Sagnac interferometer based secure communication system

• US 5,311,592 A
• Filed: 09/04/1992
• Issued: 05/10/1994
• Est. Priority Date: 06/11/1986
• Status: Expired due to Term

• Current Assignee: Mcdonnell Douglas Corporation (The Boeing Co.)
• Original Assignee: Mcdonnell Douglas Corporation (The Boeing Co.)
• Inventors: Udd, Eric
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US07/940,618
• Time in Patent Office: 613 Days
• Field of Search: 380/3, 380/4, 380/9, 380/49, 380/54, 380/59, 359/109-111, 359/115, 359/118, 359/119, 359/152, 359/164, 359/168, 359/173, 359/180, 359/183, 359/188, 359/189, 359/193, 359/195, 359/181
• US Class Current: 380/256
• CPC Class Codes: G01M 11/39 in which light is projected from both sides of the fiber or waveguide end-face
• CPC Class Codes: H04B 10/85 Protection from unauthorised access, e.g. eavesdrop protection

Abstract

A secure fiber optic communication system capable of tens of gigabits/second data transfer rates that utilizes a pair of single mode fiber optic cables in combination with one or more light sources, phase modulators, detectors and polarization scrambling elements to form a Sagnac interferometer. The phase modulator is driven so that counter propagating light beams in the Sagnac loop experience a different optical path as they pass through the loop. When the two beams are recombined on the central beamsplitter of the Sagnac loop, the two beams interfere with each other and the data impressed as phase modulation on the light beams by the phase modulator is recovered as amplitude modulation on the output detector of the Sagnac interferometer. The system can be configured to operate full duplex on two optical fibers by using light at different wavelengths or time division multiplexing data. The system can also be configured as a multi-node network. Alarms, intrusion control, random pathlength changes and the like can be included to make undetected, unauthorized access to the system even more difficult.

Claims

1. A communication system including:

a first fiber optic beamsplitter having;

a first arm;

a second arm;

a third arm; and

a fourth arm;

a first light source that produces a first beam of light into said first arm, said first fiber optic beamsplitter splitting said first beam of light into second and third beams of light on said third and fourth arms respectively;

a first optical pathway connecting said third arm to said fourth arm, said first optical pathway conducting said second and third beams of light from said third and fourth arms to said fourth and third arms respectively, said first optical pathway having;

a center;

a first optical phase modulator in said first optical pathway spaced from said center thereof said first optical phase modulator having;

an input for receiving a first information signal that said first optical phase modulator uses to phase modulate said second and third beams of light, whereby upon the return of said second and third beams of light to said first fiber optic beamsplitter, said second and third beams of light combine into an amplitude modulated fourth beam of light conducted on said second arm whose amplitude varies with said first information signal; and

a first detector connected to receive said fourth beam of light from said second arm and to produce therefrom a first output signal representative of said first information signal.

2. The communication system as defined in claim 1 further including:

a polarization scrambler positioned between said first light source and said first arm to scramble the polarization of said first beam of light.

3. The communication system as defined in claim 1 further including:

a polarization scrambler positioned in said first optical pathway to scramble the polarization of said second and third beams of light.

4. The communication system as defined in claim 1 further including:

a polarization scrambler positioned between said first light source and said first arm to scramble the polarization of said first beam of light; and

at least one polarization scrambler positioned in said first optical pathway to scramble the polarization of said second and third beams of light.

5. The communication system as defined in claim 1 further including:

a data formatter that provides the first information signal to said first optical phase modulator input in bursts spaced in time at least the twice the shortest time it takes either the second or third beam of light to travel from said first optical phase modulator to said center; and

a data reformatter connected to receive said output signal representative of the first information signal from said first detector and extract therefrom the first information signal.

6. The communication system as defined in claim 5 wherein said burst of first information signal phase modulated into said second beam of light travels to and clears said first fiber optic beamsplitter before said burst of first information signal phase modulated into said third beam of light arrives at said first fiber optic beamsplitter so that each burst of first information signal is output from said detector twice, said data reformatter including:

means to compare the first information signals for errors and produce therefrom a verified output first information signal.

7. The communication system as defined in claim 6 wherein said data reformatter includes:

means to produce an alarm signal upon finding a predetermined number of errors during the comparison.

8. The communication system as defined in claim 1 further including:

a data formatter that integrates the first information signal to said phase modulator input, the first information signal being differentiated by said system to produce the first information signal at said first detector.

9. The communication system as defined in claim 1 further including:

a data formatter that inputs the first information signal to said first optical phase modulator input in the form of sawtooth pulses, the first information signal being differentiated to square wave pulses by said system to produce the first information signal at said first detector in digital form.

10. The communication system as defined in claim 1 wherein said first optical pathway is an optical fiber pathway.

11. The communication system as defined in claim 1 further including:

a first light coupler positioned in said first optical pathway between said first fiber optic beamsplitter and said first optical phase modulator generally adjacent said first optical phase modulator that splits a portion of said third beam of light therefrom;

first intensity monitoring means connected to said first light coupler for receiving the portion of said third beam of light and producing an alarm output when the intensity of the portion of said third beam of light falls outside a predetermined range;

a second light coupler positioned in said first optical pathway between said first fiber optic beamsplitter and said center generally spaced from said center a similar distance said first light coupler is spaced therefrom that splits a portion of said second beam of light therefrom; and

second intensity monitoring means connected to said second light coupler for receiving the portion of said second beam of light and producing an alarm output when the intensity of the portion of said second beam of light falls outside a predetermined range.

12. The communication system as defined in claim 11 wherein said first intensity monitoring means has:

a first intensity output, and wherein said second intensity monitoring means has;

a second intensity output, said communication system further including;

intensity comparing means connected to receive said first and second intensity outputs from said first and second intensity monitoring means, said intensity comparing means producing an alarm output when said first and second intensity outputs from said first and second intensity monitoring means have relative variation outside a predetermined range.

13. The communication system as defined in claim 1 further including:

a pathlength changer positioned in said first optical pathway.

