MONITORING FOR DISTURBANCE OF OPTICAL FIBER
First Claim
1. A method of monitoring a length of single-mode optical fiber (104) for physical disturbance along its length, comprising the steps of:
- (i) at a first location (100), launching into the fiber polarized light having at least two different predetermined launch states of polarization (La,Lb) whose respective Stokes vectors (sLa, sLb) are linearly independent of each other;
(ii) at a second location (102) downstream from the first location, receiving the light from the fiber;
(iii) analyzing the received light using at least two different analyzer states of polarization that are characterized by respective Stokes vectors that are linearly-independent of each other;
(iv) detecting (126, 128, 130, 132) the analyzed light to provide corresponding electrical detection signals (d1, d2, d3, d4) and deriving therefrom corresponding digital detection signals (D1, D2, D3, D4);
(v) deriving from the digital detection signals (D1, D2, D3, D4) one or more representations ([sa(t1), sb(t1)], [sa(t2), sb(t2)];
M(t1,t2);
c(t1,t2);
C(t1), C(t2)) of a change in the polarization coupling properties (R) of the fiber between a first time (t1) and a second time (t2);
(vi) computing from said one or more representations at least one measure (4.14/4.15) of change in polarization coupling properties of the fiber, said at least one measure being substantially independent of said launch states and said analyzer states; and
(vii) determining with reference to preselected criteria of reportable physical disturbances whether or not said at least one measure indicates a reportable physical disturbance along said length of fiber.
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Accused Products
Abstract
Problems of excessive fading in systems for monitoring single-mode optical fiber for physical disturbances are addressed by launching into the fiber polarized light having at least two different predetermined launch states of polarization whose respective Stokes vectors are linearly-independent of each other; downstream from the first location, receiving the light from the fiber; analyzing the received light using polarization state analyzer means having at least two different analyzer states of polarization that are characterized by respective Stokes vectors that are linearly-independent of each other and detecting the analyzed light to provide corresponding detection signals; deriving from the detection signals measures of changes in polarization transformation properties of the fiber between different times that are substantially independent of said launch states and said detection states; and, on the basis of predefined acceptable physical disturbance criteria determining whether or not the measures are indicative of a reportable physical disturbance.
24 Citations
18 Claims
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1. A method of monitoring a length of single-mode optical fiber (104) for physical disturbance along its length, comprising the steps of:
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(i) at a first location (100), launching into the fiber polarized light having at least two different predetermined launch states of polarization (La,Lb) whose respective Stokes vectors (sLa, sLb) are linearly independent of each other; (ii) at a second location (102) downstream from the first location, receiving the light from the fiber; (iii) analyzing the received light using at least two different analyzer states of polarization that are characterized by respective Stokes vectors that are linearly-independent of each other; (iv) detecting (126, 128, 130, 132) the analyzed light to provide corresponding electrical detection signals (d1, d2, d3, d4) and deriving therefrom corresponding digital detection signals (D1, D2, D3, D4); (v) deriving from the digital detection signals (D1, D2, D3, D4) one or more representations ([sa(t1), sb(t1)], [sa(t2), sb(t2)];
M(t1,t2);
c(t1,t2);
C(t1), C(t2)) of a change in the polarization coupling properties (R) of the fiber between a first time (t1) and a second time (t2);(vi) computing from said one or more representations at least one measure (4.14/4.15) of change in polarization coupling properties of the fiber, said at least one measure being substantially independent of said launch states and said analyzer states; and (vii) determining with reference to preselected criteria of reportable physical disturbances whether or not said at least one measure indicates a reportable physical disturbance along said length of fiber. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A system for monitoring a length of single-mode optical fiber (104) for physical disturbance at a location or zone (L) along its length, comprises a launch unit (100) and a monitoring unit (102):
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the launch unit (100) being adapted for launching into one end of the length of fiber polarized light at a first location light having at least two different predetermined launch states of polarization (La,Lb) whose respective Stokes vectors (sLa, sLb) are linearly independent of each other; the monitoring unit (102) being adapted for receiving the light from a second end of the fiber and comprising; analyzing means for analyzing the received light using at least two different analyzer states of polarization that are characterized by respective Stokes vectors that are linearly-independent of each other; means (126, 128, 130, 132) for detecting the analyzed light and providing corresponding electrical detection signals (d1, d2, d3, d4); analog-digital conversion means (142) for deriving from the electrical detection signals corresponding digital detection signals (D1, D2, D3, D4); processing means operable for; (i) deriving from the digital detection signals (D1, D2, D3, D4) one or more representations ([sa(t1), sb(t1)], [sa(t2), sb(t2)];
M(t1,t2);
c(t1,t2);
C(t1), C(t2)) of a change in the polarization coupling properties (R) of the fiber between a first time (t1) and a second time (t2);(ii) computing from said one or more representations at least one measure (4.14/4.15) of change in polarization coupling properties of the fiber, said at least one measure being substantially independent of said launch states and said analyzer states; and (iii) determining with reference to preselected criteria of reportable physical disturbances whether or not said measure or measures indicate a reportable physical disturbance. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
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Specification