Intrusion detection system for use on single mode optical fiber using a storage register for data
First Claim
1. A method for detecting and locating movement of an optical fiber comprising:
- providing an optical fiber having first and second ends;
injecting polarized light into the first end of the optical fiber in a series of sequential pulses such that, in response to each pulse, there is returned to the first end of the fiber a light signal which includes Rayleigh backscattering components generated from positions along the fiber so that each light signal forms a trace which varies over time depending on the position along the fiber from which the light is returned;
detecting the received light signals at the first end;
comparing a part only of each received light signal, which is responsive to a pulse, relative to data obtained from previously received light signals responsive to previous ones of the pulses to detect changes of polarization of the part only of the received light signal relative to the corresponding parts of the previously received light signals from said previous ones of the pulses;
detecting movement of a portion of the fiber along the length thereof by analyzing the changes in polarization of the part only of the received light signal to determine any changes which are indicative of movement of the optical fiber at a portion thereof along the length thereof;
the part only of the received light signal which is analyzed to detect movement including light returned from the second end of the fiber;
generating an alarm in response to the detection of any such changes;
detecting, in discrete time steps, polarization of the Raleigh backscattering components of each light signal to generate, for each time step, data relating to the polarization of the Rayleigh backscattering components in that time step;
storing the data relating to the polarization of the Rayleigh backscattering components in said discrete time steps in a register for a period of time and discarding the data relating to the polarization of the Rayleigh backscattering components after the period of time and replacing it with fresh data;
such that the stored data relating to the polarization of the Rayleigh backscattering components in said discrete time steps is time dependent and thus indicative of a time of travel of the light signals and thus of a location of the position from which the Rayleigh backscattering components have originated along the fiber;
and, only in the event that movement is detected of the optical fiber by analyzing the changes in polarization of the part only of the received light signal, extracting the data relating to the polarization of the Rayleigh backscattering components in said discrete time steps from the register and analyzing the polarization of the Rayleigh backscattering components in said discrete time steps to detect the location of the movement.
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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
20 Claims
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1. A method for detecting and locating movement of an optical fiber comprising:
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providing an optical fiber having first and second ends; injecting polarized light into the first end of the optical fiber in a series of sequential pulses such that, in response to each pulse, there is returned to the first end of the fiber a light signal which includes Rayleigh backscattering components generated from positions along the fiber so that each light signal forms a trace which varies over time depending on the position along the fiber from which the light is returned; detecting the received light signals at the first end; comparing a part only of each received light signal, which is responsive to a pulse, relative to data obtained from previously received light signals responsive to previous ones of the pulses to detect changes of polarization of the part only of the received light signal relative to the corresponding parts of the previously received light signals from said previous ones of the pulses; detecting movement of a portion of the fiber along the length thereof by analyzing the changes in polarization of the part only of the received light signal to determine any changes which are indicative of movement of the optical fiber at a portion thereof along the length thereof; the part only of the received light signal which is analyzed to detect movement including light returned from the second end of the fiber; generating an alarm in response to the detection of any such changes; detecting, in discrete time steps, polarization of the Raleigh backscattering components of each light signal to generate, for each time step, data relating to the polarization of the Rayleigh backscattering components in that time step; storing the data relating to the polarization of the Rayleigh backscattering components in said discrete time steps in a register for a period of time and discarding the data relating to the polarization of the Rayleigh backscattering components after the period of time and replacing it with fresh data; such that the stored data relating to the polarization of the Rayleigh backscattering components in said discrete time steps is time dependent and thus indicative of a time of travel of the light signals and thus of a location of the position from which the Rayleigh backscattering components have originated along the fiber; and, only in the event that movement is detected of the optical fiber by analyzing the changes in polarization of the part only of the received light signal, extracting the data relating to the polarization of the Rayleigh backscattering components in said discrete time steps from the register and analyzing the polarization of the Rayleigh backscattering components in said discrete time steps to detect the location of the movement. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A method for detecting and locating movement of an optical fiber comprising:
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providing an optical fiber having first and second ends; injecting polarized light into the first end of the optical fiber in a series of sequential pulses such that, in response to each pulse, there is returned to the first end of the fiber a light signal; each light signal including light returned from the second end which is reflected and including Rayleigh backscattering components generated from positions along the fiber, so that each light signal forms a trace which varies over time depending on the position along the fiber from which the light is returned; detecting the received light signals at the first end; comparing a part only of each received light signal, which is responsive to a pulse, relative to data obtained from previously received light signals responsive to previous ones of the pulses to detect changes of polarization of the part only of the received light signal relative to the corresponding parts of the previously received light signals from said previous ones of the pulses; detecting movement of a portion of the fiber along the length thereof by analyzing the changes in polarization of the part only of the received light signal to determine any changes which are indicative of movement of the optical fiber at a portion thereof along the length thereof; the part only of the received light signal which is analyzed to detect movement including said reflected light returned from the second end of the fiber; generating an alarm in response to the detection of any such changes; detecting, in discrete time steps, polarization of the Rayleigh backscattering components of each light signal to generate, for each time step, data relating to the polarization of the Rayleigh backscattering components in that time step; storing the data relating to the polarization of the Rayleigh backscattering components in said discrete time steps in a register for a period of time and discarding the data relating to the polarization of the Rayleigh backscattering components after the period of time and replacing it with fresh data; such that the stored data relating to the polarization of the Rayleigh backscattering components in said discrete time steps is time dependent and thus indicative of a time of travel of the light signals and thus of a location of the position from which the Rayleigh backscattering components have originated along the fiber; and, only in the event that movement is detected of the optical fiber by analyzing the changes in polarization of the part only of the received light signal, extracting the data relating to the polarization of the Rayleigh backscattering components in said discrete time steps from the register and analyzing the polarization of the Rayleigh backscattering components in said discrete time steps to detect the location of the movement. - View Dependent Claims (18, 19, 20)
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Specification