Optical non-line-of-sight covert, secure high data communication system

• US 4,493,114 A
• Filed: 05/02/1983
• Issued: 01/08/1985
• Est. Priority Date: 05/02/1983
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Geller, Myer, Patterson, Richard H., Altman, Daniel E., Keenan, Thomas E.
• Primary Examiner(s): Orsino, Jr., Joseph A.
• Assistant Examiner(s): Greer, Timothy K.
• Application Number:
  US06/490,695
• Time in Patent Office: 617 Days
• Field of Search: 455/606, 455/607, 455/608, 455/617, 455/618, 455/619, 250/372
• US Class Current: 398/119
• CPC Class Codes: H04B 10/1121 One-way transmission
• CPC Class Codes: H04L 25/4902 Pulse width modulation; Pulse position modulation

Abstract

An omnidirectional non-line-of-sight communication capability is assured byransmission and reception in the "solar blind" ultraviolet spectrum. An omnidirectional ultraviolet source generates a UV carrier in the tens of watts power range. This is modulated and received by having a sensitivity to respond to scattered UV modulated energy. Pulse modulating the ultraviolet spectrum signal and providing appropriate logic circuitry associated with the wide field-of-view receiver reduces the values of bit error rate.

Claims

1. An apparatus for omnidirectionally communicating non-line-of-sight in the ultraviolet spectrum comprising:

at least one Hg-Ar discharge lamp for generating and omnidirectionally radiating an ultraviolet carrier signal in the two-hundred-thirty to two-hundred-eighty nm spectral range in the tens of watts power range;

an on/off keying device coupled to the at least one Hg-Ar discharge lamp for modulating the ultraviolet carrier signal in a series of pulses; and

means remotely disposed from and in a non-line-of-sight relationship to the at least one Hg-Ar discharge lamp for receiving and demodulating scattered parts of the pulse modulated ultraviolet signal, the receiving and demodulating means having a wide field of view to increase the received signal strength.

2. An apparatus according to claim 1 in which the demodulating means includes a "solar blind" filter on a photomultiplier tube and logic circuitry to define a time bin to enable validation from background ultraviolet radiation.

3. An apparatus according to claim 2 in which the logic circuitry is fabricated to provide a valid signal indication whenever at least two pulses of the pulse modulated ultraviolet carrier signal are received with a preset time period defining the duration of a time bin.

4. An apparatus according to claim 3 in which the Hg-Ar discharge lamp has a radiated power of watts to provide an effective omnidirectional transmission range of about one half kilometer at a 10⁴ pulse/sec rate.

5. An apparatus according to claim 3 in which the Hg-Ar discharge lamp has a radiated power of watts to provide an effective omnidirectional transmission of about one kilometer at a 10³ pulse/sec rate.

6. An apparatus according to claim 3 in which the logic circuitry includes a first one shot multivibrator that feeds shaped signals representative of pulses of pulse modulated ultraviolet carrier signals to one triggerable one shot responsive to shaped pulses to provide output pulses of selectively variable length to define a time bin, an AND gate coupled to receive the shaped pulses and output pulses and a flip/flop coupled to receive the output pulse along with output signals from the AND gate to provide for the valid signal indication.

7. An apparatus according to claim 6 in which the demodulation means is responsive to two photons per unit area for indicating a data bit to make it responsive to data bits in background noise of about 30 photons per second per unit area.

8. A method of communicating in the ultraviolet spectrum comprising:

generating an ultraviolet signal in the "solar blind" region in the tens of watts power range;

modulating the ultraviolet signal;

radiating the modulated ultraviolet signal omnidirectionally;

receiving the radiated modulated ultraviolet signal at a non-line-of-sight location anywhere within the range of the omnidirectionally radiated modulated ultraviolet signal; and

demodulating the received ultraviolet signal.

9. A method according to claim 8 in which the modulating is the pulse modulating and the receiving is the receiving of scattered parts of the ultraviolet signal.

10. A method according to claim 9 in which the generating is the operation of at least one Hg-Ar discharge lamp.

11. A method according to claim 10 in which the receiving includes the providing of a wide angle filter responsive to pass modulated ultraviolet signals in the "solar blind" region to increase the received signal strength and the further providing of a photomultiplier tube responsive to the "solar blind" region.

12. A method according to claim 11 in which the demodulating includes the validating of a pulse modulated signal from background radiation in the "solar blind" region by determining the receipt of two pulses within a preset reoccurring time period at the receiver.

13. A method according to claim 12 in which the demodulating includes being responsive to pulse modulated signals having a signal strength of about two photons per pulse in the "solar blind" region.