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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
First Claim
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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.

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