Sagnac interferometer based secure communication system

A secure communication system including:

• first optical transceiver means;
• second optical transceiver means;
• first and second optical fibers connected between said first and second optical transceiver means;
• and
• a first intruder alarm subsystem including:
• first and second distributed fiber optic sensors including first and second Sagnac interferometers, said first distributed fiber optic sensor being positioned to transmit light toward said second optical transceiver means and back toward said first optical transceiver means, and said second distributed fiber optic sensor being positioned to transmit light toward said first optical transceiver means and back toward said second optical transceiver means, to sense from opposite directions along said first and second optical fibers, the position of environmental effects affecting said first and second optical fibers indicative of an intruder attempting to tap into said first and second optical fibers.

A communication system including:

• a Sagnac interferometer including:
• an optical loop;
• a light source;
• and
• means optically connected to said light source for producing counter propagating light beams on said optical loop, for receiving said counter propagating light beams, and for producing therefrom an interferometric output;
• an optical phase modulator remote from said means and in said optical loop for impressing information on said counter propagating light beams so that said information appears in the interferometric output;
• and
• an output light detector optically connected to said optical loop for receiving the interferometric output and for producing therefrom an output signal representative of the information.

A secure communication system including:

• first optical transceiver means;
• second optical transceiver means;
• first and second optical fibers connected between said first and second optical transceiver means;
• and
• an intruder alarm subsystem including:
• an alarm;
• a first Sagnac interferometer distributed fiber optic sensor positioned adjacent said first optical transceiver means for sensing effects indicative of an intruder at said first optical fiber and producing first outputs therefrom;
• a second Sagnac interferometer distributed fiber optic sensor positioned adjacent said second optical transceiver means for sensing effects indicative of an intruder at said first optical fiber and producing second outputs therefrom;
• and
• means for combining the first and second outputs, determining therefrom the location along said first optical fiber of the effects indicative of an intruder, and activating said alarm.