Optical Counter-Phase System And Method Of RF Interference Cancellation

• US 20120251031A1
• Filed: 11/05/2009
• Published: 10/04/2012
• Est. Priority Date: 11/05/2008
• Status: Active Grant

• Current Assignee: The Trustees of Princeton University (Princeton University)
• Original Assignee: The Trustees of Princeton University (Princeton University)
• Inventors: Kravtsov, Konstantin, Prucnal, Paul R., Suarez, John
• Granted Patent: US 8,693,810 B2
• Time in Patent Office: Days
• US Class Current: 385/3
• CPC Class Codes: G02F 2/002 using optical mixing
• CPC Class Codes: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver

Abstract

A system and method for cancellation of RF interference in the optical domain. The system and method utilize two Mach-Zehnder electrooptic modulators biased for parallel counter-phase modulation. The method of signal subtraction is referred to as incoherent optical subtraction, since two independent laser sources serve as the optical carrier waves. The system has produced the broadband cancellation result while simultaneously recovering a 50 dBm signal which was initially “buried” under the broadband interference. The cancellation depths achieved by the system are due to the accurate channel tracking and precise time delays attainable with modern optical devices—unattainable with state-of-the-art electronic devices at the time of this writing.

Claims

1. An interference cancellation system comprising:

a first electro-optic modulator for receiving a first signal;

a second electro-optic modulator for receiving a second signal together with said first signal, said first and second electro-optic modulators being biased for parallel counter-phase modulation;

an optical attenuator connected to said second electro-optic modulator;

an optical delay connected to said second electro-optic modulator; and

an optical coupler connected to said first and second electro-optic modulators, said second electro-optic modulator being connected to said optical coupler through said optical attenuator and said optical delay.

2. An interference cancellation system according to claim 1, further comprising an control subsystem for automatically controlling said optical attenuator and/or said optical delay.

3. An interference cancellation system according to claim 2, wherein said control subsystem comprises an open loop control subsystem.

4. An interference cancellation system according to claim 2, wherein said control subsystem comprises a closed loop control subsystem.

5. An interference cancellation system according to claim 4, wherein said closed loop control subsystem employs a dither method of feedback control.

6. An interference cancellation system according to claim 4, wherein said closed loop control subsystem employs a parameter offset method of feedback control.

7. An interference cancellation system according to claim 1, wherein said optical delay is connected to said second electro-optic modulator through said optical attenuator.

8. An interference cancellation system according to claim 1, further comprising:

an optical attenuator connected to said first electro-optic modulator;

an optical delay connected to said first electro-optic modulator.

9. An interference cancellation system according to claim 1, wherein said electro-optic modulator comprises an interferometric optical modulator.

10. An interference cancellation system according to claim 9, where said interferometric modulator comprises a Mach-Zehnder optical modulator.

11. An interference cancellation system according to claim 1, further comprising:

a first laser serving as an input to said first electro-optic modulator; and

a second laser serving as an input to said second electro-optic modulator.

12. An interference cancellation system according to claim 1, wherein said first laser operates at a different wavelength than said second laser.

14. An interference cancellation system according to claim 8, further comprising an control subsystem for automatically controlling said optical attenuator and/or said optical delay.

15. An interference cancellation system according to claim 9, wherein said control subsystem comprises an open loop control subsystem.

16. An interference cancellation system according to claim 9, wherein said control subsystem comprises a closed loop control subsystem.

17. An interference cancellation system according to claim 11, wherein said closed loop control subsystem employs a dither method of feedback control.

18. An interference cancellation system according to claim 11, wherein said closed loop control subsystem employs a parameter offset method of feedback control.

13. An interference mitigation system for recovering a weak signal at a location in close proximity to a transmitter that is transmitting a strong signal, the system transmitted comprising:

a splitter having an output connected to an optical cancellation system for providing said strong signal to said optical cancellation system;

a receiver for receiving said weak signal, said receiver having an output connected to said optical cancellation system;

an optical cancellation system comprising;

a first electro-optic modulator for modulating said strong signal received from said splitter;

a combiner for combining said strong signal received from said splitter and said weak signal received from said receiver into a combined signal;

a second electro-optic modulator for modulating said combined signal, said first and second electro-optic modulators being biased for parallel counter-phase modulation;

an optical attenuator connected to said second electro-optic modulator;

an optical delay connected to said second electro-optic modulator; and

an optical coupler connected to said first and second electro-optic modulators, said second electro-optic modulator being connected to said optical coupler through said optical attenuator and said optical delay.

19. A method for mitigating interference with a signal comprising the steps of:

receiving a signal, said received signal comprising a desired signal and a known interfering signal;

inputting said received signal to a first electro-optic modulator;

inputting said known interfering signal to a second electro-optic modulator; and

combining outputs from said first electro-optic modulator and said second electro-optic modulator in a combiner.