14. The communication system as defined in claim 13 wherein said pathlength changer includes:

a random pathlength generator positioned near said center, said random pathlength generator including;

a piezoelectric cylinder; and

an optical fiber wrapped around said piezoelectric cylinder.

15. The communication system as defined in claim 14 wherein said pathlength changer includes:

control means connected to said random pathlength generator and operatively connected to said first optical phase modulator to coordinate pathlength changes with transmission of the first information signal so that first information signal is not lost during a pathlength change.

16. The communication system as defined in claim 13 wherein said pathlength changer includes:

at least one optical switch in said first optical pathway; and

at least one length of optical fiber connected to said optical switch so that said optical switch can add and remove said at least one length of optical fiber to said first optical pathway.

17. The communication system as defined in claim 1 further including:

a first light coupler positioned in said first optical pathway near said center thereof, said first light coupler having;

a first coupler arm in said first optical pathway facing said third arm of said first fiber optic beamsplitter;

a second coupler arm in said first optical pathway facing said first optical phase modulator;

a third coupler arm; and

a fourth coupler arm, said first light coupler splitting a portion of said second beam of light onto said fourth coupler arm and a portion of said third beam of light onto said third coupler arm;

first intensity monitoring means connected to said third coupler arm for receiving the portion of said third beam of light and producing an alarm output when the intensity of the portion of said third beam of light falls outside a predetermined range; and

second intensity monitoring means connected to said fourth coupler arm for receiving the portion of said second beam of light and producing an alarm output when the intensity of the portion of said second beam of light falls outside a predetermined range.

18. The communication system as defined in claim 17 wherein said first intensity monitoring means has:

a first intensity output, and wherein said second intensity monitoring means has;

a second intensity output, said communication system further including;

intensity comparing means connected to receive said first and second intensity outputs from said first and second intensity monitoring means, said intensity comparing means producing an alarm output when said first and second intensity outputs from said first and second intensity monitoring means have relative variation above a predetermined range.

19. The communication system as defined in claim 1 further including:

a plurality of first light couplers positioned in said first optical pathway between said first fiber optic beamsplitter and said first optical phase modulator generally adjacent said first optical phase modulator, each first light coupler splitting a portion of a different wavelength band from said third beam of light;

a plurality of first intensity monitoring means, each connected to one of said plurality of first light couplers for receiving a portion of said third beam of light and producing an alarm output when the intensity of the portion said third beam of light of the wavelength band falls outside a predetermined range;

a plurality of second light couplers positioned in said first optical pathway between said first fiber optic beamsplitter and said center generally spaced from said center a distance similar to the distance said first light couplers are spaced therefrom, each second light coupler splitting a portion of a different wavelength band from said second beam of light; and

a plurality of second intensity monitoring means, each connected to one said plurality of second light couplers for receiving the portion of said second beam of light split thereby and producing an alarm output when the intensity of the portion of said second beam of light of the wavelength band falls outside a predetermined range.

20. The communication system as defined in claim 19 wherein each of said plurality of said first intensity monitoring means has:

a first intensity output, and wherein each of said plurality of said second intensity monitoring means has;

a second intensity output, said communication system further including;

a plurality of intensity comparing means, each connected to receive said first and second intensity outputs of a single wavelength band from one of said first and second intensity monitoring means, said each of said intensity comparing means producing an alarm output when said first and second intensity outputs from said connected first and second intensity monitoring means have relative variation outside a predetermined range.

21. The communication system as defined in claim 1 further including:

a first dispersive tap positioned in said first optical pathway between said first fiber optic beamsplitter and said first optical phase modulator generally adjacent said phase modulator splitting a portion of said third beam of light into different wavelength bands;

first intensity monitoring means including;

a first detector array for receiving the different wavelength bands of the portion of said third beam of light and producing an alarm output when the intensity of the portion of said third beam of light of any of the wavelength bands falls outside a predetermined range;

a second dispersive tap positioned in said first optical pathway between said first fiber optic beamsplitter and said center generally spaced from said center a similar distance said first dispersive tap is spaced therefrom splitting a portion of said second beam of light into different wavelength bands;

second intensity monitoring means including;

a second detector array for receiving the different wavelength bands of the portion of said second beam of light and producing an alarm output when the intensity of the portion of said second beam of light of any of the wavelength bands falls outside a predetermined range.

22. The communication system as defined in claim 21 wherein said first intensity monitoring means has:

a plurality of first intensity outputs, and wherein said second intensity monitoring means has;

a plurality of second intensity outputs, said communication system further including;

intensity comparing means connected to receive said pluralities of first and second intensity outputs of a single wavelength band from one of said first and second intensity monitoring means, said intensity comparing means comparing first and second intensity outputs from the same wavelength bands and producing an alarm output when said first and second intensity outputs from the same wavelength band have relative variation outside a predetermined range.

23. The communication system as defined in claim 1 further including:

a signal generator producing low frequency output signals;

an alarm phase modulator positioned in said first optical pathway spaced from said center thereof connected to receive said low frequency output signals from said signal generator, whereby said alarm phase modulator impresses said low frequency output signal on said second and third beams of light that appears on said amplitude modulated fourth beam of light;

filter means connected to receive said output signal representative of said first information signal and extract said low frequency output signal therefrom; and

synchronous demodulator means connected to said low frequency output signals from said signal generator and said filter means to produce therefrom an alarm signal when the power level in said fourth beam of light changes beyond a predetermined amount.

24. The communication system as defined in claim 1 further including:

a signal generator producing low frequency output signals and connecting a low frequency output signal to said first optical phase modulator, whereby said first optical phase modulator impresses said low frequency output signal on said second and third beams of light that appears on said amplitude modulated fourth beam of light;

filter means connected to receive said output signal representative of said first information signal and extract said low frequency output signal therefrom; and

synchronous demodulator means connected to said low frequency output signals from said signal generator and said filter means to produce therefrom an alarm signal when the power level in said fourth beam of light changes beyond a predetermined amount.

