Patent ID: 7903977

Claim:
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.