Optical pulse synthesis using brillouin selective sideband amplification

• US 6,476,959 B2
• Filed: 01/10/2001
• Issued: 11/05/2002
• Est. Priority Date: 01/10/2000
• Status: Expired due to Fees

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Yao, X. Steve
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): CUNNINGHAM, STEPHEN C
• Application Number:
  US09/758,551
• Publication Number:
  US 20010024317A1
• Time in Patent Office: 664 Days
• Field of Search: 359/334, 359/348
• US Class Current: 359/334
• CPC Class Codes: H01S 3/302 in an optical fibre

Abstract

Techniques for producing optical pulses based on Brillouin selective sideband amplification by using a common modulation control signal to modulate both a signal beam to produce multiple sideband signals and a single pump beam to produce multiple pump beams.

Claims

1. A device, comprising:

a signal generator operable to produce a signal beam at a signal frequency;

a pump generator operable to produce a pump beam at a pump frequency that is different from said signal frequency;

a polarizing beam splitter positioned to receive said signal beam in a first linear polarization at a first port and said pump beam in a second linear polarization orthogonal to said first linear polarization at a second port to output said signal and said pump beams at a third port;

an optical medium positioned to receive said signal beam and said pump beam from said polarizing beam splitter, said optical medium exhibiting a Brillouin effect in response to said pump beam to produce at least one Brillouin signal that propagates opposite to a direction of said pump beam; and

a polarization-rotating reflector positioned to receive a transmitted optical beam from said optical medium and reflect said transmitted optical beam back to said optical medium after rotating a polarization of said transmitted optical beam by 90 degrees.

2. The device as in claim 1, wherein said signal generator is operable to modulate said signal beam to carry modulation signals in response to a modulation control signal, and wherein said pump generator is operable to modulate said pump beam to carry modulation pump signals in response to said modulation control signal, said modulation pump signals having a frequency spacing substantially equal to a frequency spacing of said modulation signals in said signal beam.

3. The device as in claim 2, wherein said pump generator includes a pump laser that is tunable in frequency and produces said pump beam, and an optical modulator to modulate said pump beam, said device further comprising:

an optical detector positioned to receive a portion of an output optical signal from said second port of said polarizing beam splitter to produce a detector output signal;

a circuit element coupled to receive said detector output signal and to produce a laser control signal; and

a laser control unit, coupled to said circuit element and said pump laser and operable to tune said pump frequency of said pump laser according to said laser control signal.

4. The device as in claim 2, wherein said signal generator includes:

a signal laser which produces said signal beam;

a signal source which produces said modulation control signal; and

a signal optical modulator positioned to receive and modulate said signal beam and coupled to receive said modulation control signal from said signal source.

5. The device as in claim 4, wherein said pump generator includes:

a pump laser which produces said pump beam; and

a pump optical modulator positioned to receive and modulate said pump beam and coupled to receive said modulation control signal from said signal source.

6. The device as in claim 4, comprising a laser control mechanism which includes:

an optical coupler to split a monitor beam from an output optical signal from said optical medium;

an optical monitor detector to convert said monitor beam into an electrical monitor signal; and

a laser control unit coupled to said optical monitor detector to adjust one of said signal laser and said pump laser to maintain overlap of frequencies of said Brillouin signals with frequencies of selected modulation signals in said signal beam, respectively.

7. The device as in claim 6, wherein said laser control mechanism further includes a signal unit to separate DC and low frequency components of said electrical monitor signal to produce a laser control feedback signal, wherein said laser control unit receives and uses said laser control feedback signal to adjust said one of said signal laser and said pump laser.

8. The device as in claim 2, wherein said signal generator includes:

an active optical feedback loop to produce said signal beam with said modulation signals, wherein said active optical feedback loop having a gain modulator to control an optical gain for said active optical feedback loop in response to said modulation control signal;

an optical path to receive a fraction of said signal beam with said modulation signals;

an optical detector at an end of said optical path to convert said fraction of said signal beam into an electronic feedback signal; and

an electrical path coupled to said optical detector to transmit said electronic feedback signal to produce said modulation control signal with a delay to produce an in-phase feedback to said gain modulator, wherein said gain modulator, said optical path, said optical detector, and said electrical path from a closed electronic-optical feedback loop that sustains an electromagnetic oscillation.

