Apparatus, method, and computer program product for controlling an interferromic phased array

• US 6,233,085 B1
• Filed: 10/19/1999
• Issued: 05/15/2001
• Est. Priority Date: 10/19/1999
• Status: Expired due to Term

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Johnson, Bartley C.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): THOMPSON, TIMOTHY J
• Application Number:
  US09/420,391
• Time in Patent Office: 574 Days
• Field of Search: 359/279, 359/245, 359/340, 359/341, 372/6, 356/5.09
• US Class Current: 359/279
• CPC Class Codes: G02F 1/0121 Operation of devices; Circuit arrangements, not otherwise provided for in this subclass
• CPC Class Codes: G02F 2203/18 adaptive optics, e.g. wavefront correction
• CPC Class Codes: G02F 2203/50 Phase-only modulation

Abstract

The present invention provides several apparatus, methods, and computer program products for phase shifts in an optical signal generated by an optical device. The present invention includes a optical phase modulator for altering the phase of the optical signals output by an optical device. The present invention also includes a detector assembly that receives an interference signal generated by an optical interference of a power signal and a reference signal. The detector assembly generates a lockin signal representing the optical phase difference between the power signal and the reference signal. Connected to both the detector assembly and the optical phase detector is a processor. The processor receives the lockin signal from the detector assembly and compares the lockin signal to at least one predetermined set point value. The predetermined set point value represents either a desired maximum lockin signal value or a range of acceptable lockin values. If the lockin signal either exceeds the set point value or is not within a range of lockin signal values defined by the predetermined set point value, the processor combines the lockin signal with a step waveform and generates a combined feedback signal having a value within desired operation parameters of the optical phase modulator. In one embodiment of the invention, the processor combines the lockin signal with an exponential step function having a step portion of 2πn.

Claims

1. An apparatus for compensating for phase shifts in an optical power signal, wherein said apparatus comprises:

an optical phase modulator for altering the phase of the optical power signal;

a detector assembly that receives an interference signal generated by optical interference of the optical power signal and a reference signal, wherein said detector assembly generates a lockin signal that is representative of an optical phase difference between the optical power signal and the reference signal; and

a processor in electrical communication with both said detector assembly and said optical phase modulator, wherein said processor receives the lockin signal and compares the lockin signal to at least one predetermined set point value, wherein if the lockin signal exceeds the set point value, said processor alters the lockin signal by combining the lockin signal with a step waveform to thereby produce a combined feedback signal that has a value within desired operation parameters of said optical phase modulator.

2. An apparatus according to claim 1, wherein said processor compares the lockin signal to two predetermined set point values defining a range of lockin values that are within desired operation parameters of said optical phase modulator, and wherein if the value of the lockin signal is outside the range of lockin values defined by the set point values, said processor combines the lockin signal with a step waveform.

3. An apparatus according to claim 2, wherein if the lockin signal is outside the range of feedback values defined by the set point values, said processor combines the lockin signal with a step exponential waveform, wherein the step exponential waveform has an initial step that is 2π

n, where n is an integer.

4. An apparatus according to claim 3, wherein if the lockin signal is outside the range of lockin values defined by the set point values, said processor combines an exponential step function with the lockin signal to generate a combined feedback signal that is altered by a factor of 2π

n, where n is an integer.

5. An apparatus according to claim 1, wherein the set point value defines a maximum desired lockin signal, and wherein if the lockin signal exceeds the set point value, said processor combines the lockin signal with a step waveform.

6. An apparatus according to claim 5, wherein if the lockin signal exceeds the set point value, said processor combines the lockin signal with a step exponential waveform, wherein the step exponential waveform has an initial step that is 2π

n, where n is an integer.

7. An apparatus according to claim 5, wherein if the feedback signal exceeds the set point value, said processor combines an exponential step function with the lockin signal to generate a combined feedback signal that is altered by a factor of 2π

n, where n is an integer.

8. An apparatus according to claim 1, wherein said detector assembly comprises a detector that receives the interference signal and an lockin amplifier in electrical communication with said detector, wherein said lockin amplifier generates the lockin signal that is representative of the optical phase difference between the reference and optical power signals.

9. An apparatus according to claim 8 further comprising a reference phase modulator optically upstream from said detector and a frequency generator in electrical communication with said reference phase modulator, wherein said frequency generator generates a selected frequency signal, and wherein said reference phase modulator receives the selected frequency signal and modulates the reference signal at the selected frequency prior to the interference of the reference and optical power signals.

10. An apparatus according to claim 9, wherein said lock-in amplifier is in electrical communication with both said detector and said frequency generator and receives both the selected frequency signal and the interference signal, and wherein said lock-in amplifier generates a feedback signal representing a component of an optical phase difference between the optical signal and the reference signal at the frequency of the selected frequency signal.

