Coupled opto-electronic oscillator

• US 5,929,430 A
• Filed: 09/25/1997
• Issued: 07/27/1999
• Est. Priority Date: 01/14/1997
• Status: Expired due to Term

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Maleki, Lute, Yao, X. Steve
• Primary Examiner(s): Westin, Edward P.
• Assistant Examiner(s): Lee, John R.
• Application Number:
  US08/937,892
• Time in Patent Office: 670 Days
• Field of Search: 250/205, 250/227.11, 250/227.12, 250/227.17, 250/227.18, 250/227.21, 250/214.1, 250/214 R, 372/12, 372/18, 359/181, 359/184, 359/187, 359/245, 359/315, 359/316, 359/317, 359/318, 359/319, 359/320
• US Class Current: 250/205
• CPC Class Codes: H01S 5/065 Mode locking; Mode suppression; Mode selection ; Self pulsating
• CPC Class Codes: H01S 5/1071 Ring-lasers
• CPC Class Codes: H01S 5/50 Amplifier structures not provided for in groups H01S5/02 - H01S5/30

Abstract

A coupled opto-electronic oscillator that directly couples a laser oscillation with an electronic oscillation to simultaneously achieve a stable RF oscillation at a high frequency and ultra-short optical pulsation by mode locking with a high repetition rate and stability. Single-mode selection can be achieved even with a very long opto-electronic loop. A multimode laser can be used to pump the electronic oscillation, resulting in a high operation efficiency. The optical and the RF oscillations are correlated to each other.

Claims

1. An opto-electronic device, comprising:

a laser, having an internal active optical feedback loop with a first loop gain greater than unity and responsive to an electrical modulation signal, said laser operating to produce a coherent optical oscillation; and

an opto-electronic feedback loop with a second loop gain greater than unity, receiving an optical signal indicative of said optical oscillation and converting said optical signal into said electrical modulation signal having a relation with said optical oscillation, said electrical modulation signal affecting said optical loop and said optical oscillation.

2. A device as in claim 1, wherein said electrical modulation signal in said opto-electronic feedback loop causes an optical modulation in said optical oscillation in said laser.

3. A device as in claim 2, wherein said optical modulation is in phase with said optical oscillation in said laser and causes mode-locking of said optical oscillation in said laser.

4. A device as in claim 1, wherein said electrical modulation signal modulates said first loop gain or a phase of said optical feedback loop.

5. A device as in claim 1, wherein said laser includes a gain medium in said optical feedback loop, said gain medium having a gain that varies with said electrical modulation signal.

6. A device as in claim 5, wherein said laser has a ring cavity.

7. A device as in claim 6, wherein said laser includes an optical fiber in said ring cavity to provide a conduit for said laser oscillation.

8. A device as in claim 6, wherein said gain medium comprises a semiconductor optical amplifier.

9. A device as in claim 5, wherein said laser includes a semiconductor laser.

10. A device as in claim 9, wherein said gain medium includes:

a semiconductor laser medium that is driven by a laser power supply, operable to cause laser oscillation; and

an electro-absorption modulator, disposed in said optical feedback loop of said semiconductor laser, said electro-absorption modulator receiving said electrical modulation signal to change optical absorption thereof, thus resulting in a change in said first loop gain.

11. A device as in claim 1, wherein said optical feedback loop and said opto-electronic feedback loop have a phase correlation with respect to each other.

12. A device as in claim 1, further comprising a phase delay element in said laser, operating to change a phase of said optical oscillation and to affect said electrical modulation signal.

13. A device as in claim 12, wherein a frequency of said electrical modulation signal is affected by said phase delay element in said laser.

14. A device as in claim 2, further comprising an optical coupler disposed relative to said laser, said optical coupler operable to split an output of said laser into a first portion as laser output and a second portion as said optical signal for feeding said opto-electronic loop.

15. A device as in claim 2, wherein said opto-electronic feedback loop further comprises an photodetector responsive to said optical signal, said photodetector deployed relative to said laser and operable to convert said optical signal into said electrical modulation signal.