9. The device as in claim 8, wherein said gain modulator includes a semiconductor optical amplifier.

10. The device as in claim 1, wherein said signal generator includes:

a signal laser which produces said signal beam;

a signal optical modulator positioned to receive and modulate said signal beam to produce modulation signals in said signal beam in response to a modulation control signal; and

a feedback loop having an optical portion that receives a portion of said signal beam output from said optical modulator, an optical delay element in said optical portion, and a photodetector converting said portion into a detector output signal, wherein said feedback loop is operable to produce said modulation control signal from said detector output signal.

11. A device, comprising:

a signal generator operable to produce a signal beam at a signal frequency and to modulate said signal beam to carry modulation signals in response to a modulation control signal;

a pump laser operable to produce a pump beam at a pump frequency that is different from said signal frequency;

a pump optical modulator positioned to receive said pump beam and operable to modulate said pump beam to carry modulation pump signals in response to said modulation control signal, said modulation pump signals having a frequency spacing substantially equal to a frequency spacing of said modulation signals in said signal beam; and

an optical medium positioned to receive said signal beam and said pump beam, said optical medium exhibiting a Brillouin effect in response to said modulation pump signals in said pump beam to produce Brillouin signals that propagate opposite to a direction of said pump beam, wherein said Brillouin signals propagate in the same direction as said signal beam and respectively overlap with selected modulation signals in said signal beam in frequency to amplify said selected modulation signals.

12. The device as in claim 11, further comprising:

a polarizing beam splitter positioned to receive said signal beam from said signal generator in a first linear polarization and said pump beam from said pump optical modulator in a second linear polarization that is orthogonal to said first linear polarization, said polarizing beam splitter operable to output said signal and said pump beams in the same direction into said optical medium; and

a polarization-rotating reflector positioned to receive a transmitted optical beam from said optical medium and reflect said transmitted optical beam back to said optical medium after rotating a polarization of said transmitted optical beam by 90 degrees.

13. The device as in claim 11, further comprising:

an optical detector positioned to receive a portion of an output optical signal from said optical medium that includes said amplified selected modulation signals to produce a detector output signal;

a circuit element coupled to receive said detector output signal and to produce a laser control signal; and

a laser control unit, coupled to said circuit element and said pump laser and operable to tune said pump frequency of said pump laser according to said laser control signal.

14. The device as in claim 11, wherein said signal generator includes:

a signal laser which produces said signal beam;

a signal source which produces said modulation control signal; and

a signal optical modulator positioned to receive and modulate said signal beam and coupled to receive said modulation control signal from said signal source.

15. The device as in claim 14, comprising a laser control mechanism which includes:

an optical coupler to split a monitor beam from an output optical signal from said optical medium;

an optical monitor detector to convert said monitor beam into an electrical monitor signal; and

a laser control unit coupled to said optical monitor detector to adjust one of said signal laser and said pump laser to maintain said overlap of said frequencies of said Brillouin signals with said frequencies of said selected modulation signals in said signal beam, respectively.

16. The device as in claim 15, wherein said laser control mechanism further includes a signal unit to separate DC and low frequency components of said electrical monitor signal to produce a laser control feedback signal, wherein said laser control unit receives and uses said laser control feedback signal to adjust said one of said signal laser and said pump laser.

17. The device as in claim 11, wherein said signal generator includes:

a signal laser which produces said signal beam;

a signal optical modulator positioned to receive and modulate said signal beam to produce said modulation signals in said signal beam; and

a feedback loop having an optical portion that receives a portion of said signal beam output from said optical modulator, an optical delay element in said optical portion, and a photodetector converting said portion into a detector output signal, wherein said feedback loop is operable to produce said modulation control signal from said detector output signal.

