Polarization-based sensor for secure fiber optic network and other security applications

1 . A method of sensing an attempted intrusion comprising:

transmitting light of at least one known state of polarization within a first optical fiber, wherein said first optical fiber is in proximity to a secured element, and wherein said light originates from a polarized source;

receiving said light at a fiber optic polarizer, wherein said fiber optic polarizer is in line with said first optical fiber; and

identifying an attempted intrusion of said secured element from a change in the state of polarization of said light.

2 . The method of claim 1 , wherein said identifying comprises:

recording one or more polarization traces from said first optical fiber;

analyzing said one or more polarization traces to create an averaged trace;

measuring changes in the state of polarization of said light transmitted through said first optical fiber to obtain an intrusion trace; and

comparing said intrusion trace to said averaged trace to determine whether said intrusion trace is an attempted intrusion in proximity of said first optical fiber.

3 . The method of claim 2 , wherein said measuring changes in the state of polarization of light includes (i) recording one or more intrusion traces, and (ii) analyzing said one or more intrusion traces.

4 . The method of claim 1 , wherein said fiber optic polarizer is either (i) a device having polarization dependent loss, (ii) a linear polarizer, (iii) a non-linear polarizer.

5 . The method of claim 1 , wherein said fiber optic polarizer is a polarimeter.

6 . The method of claim 1 , wherein said first optical fiber has a single mode.

7 . The method of claim 1 , wherein said first optical fiber has multiple modes.

8 . The method of claim 7 , further comprising:

after said transmitting said light within said first optical fiber,

(a) amplifying said light in said first optical fiber; and

(b) compensating for dispersion from said at least one known state of polarization.

9 . The method of claim 1 , further comprising:

isolating said polarized source of said light after said transmitting to block reflections of said light from affecting said polarized source.

10 . The method of claim 1 , wherein said secured element is at least a second optical fiber within a channel in proximity to said first optical fiber.

11 . The method of claim 1 , wherein said secured element is installed in proximity to a fence.

12 . The method of claim 1 , wherein said secured element is installed proximity to a structure.

13 . The method of claim 1 , wherein said attempted intrusion includes at least one of (i) an intruder tapping an optical fiber or tapping into a channel that contains at least one optical fiber, (ii) an intruder cutting, climbing, or otherwise getting past a fence, and (iii) an intruder entering, moving, or otherwise trespassing at a structure.

14 . A system for sensing an attempted intrusion comprising:

a first optical fiber in proximity to a secured element;

a transmitter, coupled to said first optical fiber, for sending polarized light of at least one known state of polarization through said first optical fiber;

a fiber optic polarizer coupled to said first optical fiber;

a receiver, coupled to said first optical fiber, for accepting said light within said first optical fiber; and

an electronic component, coupled to said receiver, for measuring changes in the state of polarization of said light, wherein said light supplies information adequate to determine one or more polarization traces, an averaged trace based on said one or more polarization traces, and an intrusion trace.

15 . The system of claim 14 , wherein said electronic component records and analyzes one or more polarization traces when measuring changes to determine an intrusion trace.

16 . The system of claim 14 , wherein said transmitter includes at least one of a Fabry-Perot laser or a distributed feedback laser.

17 . The system of claim 14 , wherein said fiber optic polarizer is either (i) a device having polarization dependent loss, (ii) a linear polarizer, (iii) a non-linear polarizer, or (iv) a polarimeter.

18 . The system of claim 14 , wherein said first optical fiber has a single mode.

19 . The system of claim 14 , wherein said first optical fiber has multiple modes.

20 . The system of claim 19 , further comprising:

an amplifier, coupled to said first optical fiber after said transmitter, to strengthen said light in said first optical fiber; and

a compensator, coupled to said amplifier, to counteract dispersion from said at least one known state of polarization of said light in said first optical fiber.

21 . The system of claim 14 , further comprising:

an isolator, coupled to said first optical fiber after said transmitter, to block reflections of said light from affecting said transmitter.

22 . The system of claim 14 , wherein said secured element is at least a second optical fiber within a channel in proximity to said first optical fiber.

23 . The system of claim 14 , wherein said secured element is installed in proximity to a fence.

24 . The system of claim 14 , wherein said secured element is installed in proximity to a structure.

25 . The system of claim 14 , wherein said attempted intrusion includes at least one of (i) an intruder tapping an optical fiber or tapping into a channel that contains at least one optical fiber, (ii) an intruder cutting, climbing, or otherwise getting past a fence, and (iii) an intruder entering, moving, or otherwise trespassing at a structure.