25. The communication system as defined in claim 1 further including:

a second fiber optic beamsplitter having;

a fifth arm;

a sixth arm;

a seventh arm; and

an eighth arm;

a second light source that produces a fifth beam of light at a center wavelength different from said first beam of light into said fifth arm, said second fiber optic beamsplitter splitting said fifth beam of light into sixth and seventh beams of light on said sixth and seventh arms respectively;

a first wavelength division multiplexing beamsplitter connecting said sixth arm to said first optical pathway between said center thereof and said first fiber optic beamsplitter;

a second wavelength division multiplexing beamsplitter connecting said seventh arm to said first optical pathway between said first optical phase modulator and said first fiber optic beamsplitter;

a third wavelength division multiplexing beamsplitter connected to said first optical pathway between said first wavelength division multiplexing beamsplitter and said first fiber optic beamsplitter;

a fourth wavelength division multiplexing beamsplitter connected to said first optical pathway between said second wavelength division multiplexing beamsplitter and said first fiber optic beamsplitter, said third and fourth wavelength division multiplexing beamsplitters being connected together, and said second fiber optic beamsplitter, said first, second, third, and fourth wavelength division multiplexing beamsplitters and connecting portions of said first optical pathway forming a second optical pathway, said second optical pathway having;

a second center positioned between said third and fourth wavelength division multiplexing beamsplitters, said second optical pathway conducting said sixth and seventh beams of light from said sixth and seventh arms to said seventh and sixth arms respectively;

a second optical phase modulator in said second optical pathway spaced from said second center thereof;

said second optical phase modulator having;

an input for receiving a second information signal that said second optical phase modulator uses to phase modulate said sixth and seventh beams of light, whereby upon the return of said sixth and seventh beams of light to said second fiber optic beamsplitter, said sixth and seventh beams of light combine into an amplitude modulated eighth beam of light conducted on said eighth arm whose amplitude varies with said second information signal; and

a second detector connected to receive said eighth beam of light from said eighth arm and to produce therefrom a second output signal representative of said second information signal.

26. The communication system as defined in claim 25 further including:

a polarization scrambler positioned between said second light source and said fifth arm to scramble the polarization of said fifth beam of light.

27. The communication system as defined in claim 25 further including:

a polarization scrambler positioned in said second optical pathway to scramble the polarization of said sixth and seventh beams of light.

28. The communication system as defined in claim 25 further including:

a first polarization scrambler positioned between said second light source and said fifth arm to scramble the polarization of said fifth beam of light; and

at least one other polarization scrambler positioned in said second optical pathway to scramble the polarization of said sixth and seventh beams of light.

29. The communication system as defined in claim 25 wherein said first optical pathway has:

first and second opposite sides, said communication system further including;

a first Sagnac interferometer distributed fiber optic sensor facing said first side;

a second Sagnac interferometer distributed fiber optic sensor facing said second side; and

a signal processor connected to said first and second Sagnac interferometer distributed fiber optic sensors to calculate the amplitude and position of any frequency dependent environmental effect that occurs between said first side and said second side.

30. The communication system as defined in claim 29 wherein said first Sagnac interferometer distributed fiber optic sensor includes:

a first length of optical fiber positioned in one of said second and third arms of said first fiber optic beamsplitter whereby said one of said second and third arms of said first fiber optic beamsplitter is optically longer than the other.

31. The communication system as defined in claim 30 further including:

a second length of optical fiber positioned in one of said fifth and sixth arms of said second fiber optic beamsplitter whereby said one of said fifth and sixth arms of said second fiber optic beamsplitter is optically longer than the other.

32. The communication system as defined in claim 31 wherein said first and second lengths of optical fiber are essentially the same length.

33. The communication system as defined in claim 29 further including:

a first relatively low frequency phase shifter positioned in one of said second and third arms of said first fiber optic beamsplitter; and

a second relatively low frequency phase shifter positioned in one of said fifth and sixth arms of said second fiber optic beamsplitter.

34. The communication system as defined in claim 33 further including:

a first oscillator producing a relatively low frequency output and driving said first relatively low frequency phase shifter therewith;

a second oscillator producing a relatively low frequency output and driving said second relatively low frequency phase shifter therewith, wherein said signal processor includes;

a first synchronous demodulator connected to receive said relatively low frequency output from said first oscillator and connected to receive said first output signal from said first detector to demodulate sensor information out of said first output signal;

a second synchronous demodulator connected to receive said relatively low frequency output from said second oscillator and connected to receive said second output signal from said second detector to demodulate sensor information out of said second output signal.

35. The communication system as defined in claim 33 further including:

a first oscillator producing a relatively low frequency output and driving said first relatively low frequency phase shifter therewith;

a second oscillator producing a relatively low frequency output and driving said second relatively low frequency phase shifter therewith, wherein said first and second detectors each have;

a high frequency portion for producing information outputs; and

a low frequency portion that produces said sensor outputs, and wherein said signal processor includes;

a first synchronous demodulator connected to receive said relatively low frequency output from said first oscillator and connected to receive said first sensor output from said first detector to demodulate said first sensor output;

a second synchronous demodulator connected to receive said relatively low frequency output from said second oscillator and connected to receive said second sensor output from said second detector to demodulate said second sensor output.

36. The communication system as defined in claim 29 wherein said first and second detectors each include:

a high frequency portion for detecting said first and second information signals respectively; and

a low frequency portion for detecting environmental effects along common portions of said first and second optical pathways.

