Phase tracking multichannel link

• US 20040208636A1
• Filed: 03/29/2002
• Published: 10/21/2004
• Est. Priority Date: 03/29/2002
• Status: Active Grant

• Current Assignee: Anthony E. Spezio, Edward M. Alexander, Timothy N. Reynolds
• Original Assignee: Anthony E. Spezio, Edward M. Alexander, Timothy N. Reynolds
• Inventors: Reynolds, Timothy N., Spezio, Anthony E., Alexander, Edward M.
• Granted Patent: US 7,024,120 B2
• Time in Patent Office: Days
• US Class Current: 398/183
• CPC Class Codes: H04B 10/25758 between a central unit and a single remote unit by means of an optical fibre
• CPC Class Codes: H04J 14/0298 with sub-carrier multiplexing [SCM]

Abstract

A phase tracking multichannel apparatus includes a plurality of optical transmitters, an optical multiplexer, a common optical link, and a user electronics. RF signals having different phases are received and are output on separate RF channels, each of which is coupled to an optical transmitter. RF-modulated optical output signals are then output to the optical multiplexer to produce a multiplexed output signal. The multiplexed signal is applied to a common optical link that at its output substantially maintains the phase separation of RF modulation components on optical carriers as received at its input. The optical output of the common optical link is then applied to an optical signal receiving system, such as an optical demultiplexer and a plurality of photodetectors. By multiplexing all of the optical signals onto the common optical fiber, all signals transmit the same path and, therefore, have the same time and phase delay. The phase tracking is preserved because all of the signals experience the same optical or expansive properties of the common optical fiber. A typical use would be to transmit multiple RF signals from an antenna array to a remote RF phase measuring receiver, such as a RF direction finding system.

Claims

1. A phase tracking multichannel apparatus, comprising:

a plurality of RF channels wherein each of said RF channels has a phase separation relative to each adjacent RF channel, and an output coupled to each of said RF channels for applying an RF output signal;

a plurality of optical transmitters, each of said optical transmitters having an input for receiving a corresponding RF output signal and an output for applying an optical output signal modulated on an optical carrier, said optical output signal having substantially the same phase as said received RF output signal;

a multiplexer having an input for receiving each of said optical output signals and an output for applying a multiplexed optical output signal having multiple-phase RF components with substantially the same phase separation as between corresponding said RF output signals;

a common optical link having an input for receiving the multiplexed optical output signal and an output for applying the multiplexed optical output signal, said common optical link substantially maintaining the phase separation between corresponding optical signals at said common optical link output as received at said common optical link input; and

an optical signal receiving system having an input for receiving the multiplexed optical output signal.

2. An apparatus as in claim 1, further comprising an antenna array for feeding each of a plurality of RF signals into a corresponding channel of said plurality of RF channels.

3. An apparatus as in claim 1, wherein said optical transmitters are laser diode transmitters.

4. An apparatus as in claim 1, wherein said optical signal receiving system further comprises:

a demultiplexer having an input for receiving the multiplexed optical output signal and a plurality of outputs for applying each of a plurality of demultiplexed RF modulated optical signals having substantially the same phase separation between modulated RF signals on the optical carriers as between corresponding said RF output signals;

a plurality of photodetectors, each said photodetector having an input for receiving one of said demultiplexed RF modulated optical signals from a corresponding demultiplexer output and an output for applying an RF signal output representative of said photodetector input; and

a user electronics for receiving and processing said photodetectors RF signal outputs.

5. An apparatus as in claim 1, wherein said apparatus comprises phase-matched components for phase tracking of RF signals within said apparatus.

6. An apparatus as in claim 1, wherein the antenna array is a phased array antenna.

7. An apparatus as in claim 1, wherein the user electronics includes a coherent receiver.

8. An apparatus as in claim 7, wherein the apparatus is an RF direction finder.

9. An apparatus as in claim 1, wherein the multiplexer is a wave division multiplexer.

10. An apparatus as in claim 1, wherein the common optical link comprises single mode, non-zero dispersion shifted optical fiber.

11. A phase tracking multichannel apparatus, comprising:

a plurality of RF channels wherein each of said RF channels has a phase separation relative to each adjacent RF channel, and an output coupled to each of said RF channels for applying an RF output signal;

a plurality of fixed output light sources, each of said fixed output light sources having an output for applying an optical carrier;

a plurality of modulators, wherein each said modulator includes a first input for receiving a corresponding optical carrier, a second input for receiving a corresponding RF output signal, a third input for receiving a bias control signal, and an output for applying an RF modulated optical output signal;

a plurality of fiber couplers, each said fiber coupler including an input for receiving one of said RF modulated optical output signals, a first output for applying an initial fiber coupler output signal, and a second output for applying a bias-adjusted optical modulator output signal;

a plurality of monitor photodetectors, each said monitor photodetector including an input for receiving a corresponding fiber coupler output signal and an output for applying a monitor photodetector output control signal;

a plurality of bias control circuits, each said bias control circuit including an input for receiving a corresponding monitor photodetector output control signal and an output for applying a bias control signal at said third input of a corresponding optical modulator and thereby bias-adjust each said fiber coupler second output;

a multiplexer having an input for receiving each of said modulator output signals and an output for applying a multiplexed optical output signal having multiple RF modulation components with substantially the same phase separation as between corresponding said RF output signals;

a common optical link having an input for receiving the multiplexed optical output signal and an output for applying the multiplexed optical output signal, said common optical link substantially maintaining the phase separation between RF modulation components on the multiplexed optical signal at said common optical link output as received at said common optical link input; and

an optical signal receiving system having an input for receiving the multiplexed optical output signal.