11. An apparatus according to claim 1 further comprising at least one fiber amplifier optically upstream from said detector assembly, wherein said fiber amplifier amplifies at least one of the reference and optical power signals.

12. An apparatus according to claim 1 further comprising a gain amplifier in electrical communication with both said processor and said optical phase modulator, wherein said gain amplifier amplifies the combined feedback signal generated by said processor such that the combined feedback signal has sufficient gain for application to said optical phase modulator.

13. A method for compensating for phase shifts in an optical power signal generated by an optical device having an optical phase modulator for altering the phase of the optical power signal, wherein said method comprises the steps of:

receiving an interference signal generated by optical interference of an optical signal and a reference signal;

generating a lockin signal representative of an optical phase difference between the optical power signal and the reference signal;

comparing the lockin signal to at least one predetermined set point value; and

combining the lockin signal with a step waveform to create a combined feedback signal if the lockin signal exceeds the set point value, such that the combined feedback signal has a value within desired operation parameters of said optical phase modulator.

14. A method according to claim 13, wherein said comparing step comprises comparing the lockin signal to two predetermined set point values defining a range of lockin values that are within desired operation parameters of the optical phase modulator, and wherein if the value of the lockin signal is outside the range of lockin values defined by the set point values, said combining step comprises combining the lockin signal with a step waveform.

15. A method according to claim 14, wherein if the value of the lockin signal is outside the range of lockin values defined by the set point values, said combining step comprises combining the lockin signal with a step exponential waveform, wherein the step exponential waveform has an initial step that is 2π

n, where n is an integer.

16. A method according to claim 13, wherein the set point value defines a maximum lockin signal, wherein if the lockin signal exceeds the set point value, said combining step comprises combining the lockin signal with a step waveform.

17. A method according to claim 16, wherein if the lockin signal exceeds the set point value, said combining step comprises combining the lockin signal with a step exponential waveform, wherein the step exponential waveform has an initial step that is 2π

n, where n is an integer.

18. A method according to claim 16, wherein if the lockin signal exceeds the set point value, said combining step comprises the step of combining an exponential step function with the lockin signal to generate a combined feedback signal that is altered by a factor of 2π

n, where n is an integer.

19. A method according to claim 13 further comprising prior to said detecting step the steps of generating a selected frequency signal and modulating the reference signal at the selected frequency prior to the interference of the reference and optical power signals.

20. A method according to claim 19, wherein said generating step comprises generating a lockin signal representative of a component of an optical phase difference between the optical power signal and the reference signal at the frequency of the selected frequency signal.

21. A method according to claim 13 further comprising the step of amplifying at least one of the reference and optical power signals prior to said detecting step.

22. A method according to claim 13 further comprising the step of gain amplifying the feedback signal generated in said generating step such that the feedback signal has sufficient gain for application to the optical phase modulator.

23. An apparatus for individually compensating for phase shifts in each of a plurality of optical power signals, wherein said apparatus comprises:

a plurality of optical phase modulators for altering the phase of an associated optical power signal;

a plurality of detector assemblies that each receive an interference signal generated by optical interference of an optical power signal and a reference signal associated with each detector assembly, wherein each of said detector assemblies generates a respective lockin signal representative of an optical phase difference between the optical power signal and the reference signal associated with said detector assembly; and

a processor in electrical communication with both said plurality of detector assemblies and said plurality of optical phase modulators, wherein said processor receives a lockin signal generated by each of said detector assemblies and compares the respective lockin signal to at least one predetermined set point value for the respective optical phase modulator, wherein if the lockin signal exceeds the set point value said processor alters the lockin signal by combining the lockin signal with a step waveform to thereby produce a combined feedback signal that has a value within desired operation parameters of said optical phase modulator.

24. An apparatus according to claim 23, wherein said processor compares the respective lockin signal to two predetermined set point values defining a range of lockin values that are within desired operation parameters of said respective optical phase modulator, and wherein if the lockin signal is outside the range of lockin values defined by the set point values, said processor combines the lockin signal with a step waveform.

25. An apparatus according to claim 24, wherein if the lockin signal is outside the range of lockin values defined by the set point values, said processor combines the lockin signal with a step exponential waveform, wherein the step exponential waveform has an initial step that is 2π

n, where n is an integer.

26. An apparatus according to claim 24, wherein if the lockin signal is outside the range of lockin values defined by the set point values, said processor, said processor combines an exponential step function with the lockin signal to generate a combined feedback signal that is altered by a factor of 2π

n, where n is an integer.