37. The communication system as defined in claim 1 further including:

a second optical phase modulator positioned in said first optical pathway;

a second fiber optic beamsplitter having;

a fifth arm;

a sixth arm;

a seventh arm; and

an eighth arm;

a third fiber optic beamsplitter having;

a ninth arm;

a tenth arm;

an eleventh arm; and

a twelfth arm;

a second light source that produces a fifth beam of light into said fifth arm, said second fiber optic beamsplitter splitting said fifth beam of light into sixth and seventh arms respectively;

first and second optical switches connecting said sixth and seventh arms to said first optical pathway on opposite sides of said first optical phase modulator;

third and fourth optical switches connected to said first optical pathway on opposite sides of said first fiber optic beamsplitter;

a third optical phase modulator positioned off of said first optical pathway between said third and fourth optical switches, said third and fourth optical switches being connected together by said third optical phase modulator;

a third light source that produces a ninth beam of light into said ninth arm, said third fiber optic beamsplitter splitting said ninth beam of light into tenth and eleventh beams of light on said tenth and eleventh arms respectively;

fifth and sixth optical switches connected to said first optical pathway on opposite sides of said second optical phase modulator, said second fiber optic beamsplitter, said first, second, third, fourth, fifth, and sixth optical switches, said second and third optical phase modulators and connecting portions of said first optical pathway forming a second optical pathway that conducts said sixth and seventh beams of light from said sixth and seventh arms to said seventh and sixth arms respectively to form an eighth beam of light on said eighth arm, and said third fiber optic beamsplitter, said first, second, third, fourth, firth and sixth optical switches, said first and third optical phase modulators and connecting portions of said first optical pathway forming a third optical pathway that conducts said tenth and eleventh beams of light from said tenth and eleventh arms to said eleventh and tenth arms respectively to form a twelfth beam of light on said twelfth arm, said second optical phase modulator having;

an input for receiving a second information signal that said optical phase modulator uses to phase modulate said second and third beams of light and said sixth and seventh beams of light, whereby upon the return of said sixth and seventh beams of light to said second fiber optic beamsplitter, said sixth and seventh beams of light combine into an amplitude modulated eighth beam of light conducted on said eighth arm whose amplitude varies with said second information signal, said fourth beam of light has amplitudes that vary with said second information signal;

a second detector connected to receive said eighth beam of light from said eighth arm and to produce therefrom a second output signal representative of said first and second information signals, said third optical phase modulator having;

an input for receiving a third information signal that said third optical phase modulator uses to phase modulate said sixth and seventh and said tenth and eleventh beams of light, whereby upon the return of said tenth and eleventh beams of light to said third fiber optic beamsplitter, said tenth and eleventh beams of light combine into an amplitude modulated twelfth beam of light conducted on said twelfth arm whose amplitude varies with said third information signal, and wherein said eighth beam of light has amplitudes that vary with said third information signal; and

a third information detector connected to receive said twelfth beam of light from said twelfth arm and to produce therefrom a third output signal representative of said second and third information signals, said first output signal being representative of said first and third information signals.

38. The communication system as defined in claim 37 further including:

means to coordinate said first, second and third optical phase modulators so that only one modulates the light beams passing through said system at a time.

39. The communication system as defined in claim 37 further including:

means to coordinate said first, second, third, fourth, fifth, and sixth optical switches so that only one optical pathway from a fiber optic beamsplitter through at least two optical phase modulators and back to said fiber optic beamsplitter is established at a time.

40. The communication system as defined in claim 37 further including:

a second optical repeater located a similar predetermined distance from said first fiber optic beamsplitter as said first optical repeater between said center and said fourth arm, wherein said first and second optical repeaters each include;

a fiber amplifier positioned in said first optical pathway;

a pump laser driver;

a pump laser driven by said pump laser driver, which is connected thereto to produce a laser light output; and

an amplifier optical coupler connecting said laser light output to said fiber amplifier.

41. The communication system as defined in claim 40 wherein said first and second optical repeaters each further include:

a first tap in said first optical pathway to split a portion of light amplified by said fiber amplifier in a first direction;

a first amplifier detector connected to receive the portion of light split by said first tap and to produce therefrom a first control signal to said pump laser driver;

a second tap in said first optical pathway to split a portion of light amplified by said fiber amplifier in a direction opposite to said first direction; and

a second amplifier detector connected to receive the portion of light split by said second tap and to produce therefrom a second control signal to said pump laser driver.

42. The communication system as defined in claim 1 further including:

a first optical repeater located a predetermined distance from said first fiber optic beamsplitter between said center and said third arm.

43. The communication system as defined in claim 1 further including:

an intruder alarm subsystem including;

first and second Sagnac interferometer distributed fiber optic sensors positioned to face opposite directions to sense environmental effects indicative of an intruder over at least one portion of said first optical pathway.

44. The communication system as defined in claim 43 wherein said first optical pathway has:

first and second opposite sides, and wherein said first Sagnac interferometer distributed fiber optic sensor includes;

a first sensor central beamsplitter at least having;

first, second, third, and fourth sensor arms;

a first sensor light source feeding a first sensor light beam into said first sensor arm, which first sensor light beam is split by said first sensor central beamsplitter into second and third sensor light beams traveling on said second and third sensor arms respectively;

first means coupling said second and third sensor light beams from said second and third sensor arms into and out of said first optical pathway at said first side thereof for traverse through at least a predetermined portion of said first optical pathway to be secured by said intruder alarm subsystem;

second means coupling said second and third sensor light beams out of and into said first optical pathway at said second side thereof, said second and third light beams recombining on said first sensor central beamsplitter to form a fourth sensor light beam on said fourth sensor arm;

a first detector positioned to receive said fourth light beam from said fourth sensor arm and produce therefrom a first sensor output whose intensity is an indication of the position and amount of disturbance in said predetermined portion of said first optical pathway to be secured by said intruder alarm subsystem, and wherein said second Sagnac interferometer distributed fiber optic sensor includes;

a second sensor central beamsplitter at least having;

fifth, sixth, seventh, and eighth sensor arms;

a second sensor light source feeding a fifth sensor light beam into said fifth sensor arm, which fifth sensor light beam is split by said second sensor central beamsplitter into sixth and seventh sensor light beams traveling on said sixth and seventh sensor arms respectively;

third means coupling said sixth and seventh sensor light beams from said sixth and seventh sensor arms into and out of said first optical pathway at said second side thereof for traverse through at least a predetermined portion of said first optical pathway to be secured by said intruder alarm subsystem;

fourth means coupling said sixth and seventh sensor light beams out of and into said first optical pathway at said first side thereof, said sixth and seventh light beams recombining on said second sensor central beamsplitter to form a eighth sensor light beam on said eighth sensor arm;

a second detector positioned to receive said eighth light beam from said eighth sensor arm and produce therefrom a second sensor output whose intensity is an indication of the position and amount of disturbance in said predetermined portion of said first optical pathway to be secured by said intruder alarm subsystem; and

a signal processor connected to said first and second sensor outputs to produce therefrom a position output and a amplitude output indicative of the position and amplitude of any disturbance in said first optical pathway secured by said intruder alarm subsystem.

