Secure two-way submarine communication system

• US 5,038,406 A
• Filed: 09/19/1989
• Issued: 08/06/1991
• Est. Priority Date: 09/19/1989
• Status: Expired due to Term

• Current Assignee: General Dynamics Government Systems Corporation (General Dynamics Corporation)
• Original Assignee: GTE Government Systems Corporation (General Dynamics Corporation)
• Inventors: Martin, Frederick, Cotterman, Robert W., Titterton, Paul J., Radecki, Dan J.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/409,174
• Time in Patent Office: 686 Days
• Field of Search: 455/604, 455/605, 455/606, 455/607, 455/617, 342/45
• US Class Current: 398/125
• CPC Class Codes: H04B 10/11 Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
• CPC Class Codes: H04B 13/02 Transmission systems in which the medium consists of the earth or a large mass of water thereon, e.g. earth telegraphy

Abstract

An arrangement for secure two-way tactical laser communications between a submarine submerged in an ocean and an airborne platform. During an initital acquisition mode, the airborne transceiver sends a downlink pulse-modulated blue-green laser beam to the ocean surface and below using a predetermined IFF code to identify the transceiver to the submarine. In the preferred embodiment the transmit optics spread the beam out into an elongated elliptically-shaped pattern to maximize coverage of the search area. When the downlink beam energy is within range of the submarine, an optical receiver on the submarine detects the beam, filters out the background light with a very narrow-band filter, and converts the light pulses to equivalent electrical pulse. A signal processor in the submarine receiver decodes the electrical pulses and verifies the IFF code to prevent the submarine from responding to a laser beam from an unfriendly source. If the IFF is verified, the submarine laser transceiver transmits a pulse-modulated uplink beam response at the same wavelength, but timed so that the light pulses are time interleaved with the downlink pulses. The uplink beam power is carefully controlled to the minimum power level required by the airborne receiver to recover the uplink beam. As soon as the airborne receiver verifies the uplink IFF code, communications being over the laser link for the duration of time that the airborne platform receiver is within range of the uplink beam. In one embodiment of this invention, both receivers employ a Cesium filled atomic resonance filter (ARF) to separate the blue-green beam from any background light.

Claims

1. A secure laser communication system providing two-way communications between a submerged platform in an ocean and an airborne platform travelling above the ocean, said communications system comprising:

submerged transceiver means for transmitting an uplink beam comprising an uplink pulse-modulated laser beam and for receiving a downlink beam;

airborne transceiver means for transmitting a downlink beam comprising a downlink pulse-modulated laser beam and for receiving said uplink beam, said airborne transceiver means having two operating modes;

an acquisition mode during which the airborne platform searches for the location of the submerged platform, and a communicating mode during which communications occur between said airborne transceiver means and said submerged transceiver means, said airborne transceiver means comprising;

first laser means for generating a first laser beam having a blue-green wavelength λ

₁ ;

first modulating means for pulse-modulating said first laser beam with encoded downlink information whereby to produce said downlink pulse-modulated laser beam, said downlink information comprising;

(i) a predetermined downlink IFF code for use at least during said acquisition mode, and (ii) supervisory data;

first optical transmitting means for transmitting said downlink pulse-modulated laser beam to said submerged transceiver means, said first optical transmitting means including means for controlling the divergence and pointing angle of said downlink beam, such that at least during said acquisition mode said downlink beam has an elongated elliptically-shaped cross-sectional pattern with a wide dimension transverse to the direction of travel of said platform and a narrow dimension parallel to the direction of travel of said platform,

said submerged transceiver means having standby and communicating modes of operation corresponding to said acquisition and communicating modes of operation of said airborne transceiver means, respectively, said submerged transceiver means further comprising;

first optical receiver means for receiving said downlink beam from said airborne transceiver means;

first optical filter means for converting said downlink beam from said first optical receiver means into electrical pulses, said first optical filter means having a very narrow passband centered at the wavelength λ

