Monitoring eDC polarization inverse filter coefficients to identify real-time physical intrusion into a core or metro optical network

• US 8,494,313 B2
• Filed: 04/06/2009
• Issued: 07/23/2013
• Est. Priority Date: 04/06/2009
• Status: Expired due to Fees

• Current Assignee: RPX Clearinghouse LLC (RPX Corporation)
• Original Assignee: Rockstar Consortium US LP (Rockstar Consortium Inc.)
• Inventors: Schofield, Bruce
• Primary Examiner(s): Vanderpuye, Kenneth N
• Assistant Examiner(s): Alagheband, Abbas H
• Application Number:
  US12/418,919
• Publication Number:
  US 20100254649A1
• Time in Patent Office: 1,569 Days
• Field of Search: 398/65, 398/152, 398/184, 398/205, 398/177, 398/33, 398/39, 398/40, 385/11
• 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 a first state of polarization of an optical fiber;

waiting for a time period that is less than a time during which the first state of polarization of the optical fiber is expected to drift;

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

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.

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

determining alternately that a fiber tap has occurred if the first 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 first predetermined amount is approximately 2.4 radians.

4. Apparatus comprising:

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

logic for waiting for a time period that is less than a time during which the first state of polarization of the optical fiber is expected to drift;

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

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.

5. The apparatus of claim 4 further comprising:

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

6. The apparatus of claim 4 wherein the first predetermined amount is approximately 2.4 radians.

7. A computer program product comprising a non-transitory computer readable medium having embodied therein a computer program for storing data, the computer program comprising:

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

logic for waiting a time period that is less than a time during which the first state of polarization of the optical fiber is expected to drift;

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

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.

8. The program product of claim 7 further comprising:

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

9. The program product of claim 7 wherein the first predetermined amount is approximately 2.4 radians.