Mode-locked multi-mode fiber laser pulse source

• US 20010024458A1
• Filed: 02/16/2001
• Published: 09/27/2001
• Est. Priority Date: 11/25/1998
• Status: Active Grant

• Current Assignee: Martin E. Fermann
• Original Assignee: Martin E. Fermann
• Inventors: Fermann, Martin E.
• Granted Patent: US 8,873,593 B2
• Time in Patent Office: Days
• US Class Current: 372/6
• CPC Class Codes: G02B 6/26 Optical coupling means G02B6/36, G02B6/42 take precedence
• CPC Class Codes: H01S 3/0092 Nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity nonlinear frequency conversion per se G02F1/35
• CPC Class Codes: H01S 3/067 Fibre lasers
• CPC Class Codes: H01S 3/06704 Housings; Packages
• CPC Class Codes: H01S 3/06708 Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering optical fibres as passive waveguides G02B6/02
• CPC Class Codes: H01S 3/06712 Polarising fibre; Polariser
• CPC Class Codes: H01S 3/06716 Fibre compositions per se C03C13/04or doping with active elements lasing materials in general H01S3/14
• CPC Class Codes: H01S 3/06725 Fibre characterized by a specific dispersion, e.g. for pulse shaping in soliton lasers or for dispersion compensating [DCF]
• CPC Class Codes: H01S 3/06729 Peculiar transverse fibre profile
• CPC Class Codes: H01S 3/06733 Fibre having more than one cladding
• CPC Class Codes: H01S 3/06737 Fibre having multiple non-coaxial cores, e.g. multiple active cores or separate cores for pump and gain
• CPC Class Codes: H01S 3/06745 Tapering of the fibre, core or active region
• CPC Class Codes: H01S 3/06783 Amplifying coupler
• CPC Class Codes: H01S 3/08045 Single-mode emission
• CPC Class Codes: H01S 3/08054 Passive cavity elements acting on the polarization, e.g. a polarizer for branching or walk-off compensation quarter-wave plates in a Q-switch laser H01S3/1124, H01S3/115
• CPC Class Codes: H01S 3/094007 Cladding pumping, i.e. pump light propagating in a clad surrounding the active core
• CPC Class Codes: H01S 3/094019 Side pumped fibre, whereby pump light is coupled laterally into the fibre via an optical component like a prism, or a grating, or via V-groove coupling
• CPC Class Codes: H01S 3/094042 of a fibre laser
• CPC Class Codes: H01S 3/094069 Multi-mode pumping
• CPC Class Codes: H01S 3/1106 Mode locking
• CPC Class Codes: H01S 3/1109 : Active mode locking
• CPC Class Codes: H01S 3/1115 : using intracavity saturable absorbers
• CPC Class Codes: H01S 3/1118 : Semiconductor saturable absorbers, e.g. semiconductor saturable absorber mirrors [SESAMs]; Solid-state saturable absorbers, e.g. carbon nanotube [CNT] based
• CPC Class Codes: H01S 3/1608 : erbium
• CPC Class Codes: H01S 3/1618 : ytterbium

Abstract

A laser utilizes a cavity design which allows the stable generation of high peak power pulses from mode-locked multi-mode fiber lasers, greatly extending the peak power limits of conventional mode-locked single-mode fiber lasers. Mode-locking may be induced by insertion of a saturable absorber into the cavity and by inserting one or more mode-filters to ensure the oscillation of the fundamental mode in the multi-mode fiber. The probability of damage of the absorber may be minimized by the insertion of an additional semiconductor optical power limiter into the cavity.

Claims

1. A laser for generating ultra-short optical pulses, comprising:

a cavity which repeatedly passes light energy along a cavity axis;

a length of multi-mode optical fiber doped with a gain medium and positioned along said cavity axis;

a pump for exciting said gain medium;

a mode locking mechanism positioned on said cavity axis; and

an optical guide positioned on said cavity axis which confines the light amplified by said multi-mode optical fiber to preferentially the fundamental mode of said multi-mode optical fiber.

2. A laser for generating ultra-short optical pulses as defined in

claim 1

wherein said mode locking mechanism comprises a passive mode locking element.

3. A laser for generating ultra-short optical pulses as defined in

claim 2

wherein said passive mode locking element comprises a saturable absorber.

4. A laser for generating ultra-short optical pulses as defined in

claim 3

wherein said saturable absorber comprises InGaAsP.

5. A laser for generating ultra-short optical pulses as defined in

claim 3

additionally comprising a power limiter for protecting said saturable absorber.

6. A laser for generating ultra-short optical pulses as defined in

claim 5

wherein said power limiter comprises a two photon absorber.