16. A device as in claim 15, wherein said opto-electronic feedback loop further comprises an RF amplifier.

17. A device as in claim 15, wherein said opto-electronic feedback loop further comprises a variable RF delay element for changing a phase of said opto-electronic feedback loop.

18. A device as in claim 15, wherein said opto-electronic feedback loop further comprises an RF bandpass filter for changing a frequency characteristic of said electrical modulation signal.

19. A device as in claim 15, wherein said opto-electronic feedback loop further comprises a variable RF attenuator for changing said second loop gain.

20. A device as in claim 15, wherein said opto-electronic feedback loop further comprises an RF coupler.

21. A device as in claim 20, wherein said RF coupler couples an external RF modulation signal into said opto-electronic feedback loop.

22. A device as in claim 20, wherein said RF coupler generates an RF output.

23. A device as in claim 15, wherein said opto-electronic feedback loop further comprises an optical delay line.

24. A device as in claim 23, wherein said optical delay line includes an optical fiber.

25. A device as in claim 23, wherein said optical delay line includes a variable optical phase delay element.

26. A device as in claim 25, wherein said optical delay line includes a variable optical attenuator.

27. A device as in claim 1, wherein said laser further includes an external optical light source to supply power to said optical oscillation.

28. A device as in claim 1, wherein said optical oscillation in said laser is energized by an electrical power supply.

29. A device as in claim 1, wherein said laser is a multi-mode laser.

30. A device as in claim 5, wherein said laser has a Fabry-Perot cavity.

31. An opto-electronic device, comprising:

an active optical feedback loop configured to have a first loop gain greater than unity and operable to produce a laser oscillation therein, said optical loop having an electro-optical element operable to affect said first loop gain; and

an opto-electronic feedback loop having a second loop gain greater than unity and being coupled with said optical loop, said opto-electronic loop including a photodetector that receives an optical signal indicative of said laser oscillation in said optical loop and produces an electrical modulation signal, wherein said electrical modulation signal is fed into said electro-optical element in said optical loop to couple said optical loop and said opto-electronic loop with each other.

32. A device as in claim 31, wherein said optical loop comprises a first optical fiber loop.

33. A device as in claim 32, wherein said electro-optical element is a semiconductor optical amplifier that is optically coupled to said first optical fiber loop and is electrically connected to said opto-electronic loop to receive said electrical modulation signal, said semiconductor optical amplifier having a gain that is modulated by said electrical modulation signal.

34. A device as in claim 32, wherein said first optical fiber loop includes an optical phase delay element.

35. A device as in claim 31, wherein said opto-electronic loop comprises a second optical fiber loop having one end that is optically coupled to said optical loop for receiving said optical signal and another end that is connected to said photodetector, said second optical fiber loop effecting a delay in said opto-electronic loop.

36. A device as in claim 35, wherein said second optical fiber loop includes an fiber stretcher for changing a phase delay in said opto-electronic loop and tuning a modulation frequency of said electrical modulation signal.

37. A device as in claim 35, wherein said second optical fiber loop includes a variable optical attenuator to change said second loop gain.

38. A device as in claim 31, wherein said opto-electronic feedback loop further comprises an RF amplifier.

39. A device as in claim 31, wherein said opto-electronic loop further comprises a variable RF delay element operable to change a phase of said opto-electronic loop.

40. A device as in claim 31, wherein said opto-electronic loop further comprises an RF band-pass filter operable to change a frequency characteristic of said electrical modulation signal.

41. A device as in claim 31, wherein said opto-electronic loop further comprises a variable RF attenuator operable to change said second loop gain.

42. A device as in claim 31, wherein said opto-electronic loop further comprises an RF coupler.

43. A device as in claim 31, wherein said optical feedback loop and said opto-electronic feedback loop has a phase correlation with respect to each other.

