Method and apparatus using polarisation optical time domain reflectometry for security applications
First Claim
1. An intrusion detection system for detecting a disturbance at a determinable portion of a structure comprising:
- (a) transmitter leg for launching a wavelength invariant pulsed polarized optical signal;
(b) a sensor leg for arrangement along the structure, the sensor leg comprising a sensing optical fiber to carry a portion of said polarized optical signal sensitive to a disturbance therealong; and
(c) a receiver leg for receiving a portion of a backscattered optical signal from said sensor leg;
wherein said backscattered optical signal provides polarization change and timing information relative to said pulsed polarized optical signal, sufficient to determine a location of the disturbance along said sensor leg; and
wherein the location of the disturbance along the sensor leg can be mapped to the determinable portion of the structure.
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Accused Products
Abstract
A preferred apparatus and method is presented in which a distributed fiber optic sensor is used in order to detect a disturbance along its length. A pulse of polarized light is launched into an optical fiber; as the pulse propagates along the optical fiber, it continuously loses a small portion of its energy due to Rayleigh backscatter. The Rayleigh backscattered light is analyzed using a polarization sensitive element such as a fiber polarizer. The dynamics of the time dependence of the polarization analyzed backscattered light is used to ascertain if there has been a disturbance along the length of the optical fiber. This technique can be used for applications in areas such as fiber optic telecommunications, perimeter security, fire detection, and pipelines.
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Citations
23 Claims
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1. An intrusion detection system for detecting a disturbance at a determinable portion of a structure comprising:
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(a) transmitter leg for launching a wavelength invariant pulsed polarized optical signal; (b) a sensor leg for arrangement along the structure, the sensor leg comprising a sensing optical fiber to carry a portion of said polarized optical signal sensitive to a disturbance therealong; and (c) a receiver leg for receiving a portion of a backscattered optical signal from said sensor leg; wherein said backscattered optical signal provides polarization change and timing information relative to said pulsed polarized optical signal, sufficient to determine a location of the disturbance along said sensor leg; and wherein the location of the disturbance along the sensor leg can be mapped to the determinable portion of the structure. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method of detecting a disturbance at a determinable portion along a length of optical fiber using backscattered optical signals that provide polarization change and time information sufficient to determine a location of said disturbance, said method comprising:
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launching a pulsed polarized optical signal for carrying within an optical fiber; capturing a predetermined number of reflected polarized signal traces from said optical fiber; digitally filtering said predetermined number of reflected polarized signal traces to form a plurality of digitally filtered traces; averaging said digitally filtered traces to form an average trace; obtaining a disturbance trace from said optical fiber; and comparing said disturbance trace to said average trace so as to determine a disturbance at a portion of said optical fiber. - View Dependent Claims (16)
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17. An intrusion detection system for detecting an intrusion along a determinable portion of a structure comprising:
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(a) a transmitter leg for launching a wavelength invariant pulsed polarized optical signal; (b) a sensor leg for arrangement along the structure, the sensor lea comprising a sensor cable including a locating optical fiber to carry a portion of said pulsed polarized optical signal sensitive to a disturbance therealong and a non-locating sensor cable; (c) a receiver leg for accepting a portion of a backscattered optical signal from said sensor leg; and (d) a signal processor for providing a signal response output indicative of a disturbance along said non-locating sensor cable; wherein said backscattered optical signal provides polarization change and timing information relative to said pulsed polarized optical signal sufficient to determine a location of the disturbance along the locating optical fiber; and wherein the location of the disturbance along the sensor leg can be mapped to the determinable portion of the structure. - View Dependent Claims (18, 19, 20, 21, 22, 23)
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Specification