12. An apparatus as in claim 11, further comprising an antenna array for feeding each of a plurality of RF signals into a corresponding channel of said plurality of RF channels.

13. An apparatus as in claim 11, wherein the fixed output light sources are laser diodes.

14. An apparatus as in claim 11, wherein said optical signal receiving system comprises:

a demultiplexer having an input for receiving the multiplexed optical output signal and a plurality of outputs for applying each of a plurality of demultiplexed modulated optical signals having substantially the same phase separation between adjacent frequencies as said RF output signals;

a plurality of photodetectors, each said photodetector having an input for receiving a demultiplexed modulated optical signal from a corresponding demultiplexer output and an output for applying an RF signal output representative of said photodetector input; and

a user electronics for receiving and processing said photodetector RF signal outputs.

15. An apparatus as in claim 14, wherein the photodetectors are photodiodes.

16. An apparatus as in claim 11, wherein said apparatus comprises phase-matched components for phase tracking of RF signals within said apparatus.

17. An apparatus as in claim 11, wherein the user electronics includes a coherent receiver.

18. An apparatus as in claim 11, wherein the apparatus is an RF direction finder.

19. An apparatus as in claim 11, wherein the multiplexer is a wave division multiplexer.

20. An apparatus as in claim 11, wherein the common optical link comprises single mode, non-zero dispersion shifted optical fiber.

21. A phase tracking multichannel apparatus, comprising:

a plurality of RF channels wherein each of said RF channels has a phase separation relative to each adjacent RF channel, and an output coupled to each of said RF channels for applying an RF output signal;

a plurality of fixed output light sources, each of said fixed output light sources having an output for applying an optical carrier;

a plurality of modulators, wherein each said modulator includes a first input for receiving a corresponding optical carrier, a second input for receiving a corresponding RF output signal, and an output for applying an RF modulated optical output signal;

a multiplexer having an input for receiving each of said RF modulated optical output signals and an output for applying a multiplexed optical output signal having multiple RF modulation components with substantially the same phase separation as between corresponding said RF output signals;

a common optical link having an input for receiving the multiplexed optical output signal and an output for applying the multiplexed optical output signal, said common optical link substantially maintaining the phase separation between RF modulation components at said common optical link output as received at said common optical link input; and

an optical signal receiving system having an input for receiving the multiplexed optical output signal.

22. An apparatus as in claim 21, further comprising an antenna array for feeding each of a plurality of RF signals into a corresponding channel of said plurality of RF channels.

23. An apparatus as in claim 21, wherein the fixed output light sources are laser diodes.

24. An apparatus as in claim 21, wherein said optical signal receiving system comprises:

a demultiplexer having an input for receiving the multiplexed optical output signal and a plurality of outputs for applying each of a plurality of modulated optical signals having substantially the same phase separation between adjacent frequencies as said RF output signals;

a plurality of photodetectors, each said photodetector having an input for receiving a demultiplexed RF modulated optical signal from a corresponding demultiplexer output and an output for applying an RF signal output representative of said photodetector input; and

a user electronics for receiving and processing said photodetector RF signal outputs.

25. An apparatus as in claim 24, wherein the photodetectors are photodiodes.

26. A method for processing an RF signal, comprising the steps of:

receiving a plurality of RF output signals having a relative phase separation therebetween;

modulating each of said plurality of RF output signals upon a plurality of optical carriers to form a plurality of modulated optical output signals;

multiplexing said plurality of RF modulated optical output signals to form a multiplexed optical output signal having multiple RF modulation components with substantially the same phase separation as between corresponding said RF output signals;

transmitting said multiplexed optical output signal in a common optical link, said common optical link substantially maintaining the phase separation between RF modulation components on optical carriers at said common optical link output as received at said common optical link input; and

receiving said multiplexed optical output signal in a user electronics.

27. A method as in claim 26, further comprising the step of applying a plurality of bias control signals while modulating each of said plurality of RF output signals upon an optical carrier to form a plurality of RF modulated optical output signals.

28. A method as in claim 26, further comprising the step of phase tracking.

29. A method as in claim 26, wherein the step of receiving a plurality of RF output signals having a relative phase separation therebetween is performed by a phased array antenna.

30. A method as in claim 26, further comprising the step of converting the multiplexed RF modulated optical output signal into a plurality of demultiplexed RF modulated optical signals.

31. A method as in claim 30, further comprising the step of processing the RF signals using a coherent receiver.

32. A method as in claim 31, further comprising the step of determining a direction of the received wavefront.

33. A method as in claim 26, wherein the multiplexing step comprises wave division multiplexing.

34. A method as in claim 26, wherein the step of maintaining the phase separation between RF modulation components on multiplexed optical carriers on a common optical link is conducted using a single mode, non-zero dispersion shifted optical fiber as the common optical link.