44. An opto-electronic device, comprising:

an active optical feedback loop with a first loop gain greater than unity and a first loop delay, said optical loop operable to generate a laser oscillation therein and having an electro-optical gain element that is operable to affect said first loop gain; and

an opto-electronic feedback loop coupled with said optical loop, having a second loop gain greater than unity and a second loop delay greater than said first loop delay, said opto-electronic loop including;

an optical delay line having one end coupled to said optical loop to receive an optical signal indicative of said laser oscillation and another end connected to a photodetector that converts said optical signal into an electrical modulation signal,

an RF delay line having one end connected to said photodetector to receive said electrical modulation signal and another end connected to said electro-optical gain element, and

an RF bandpass filter connected in said RF delay line, having a center frequency that is substantially equal to a RF beat frequency of different modes of said optical loop, whereby said optical loop is mode-locked to produce pulsed laser oscillations.

45. A device as in claim 44, where in said RF bandpass filter has a bandwidth that is smaller than a mode spacing of said optical loop.

46. A device as in claim 44, wherein said RF delay line comprises an RF amplifier.

47. A device as in claim 44, wherein said RF delay line further comprises a variable RF delay element for changing a phase of said opto-electronic loop.

48. A device as in claim 44, wherein said RF delay line further comprises a variable RF attenuator for changing said second loop gain.

49. A device as in claim 44, wherein said RF delay line further comprises an RF coupler.

50. A device as in claim 44, wherein said first loop delay has a relation with said second loop delay so that one of RF oscillation modes in said opto-electronic loop is substantially in resonance with a mode beat frequency of said active optical feed loop.

51. A method for generating an opto-electronic oscillation, comprising:

providing an active optical feedback loop with a first loop gain greater than unity and responsive to an electrical modulation signal, said optical loop operating to produce a laser oscillation;

providing an opto-electronic loop with a second loop gain greater than unity, said opto-electronic loop having an optical delay line with a photodetector and an RF delay line;

optically coupling said optical delay line of said opto-electronic loop with said optical loop to receive an optical signal indicative of said laser oscillation;

converting said optical signal into said electrical modulation signal with said photodetector, said electrical modulation signal having a relation with said laser oscillation; and

electrically coupling said RF delay line with said optical loop to feed said electrical modulation signal to affect said optical loop.

52. A method as in claim 51, wherein said optical feedback loop includes an active semiconductor gain medium formed on a semiconductor substrate and positioned between two reflective surfaces formed on said semiconductor substrate.

53. A method as in claim 52, wherein said optical delay line includes an optical fiber coupled to said semiconductor substrate to receive transmitted light from one of said reflective surfaces.

54. A method as in claim 52, further comprising electrically modulating a portion of said active semiconductor gain medium in response to said electrical modulation signal to produce a gain modulation in said portion, wherein said first loop gain changes with said gain modulation.

55. An opto-electronic device, comprising:

a semiconductor gain medium formed on a substrate and operable to produce an optical gain in response to an electrical excitation signal;

two reflective elements formed on said substrate and spaced from each other to enclose said semiconductor gain medium, one of said reflective elements being partially transmissive to allow transmission of light generated by said semiconductor gain medium, wherein said semiconductor gain medium and said reflective elements form an optical loop which operable to produce a first loop gain greater than unity and to sustain a laser oscillation; and

an opto-electronic feedback loop having a second loop gain greater than unity and an optical fiber coupled to said substrate to receive a portion of transmitted light from one of said reflective elements, wherein said opto-electronic loop includes a photodetector coupled to convert light from said optical fiber into an electrical modulation signal,

wherein said electrical modulation signal is applied to said semiconductor gain medium to modulate said first loop gain and to couple said optical loop and said opto-electronic loop with each other.

56. A device as in claim 55, wherein said semiconductor gain medium comprises at least:

a first gain section connected to receive said electrical modulation signal from said opto-electronic feedback loop and produce a variable gain in response to said electrical modulation signal, thereby effecting an electro-absorption modulator; and

a second gain section that has a section optical gain that is substantially independent of said electrical modulation signal.

57. A device as in claim 55, wherein said opto-electronic feedback loop comprises an electronic signal amplifier connected to amplify said electrical modulation signal.