Intrusion detection system for secure fiber optics
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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Abstract
Methods and apparatus are disclosed for an intrusion detection system for secure fiber optic communication systems. A guard signal is transmitted over the optical fiber communication link and both the modal power and modal phase delay of this signal are monitored. Intrusions into the link for the purpose of intercepting information being transmitted, cause changes in the modal phase delay and power of the guard signal. These changes, when detected by the monitoring system, indicate the presence of an intruder. A fiber profile which is optimal for both transmission and intrusion detection purposes is described.
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Citations
17 Claims
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1. A system for detecting intrusions into a fiber optic communication system comprising:
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(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. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An intrusion detection system for a fiber optic communication system comprising:
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(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 connected to one end of said fiber to launch a guard signal modulated optical beam into an entry point of said fiber; and
(c) second means optically coupled to the other end of said fiber to monitor the modal delays of said guard beam. - View Dependent Claims (8, 9)
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10. An intrusion detection system for a fiber optic communications system comprising:
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(a) an optical fiber operating as a single mode fiber at the data transmission wavelength;
(b) first means optically coupled to one end of said fiber to launch a guard signal modulated optical beam into an entry point of said fiber, said guard beam having a wavelength such that said fiber acts as a multi-mode fiber at said guard beam wavelength; and
(c) second means optically coupled to the other end of said fiber to monitor the modal delays of said guard beam. - View Dependent Claims (11)
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12. A method of detecting intrusion into a fiber optic communication system comprising the steps of:
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(a) transmitting a guard signal modulated optical beam through a primary core of an optical fiber, said primary core having an index profile with at least first, second and third graded index regions with intermediate step index regions interposed between first and second, and second and third graded index regions, respectively;
(b) monitoring the differential modal phase delays of said guard signal modulated optical beam; and
(c) detecting changes in the differential modal phase delays to detect the presence of said intrusion. - View Dependent Claims (13, 14)
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15. A method of selecting optical fibers, suitable for use in a secure optical communication system, from a plurality of optical fibers suitable for optical communication, comprising the steps of:
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(a) launching a guard signal modulated optical beam into an entry point of each one of said plurality of optical fibers;
(b) measuring a first modal delay profile of each one of said plurality of optical fibers without perturbation;
(c) perturbing each one of said plurality of optical fibers by applying perturbation of the same minimal magnitude;
(d) measuring a second modal delay profile of each one of said plurality of optical fibers when subjected to said perturbation; and
(e) comparing the first and second modal delay profile of each one of said plurality of optical fibers so as to ascertain the extent of fluctuation in modal phase delay magnitude with said minimal perturbation; and
(f) selecting optical fibers exhibiting sufficient fluctuation in modal phase delay magnitude for purposes of intrusion detection.
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16. An apparatus for testing fibers to determine their suitability for use in intrusion detection systems for secure optical communications comprising:
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(a) said fiber;
(b) first means optically coupled to one end of said fiber to launch a guard signal modulated optical beam into an entry point of said fiber;
(c) second means optically coupled to the other end of said fiber to determine the modal delay profile of said fiber; and
(d) third means connected to said fiber at some intermediate point between said one end and said other end for perturbing said fiber.
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17. An optical fiber for secure transmission of an optical beam therethrough and for enhanced sensitivity to intrusion, comprising:
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a cladding, and a primary core having a cross-sectional index profile, said index profile having at least first, second and third regions having a graded index, a first step index region interposed between said first and second regions, and a second step index region interposed between said second and third regions, said index profile being uniform along the length of said fiber, said index profile for enhancing modal phase delay variation in said beam responsively to said intrusion.
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Specification