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