Method for polarization-based intrusion monitoring in fiberoptic links

• US 20060072922A1
• Filed: 10/06/2005
• Published: 04/06/2006
• Est. Priority Date: 10/06/2004
• Status: Active Grant

• Current Assignee: The Board of Regents of the University of Colorado (University of Colorado System)
• Original Assignee: The Board of Regents of the University of Colorado (University of Colorado System)
• Inventors: MacDonald, Gregory G., Sluss, James J. Jr.
• Granted Patent: US 7,903,977 B2
• Time in Patent Office: Days
• US Class Current: 398/152
• CPC Class Codes: H04B 10/85 Protection from unauthorised access, e.g. eavesdrop protection

Abstract

A fiber optic communication system including a fiber optic link, a transmitter system and a receiver system. The transmitter system includes a laser source producing a light beam, and a polarization controller receiving the light beam and providing an expected pattern of changing states of polarization to the light beam to output light signals into the fiber optic link to cause the expected pattern of changing states of polarization to be transmitted along the fiber optic link. The receiver system is provided with a polarization analyzer, and a light detector. The light detector receives the light signals transmitted by the transmitter, and forwards data indicative of the light signals to the polarization analyzer. The polarization analyzer analyzing the data with an inverse polarization reference frame and generates an alert based on deviations of the data from the expected pattern of changing states of polarization.

Claims

1. A fiber optic communication system, comprising:

a fiber optic link;

a transmitter system comprising;

a laser source producing a light beam; and

a polarization controller receiving the light beam and providing an expected pattern of changing states of polarization to the light beam to output light signals into the fiber optic link to cause the expected pattern of changing states of polarization to be transmitted along the fiber optic link;

a receiver system comprising;

a polarization analyzer; and

a light detector receiving the light signals transmitted by the transmitter, and forwarding data indicative of the light signals to the polarization analyzer, the polarization analyzer analyzing the data with an inverse polarization reference frame and generating an alert based on deviations of the data from the expected pattern of changing states of polarization.

2. The fiber optic communication system of claim 1, wherein the inverse polarization reference frame is periodically recalibrated to account for a slow time-varying birefringence component of the fiber optic link.

3. The fiber optic communication system of claim 1, wherein the polarization controller embeds calibration symbols in the expected pattern of changing states of polarization.

4. The fiber optic communication system of claim 3, wherein the polarization analyzer receives data indicative of the embedded calibration symbols, and uses the embedded calibration symbols to recalibrate the inverse polarization reference frame.

5. A method for polarization-based intrusion monitoring in a fiber optic link, comprising the steps of:

transmitting a light signal having an expected pattern of changing states of polarization along the fiber optic link;

receiving the light signal and generating data indicative of the light signal; and

analyzing the data with an inverse polarization reference frame;

generating an alert based on deviations of the data from the expected pattern of changing states of polarization.

6. The method of claim 5, further comprising the step of periodically recalibrating the inverse polarization reference frame to account for a slow time-varying birefringence component of the fiber optic link.

7. The method of claim 5, wherein the step of transmitting the light signal further comprising the step of embedding multiple calibration symbols in the expected pattern of changing states of polarization to construct a calibration sequence.

8. The method of claim 7, wherein the polarization analyzer receives data indicative of the embedded calibration symbols, and uses the embedded calibration symbols to recalibrate the inverse polarization reference frame.