45. The communication system as defined in claim 44 wherein first and second sensor light sources each include:

intensity maintenance means associated therewith.

46. The communication system as defined in claim 44 further including:

a first length of optical fiber positioned in one of said second and third arms of said first sensor central beamsplitter whereby said one of said second and third arms of said first sensor central beamsplitter is optically longer than the other.

47. The communication system as defined in claim 46 further including:

a second length of optical fiber positioned in one of said fifth and sixth arms of said second sensor central beamsplitter whereby said one of said fifth and sixth arms of said second sensor central beamsplitter is optically longer than the other.

48. The communication system as defined in claim 47 wherein said first and second lengths of optical fiber are essentially the same length.

49. The communication system as defined in claim 44 further including:

a first relatively low frequency phase shifter positioned in one of said second and third arms of said first sensor central beamsplitter; and

a second relatively low frequency phase shifter positioned in one of said fifth and sixth arms of said second sensor central beamsplitter.

50. The communication system as defined in claim 49 further including:

a first oscillator producing a relatively low frequency output and driving said first relatively low frequency phase shifter therewith; and

a second oscillator producing a relatively low frequency output and driving said second relatively low frequency phase shifter therewith, wherein said signal processor includes;

a first synchronous demodulator connected to receive said relatively low frequency output from said first oscillator and connected to receive said first sensor output from said first detector to demodulate said first sensor output; and

a second synchronous demodulator connected to receive said relatively low frequency output from said second oscillator and connected to receive said second sensor output from said second detector to demodulate said second sensor output.

51. The communication system as defined in claim 43 wherein said first optical pathway has:

first and second opposite sides, and wherein said first Sagnac interferometer distributed fiber optic sensor includes;

a first sensor central beamsplitter at least having;

first, second, third, fourth, and fifth sensor arms;

a first sensor light source feeding a first sensor light beam into said first sensor arm, which first sensor light beam is split by said first sensor central beamsplitter into second and third sensor light beams traveling on said second and third sensor arms respectively;

first means coupling said second and third sensor light beams from said second and third sensor arms into and out of said first optical pathway at said first side thereof for traverse through at least a predetermined portion of said first optical pathway to be secured by said intruder alarm subsystem;

second means coupling said second and third sensor light beams out of and into said first optical pathway at said second side thereof, said second and third light beams recombining on said first sensor central beamsplitter to form a fourth sensor light beam on said fourth sensor arm and a fifth sensor light beam on said fifth sensor arm;

a first detector positioned to receive said fourth light beam from said fourth sensor arm and produce therefrom a first output whose intensity is an indication of the position and amount of disturbance in said predetermined portion of said first optical pathway to be secured by said intruder alarm subsystem;

a second detector positioned to receive said fifth light beam from said fifth sensor arm and produce therefrom a second output whose intensity is an indication of the position and amount of disturbance in said predetermined portion of said first optical pathway to be secured by said intruder alarm subsystem, and wherein said second Sagnac interferometer distributed fiber optic sensor includes;

a second sensor central beamsplitter at least having;

sixth, seventh, eighth, ninth, and tenth sensor arms;

a second sensor light source feeding a sixth sensor light beam into said sixth sensor arm, which sixth sensor light beam is split by said second sensor central beamsplitter into seventh and eighth sensor light beams traveling on said seventh and eighth sensor arms respectively;

third means coupling said seventh and eighth sensor light beams from said seventh and eighth sensor arms into and out of said first optical pathway at said second side thereof for traverse through at least a predetermined portion of said first optical pathway to be secured by said intruder alarm subsystem;

fourth means coupling said seventh and eighth sensor light beams out of and into said first optical pathway at said first side thereof, said seventh and eighth light beams recombining on said second sensor central beamsplitter to form a ninth sensor light beam on said ninth sensor arm and a tenth sensor light beam on said tenth sensor arm;

a third detector positioned to receive said ninth light beam from said ninth sensor arm and produce therefrom a third output whose intensity is an indication of the position and amount of disturbance in said predetermined portion of said first optical pathway to be secured by said intruder alarm subsystem;

a fourth detector positioned to receive said tenth light beam from said tenth sensor arm and produce therefrom a fourth output whose intensity is an indication of the position and amount of disturbance in said predetermined portion of said first optical pathway to be secured by said intruder alarm subsystem; and

a signal processor connected to said first, second, third, and fourth sensor outputs to produce therefrom a position output and a amplitude output indicative of the position and amplitude of any disturbance in said first optical pathway secured by said intruder alarm subsystem.

52. The communication system as defined in claim 51 wherein first, second, third, and fourth sensor light sources each include:

intensity maintenance means associated therewith.

53. The communication system as defined in claim 51 further including:

a first length of optical fiber positioned in one of said second and third arms of said first sensor whereby said one of said second and third arms of said first sensor is optically longer than the other.

54. The communication system as defined in claim 53 further including:

a second length of optical fiber positioned in one of said seventh and eighth arms of said second sensor whereby said one of said seventh and eighth arms of said second sensor is optically longer than the other.

55. The communication system as defined in claim 54 wherein said first and second lengths of optical fiber are essentially the same length.

56. The communication system as defined in claim 51 further including:

a first relatively low frequency phase shifter positioned in one of said second and third arms of said first sensor;

a second relatively low frequency phase shifter positioned in one of said seventh and eighth arms of said second sensor.

57. The communication system as defined in claim 56 further including:

a first oscillator producing a relatively low frequency output and driving said first relatively low frequency phase shifter therewith; and

a second oscillator producing a relatively low frequency output and driving said second relatively low frequency phase shifter therewith, wherein said signal processor includes;

a first synchronous demodulator connected to receive said relatively low frequency output from said first oscillator and connected to receive said first sensor output from said first detector to demodulate said first sensor output; and

a second synchronous demodulator connected to receive said relatively low frequency output from said second oscillator and connected to receive said second sensor output from said second detector to demodulate said second sensor output.

