Method for polarization-based intrusion monitoring in fiberoptic links

• US 7,903,977 B2
• Filed: 10/06/2005
• Issued: 03/08/2011
• 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.
• Primary Examiner(s): Bello; Agustin
• Application Number:
  US11/244,665
• Publication Number:
  US 20060072922A1
• Time in Patent Office: 1,979 Days
• Field of Search: 398/40, 398/151, 398/152, 380/256
• 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 coupled to the fiber optic link, the transmitter system comprising;

a laser source producing light beams; and

a polarization controller receiving the light beams and encoding symbols into the light beams to provide an expected pattern of changing states of polarization to the light beams to output light signals into the fiber optic link to cause the light beams having the expected pattern of changing states of polarization to be transmitted along the fiber optic link;

a receiver system coupled to the fiber optic link, the 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 to (1) monitor the fiber optic link for a possible physical intrusion/disturbance based on deviations of the data from the symbols encoded into the light beams and (2) generate an alert indicative of a possible physical intrusion of the fiber optic link, wherein the transmitter system and the receiver system are not coupled to the fiber optic link with the same element.

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:

encoding symbols into light signals to form an expected pattern of changing states of polarization into the light signals;

transmitting the light signals along the fiber optic link

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

analyzing the data with an inverse polarization reference frame to monitor the fiber optic link for a possible physical intrusion/disturbance based on deviations of the data from symbols encoded into the light signals wherein the steps of transmitting the light signals and receiving the light signals do not use the same element to couple to the fiber optic link; and

generating an alert indicative of a possible physical intrusion of the fiber optic link.

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 a polarization analyzer receives data indicative of the embedded calibration symbols, and uses the embedded calibration symbols to recalibrate the inverse polarization reference frame.