₁ and providing high attenuation to background radiation;

first signal processing means for receiving and decoding said electrical pulses from said first optical filter means and for outputting said downlink information, said first signal processing means including means for verifying said predetermined downlink IFF code in said downlink information;

second laser means for generating a second laser beam of wavelength λ

₁ only in response to said verified downlink IFF code;

second modulating means for pulse-modulating said second laser beam with encoded uplink information whereby to produce said uplink pulse-modulated laser beam, said uplink information including a predetermined uplink IFF code for use in responding to said encoded predetermined downlink IFF code;

second optical transmitting means for transmitting said uplink pulse-modulated laser beam to said airborne transceiver means, said second optical transmitting means including means for varying the output energy in said uplink beam in response to said decoded supervisory data;

said airborne transceiver means further comprising;

second optical receiver means having a variable field of view for scanning a spatial area for detecting said uplink laser beam during said acquisition mode, and for receiving said uplink beam from a substantially stationary terrestial location during said communicating mode;

second optical filter means for converting said received uplink beam from said second optical receiver means into electrical pulses, said second optical filter means including a first atomic resonant filter having a very narrow passband centered at the wavelength λ

₁ and providing high attenuation to background radiation; and

second signal processing means for receiving and decoding said electrical pulses from said second optical filter means, said second signal processing means including means for generating a correction signal related to the S/N of said received uplink beam, said correction signal being coupled to said second modulating means for encoding as part of said supervisory data.

2. A secure laser communication system as defined in claim 1 wherein said second laser means generates said second laser beam only so long as said first optical receiver means receives said downlink beam.

3. A secure laser communication system as defined in claim 2 wherein said field of view of said second optical receiver means is varied to optimize said S/N during said communicating mode.

4. A secure laser communication system as defined in claim 3 wherein said second optical filter means further comprises a second atomic resonant filter tuned to the wavelength λ

₁.

5. A secure laser communication system as defined in claim 4 wherein said first optical transmitting means is optically coupled to said first laser means and said second optical transmitting means is optically coupled to said second laser means.

6. A secure laser communication system as defined in claim 5 wherein said first and second modulating means pulse-position modulate said downlink and uplink laser beams, respectively.

7. A secure laser communication system as defined in claim 6 wherein said predetermined uplink IFF code and said predetermined downlink IFF code are different codes.

8. A secure laser communication system as defined in claim 7 wherein said first optical transmitter means broadens said downlink beam to have an elongated elliptically-shaped cross-sectional pattern during both of said operating modes.

9. A secure laser communication system as defined in claim 6 wherein said first and second modulating means further comprises:

first and second timing means respectively, for time-division interleaving light pulses in said downlink laser beam with light pulses in said uplink laser beam.

10. A secure laser communication system providing two-way communications between a submarine submerged in an ocean and an airborne platform travelling above the ocean, said communications system comprising:

submarine transceiver means for transmitting an uplink beam comprising an uplink pulse-modulated laser beam and for receiving a downlink beam;

airborne transceiver means for transmitting a downlink beam comprising a downlink pulse-modulated laser beam and for receiving said uplink beam, said airborne transceiver means having two operating modes;

an acquisition mode during which the airborne platform searches for the location of the submerged submarine, and a communicating mode during which duplex communications occur between said airborne transceiver means and said submarine transceiver means, said airborne transceiver means comprising;

first laser means for generating a first laser beam having a blue-green wavelength λ

₁ ;

first modulating means for pulse-modulating said first laser beam with encoded downlink information whereby to produce said

downlink pulse-modulated laser beam, said downlink information comprising;

(i) a predetermined downlink IFF code for use during at least said acquisition mode, (ii) message data for use during said communicating mode, and (iii) supervisory data;

first optical transmitting means for transmitting said down link pulse-modulated laser beam with a beam axis pointing toward said ocean, said transmitting means including means for controlling the divergence and pointing angle of said downlink beam, such that, during said acquisition mode said downlink beam has an elongated generally elliptically-shaped cross-sectional pattern with a wide dimension transverse to the direction of travel of said platform and a narrow dimension parallel to the direction of travel of said platform, and during said communicating mode said downlink beam has a substantially circular cross-sectional spot pattern with said beam axis pointing at a substantially fixed terrestial location;

first optical receiver means for scanning a spatial area to detect said uplink beam during said acquisition mode and for receiving said uplink beam from said substantially fixed terrestial location during said communicating mode, said first optical receiver means having a variable field of view;

first optical filter means for converting said uplink beam from said first optical receiver means into electrical pulses, said first optical filter means including a first atomic resonant filter having a very narrow passband centered at the wavelength λ

