System and method for free space optical communications using time division multiplexing of digital communication signals

• US 6,246,498 B1
• Filed: 10/19/2000
• Issued: 06/12/2001
• Est. Priority Date: 05/12/1998
• Status: Expired due to Term

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Dishman, John F., Beadle, Edward R.
• Primary Examiner(s): NEGASH, KINFE MICHAEL
• Application Number:
  US09/692,066
• Time in Patent Office: 236 Days
• Field of Search: 359/123, 359/124, 359/135, 359/172, 370/310, 370/478
• US Class Current: 398/96
• CPC Class Codes: G02F 1/291 Two-dimensional analogue deflection
• CPC Class Codes: G02F 1/292 by controlled diffraction or phased-array beam steering controlled diffraction for optical switching G02F1/31
• CPC Class Codes: H04B 10/118 specially adapted for satellite communication
• CPC Class Codes: H04B 7/18513 Transmission in a satellite or space-based system
• CPC Class Codes: H04B 7/18521 Systems of inter linked satellites, i.e. inter satellite service for optical links between satellites H04B10/118

Abstract

A method and system of communicating in free space using an optical communication system, such as for intersatellite and satellite-to-ground communications, is disclosed. Digital communication signals are multiplexed with a plurality of other analog communication signals into a single broad band frequency division multiplexed signal. A laser generates an optical carrier and an electro-optic modulator modulates the optical carrier signal with the frequency division multiplexed signal to produce a phase modulated optical communications signal. A receiver is positioned, such as in a satellite, to receive the phase modulated optical communications signal. The receiver includes a demodulator for demodulating the phase modulated optical communication system back into the broad band frequency division multiplexed signal and a demultiplexer for demultiplexing the broad band frequency division multiplexed signal into the plurality of communication signals. The portion of those signals that were previously digital data can be demodulated back into the digital communication signals.

Claims

1. A method of communicating in free space comprising the steps of:

generating a plurality of digital communication signals;

time division multiplexing the digital communication signals into a plurality of time division multiplexed data streams;

modulating the multiplexed data streams to produce a plurality of analog communication signals;

frequency division multiplexing the plurality of communication signals into a single broad band frequency division multiplexed signal;

generating with a laser an optical carrier signal;

phase modulating the optical carrier signal with the broad band frequency division multiplexed signal by mixing the multiplexed signal with the optical carrier signal in an electro-optic modulator;

transmitting the phase modulated optical communications signal to a receiver;

demodulating the phase modulated optical communications signal back into the frequency division multiplexed signal;

demultiplexing the frequency division multiplexed signal into the plurality of analog communication signals;

demodulating the analog communication signals into the time division multiplexed data streams; and

demultiplexing the data streams into the plurality of digital data streams.

2. A method according to claim 1, and further comprising the step of phase modulating the optical carrier signal by mixing the optical carrier signal and the broad band frequency division multiplexed signal within a Mach-Zender electro-optic modulator.

3. A method according to claim 1, and further comprising the steps of up converting each of the plurality of analog communication signals into a defined frequency slot, and combining the frequencies to create the frequency division multiplexed signal.

4. A method according to claim 1, and further comprising the step of non-mechanically steering the phase modulated optical communications signal by passing the communications signal through a Bragg cell and liquid crystal display.

5. A method according to claim 1, and further comprising the step of beam spoiling the phase modulated optical communications signal by increasing the beam convergence of the communications signal during transmission.

6. A method according to claim 1, and further comprising the step of demodulating the phase modulated optical communications signal by phase locked loop detection.

7. A system for communicating in free space comprising:

means for generating a plurality of digital communications signals;

a time division multiplexer that receives the plurality of digital communication signals and multiplexes the digital communications signals into a plurality of time division multiplexed data streams;

a modulator for receiving and modulating the time division multiplexed data streams into a plurality of communication signals;

means for multiplexing the plurality of broad band analog communication signals into a single broad band frequency division multiplexed signal;

a laser for generating an optical carrier signal;

an electro-optic modulator that receives said broad band frequency division multiplexed signal and said laser generated optical carrier and phase modulates the optical carrier signal with the multiplexed signal to produce a phase modulated optical communications signal;

a receiver that receives the phase modulated optical communications signal, said receiver further comprising;

a demodulator for demodulating the phase modulated optical communications signal back into the broad band frequency division multiplexed signal,

a demultiplexer for demultiplexing the broad band frequency division multiplexed signal into the plurality of analog communication signals,

means for demodulating the analog communications signals into the time division multiplexed data streams, and

means for demultiplexing the data streams into the plurality of digital data streams.

