date: 10/25/1985
  • Status: Active Grant
First Claim
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1. A system for detecting intrusions into a fiber optic communication system comprising:

  • (a) an optical fiber having a cladding and a primary core having an index profile with at least first, second and third graded index regions with intermediate first and second step index regions interposed between first and second, and second and third graded index regions, respectively, said index profile being uniform along the length of said fiber, said index profile for enhancing modal delay variation;

    (b) first means optically coupled to one end of said fiber to launch a guard signal modulated optical beam in an entry point of said fiber for transmission by said fiber, said guard beam being capable of experiencing fluctuation in the magnitudes of modal delay and power attenuation responsively to intrusion into said fiber; and

    (c) second means optically coupled to the other end of said fiber for detecting the fluctuations in the magnitudes of the differential modal delay and power attenuation of said guard beam.

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