18. The device as in claim 11, wherein said signal generator includes:

an active optical feedback loop to produce said signal beam with said modulation signals, wherein said active optical feedback loop having a gain modulator to control an optical gain for said active optical feedback loop in response to said modulation control signal;

an optical path to receive a fraction of said signal beam with said modulation signals;

an optical detector at an end of said optical path to convert said fraction of said signal beam into an electronic feedback signal; and

an electrical path coupled to said optical detector to transmit said electronic feedback signal to produce said modulation control signal with a delay to produce an in-phase feedback to said gain modulator, wherein said gain modulator, said optical path, said optical detector, and said electrical path form a closed electronic-optical feedback loop that sustains an electromagnetic oscillation.

19. The device as in claim 18, wherein said gain modulator includes a semiconductor optical amplifier.

20. A method, comprising:

providing an optical medium that exhibits a Brillouin effect;

coupling a pump beam into said optical medium from a first side of said optical medium along a first direction to produce at least one Brillouin signal that propagates against said first direction;

controlling said pump beam to have a first linear polarization when entering said optical medium;

coupling a signal beam into said optical medium from said first side along said first direction;

controlling said pump beam to have second linear polarization orthogonal to said first linear polarization when entering said optical medium;

reflecting said signal and said pump beams that transmit through said optical medium from a second side that is opposite to said first side; and

rotating a polarization of each of said signal and said pump beams by 90 degrees upon said reflection.

21. The method as in claim 20, further comprising modulating said signal and said pump beams according to a common modulation control signal before coupling said signal and said pump beams into said optical medium.

22. The method as in claim 21, wherein said modulation includes a modulation of a phase of said signal beam or said pump beam.

23. The method as in claim 21, wherein said modulation includes a modulation of an amplitude of said signal beam or said pump beam.

24. A method, comprising:

producing a signal beam at a signal frequency and a pump beam at a pump frequency that is different from said signal frequency;

using a common modulation control signal to modulate said signal beam to carry modulation signals and said pump beam to carry modulation pump signals, wherein a frequency spacing between two adjacent modulation pump signals is substantially equal to a frequency spacing of said modulation signals in said signal beam;

coupling said pump beam into an optical medium which exhibits a Brillouin effect in response to said modulation pump signals to produce Brillouin signals that propagate opposite to a direction of said pump beam;

coupling said signal beam into said optical medium to spatially overlap with said Brillouin signals and to propagate in the same direction of said Brillouin signals; and

adjusting a frequency spacing between said signal frequency and said pump frequency to overlap frequencies of said Brillouin signals with frequencies of selected modulation signals in said signal beam to amplify said selected modulation signals.

25. The method as in claim 24, further comprising:

controlling said pump beam to have a first linear polarization when entering said optical medium from a first side of said optical medium;

controlling said signal beam to have a second linear polarization orthogonal to said first linear polarization and to enter said optical medium from said first side; and

reflecting any optical signal that transmits through said optical medium from said first side of said optical medium through a second, opposite side of said optical medium, to propagate back to said optical medium as a reflected optical signal; and

rotating a polarization of said reflected optical signal by 90 degrees upon reflection.

26. The method as in claim 24, wherein said signal beam with said modulation signals is produced by using an optical modulator to modulate a laser signal beam to produce said signal beam, and wherein said pump beam with said modulation pump signals is produced by:

converting a fraction of said signal beam with said modulation signals into an electronic feedback signal;

producing a delay in said electronic feedback signal;

using said electronic feedback signal with said delay to control said optical modulator to modulate said signal beam to form a closed electronic-optical loop that sustains an oscillation;

splitting a portion of said electronic feedback signal to control a pump optical modulator; and

using said pump optical modulator to produce said modulation pump signals in said pump beam.

27. The method as in claim 26, wherein said delay is caused by an optical delay device in an optical path of said fraction of said signal beam prior to said conversion.