27. An apparatus according to claim 23, wherein the set point value defines a maximum lockin signal value, and wherein if the lockin signal exceeds the set point value, said processor combines the lockin signal with a step waveform.

28. An apparatus according to claim 27, wherein if the respective lockin signal exceeds the set point value, said processor combines the lockin signal with a step exponential waveform, wherein the step exponential waveform has an initial step that is 2π

n, where n is an integer.

29. An apparatus according to claim 28, wherein if the respective lockin signal exceeds the set point value, said processor combines an exponential step function with the lockin signal to generate a combined feedback signal that is altered by a factor of 2π

n, where n is an integer.

30. An apparatus according to claim 23, wherein each of said plurality of detector assemblies comprises a detector that receives a respective interference signal and a lockin amplifier in electrical communication with said detector, wherein said lockin amplifier generates the lockin signal that is representative of the optical phase difference between the respective reference and optical power signals.

31. An apparatus according to claim 30 further comprising a plurality of reference phase modulators optically upstream from each of said plurality of detectors and a frequency generator in electrical communication with each of said reference phase modulators, wherein said frequency generator generates a selected frequency signal, and wherein each of said reference phase modulators receive the selected frequency signal and modulate a respective reference signal at the selected frequency prior to the interference of the reference and optical power signals.

32. An apparatus according to claim 31, wherein each of said lock-in amplifiers is in electrical communication with both a respective detector and said frequency generator and receives both the selected frequency signal from said frequency generator and an interference signal from said detector, and wherein each of said lock-in amplifiers generates a lockin signal representative of a component of an optical phase difference between the optical power signal and the reference signal at the frequency of the selected frequency signal.

33. An apparatus according to claim 23 further comprising a plurality of fiber amplifiers optically upstream from said plurality of detector assemblies, wherein said fiber amplifiers amplify at least one of an associated reference and optical power signals.

34. An apparatus according to claim 23 further comprising a plurality of gain amplifiers in electrical communication with both said processor and a respective optical phase modulator, wherein said gain amplifiers amplify an associated combined feedback signal generated by said processor such that the associated combined feedback signal has sufficient gain for application to said optical phase modulator.

35. An apparatus according to claim 23 further comprising a collimating lens upstream from said plurality of detector assemblies, wherein said collimating lens collimates the reference signal.

36. A computer program product for compensating for phase shifts in an optical power signal generated by an optical device, wherein the optical device includes an optical phase modulator for altering the phase of the optical signal and a detector assembly that generates a lockin signal that is representative of an optical phase difference between the optical power signal and a reference signal, wherein the computer program product comprises:

a computer readable storage medium having computer readable program code means embodied in said medium, said computer-readable program code means comprising;

first computer-readable program code means for comparing the lockin signal to at least one predetermined set point value; and

second computer-readable program code means for combining the lockin signal with a step waveform to create a combined feedback signal if the lockin signal exceeds the set point value, such that the combined feedback signal has a value within desired operation parameters of said optical phase modulator.

37. A computer program product as defined in claim 36, wherein said first computer-readable program code means comprises computer readable program code means for comparing the lockin signal to two predetermined set point values defining a range of feedback values that are within desired operation parameters of the optical phase modulator, and wherein said second computer-readable program code means comprises computer readable program code means for combining the lockin signal with a step waveform, if the value of the lockin signal is outside the range of lockin values defined by the set point values.

38. A computer program product as defined in claim 37, wherein said second computer-readable program code means comprises computer readable program code means for combining the lockin signal with a step exponential waveform, wherein the step exponential waveform has an initial step that is 2π

n, where n is an integer, if the value of the lockin signal is outside the range of lockin values defined by the set point values.

39. A computer program product as defined in claim 37, wherein said second computer-readable program code means comprises computer readable program code means for combining an exponential step function with the lockin signal to create a combined feedback signal that is altered by a factor of 2π

n, where n is an integer, if the value of the lockin signal is outside the range of lockin values defined by the set point values.

40. A computer program product as defined in claim 36, wherein the set point value defines a desired maximum lockin signal, and wherein said second computer-readable program code means comprises computer readable program code means for combining the lockin signal with a step waveform, if the lockin signal exceeds the set point value.

41. A computer program product as defined in claim 40, wherein said second computer-readable program code means comprises computer readable program code means for combining the lockin signal with a step exponential waveform, wherein the step exponential waveform has an initial step that is 2π

n, where n is an integer, if the lockin signal exceeds the set point value.

42. A computer program product as defined in claim 40, wherein said second computer-readable program code means comprises computer readable program code means for combining an exponential step function with the lockin signal to create a combined feedback signal that is altered by a factor of 2π

n, where n is an integer, if the lockin signal exceeds the set point value.