58. The communication system as defined in claim 1 wherein said first arm includes:

a first optical fiber having;

a first end adjacent said first light source having;

anti-reflection means to suppress reflections back toward said third and fourth arms, and wherein said second optical arm includes;

a second optical fiber having;

a second end adjacent said first detector having;

anti-reflection means to suppress reflections back toward said third and fourth arms.

59. The communication system as defined in claim 1 wherein said first arm includes:

a first optical fiber having;

a first end adjacent said first light source, and wherein said second arm includes;

a second optical fiber having;

a second end adjacent said first detector, said first and second fibers being similar in length and said first and second ends reflecting similar amounts of light energy back toward said third and fourth arms.

60. The communication system as defined in claim 1 wherein said input includes:

means to integrate a first information signal that is an analog signal, whereby said communication system differentiates the integrated analog first information signal to reconstruct the analog first information signal.

61. The communication system as defined in claim 1 wherein the first information signal is an analog signal, whereby said communication system differentiates the analog first information signal into the first output signal.

62. 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.

63. The secure communication system as defined in claim 62 wherein said first and second optical transceiver means include:

third and fourth Sagnac interferometers.

64. The secure communication system as defined in claim 63 wherein said third Sagnac interferometer has:

a first light source operating in a first spectral band, and said fourth Sagnac interferometer has;

a second light source operating in a second spectral band discrete from said first spectral band.

65. The secure communication system as defined in claim 64 wherein said third and fourth Sagnac interferometers have:

a first common leg;

a second common leg;

first light amplifier means in said first common leg; and

second light amplifier means in said second common leg.

66. The secure communication system as defined in claim 62 wherein said first and second optical transceiver means are included in said first and second Sagnac interferometers, said first and second optical transceiver means operating at higher frequencies than said first and second distributed fiber optic sensors.

67. The secure communication system as defined in claim 62 wherein said portions of the first and second optical fibers to be secured by said first intruder alarm subsystem are in a single fiber cable, said portion of said first optical fiber to be secured by said first intruder alarm subsystem being acoustically enhanced, and said portion of said second optical fiber to be secured by said first intruder alarm subsystem being acoustically shielded.

68. The secure communication system as defined in claim 62 wherein the portions of the first and second optical fibers to be secured by said first intruder alarm subsystem are physically separated so that a particular environmental effect indicative of an intruder attempting to tap there into can occur only on one of the optical fibers.

69. The secure communication system as defined in claim 62 wherein said first distributed fiber optic sensor includes:

a first sensor central beamsplitter at least having;

first, second, third, and fourth sensor arms;

a first sensor light source feeding a first sensor light beam into said first sensor arm, which first sensor light beam is split by said first sensor central beamsplitter into second and third sensor light beams traveling on said second and third sensor arms respectively;

first means coupling said second and third sensor light beams from said second and third sensor arms into and out of said first and second optical fibers at said first side thereof for traverse through at least a predetermined portion thereof to be secured by said first intruder alarm subsystem;

second means coupling said second and third sensor light beams out of and into said first and second optical fibers at said second side thereof, said second and third light beams recombining on said first sensor central beamsplitter to form a fourth sensor light beam on said fourth sensor arm;

a first detector positioned to receive said fourth light beam from said fourth sensor arm and produce therefrom a first output whose intensity is an indication of the position and amount of disturbance in said predetermined portion of said first and second optical fibers to be secured by said first intruder alarm subsystem, and wherein said second distributed fiber optic sensor includes;

a second sensor central beamsplitter at least having;

fifth, sixth, seventh, and eighth sensor arms;

a second sensor light source feeding a fifth sensor light beam into said fifth sensor arm, which fifth sensor light beam is split by said second sensor central beamsplitter into sixth and seventh sensor light beams traveling on said sixth and seventh sensor arms respectively;

third means coupling said sixth and seventh sensor light beams from said sixth and seventh sensor arms into and out of said first and second optical fibers at said second side thereof for traverse through at least a predetermined portion of said first and second optical fibers to be secured by said first intruder alarm subsystem;

fourth means coupling said sixth and seventh sensor light beams out of and into said first and second optical fibers at said first side thereof, said sixth and seventh light beams recombining on said second sensor central beamsplitter to form a eighth sensor light beam on said eighth sensor arm;

a second detector positioned to receive said eighth light beam from said eighth sensor arm and produce therefrom a second output whose intensity is an indication of the position and amount of disturbance in said predetermined portion of said first and second optical fibers to be secured by said first intruder alarm subsystem; and

a signal processor connected to said first and second sensor outputs to produce therefrom a position output and a amplitude output indicative of the position and amplitude of any disturbance in said first and second optical fibers secured by said first intruder alarm subsystem.

70. The secure communication system as defined in claim 69 wherein the portions of said first and second optical fibers to be secured by said first intruder alarm subsystem are in a single fiber cable, the portion of said first optical fiber to be secured by said first intruder alarm subsystem being covered with an acoustic enhancing coating, and portion of said second optical fiber to be secured by said first intruder alarm subsystem being covered with acoustic shielding.

71. The secure communication system as defined in claim 69 wherein the portion of said first and second optical fibers to be secured by said first intruder alarm subsystem are physically separated so that a particular environmental effect indicative of an intruder attempting to tap there into can occur only on one of the optical fibers.