₁ and providing high attenuation to background radiation;

first signal processing means for receiving and decoding said electrical pulses from said first optical filter, said first signal processing means including means for generating a correction signal related to the S/N of said received uplink beam, said correction signal being coupled to said first modulating means for being encoded as part of said supervisory data;

said submarine transceiver means having standby and communicating modes of operation corresponding to said acquisition and communicating modes of operation of said airborne transceiver means, respectively, said submarine transceiver means further comprising;

second optical receiver means for receiving said downlink beam from said airborne transceiver means;

second optical filter means for converting said downlink beam from said second optical receiver means into electrical pulses, said second optical filter means including a second atomic resonant filter means having a very narrow passband centered at the wavelength λ

₁ and providing high attenuation to background radiation;

second signal processing means for receiving and decoding said electrical pulses from said second optical filter means and for outputting said downlink information, said second signal processing means including means for verifying said predetermined downlink IFF code in said downlink information;

second laser means for generating a second laser beam of wavelength λ

₁ only in response to said verified downlink IFF code;

second modulating means for pulse-modulating said second laser beam with encoded uplink information whereby to produce said uplink pulse-modulated laser beam, said uplink information including;

(i) a predetermined uplink IFF code for use in responding to said encoded predetermined downlink IFF code, and (ii) message data for use during said communicating mode; and

second optical transmitting means for directing said uplink beam from said submarine transceiver means, said second optical transmitting means including means for varying the output energy in said uplink beam in response to said decoded supervisory data.

11. A secure laser communication system as defined in claim 10 wherein said first and second modulating means pulse-position modulate said downlink and uplink laser beams, respectively.

12. A secure laser communication system as defined in claim 11 wherein said first and second modulating means further comprises:

first and second timing means respectively, for time-division interleaving light pulses in said downlink laser beam with light pulses in said uplink laser beam.

13. A secure laser communication system as defined in claim 12 wherein said field of view of said first optical receiver means is varied to optimize said S/N during said communicating mode and is varied to maximize the likelihood of detecting said uplink laser beam during said acquisition mode.

14. A secure laser communication system as defined in claim 13 wherein said substantially fixed terrestial location is defined by the surface area on the ocean from which said uplink beam emerges.

15. A secure laser communication system as defined in claim 14 wherein said second laser means generates a second laser beam only so long as said second optical receiver means receives said downlink beam.

16. A secure laser communication system as defined in claim 15 wherein the spatial area scanned by said first optical receiver means is offset from said downlink beam pattern during said acquisition mode and is substantially coincident therewith during said communicating mode.

17. A secure laser communication system as defined in claim 14 wherein said means for varying the output energy in said uplink beam adjusts the energy such that said S/N is at least 19 dB for a substantial portion of said communicating mode.

18. A secure laser communication system as defined in claim 17 wherein said λ

₁ wavelength is matched to the filter absorption line of said first atomic resonant filter.

19. A secure laser communication system providing two-way communications between a submarine submerged in an ocean and an airborne platform travelling above the ocean, said communications system comprising:

submarine transceiver means for transmitting an uplink beam comprising an uplink pulse-modulated laser beam and for receiving a downlink beam;

airborne transceiver mean$ for transmitting a downlink beam comprising a downlink pulse-modulated laser beam and for receiving said uplink beam, said airborne transceiver means having two operating modes;

an acquisition mode during which the airborne platform searches for the location of the submerged submarine, and a communicating mode during which communications occur between said airborne transceiver means and said submarine transceiver means, said airborne transceiver means comprising;

first laser means for generating a first laser beam having a blue-green wavelength λ

₁ ;

first modulating means for pulse-modulating said first laser beam with encoded downlink information thereby producing said downlink pulse-modulated laser beam, said downlink information including;

