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

• US 20100254649A1
• Filed: 04/06/2009
• Published: 10/07/2010
• Est. Priority Date: 04/06/2009
• Status: Active Grant

• Current Assignee: RPX Clearinghouse LLC (RPX Corporation)
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Schofield, Bruce
• Granted Patent: US 8,494,313 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 comprising the steps of:

monitoring the state of polarization of an optical fiber;

determining that a fiber tap has occurred if the state of polarization changes beyond a first predetermined amount.

2. The method of claim 1 further comprising the step of:

determining alternately that a fiber tap has occurred if the state of polarization changes beyond a second predetermined amount and in an approximately continuous, non-random direction.

3. The method of claim 1 wherein the step of monitoring comprises the steps of:

monitoring a first state of polarization of an optical fiber;

waiting for a time period;

monitoring a second state of the polarization of the optical fiber;

and wherein the step of determining comprises;

determining that a fiber tap has occurred if the second state of polarization changes beyond a first predetermined amount from the first state of polarization.

4. The method of claim 3 wherein the time period is chosen to be less than a time during which the state of polarization of the optical fiber is expected to drift.

5. The method of claim 4 wherein the first predetermined amount is approximately 2.4 radians.

6. Apparatus comprising:

logic for monitoring the state of polarization of an optical fiber;

logic for determining that a fiber tap has occurred if the state of polarization changes beyond a first predetermined amount.

7. The apparatus of claim 6 further comprising:

apparatus for determining alternately that a fiber tap has occurred if the state of polarization changes beyond a second predetermined amount and in an approximately continuous, non-random direction.

8. The apparatus of claim 6 wherein the logic for monitoring comprises:

logic for monitoring a first state of polarization of an optical fiber;

logic for waiting for a time period;

logic for monitoring a second state of the polarization of the optical fiber;

and wherein the logic for determining comprises;

logic for determining that a fiber tap has occurred if the second state of polarization changes beyond a first predetermined amount from the first state of polarization.

9. The apparatus of claim 8 wherein the time period is chosen to be less than a time during which the state of polarization of the optical fiber is expected to drift.

10. The apparatus of claim 9 wherein the first predetermined amount is approximately 2.4 radians.

11. A program product comprising a computer readable medium having embodied therein a computer program for storing data, the computer program comprising:

logic for monitoring the state of polarization of an optical fiber;

logic for determining that a fiber tap has occurred if the state of polarization changes beyond a first predetermined amount.

12. The program product of claim 11 further comprising:

logic for determining alternately that a fiber tap has occurred if the state of polarization changes beyond a second predetermined amount and in an approximately continuous, non-random direction.

13. The program product of claim 11 wherein the logic for monitoring comprises:

logic for monitoring a first state of polarization of an optical fiber;

logic for waiting for a time period;

logic for monitoring a second state of the polarization of the optical fiber;

and wherein the logic for determining comprises;

logic for determining that a fiber tap has occurred if the second state of polarization changes beyond a first predetermined amount from the first state of polarization.

14. The program product of claim 13 wherein the time period is chosen to be less than a time during which the state of polarization of the optical fiber is expected to drift.

15. The program product of claim 14 wherein the first predetermined amount is approximately 2.4 radians.