72. The secure communication system as defined in claim 62 wherein said first and second optical fibers have:

first and second opposite sides, and wherein said first distributed fiber optic sensor includes;

a first sensor central beamsplitter at least having;

first, second, third, fourth, and fifth sensor arms;

a first sensor light source feeding a first sensor light beam into said first sensor arm, which first sensor light beam is split by said first sensor central beamsplitter into second and third sensor light beams traveling on said second and third sensor arms respectively;

first means coupling said second and third sensor light beams from said second and third sensor arms into and out of said first and second optical fibers at said first side thereof for traverse through at least a predetermined portion of said first and second optical fibers to be secured by said first intruder alarm subsystem;

second means coupling said second and third sensor light beams out of and into said first and second optical fibers at said second side thereof, said second and third light beams recombining on said first sensor central beamsplitter to form a fourth sensor light beam on said fourth sensor arm and a fifth sensor light beam on said fifth sensor arm;

a first detector positioned to receive said fourth light beam from said fourth sensor arm and produce therefrom a first output whose intensity is an indication of the position and amount of disturbance in said predetermined portion of said first and second optical fibers to be secured by said first intruder alarm subsystem;

a second detector positioned to receive said fifth light beam from said fifth sensor arm and produce therefrom a second output whose intensity is an indication of the position and amount of disturbance in said predetermined portion of said first and second optical fibers to be secured by said first intruder alarm subsystem, and wherein said second distributed fiber optic sensor includes;

a second sensor central beamsplitter at least having;

sixth, seventh, eighth, ninth, and tenth sensor arms;

a second sensor light source feeding a sixth sensor light beam into said sixth sensor arm, which sixth sensor light beam is split by said second sensor central beamsplitter into seventh and eighth sensor light beams traveling on said seventh and eighth sensor arms respectively;

third means coupling said seventh and eighth sensor light beams from said seventh and eighth sensor arms into and out of said first and second optical fibers at said second side thereof for traverse through at least a predetermined portion of said first and second optical fibers to be secured by said first intruder alarm subsystem;

fourth means coupling said seventh and eighth sensor light beams out of and into said first and second optical fibers at said first side thereof, said seventh and eighth light beams recombining on said second sensor central beamsplitter to form a ninth sensor light beam on said ninth sensor arm and a tenth sensor light beam on said tenth sensor arm;

a third detector positioned to receive said ninth light beam from said ninth sensor arm and produce therefrom a third output whose intensity is an indication of the position and amount of disturbance in said predetermined portion of said first and second optical fibers to be secured by said first intruder alarm subsystem;

a fourth detector positioned to receive said tenth light beam from said tenth sensor arm and produce therefrom a fourth output whose intensity is an indication of the position and amount of disturbance in said predetermined portion of said first and second optical fibers to be secured by said first intruder alarm subsystem; and

a signal processor connected to said first, second, third, and fourth sensor outputs to produce therefrom a position output and a amplitude output indicative of the position and amplitude of any disturbance in said first and second optical fibers secured by said first intruder alarm subsystem.

73. The secure communication system as defined in claim 62 wherein first and second optical transceiver means include:

third and fourth Sagnac interferometers each having;

Sagnac loops, each Sagnac loop of said third and fourth Sagnac interferometers having;

phase shifter means therein connected to impress data there into.

74. The secure communication system as defined in claim 73 wherein said Sagnac loop of at least said third Sagnac interferometer includes:

means to split a beam of light into at least two beams of light that counter propagate about said Sagnac loop of said third Sagnac interferometer; and

means to change the length of said Sagnac loop of at least said third Sagnac interferometer positioned generally opposite to said means to split a beam of light.

75. The secure communication system as defined in claim 74 wherein said means to change the length of said Sagnac loop of at least said third Sagnac interferometer include:

control means connected to said means to change the length of said Sagnac loop of at least said third Sagnac interferometer to coordinate pathlength changes with the transmission of the information over said system so that information is not lost during a pathlength change;

a piezoelectric cylinder;

means to provide different voltages to said piezoelectric cylinder connected to said control means; and

an optical fiber that is part of said Sagnac loop of said third Sagnac interferometer wrapped around said piezoelectric cylinder.

76. The secure communication system as defined in claim 74 wherein said means to change the length of said Sagnac loop of at least said third Sagnac interferometer further include:

control means connected to said means to change the length of said Sagnac loop of at least said third Sagnac interferometer to coordinate pathlength changes with transmission of the information thereover so that information is not lost during a pathlength change;

a variable pathlength changer;

means to control the amount of pathlength change said variable pathlength changer makes to said Sagnac loop of at least said third Sagnac interferometer;

at least one optical switch in said Sagnac loop of at least said third Sagnac interferometer adjacent said variable pathlength changer; and

at least one length of optical fiber connected to said optical switch so that said optical switch can add and remove said at least one length of optical fiber to said Sagnac loop of at least said third Sagnac interferometer.

77. The secure communication system as defined in claim 74 wherein said means to change the length of said Sagnac loop of at least said third Sagnac interferometer include:

control means connected to said means to change the length of said Sagnac loop of at least said third Sagnac interferometer to coordinate pathlength changes with transmission of the information thereover so that information is not lost during a pathlength change;

at least one optical switch in said Sagnac loop of at least said third Sagnac interferometer; and

at least one length of optical fiber connected to said optical switch so that said optical switch can add and remove said at least one length of optical fiber to said Sagnac loop of at least said third Sagnac interferometer.

78. The secure communication system as defined in claim 73 wherein at least said Sagnac loop of said third Sagnac interferometer includes:

means to split a beam of light into at least two beams of light that counter propagate about said Sagnac loop of said third Sagnac interferometer;

a first alarm tap connected thereto at a predetermined location from said means to split a beam of light;

first alarm sensor means to measure the intensity of any light tapped off said Sagnac loop of said third Sagnac interferometer by said first alarm tap and produce an alarm output whenever the tapped light intensity is out of a predetermined range;

a second alarm tap connected thereto at said predetermined location from said means to split a beam of light on the opposite side of said Sagnac loop of said third Sagnac interferometer; and

second alarm sensor means to measure the intensity of any light tapped off said Sagnac loop of said third Sagnac interferometer by said second alarm tap and produce an alarm output whenever the tapped light intensity is out of a predetermined range.

79. The secure communication system as defined in claim 73 wherein at least said Sagnac loop of said third Sagnac interferometer includes:

means to split a beam of light into at least two beams of light that counter propagate about said Sagnac loop of said third Sagnac interferometer;

a first alarm tap connected thereto at a predetermined location from said means to split a beam of light;

first alarm sensor means to measure the intensity of any light tapped off said Sagnac loop of said third Sagnac interferometer by said first alarm tap and produce output therefrom;

a second alarm tap connected thereto at said predetermined location from said means to split a beam of light on the opposite side of said Sagnac loop of said third Sagnac interferometer; and

second alarm sensor means to measure the intensity of any light tapped off said Sagnac loop of said third Sagnac interferometer by said first alarm tap and produce output therefrom; and

comparison means connected to receive said outputs from said first and second alarm sensor means to produce therefrom an alarm output whenever said outputs of said first and second alarm sensor means differ by more than a predetermined amount.