(i) a predetermined downlink IFF code for use during said acquisition mode, (ii) message data for use during said communicating mode, and (iii) supervisory data for use during both of said operating modes;

first optical transmitting means for transmitting said downlink pulse-modulated laser beam to said submarine transceiver means, said first optical transmitting means including means for controlling the divergence and pointing angle of said downlink beam from said airborne transceiver means, such that said downlink beam has a generally elliptically-shaped cross-sectional pattern with a wide dimension transverse to the direction of travel of said platform and a narrow dimension parallel to the direction of travel of said platform and with a central beam axis intersecting the center of said beam pattern, said central beam axis pointing at a relatively fixed terrestial location during said communicating mode;

said submarine transceiver means having standby and communicating modes of operation corresponding to said acquisition and communicating modes of operation of said airborne transceiver means, said submarine transceiver means further comprising;

first optical receiver means for receiving said downlink beam from said airborne transceiver means;

first optical filter means for converting said downlink beam from said first optical receiver means into corresponding electrical pulses, said first optical filter means including a first atomic resonant filter means having a very narrow passband centered at the wavelength λ

₁ and providing high attenuation to background radiation;

first signal processing means for receiving and decoding said electrical pulses from said first optical filter means and for outputting said downlink information, said first signal processing means including means for verifying said predetermined downlink IFF code in said downlink information;

second laser means for generating a second laser beam of wavelength λ

₁ only in response to said verified downlink IFF code;

second modulating means for pulse-modulating said second laser beam with encoded uplink information and thereby producing said uplink pulse-modulated laser beam, said uplink information including;

(i) a predetermined uplink IFF code for use in responding to said encoded predetermined downlink IFF code, and (ii) message data for use during said communicating mode; and

second optical transmitting means for directing said uplink beam from said submarine transceiver means, said second optical transmitting means including means for varying the output energy in said uplink beam in response to said decoded supervisory data;

said airborne transceiver means further comprising;

second optical receiver means having a variable field of view, said second optical receiver means having means for scanning a spatial area to receive said uplink laser beam during said acquisition mode and for receiving said uplink beam from said relatively fixed terrestial location during said communicating mode;

second optical filter means for converting said received uplink beam from said second optical receiver means into electrical pulses, said second optical filter means including an atomic resonant filter having a very narrow passband centered at the wavelength λ

₁ and providing high attenuation to background radiation;

second signal processing means for receiving and decoding said electrical pulses from said second optical filter means, said first processing means including means for generating a correction signal related to the S/N of said received uplink beam, said correction signal being coupled to said second modulating means for encoding as part of said supervisory data.

20. A secure laser communication system as defined in claim 19 wherein said first and second modulating means pulse-position modulate said downlink and uplink laser beams, respectively.

21. A secure laser communication system as defined in claim 20 wherein said first and second modulating means further comprises:

first and second timing means respectively, for time-division interleaving light pulses in said downlink laser beam with light pulses in said uplink laser beam.

22. A secure laser communication system as defined in claim 21 wherein said relatively fixed terrestial location is defined by the area on the ocean surface from which said uplink beam emerges.

23. A secure laser communication system as defined in claim 22 wherein said second laser means generates a second laser beam for only so long as said first optical receiver means receives said downlink beam;

24. A secure laser communication system as defined in claim 23 wherein said means for varying the output energy in said uplink beam adjusts the energy such that said S/N is at least 19 dB for a substantial portion of said communicating mode.

25. A secure laser communication system as defined in claim 24 wherein said first optical transmitting means is optically coupled to said first laser means and said second optical transmitting means is optically coupled to said second laser means.

26. A secure laser communication system as defined in claim 25 wherein said field of view of said second optical receiver means is varied to optimize said S/N during said communicating mode.

27. A secure laser communication system as defined in claim 26 wherein said λ

₁ wavelength is matched to the filter absorption line of said first atomic resonant filter.