28. The method as in claim 24, further comprising:

controlling said pump beam to have a first polarization when entering said optical medium from a first side of said optical medium;

controlling said signal beam to have a second polarization orthogonal to said first polarization and to enter said optical medium from said first side; and

reflecting any transmitted light that transmits through said optical medium from said first side of said optical medium through a second, opposite side of said optical medium, to propagate back to said optical medium as reflected light; and

upon said reflection, making a polarization of said reflected light to be orthogonal to a polarization of said transmitted light prior to said reflection.

29. The method as in claim 24, further comprising:

using a signal laser to produce said signal beam;

using a separate pump laser to produce signal pump beam; and

adjusting one of said signal laser and said pump laser to maintain said overlap of said frequencies of said Brillouin signals with said frequencies of said selected modulation signals in said signal beam, respectively.

30. The method as in claim 29, further comprising:

splitting a monitor beam from an output optical signal from said optical medium;

converting said monitor beam into an electrical monitor signal; and

using information in DC and low frequency components of said electrical monitor signal to adjust said one of said signal laser and said pump laser.

31. A device, comprising:

a signal laser to produce a signal beam at a signal frequency;

a signal optical modulator to modulate said signal beam to carry modulation signals in response to a laser modulation control signal;

a modulation control module to produce said laser modulation control signal;

a pump laser to produce a pump beam at a pump frequency different from said signal frequency;

a pump optical modulator to modulate said pump beam to carry modulation pump signals in response to said laser modulation control signal, wherein said modulation pump signals have a frequency spacing substantially equal to a frequency spacing of said modulation signals in said signal beam;

an optical medium positioned to receive said pump beam in a first polarization from said pump optical modulator and said signal beam from said signal optical modulator in a second polarization orthogonal to said first polarization, said optical medium exhibiting a Brillouin effect in response to said modulation pump signals in said pump beam to produce Brillouin signals that propagate opposite to a direction of said pump beam and overlap with frequencies of selected modulation signals in said signal beam; and

an optical polarization-changing reflector module optically coupled to receive transmitted light from said optical medium and to reflect said transmitted light back to said optical medium as reflected light with a polarization orthogonal to a polarization of said transmitted light.

32. The device as in claim 31, further comprising an output module to output light output from said optical medium in a direction along a direction from said optical reflector module to said optical medium.

34. The device as in claim 31, wherein said modulation control module includes a RF driver to produce said laser modulation control signal at a RF modulation frequency.

35. The device as in claim 31, wherein said modulation control module includes:

an optical path to receive a fraction of said signal beam with said modulation signals;

an optical detector at an end of said optical path to convert said fraction of said signal beam into an electronic feedback signal; and

an electrical path coupled to said optical detector to transmit said electronic feedback signal to produce said laser modulation control signal with a delay to produce an in-phase feedback to said signal optical modulator, wherein said signal optical modulator, said optical path, said optical detector, and said electrical path form a closed electronic-optical feedback loop that sustains an electromagnetic oscillation.

36. The device as in claim 35, wherein said modulation control module includes an optical delay element in said optical path to cause a portion of said delay.

37. The device as in claim 35, wherein said optical path includes a second Brillouin optical medium, and wherein said modulation control module includes:

a second pump laser to produce a second pump beam; and

an optical coupler to couple said pump into said second Brillouin optical medium in a direction opposite to said fraction of said signal beam to amplify said fraction of said signal beam in a selected mode.

38. The device as in claim 31, wherein said optical polarization-changing reflector module include a Faraday rotator and a reflector.

39. The device as in claim 38, wherein said laser control mechanism further includes a signal unit to separate DC and low frequency components of said electrical monitor signal to produce a laser control feedback signal, wherein said laser control unit receives and uses said laser control feedback signal to adjust said one of said signal laser and said pump laser.

40. The device as in claim 31, further comprising a laser control mechanism which includes:

an optical coupler to split a monitor beam from an output optical signal from said optical medium;

an optical monitor detector to convert said monitor beam into an electrical monitor signal; and

a laser control unit coupled to said optical monitor detector to adjust one of said signal laser and said pump laser to maintain said overlap of said frequencies of said Brillouin signals with said frequencies of said selected modulation signals in said signal beam.

33. The device as in claim 33, wherein said output module includes an optical circulator.