High power, passively modelocked fiber laser, and method of construction

• US 6,034,975 A
• Filed: 03/09/1998
• Issued: 03/07/2000
• Est. Priority Date: 03/09/1998
• Status: Expired due to Term

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Harter, Donald J., Fermann, Martin E., Jiang, Min
• Primary Examiner(s): Scott, Jr., Leon
• Application Number:
  US09/040,252
• Time in Patent Office: 729 Days
• Field of Search: 372/18, 372/6, 372/27, 372/92
• US Class Current: 372/18
• CPC Class Codes: H01S 3/067 Fibre lasers
• CPC Class Codes: H01S 3/1115 using intracavity saturable absorbers

Abstract

The output power of a passively modelocked fiber laser is increased by distributing optical losses throughout the cavity. The laser cavity includes a saturable absorber and a polarizing element that serves as the output coupler, and these are positioned on opposite sides of the fiber gain medium. The pump light is preferably injected towards the side of the laser cavity that includes the saturable absorber. The laser cavity compensates for polarization drifts and is environmentally stable.

Claims

1. An optical cavity for a short pulse modelocked fiber laser, comprising:

first and second reflectors which are each at least partially reflecting, respectively defining first and second ends of said cavity;

a fiber including a gain medium disposed between said first and second cavity ends;

a pump signal injector connected to introduce pump light into said fiber toward said first cavity end, said pump light exciting said gain medium to produce a laser signal;

a saturable absorber proximate said first cavity end, said saturable absorber inducing modelocking of said laser signal; and

an output coupler proximate said second cavity end and outcoupling a portion of said laser signal in the form of short output pulses.

2. The optical cavity of claim 1, in which said output coupler comprises a polarizing element.

3. The optical cavity of claim 1, further comprising first and second Faraday rotators respectively proximate said first and second cavity ends and compensating for polarization drifts.

4. The optical cavity of claim 1, further comprising a lens proximate said first cavity end and between said saturable absorber and said fiber.

5. The optical cavity of claim 1, in which said saturable absorber is disposed directly on said first reflector.

6. The optical cavity of claim 1, in which said gain medium comprises a rare earth element.

7. The optical cavity of claim 6, in which said rare earth element is erbium or ytterbium.

8. The optical cavity of claim 1, in which said pump signal injector comprises a wavelength division multiplexer.

9. The optical cavity of claim 1, additionally comprising a polarizer proximate said second cavity end.

10. The optical cavity of claim 1 wherein said saturable absorber removes a first percentage of light proximate to one end of said cavity, and said output coupler removes a second percentage of light proximate to the other end of said cavity, and wherein said first percentage is less than said second percentage.

11. The optical cavity of claim 10 wherein said first percentage is between 10 and 60 percent, and wherein said second percentage is above 60 percent.

12. An optical cavity for a short pulse modelocked fiber laser, comprising:

first and second reflectors which are each at least partially reflecting, respectively defining first and second ends of said cavity;

a fiber including a gain medium disposed between said first and second cavity ends;

a pump signal injector connected to introduce pump light into said fiber, said pump light exciting said gain medium to produce a laser signal;

a saturable absorber proximate said first cavity end, said saturable absorber inducing modelocking of said laser signal; and

a polarizing output coupler proximate said second cavity end and outcoupling a portion of said laser signal in the form of short output pulses.

13. The optical cavity of claim 12, in which said polarizing output coupler comprises a polarization beam splitter.

14. The optical cavity of claim 12, further comprising first and second Faraday rotators respectively proximate said first and second cavity ends and compensating for polarization drifts.

15. The optical cavity of claim 12, further comprising a lens proximate said first cavity end and between said saturable absorber and said fiber.

16. The optical cavity of claim 12, in which said saturable absorber is disposed directly on said first reflector.

17. The optical cavity of claim 12, in which said gain medium comprises a rare earth element.

18. The optical cavity of claim 17, in which said rare earth element is erbium or ytterbium.

19. The optical cavity of claim 12, in which said pump signal injector comprises a wavelength division multiplexer.

20. The optical cavity of claim 12, in which said pump signal injector introduces said pump light into said fiber toward said first cavity end.

21. The optical cavity of claim 12 wherein said saturable absorber removes a first percentage of light proximate to one end of said cavity, and said output coupler removes a second percentage of light proximate to the other end of said cavity, and wherein said first percentage is less than said second percentage.

22. The optical cavity of claim 12 wherein said first percentage is between 10 and 60 percent, and wherein said second percentage is above 60 percent.

