Intrusion detection system for use on single mode optical fiber using a simplified polarimeter
First Claim
1. A method for detecting movement of an optical fiber comprising:
- providing a optical fiber having a first end and a second end;
detecting movement of a portion of the fiber along the length thereof by;
injecting polarized light into one end of the optical fiber;
detecting at one end of the fiber a series of received light signals which have been transmitted along the fiber;
comparing at least some of the received light signals relative to data obtained from previously received ones of the received light signals to detect changes of polarization of the received light signals relative to the previously received light signals;
analyzing the changes in polarization to determine any changes which are indicative of manipulation of the optical fiber causing movement of a portion thereof along the length thereof;
and generating an alarm in response to the detection of any such changes which are indicative of manipulation of the optical fiber causing movement of a portion thereof along the length thereof;
wherein the changes in polarization are detected by splitting the received light signals into no more than three paths including first and second paths and using the first path to detect an amplitude of the light in the path when polarized in a linear direction and using the second path to detect an amplitude of the light in the path when polarized in a circular direction; and
wherein the splitter is selected such that the state of polarization (SOP) of the signals in the separate paths are NOT maintained relative to an absolute reference as would be required in a standard polarimeter; and
wherein the light in the second path is circularly polarized by a quarter wave retarder and a linear polarizer and wherein the second path is fed back to the optical switch so as to use a single linear polarizer for both the first and second paths.
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Accused Products
Abstract
A telecommunications optical fiber is secured against intrusion by detecting manipulation of the optical fiber prior to an intrusion event. This can be used in a non-locating system where the detection end is opposite the transmit end or in a locating system which uses Fresnel reflections and Rayleigh backscattering to the transmit end to detect and then locate the motion. The Rayleigh backscattering time sliced data can be stored in a register until an intrusion event is detected. The detection is carried out by a polarization detection system which includes an optical splitter which is manufactured in simplified form for economic construction. This uses a non-calibrated splitter and less than all four of the Stokes parameters. It can use a polarimeter type function limited to linear and circular polarization or two linear polarizers at 90 degrees.
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Citations
15 Claims
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1. A method for detecting movement of an optical fiber comprising:
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providing a optical fiber having a first end and a second end; detecting movement of a portion of the fiber along the length thereof by; injecting polarized light into one end of the optical fiber; detecting at one end of the fiber a series of received light signals which have been transmitted along the fiber; comparing at least some of the received light signals relative to data obtained from previously received ones of the received light signals to detect changes of polarization of the received light signals relative to the previously received light signals; analyzing the changes in polarization to determine any changes which are indicative of manipulation of the optical fiber causing movement of a portion thereof along the length thereof; and generating an alarm in response to the detection of any such changes which are indicative of manipulation of the optical fiber causing movement of a portion thereof along the length thereof; wherein the changes in polarization are detected by splitting the received light signals into no more than three paths including first and second paths and using the first path to detect an amplitude of the light in the path when polarized in a linear direction and using the second path to detect an amplitude of the light in the path when polarized in a circular direction; and wherein the splitter is selected such that the state of polarization (SOP) of the signals in the separate paths are NOT maintained relative to an absolute reference as would be required in a standard polarimeter; and wherein the light in the second path is circularly polarized by a quarter wave retarder and a linear polarizer and wherein the second path is fed back to the optical switch so as to use a single linear polarizer for both the first and second paths. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for detecting movement of an optical fiber comprising:
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providing a optical fiber having a first end and a second end; detecting movement of a portion of the fiber along the length thereof by; injecting polarized light into one end of the optical fiber; detecting at one end of the fiber a series of received light signals which have been transmitted along the fiber; comparing at least some of the received light signals relative to data obtained from previously received ones of the received light signals to detect changes of polarization of the received light signals relative to the previously received light signals; analyzing the changes in polarization to determine any changes which are indicative of manipulation of the optical fiber causing movement of a portion thereof along the length thereof; and generating an alarm in response to the detection of any such changes which are indicative of manipulation of the optical fiber causing movement of a portion thereof along the length thereof; wherein the changes in polarization are detected by splitting the received light signals into no more than three paths including first and second paths and using the first path to detect an amplitude of the light in the path when polarized in a linear direction and using the second path to detect an amplitude of the light in the path when polarized in a circular direction; and wherein the splitter is selected such that the state of polarization (SOP) of the signals in the separate paths are NOT maintained relative to an absolute reference as would be required in a standard polarimeter; and wherein there is provided a second optical switch or a coupler for supplying the signals from the separate paths to a single receiving system for analyzing the amplitude. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15)
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Specification