MONITORING eDC POLARIZATION INVERSE FILTER COEFFICIENTSW TO IDENTIFY REAL-TIME PHYSICAL INTRUSION INTO A CORE OR METRO OPTICAL NETWORK

• US 20130182993A1
• Filed: 03/04/2013
• Published: 07/18/2013
• Est. Priority Date: 04/06/2009
• Status: Active Grant

• Current Assignee: RPX Clearinghouse LLC (RPX Corporation)
• Original Assignee: Rockstar Consortium US LP (Rockstar Consortium Inc.)
• Inventors: Schofield, Bruce
• Granted Patent: US 9,002,148 B2
• Time in Patent Office: Days
• US Class Current: 385/11
• CPC Class Codes: G02B 6/278 Controlling polarisation mode dispersion [PMD], e.g. PMD compensation or emulation PMD minimised transmission systems H04B10/2569
• CPC Class Codes: H04B 10/85 Protection from unauthorised access, e.g. eavesdrop protection

Abstract

A fiber network is monitored in order to detect physical intrusion. The state of polarization of an optical fiber is monitored. A fiber tap is determined to have occurred if the state of polarization of the fiber changes beyond a predetermined amount found to be associated with all types of fiber taps. Alternately, it may be determined that a fiber tap has occurred if the state of polarization changes beyond a second predetermined amount and in a predetermined direction. Monitoring of the state of polarization occurs before and after a time period chosen to be less than a time during which the state of polarization of the optical fiber is expected to drift. This step eliminates false positives due to natural fiber PMD drift.

Claims

1. A method of monitoring a physical condition of an optical waveguide, the method comprising:

monitoring a state of polarization of an optical signal propagating on the optical waveguide over a time interval; and

when the state of polarization changes by more than an amount of drift expected during the time interval, signaling that the physical condition of the optical waveguide has changed.

2. The method of claim 1, wherein:

the optical waveguide is part of a system which comprises an electronic dispersion compensator, the electronic dispersion compensation monitor being configured to dynamically calculate electronic dispersion compensation coefficients used to control dynamic electronic dispersion compensation of the optical signal propagating on the optical waveguide; and

monitoring a state of polarization of the optical signal comprises monitoring the electronic dispersion compensation coefficients to infer changes in the state of polarization of the optical signal propagating on the optical waveguide.

3. The method of claim 1, wherein monitoring the state of polarization of the optical signal over a time interval, comprises:

determining the state of polarization at a first time;

determining the state of polarization at a second time, the second time differing from the first time by a predetermined time interval;

comparing the state of polarization at the first time to state of polarization at the second time to determine a change in the state of polarization; and

comparing the change in state of polarization of the optical signal to a predetermined amount of drift expected during the predetermined time interval.

4. The method of claim 3, wherein the predetermined time interval is set short enough that less than 90 degrees of polarization drift is expected during the predetermined time interval.

5. The method of claim 3, wherein the predetermined time interval is set at less than or equal to 10 minutes.

6. The method of claim 1, wherein signaling that the physical condition of the optical waveguide has changed is used to infer physical manipulation of the optical waveguide.

7. The method of claim 6, wherein signaling that the physical condition of the optical waveguide has changed is used to identify a deliberately manipulated optical waveguide.

8. The method of claim 6, wherein signaling that the physical condition of the optical waveguide has changed is used to infer tampering with the optical waveguide.

9. The method of claim 6, wherein signaling that the physical condition of the optical waveguide has changed is used to infer tapping of the optical waveguide.

10. The method of claim 1, wherein the optical waveguide is an optical fiber.

11. A method of monitoring a physical condition of an optical waveguide, the method comprising:

monitoring a state of polarization of an optical signal propagating on the optical waveguide over a time interval; and

when the state of polarization changes by more than a predetermined amount in an approximately continuous, non-random direction, signaling that the physical condition of the optical waveguide has changed.

12. The method of claim 11, wherein:

the optical waveguide is part of a system which comprises an electronic dispersion compensator, the electronic dispersion compensation monitor being configured to dynamically calculate electronic dispersion compensation coefficients used to control dynamic electronic dispersion compensation of the optical signal propagating on the optical waveguide; and

monitoring a state of polarization of the optical signal comprises monitoring the electronic dispersion compensation coefficients to infer changes in the state of polarization of the optical signal propagating on the optical waveguide.

13. The method of claim 11, wherein monitoring the state of polarization of the optical signal over a time interval, comprises:

determining the state of polarization at a first time;

determining the state of polarization at a second time, the second time differing from the first time by a predetermined time interval;

comparing the state of polarization at the first time to state of polarization at the second time to determine a change in the state of polarization; and

comparing the change in state of polarization of the optical signal to a predetermined amount of drift expected during the predetermined time interval.

14. The method of claim 13, wherein the predetermined time interval is set short enough that less than 90 degrees of polarization drift is expected during the predetermined time interval.

15. The method of claim 13, wherein the predetermined time interval is set at less than or equal to 10 minutes.

16. The method of claim 11, wherein signaling that the physical condition of the optical waveguide has changed is used to infer physical manipulation of the optical waveguide.

17. The method of claim 16, wherein signaling that the physical condition of the optical waveguide has changed is used to identify a deliberately manipulated optical waveguide.

18. The method of claim 16, wherein signaling that the physical condition of the optical waveguide has changed is used to infer tampering with the optical waveguide.

19. The method of claim 16, wherein signaling that the physical condition of the optical waveguide has changed is used to infer tapping of the optical waveguide.

20. The method of claim 11, wherein the optical waveguide is an optical fiber.