23. A method of generating short pulses from a fiber laser, wherein said fiber laser includes (a) a fiber having a gain medium, said fiber disposed between said first and second cavity ends, (b) first and second reflectors which are each at least partially reflecting, respectively defining said first and second cavity ends, and (c) a pump signal injector connected to introduce pump light into said fiber, said pump light exciting said gain medium to produce a laser signal, comprising:

absorbing a portion of said laser signal proximate said first cavity end to modelock said laser signal;

connecting said pump signal injector to inject said pump light toward said first cavity end; and

outputting a portion of said laser signal proximate said second cavity end in the form of short output pulses.

24. The method of claim 23, in which said output step additionally comprises polarizing said short output pulses.

25. The method of claim 23, further comprising compensating for polarization drifts within said fiber.

26. The method of claim 23, further comprising focusing said laser signal proximate said first cavity end.

27. The method of claim 23, additionally comprising wavelength division multiplexing said laser signal and said pump signal.

28. The method of claim 23, additionally comprising polarizing said laser signal proximate said second cavity end.

29. The method of claim 23 wherein said absorbing step removes a first percentage of light proximate to one end of said cavity, and said outputting step removes a second percentage of light proximate to the other end of said cavity, and wherein said first percentage is less than said second percentage.

30. The method of claim 28 wherein said first percentage is between 10 and 60 percent, and wherein said second percentage is above 60 percent.

31. A method of generating short pulses from a fiber laser, wherein said fiber laser includes (a) a fiber having a gain medium, said fiber disposed between said first and second cavity ends, (b) first and second reflectors which are each at least partially reflecting, respectively defining said first and second cavity ends, and (c) a pump signal injector connected to introduce pump light into said fiber, said pump light exciting said gain medium to produce a laser signal, comprising:

absorbing a portion of said laser signal proximate said first cavity end to modelock said laser signal; and

polarizing a portion of said laser signal proximate said second cavity end to output short pulses from said cavity.

32. The method of claim 31, further comprising compensating for polarization drifts within said fiber.

33. The method of claim 31, further comprising focusing said laser signal proximate said first cavity end.

34. The method of claim 31, additionally comprising wavelength division multiplexing said laser signal and said pump signal.

35. The method of claim 31 wherein said absorbing step removes a first percentage of light proximate to one end of said cavity, and said polarizing step removes a second percentage of light proximate to the other end of said cavity, and wherein said first percentage is less than said second percentage.

36. The method of claim 31 wherein said first percentage is between 10 and 60 percent, and wherein said second percentage is above 60 percent.

37. A method of producing modelocked laser output pulses from a fiber laser optical cavity, comprising:

injecting pump light into said fiber laser to generate a laser signal;

absorbing a portion of said laser signal to modelock said laser signal;

outcoupling a fraction of said laser signal to produce said output pulses; and

distributing optical losses within the cavity by undertaking said absorbing and outcoupling steps at opposite ends of said cavity, to enhance the power of said output pulses.

38. The method of claim 37, in which said distributing step does not substantially increase the pulse width of pulses from the modelocked laser signal.

39. An optical cavity for a modelocked fiber laser, comprising:

two reflectors, each at least partially reflecting, said reflectors defining opposite ends of said cavity;

a fiber including a gain medium disposed between said opposite ends of said cavity;

an optical element for injecting a pump signal into said cavity, the pump signal exciting said gain medium in said fiber to produce a laser signal;

a saturable absorber for modelocking said laser signal; and

an output coupler for outcoupling a portion of said laser signal, said output coupler and said saturable absorber located within and on said opposite ends of said cavity.

40. An optical cavity as defined in claim 39, wherein said output coupler polarizes said laser signal.

41. An optical cavity as defined in claim 40, wherein said output coupler comprises a polarization beam splitter.

42. An optical cavity as defined in claim 39 wherein said optical element injects said pump signal in a direction away from said output coupler.

43. An optical cavity as defined in claim 39 additionally comprising:

a pair of Faraday rotators within said cavity to compensate for polarization drift.

44. A method of producing modelocked laser output from an optical cavity having a gain medium, comprising:

amplifying an optical signal in said gain medium to produce an amplified optical signal;

directing said amplified optical signal through a saturable absorber to produce a modelocked optical signal;

amplifying said modelocked optical signal in said gain medium to produce an amplified modelocked optical signal; and

outcoupling a fraction of said amplified modelocked optical signal with a polarizing element.

45. A method of producing modelocked laser output from an optical cavity having a gain medium, comprising:

pumping said gain medium with pump light having a first direction;

amplifying an optical signal in said gain medium to produce an amplified optical signal;

directing said amplified optical signal through a saturable absorber to produce a modelocked optical signal;

amplifying said modelocked optical signal by passing said modelocked optical signal through said gain medium in a direction opposite said first direction to produce an amplified modelocked optical signal; and

outcoupling a fraction of said amplified modelocked optical signal.