8. A system according to claim 7, and wherein said electro-optic modulator further comprises a Mach-Zender electro-optic modulator.

9. A system according to claim 7, wherein said means for multiplexing further comprises a respective mixer for up converting respective analog signals into a defined frequency channel, and a combiner for combining the up converted frequencies into the frequency division multiplexed signal.

10. A system according to claim 7, and further comprising a Bragg cell and liquid crystal display that receive the phase modulated optical communications signal for non-mechanically steering the phase modulated optical communications signal.

11. A system according to claim 7, and further comprising a beam spoiler that receives the phase modulated optical communications signal for increasing the beam divergence of the phase modulated optical communications signal during transmission.

12. A system according to claim 7, and further comprising a heterodyne detector for demodulating the phase modulated optical communications signal.

13. A method of communicating in free space comprising the steps of:

time division multiplexing a plurality of digital communication signals into a plurality of time division multiplexed data streams;

modulating the multiplexed data streams to produce a plurality of analog communication signals;

frequency division multiplexing the plurality of communication signals into a single broad band frequency division multiplexed signal;

phase modulating an optical carrier signal with the broad band frequency division multiplexed signal by mixing the multiplexed signal with an optical carrier signal in an electro-optic modulator;

demodulating within a receiver the phase modulated optical communications signal back into the frequency division multiplexed signal; and

demultiplexing the frequency division multiplexed signal into the plurality of analog communication signals.

14. a method according to claim 13, and further comprising the steps of:

demodulating the analog communication signals into the time division multiplexed data streams; and

demultiplexing the data streams into the plurality of digital data streams.

15. A method according to claim 13, and further comprising the step of phase modulating the optical carrier signal by mixing the optical carrier signal and the broad band frequency division multiplexed signal within a Mach-Zender electro-optic modulator.

16. A method according to claim 13, and further comprising the steps of up converting each of the plurality of analog communication signals into a defined frequency slot, and combining the frequencies to create the frequency division multiplexed signal.

17. A method according to claim 13, and further comprising the step of non-mechanically steering the phase modulated optical communications signal by passing the communications signal through a Bragg cell and liquid crystal display.

18. A method according to claim 13, and further comprising the step of beam spoiling the phase modulated optical communications signal by increasing the beam convergence of the communications signal during transmission.

19. A method according to claim 13, and further comprising the step of demodulating the phase modulated optical communications signal by phase locked loop detection.

20. A system for communicating in free space comprising:

a time division multiplexer for receiving a plurality of digital communication signals and multiplexing the digital communications signals into a plurality of time division multiplexed data streams;

a modulator for receiving and modulating the time division multiplexed data streams into a plurality of analog communication signals;

a multiplexer for multiplexing the plurality of broad band analog communication signals into a broad band frequency division multiplexed signal;

an electro-optic modulator that receives said broad band frequency division multiplexed signal and an optical carrier signal and phase modulates the optical carrier signal with the multiplexed signal to produce a phase modulated optical communications signal;

a demodulator for demodulating the phase modulated optical communications signal back into the broad band frequency division multiplexed signal; and

a demultiplexer for demultiplexing the broad band frequency division multiplexed signal into the plurality of analog communication signals.

21. A system according to claim 20, and further comprising a demodulator for demodulating the analog communications signals into the time division multiplexed data streams.

22. A system according to claim 21, and further comprising a demultiplexer for demultiplexing the data streams into the plurality of digital data streams.

23. A system according to claim 20, and wherein said electro-optic modulator further comprises a Mach-Zender electro-optic modulator.

24. A system according to claim 20, and further comprising a mixer for up converting analog signals into a defined frequency channel, and a combiner for combining the up converted frequencies into the frequency division multiplexed signal.

25. A system according to claim 20, and further comprising a Bragg cell and liquid crystal display that receive the phase modulated optical communications signal for non-mechanically steering the phase modulated optical communications signal.

26. A system according to claim 20, and further comprising a beam spoiler that receives the phase modulated optical communications signal for increasing the beam divergence of the phase modulated optical communications signal during transmission.

27. A system according to claim 20, and further comprising a heterodyne detector for demodulating the phase modulated optical communications signal.