Remotely locatable RF power amplification system

• US 20030090777A1
• Filed: 04/05/2002
• Published: 05/15/2003
• Est. Priority Date: 11/15/2001
• Status: Active Grant

• Current Assignee: HRL Laboratories LLC (The Boeing Co.)
• Original Assignee: HRL Laboratories LLC (The Boeing Co.)
• Inventors: Yap, Daniel
• Granted Patent: US 6,724,523 B2
• Time in Patent Office: Days
• US Class Current: 359/333
• CPC Class Codes: H01Q 3/2676 Optically controlled phased array
• CPC Class Codes: H04B 10/25752 Optical arrangements for wireless networks

Abstract

A RF amplification system which includes a RF modulation unit fed by an optical carrier and an RF input signal, the modulation unit modulating the RF input signal onto the optical carrier to produce a modulated RF optical signal; an array of optical amplifiers coupled to the modulation unit for receiving and amplifying the modulated RF optical signals; and a detecting unit having at least one photodetector coupled to the array of optical amplifiers for receiving and detecting the modulated RF optical signals, the at least one photodetector producing an amplified RF output in response thereto.

Claims

1. A RF amplification system comprising:

(a) a RF modulation unit fed by an optical carrier and a RF input signal, the modulation unit modulating the RF input signal onto the optical carrier to produce a modulated RF optical signal;

(b) an array of optical amplifiers coupled to the modulation unit for receiving and amplifying the modulated RF optical signals; and

(c) a detecting unit having at least one photodetector coupled to the array of optical amplifiers for receiving and detecting the modulated RF optical signals, the at least one photodetector producing an amplified RF output in response thereto.

2. The RF amplification system of claim 1 wherein the array of optical amplifiers are coupled to said modulation unit solely by means of an array of optical fiber cables, whereby the modulation unit may be located at a remote location relative to the location of the array of optical amplifiers.

3. The RF amplification system of claim 2 wherein the at least one photodetector is coupled by means of one or more fiber optic cables to the array of optical amplifiers whereby the detecting unit may be located at a remote location relative to the location of the RF modulation unit.

4. The RF amplification system of claim 1 wherein the array of optical amplifiers are optical fiber amplifiers.

5. The RF amplification system of claim 1 wherein the RF modulation unit includes a plurality of lasers for pumping the array of optical amplifiers.

6. The RF amplification system of claim 1 wherein the RF modulation unit includes:

(i) a plurality of dual tone laser generators;

(ii) an optical intensity modulator for receiving the RF input signal; and

(iii) a wavelength division multiplexer coupled to said plurality of dual tone laser generators for combining the outputs thereof as an optical input to the optical intensity modulator, the optical intensity modulator modulating the output of the wavelength division multiplexer with the RF input signal, the optical intensity modulator having an output coupled to the array of optical amplifiers.

7. The RF amplification system of claim 6 wherein each of the dual tone laser generators in said plurality of dual tone laser generators emit light having different wavelengths from every other dual tone laser generator in said plurality of dual tone laser generators.

8. The RF amplification system of claim 6 wherein the array of optical amplifiers includes a second wavelength division multiplexer, the second wavelength division multiplexer being coupled to receive light from the RF modulation unit and splitting that light onto a plurality of outputs by wavelength, each output of the second wavelength division multiplexer corresponding to the dual tone laser signal produced by a given dual tone laser generator as subsequently modulated by the RF input signal.

9. The RF amplification system of claim 8 wherein the wavelengths of the plurality of dual tone laser generators are adapted to being combined by the first mentioned wavelength division multiplexer and being split by the second wavelength division multiplexer.

10. The RF amplification system of claim 9 wherein the array of optical amplifiers is coupled to a third wavelength division multiplexer, the third wavelength division multiplexer being coupled to receive light from the optical amplifiers and to combine the light from the optical amplifier onto a single output which is coupled to the at least one photodetector.

11. The RF amplification system of claim 10 wherein the third wavelength division multiplexer comprises a plurality of third wavelength division multiplexers and wherein the array of optical amplifiers are arranged in sets with each set of optical amplifiers being associated with a different one of said plurality of third wavelength division multiplexers.

12. The RF amplification system of claim 11 wherein each one of said third wavelength division multiplexers is connected to a different load.

13. The RF amplification system of claim 12 further including a set of bandpass filters each of which is coupled to an output of one of said third wavelength division multiplexers and a RF waveform power combiner connected to receive an output of each of said set of bandpass filters.

14. The RF amplification system of claim 8 wherein the at least one photodetector comprises a plurality of photodetectors arranged in a plurality of sets, with each photodetector in a given set being connected to a common load.

15. The RF amplification system of claim 14 further including a set of bandpass filters each of which is coupled to the common load associated with each set and a RF waveform power combiner connected to receive an output of each of said set of bandpass filters.

16. The RF amplification system of claim 1 further including an antenna system coupled to the at least one photodetector.

17. The RF amplification system of claim 16 wherein the antenna system is coupled to the at least one photodetector by means of at least one band pass filter.