28. A secure laser communication system providing two-way communications between a submarine submerged in an ocean and an airborne platform travelling above the ocean, said communications system comprising:

submarine transceiver means for transmitting an uplink beam comprising an uplink pulse-modulated laser beam and for receiving a downlink beam;

airborne transceiver means for transmitting a downlink beam comprising a downlink pulse-modulated laser beam and for receiving said uplink beam, said airborne transceiver means having two operating modes;

a acquisition mode during which the airborne platform searches for the location of the submerged submarine, and a communicating mode during which duplex communications occur between said airborne transceiver means and said submarine transceiver means, said airborne transceiver means comprising;

first laser means for generating a first laser beam having a blue-green wavelength λ

₁ ;

first modulating means for pulse-modulating said first laser beam with encoded downlink information thereby producing said downlink beam, said downlink information including;

(i) a predetermined downlink IFF code for use during said acquisition mode, (ii) message data for use during said communicating mode, and (iii) supervisory data for use during both of said operating modes;

first optical transmitting means for controlling the pointing angle of said downlink beam from said airborne transceiver means, such that, during said acquisition mode said downlink beam scans from side-to-side transverse to the direction of travel of said platform, and during said communicating mode said downlink beam points at a relatively fixed terrestial location on said ocean;

first optical receiver means having a variable field of view, said first optical receiver means for scanning a spatial area to receive said uplink laser beam during said acquisition mode, and for tracking and receiving said uplink beam from said fixed terrestial location during said communicating mode;

first optical filter means for converting said received uplink beam from said first optical receiver means into electrical pulses, said first optical filter means including a first atomic resonant filter having a very narrow passband centered at the wavelength λ

₁ and providing high attenuation to background radiation;

first signal processing means for receiving and decoding said electrical pulses from said first optical filter means, said first processing means including means for generating a correction signal related to the S/N of said received uplink beam, said correction signal being coupled to said first modulating means for encoding as part of said supervisory data;

said submarine transceiver means having standby and communicating modes of operation corresponding, respectively, to said acquisition and communicating modes of operation of said airborne transceiver means, said submarine transceiver means further comprising;

second optical receiver means for receiving said downlink beam from said airborne transceiver means;

second optical filter means for converting said downlink beam from said second optical receiver means into corresponding electrical pulses, said second optical filter means including a second atomic resonant filter having a very narrow passband centered at the wavelength λ

₁ and providing high attenuation to background radiation;

second signal processing means for receiving and decoding said electrical pulses from said second optical filter means and for outputting said downlink information, said second signal processing means including means for verifying said predetermined downlink IFF code in said downlink information;

second laser means for generating a second laser beam of wavelength λ

₁ only in response to said verified downlink IFF code and continuing only so long as said second optical receiver means receives said downlink beam;

second modulating means for pulse-modulating said uplink beam with encoded uplink information and thereby producing said uplink beam, said uplink information including;

(i) a predetermined uplink IFF code for use in responding to said encoded predetermined downlink IFF code, and (ii) message data for use during said communicating mode; and

second optical transmitting means for directing said uplink beam from said submarine transceiver means, said second optical transmitting means including means for varying the output energy in said uplink beam in response to said decoded supervisory data.

29. A secure laser communication system as defined in claim 28 wherein said first and second modulating means pulse-position modulate said downlink and uplink laser beams, respectively.

30. A secure laser communication system as defined in claim 29 wherein said first and second modulating means further comprises:

first and second timing means respectively, for time-division interleaving light pulses in said downlink laser beam with light pulses in said uplink laser beam.

31. A secure laser communication system as defined in claim 30 wherein said relatively fixed terrestial location is defined by the area on the ocean surface from which said uplink beam emerges.

32. A secure laser communication system as defined in claim 31 wherein said second laser means generates a second laser beam only so long as said second optical receiver means receives said downlink beam;

33. A secure laser communication system as defined in claim 32 wherein said means for varying the output energy in said uplink beam adjusts the energy such that said S/N is at least 19 dB for a substantial portion of said communicating mode.

34. A secure laser communication system as defined in claim 33 wherein said first optical transmitting means is optically coupled to said first laser means and said second optical transmitting means is optically coupled to said second laser means.

35. A secure laser communication system as defined in claim 34 wherein said field of view of said first optical receiver means within said airborne transceiver means is varied to optimize said S/N of said received uplink beam, during said communicating mode.

36. A secure laser communication system as defined in claim 35 wherein said λ

₁ wavelength is matched to the filter absorption line of said first atomic resonant filter.

37. A secure laser communication system as defined in claim 35 wherein said λ

₁ wavelength is approximately 455 nm.

38. A secure laser communication system as defined in claim 35 wherein said λ

₁ wavelength is approximately 459 nm.