80. The secure communication system as defined in claim 73 wherein at least said Sagnac loop of said third Sagnac interferometer includes:

means to split a beam of light into at least two beams of light that counter propagate about said Sagnac loop of said third Sagnac interferometer;

an alarm beamsplitter connected thereto at the opposite side of the Sagnac loop of said third Sagnac interferometer from said means to split a beam of light, said alarm beamsplitter having;

first and second arms in said Sagnac loop of said third Sagnac interferometer; and

third and fourth arms;

first alarm sensor means to measure the intensity of light on said third arm and producing an alarm output therefrom; and

second alarm sensor means to measure the intensity of light on said third arm and producing an alarm output therefrom.

81. The secure communication system as defined in claim 73 wherein at least said Sagnac loop of said third Sagnac interferometer includes:

means to split a beam of light into at least two beams of light that counter propagate about said Sagnac loop of said third Sagnac interferometer;

at least one first alarm tap connected thereto at a predetermined location from said means to split a beam of light to tap off light in a narrow spectrum;

first alarm sensor means to measure the intensity of any light tapped off said Sagnac loop of said third Sagnac interferometer by said first alarm tap and produce an alarm output therefrom;

at least one second alarm tap connected thereto at a predetermined location from said means to split a beam of light to tap off light in a narrow spectrum; and

second alarm sensor means to measure the intensity of any light tapped off said Sagnac loop of said third Sagnac interferometer by said first alarm tap and produce an alarm output therefrom.

82. The secure communication system as defined in claim 73 wherein at least said Sagnac loop of said third Sagnac interferometer includes:

means to split a beam of light into at least two beams of light that counter propagate about said Sagnac loop of said third Sagnac interferometer;

at least one first dispersive alarm tap connected thereto at a predetermined location from said means to split a beam of light to tap off light in separate narrow spectrums;

first alarm sensor means to measure the intensity of at least one spectrum of any light tapped off said Sagnac loop of said third Sagnac interferometer by said first dispersive alarm tap and produce a first alarm output therefrom;

at least one second dispersive alarm tap connected thereto at a predetermined location from said means to split a beam of light to tap off light in separate narrow spectrums; and

second alarm sensor means to measure the intensity of at least one spectrum of any light tapped off said Sagnac loop of said third Sagnac interferometer by said second dispersive alarm tap and produce a second alarm output therefrom.

83. The secure communication system as defined in claim 73 wherein at least said third Sagnac interferometer includes:

alarm sensor means to measure the average intensity of at least one spectrum of any light output of said third Sagnac interferometer and to produce a alarm output therefrom whenever said average intensity is out of a predetermined range.

84. The secure communication system as defined in claim 83 wherein at least said third Sagnac interferometer includes:

a source of a first light beam;

beamsplitter means to split said first beam of light into at least second and third beams of light that counter propagate about said Sagnac loop of said third Sagnac interferometer for phase shifting by said phase shifter means before return to said beamsplitter means for combining into a fourth beam of light;

means in said Sagnac loop of said third Sagnac interferometer for impressing a relatively low frequency signal on said second and third light beams; and

means for determining the average intensity of said relatively low frequency signal and to produce a alarm output therefrom whenever said average intensity is out of a predetermined range.

85. The secure communication system as defined in claim 62 wherein said first and second Sagnac interferometers each have:

a light source;

a 3 by 3 coupler connected to receive light from said light source and provide the light to said first and second optical fibers;

bypass means to transmit light around said 3 by 3 coupler of said other of said first and second Sagnac interferometers so that the light returns to said 3 by 3 coupler; and

a pair of detectors positioned to receive the returning light and to produce first and second intruder signals therefrom, said secure communication system including;

computational means connected to receive said first and second intruder signals from said first and second intruder signals to produce therefrom the location of an intruder.

86. The secure communication system as defined in claim 85 wherein said first and second optical transceiver means include:

third and fourth Sagnac interferometers each having;

a communication light source producing a first communication light beam;

means to split said first communication light beam into second and third communication light beams;

means to couple said second and third communication light beams onto said first and second optical fibers;

bypass means to transmit second and third communication light beams around said means to split of said other of said third and fourth Sagnac interferometers so that said second and third communication light beams return to said means to split;

phase modulator means to impress information on said second and third communication light beams; and

detector means positioned to receive said second and third communication light beams after their return to said means to split to extract the information therefrom.

87. The secure communication system as defined in claim 85 wherein said first optical fiber is acoustically enhanced and said second optical fiber is acoustically shielded.

88. The secure communication system as defined in claim 85 wherein said first optical fiber is physically spaced from said second optical fiber.

89. The secure communication system as defined in claim 85 wherein said first and second optical fibers run adjacent two each other, said first and second distributed fiber optic sensors each including:

means to shift the length of one of said first and second optical fibers with respect to the other positioned adjacent said 3 by 3 coupler.

90. 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.

91. The communication system of claim 90 wherein said optical loop has:

first and second portions on opposite sides of said optical phase modulator, said communication system further including;

a first Sagnac interferometer distributed sensor having;

a second light source positioned generally adjacent said optical phase modulator and connected to transmit light over said first and second portions of said optical loop;

a second Sagnac interferometer distributed sensor having;

a third light source positioned generally adjacent said optical phase modulator and connected to transmit light over said first and second portions of said optical loop; and

a signal processor connected to said first and second Sagnac interferometer distributed sensors for calculating the amplitude and position of effects that occur to said first portion of said optical loop.

92. The communication system of claim 90 further including:

an intruder alarm subsystem including;

first and second Sagnac interferometer distributed fiber optic sensors positioned to sense effects indicative of an intruder from different locations about said optical loop.

93. 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.