18. A method of reusing power in an optically based power amplification system comprising the steps of:

(a) photodecting, in a plurality of photodectors, optical outputs of a plurality of optical amplifiers, the outputs of the plurality of optical amplifiers each carrying modulated laser light, the photodectors each having a photodector output;

(b) combining the outputs of the photodectors at a load to form a combined output signal;

(c) separating the relatively lower frequency portions of the combined output signal from the relatively high frequency portions of the combined output signal;

(d) generating DC power for the photodectors by converting the relatively lower frequency portions of the combined output signal to DC power; and

(e) coupling the relatively high frequency portions of the combined output signal to a high frequency RF output of the power amplification system.

19. The method of claim 18 wherein step (a) includes heterodyning, in the plurality of photodectors, optical outputs of the plurality of optical amplifiers, the outputs of the optical amplifiers each carrying multi-tone modulated laser light.

20. The method of claim 18 further including:

(f) generating a plurality of dual tone laser lines by a plurality of dual tone lasers;

(g) modulating the dual tone laser lines with a RF input signal; and

(h) supplying the modulated dual tone lines to said plurality of optical amplifiers.

21. The method of claim 20 further including:

(i) combining the dual tone laser lines as a single optical signal before modulating the dual tone lines; and

(ii) separating the modulated dual tone lines onto a plurality of signal outputs of a wavelength division multiplexer, each output of the wavelength division multiplexer having a single pair of laser lines corresponding to the laser lines generated by one of said plurality of dual tone lasers.

22. A method of optically amplifying a RF signal comprising the steps of:

(a) feeding an optical carrier comprising a plurality of dual tones and the RF signal to be amplified into a RF modulation unit, the modulation unit modulating the RF signal onto the optical carrier to produce a modulated RF optical signal;

(b) optically amplifying the modulated RF optical signal by an array of optical amplifiers coupled to the modulation unit for receiving and amplifying the modulated RF optical signal; and

(c) receiving and detecting the modulated RF optical signal in a detecting unit having at least one photodetector coupled to the array of optical amplifiers, the at least one photodetector producing an amplified RF output in response thereto.

23. The method of claim 22 wherein the array of optical amplifiers are coupled to said RF modulation unit solely by means of an array of optical fiber cables, whereby the modulation unit may be located at a remote location relative to the location of the array of optical amplifiers.

24. The method of claim 23 wherein the array of optical amplifiers are optical fiber amplifiers which are pumped by a plurality of lasers remotely located away from the detecting unit.

25. The method of claim 22 wherein the RF modulation unit includes a plurality of lasers for pumping the array of optical amplifiers, the plurality of lasers being remotely located away from the detecting unit.

26. The method of claim 22 wherein the RF modulation unit includes:

(i) a plurality of dual tone laser generators;

(ii) an optical intensity modulator for receiving the RF input signal; and

(iii) a wavelength division multiplexer, coupled to said plurality of dual tone laser generators, combining the outputs thereof as an optical input to the optical intensity modulator, the optical intensity modulator modulating the output of the wavelength division multiplexer with the RF input signal, the optical intensity modulator having an output coupled to the array of optical amplifiers.

27. The method of claim 26 wherein each of the dual tone laser generators in said plurality of dual tone laser generators emit light having different wavelengths from every other dual tone laser generator in said plurality of dual tone laser generators.

28. The method of claim 26 wherein the array of optical amplifiers includes a second wavelength division multiplexer which receives light from the RF modulation unit and splits that light onto a plurality of outputs by wavelength, each output of the second wavelength division multiplexer corresponding to the dual tone laser signal produced by a given dual tone laser generator as subsequently modulated by the RF input signal.

29. The method of claim 28 wherein the array of optical amplifiers is coupled to a third wavelength division multiplexer, the third wavelength division multiplexer being coupled to receive light from the optical amplifiers and to combine the light from the optical amplifier onto a single output which is coupled to the at least one photodetector.

30. The method of claim 29 wherein the third wavelength division multiplexer comprises a plurality of third wavelength division multiplexers and wherein the array of optical amplifiers are arranged in sets with each set of optical amplifiers being associated with a different one of said plurality of third wavelength division multiplexers.

31. The method of claim 30 wherein each one of said third wavelength division multiplexers is connected to a different load.

32. The method of claim 30 further including a set of bandpass filters each of which is coupled to an output of one of said third wavelength division multiplexers and a RF waveform power combiner connected to receive an output of each of said set of bandpass filters.

33. The method of claim 28 wherein the at least one photodetector comprises a plurality of photodetectors arranged in a plurality of sets, with each photodetector in a given set being connected to a common load.

34. The method of claim 33 further including a set of bandpass filters each of which is coupled to the common load associated with each set and a RF waveform power combiner connected to receive an output of each of said set of bandpass filters.

35. The method of claim 22 further including an antenna system coupled to the at least one photodetector.

36. The method of claim 35 wherein the antenna system is coupled to the at least one photodetector by means of at least one band pass filter.