Method and apparatus for providing radio frequency photonic filtering

• US 9,097,790 B2
• Filed: 02/02/2012
• Issued: 08/04/2015
• Est. Priority Date: 02/02/2012
• Status: Active Grant

• Current Assignee: The United States Government As Represented By The Secretary Of The Army
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Zhou, Weimin
• Primary Examiner(s): Vanderpuye, Ken
• Assistant Examiner(s): SANCHEZ, DIBSON J
• Application Number:
  US13/364,401
• Publication Number:
  US 20130202305A1
• Time in Patent Office: 1,279 Days
• Field of Search: 398115-117, 398182-214, 398/85, 455/180.3, 455/260, 455/265, 331/16, 359237-324
• US Class Current: 1/1
• CPC Class Codes: G01S 7/282 Transmitters
• CPC Class Codes: H04B 2210/006 Devices for generating or processing an RF signal by optical means

Abstract

A method and apparatus for providing RF-photonic filtering link. Specifically, one embodiment is an apparatus comprising a radio frequency (RF)-photonic filter for filtering an RF signal, where the RF-photonic filter comprises a loop comprising an electro-optical modulator, an optical fiber, a photo detector. Another embodiment is a method of operating an RF-photonic filter comprising applying a reference signal to the RF-photonic filter; selecting a reference frequency for the RF-photonic filter upon the RF-photonic filter locking to the reference frequency, disconnecting the reference signal; and applying an RF input signal to the RF-photonic filter to lock the RF input signal to the RF-photonic filter.

Claims

1. An apparatus comprising:

an input connected to an antenna which receives RF signals;

a RF reference source configured to generate a RF reference signal;

a RF-photonic filter for filtering RF signals, wherein the RF-photonic filter comprises a loop comprising a light source, an electro-optical modulator, an optical fiber, a photo detector, a tunable phase shifter, and a frequency/phase locking circuit; and

a controller configured to apply the RF reference signal to the loop to cause the loop to initially resonate at the frequency of the RF reference signal, disconnect the RF reference signal from the loop, and then apply a RF signal received from an antenna to the loop to lock the loop'"'"'s resonance frequency to the frequency of the received RF signal.

2. The apparatus of claim 1 wherein the RF-photonic filter further comprises:

a reference lock module in the frequency/phase locking circuit for tuning and locking the filter to the RF reference signal; and

a signal lock module for injection locking the loop of the RF-photonic filter to a desired RF input signal.

3. The apparatus of claim 2 wherein the reference frequency lock module comprises a phase locked loop circuit for tuning the RF-photonic filter to a reference frequency of the RF reference signal.

4. The apparatus of claim 2 wherein a frequency of the RF reference signal and the frequency of the desired RF input signal are substantially similar.

5. The apparatus of claim 1 wherein the optical fiber has a predetermined length to establish a particular Q for the RF-photonic filter.

6. The apparatus of claim 1 wherein the loop comprises a fiber splitter providing an optical output to enable remote processing of an input signal after passing through the RF-photonic filter.

7. The apparatus of claim 1 wherein the loop supports a single RF mode.

8. The apparatus of claim 1 wherein the loop comprises an RF combiner for combining a RF input signal with a filtered RF input signal.

9. A RF-photonic filter for filtering a RF signal comprising:

an input configured to provide RF signals received from an antenna;

a loop operating as a resonator that amplifies a desired input RF frequency signal and suppresses undesired input RF frequency signals;

a frequency/phase locking circuit included in said loop that is configured to tune the loop to a reference RF frequency corresponding to a reference RF signal by applying the reference RF signal to the loop so as to cause the loop to initially resonate at the reference RF frequency; and

a controller configured to disconnect the reference RF signal initially provided by the frequency/phase locking circuit to the loop, and then connect a RF signal received from the antenna at the input to the loop to lock the loop'"'"'s resonance frequency to the frequency of the received RF signal.

10. The RF-photonic filter of claim 9, wherein the loop comprises:

a laser, an electro-optical modulator, an optical fiber, a photo detector, an RF-amplifier, a tunable phase shifter and a RF combiner to combine the input RF signal with an RF oscillating signal of the loop.

11. The RF-photonic filter of claim 9, wherein the loop comprises at least one RF coupler configured to provide an RF output of the filtered RF signal and for use in the frequency/phase locking circuit.

12. The RF-photonic filter of claim 9, wherein the loop comprises a fiber splitter configured to provide an optical output of the filtered RF signal.

13. The RF-photonic filter of claim 12, wherein the fiber splitter couples an optical representation of an RF signal to a second photo detector via an optical cable.

14. The RF-photonic filter of claim 13, wherein the second photo detector converts the optical representation of an RF signal to a second RF signal for time delay or remotely transporting the RF signal.

15. The RF-photonic filter of claim 9, wherein the frequency/phase locking circuit comprises:

a phased-locked loop (PLL) configured to select the reference RF signal, and a switch configured to apply either the reference RF frequency or an input signal to the loop.

16. The RF-photonic filter of claim 9, wherein the controller is configured to determine when a frequency of the reference RF signal and the frequency of the RF signal at said desired input RF frequency are substantially similar, and based on said determination, to execute said disconnecting of the reference RF signal and said connecting of the RF signal to the loop.

17. The RF-photonic filter of claim 9, further comprising a RF reference source configured to generate the RF reference signal.

18. A method for operating the RF-photonic filter of claim 9 comprising:

tuning the loop to the reference RF frequency; and

subsequently locking the loop to the frequency of the received RF signal.

19. The method of claim 18, further comprising:

upon tuning the loop to the reference RF frequency, disconnecting the reference RF signal from the loop; and

connecting the received RF signal to the loop.

20. The method of claim 18, further comprising:

selecting the reference RF frequency for tuning the loop.