7. A laser for generating ultra-short optical pulses as defined in

claim 1

wherein said optical guide comprises a single-mode mode-filter fiber on said cavity axis.

8. A laser for generating ultra-short optical pulses as defined in

claim 7

wherein said single-mode mode-filter fiber is fusion spliced onto one end of said multi-mode optical fiber.

9. A laser for generating ultra-short optical pulses as defined in

claim 8

wherein said multi-mode fiber is tapered at said fusion splice.

10. A laser for generating ultra-short optical pulses as defined in

claim 8

wherein said single-mode mode-filter fiber is tapered at said fusion splice.

11. A laser for generating ultra-short optical pulses as defined in

claim 8

wherein both said single-mode mode-filter fiber and said multi-mode fiber are tapered at said fusion splice.

12. A laster for generating ultra-short optical pulses as defined in

claim 1

wherein said pump is coupled to said multi-mode fiber along said cavity axis.

13. A laser for generating ultra-short optical pulses as defined in

claim 1

wherein said pump is coupled to the side of said multi-mode fiber.

14. A laser for generating ultra-short optical pulses as defined in

claim 13

additionally comprising an optical coupler for coupling said pump to said multi-mode fiber.

15. A laser for generating ultra-short optical pulses as defined in

claim 13

additionally comprising a v-groove on said multi-mode optical fiber for coupling said pump to said multi-mode fiber.

16. A laser for generating ultra-short optical pulses as defined in

claim 1

additionally comprising a polarization beam splitter for outputting said ultra-short optical pulses from said laser.

17. A laser for generating ultra-short optical pulses as defined in

claim 1

wherein said cavity comprises a pair of reflectors at its opposite ends.

18. A laser for generating ultra-short optical pulses as defined in

claim 17

wherein one of said pair of reflectors is partially reflecting and provides the output for said cavity.

19. A laser for generating ultra-short optical pulses as defined in

claim 17

wherein said mode locking mechanism comprises a saturable absorber, and wherein one of said reflectors is formed on a surface of said saturable absorber.

20. A laser for generating ultra-short optical pulses as defined in

claim 19

wherein said mode locking mechanism additionally comprises a power limiter for protecting said saturable absorber, and wherein said saturable absorber is formed on a surface of said power limiter opposite said one of said reflectors.

21. A laser for generating ultra-short optical pulses as defined in

claim 20

wherein said power limiter comprises a two-photon absorber.

22. A laser for generating ultra-short optical pulses as defined in

claim 1

additionally comprising a linear phase drift compensator on said cavity axis.

23. A laser for generating ultra-short optical pulses as defined in

claim 22

wherein said linear phase drift compensator comprises a Faraday rotator.

24. A laser for generating ultra-short optical pulses as defined in

claim 23

wherein said linear phase drift compensator comprises a pair of Faraday rotators.

25. A laser for generating ultra-short optical pulses as defined in

claim 22

additionally comprising a linear polarization transformer on said cavity axis.

26. A laser for generating ultra-short optical pulses as defined in

claim 25

wherein said linear polarization transformer comprises a wave plate.

27. A laser for generating ultra-short optical pulses as defined in

claim 1

wherein said mode locking mechanism comprises an active mode locking element.

28. A laser for generating ultra-short optical pulses as defined in

claim 27

wherein said active mode locking element comprises an optical amplitude modulator.

29. A laser for generating ultra-short optical pulses as defined in

claim 27

wherein said active mode locking element comprises an optical frequency modulator.

30. A laser for generating ultra-short optical pulses as defined in

claim 1

wherein said ultra-short optical pulses preferentially in the fundamental mode of said multi-mode optical fiber have a pulse width below 500 psec.

31. A laser for generating ultra-short optical pulses as defined in

claim 1

additionally comprising an environmental stabilizer on said cavity axis to assure that said cavity remains environmentally stable.

32. A laser for generating ultra-short optical pulses as defined in

claim 31

wherein said environmental stabilizer comprises a Faraday rotator.

33. A laser for generating ultra-short optical pulses as defined in

claim 32

wherein said environmental stabilizer comprises a pair of Faraday rotators.

34. A laser for generating ultra-short optical pulses as defined in

claim 1

wherein said optical guide comprises an optical fiber doped with an amplifying medium to provide gain guiding.

35. A laser for generating ultra-short optical pulses as defined in

claim 34

wherein said amplifying medium is concentrated centrally within a fraction of the core diameter of said optical fiber.

36. A laser for generating ultra-short optical pulses as defined in

claim 1

wherein said optical guide comprises a single-mode optical fiber on said cavity axis.

37. A laser for generating ultra-short optical pulses as defined in

claim 1

wherein said optical guide comprises a mode-filter on said cavity axis.

38. A laser for generating ultra-short optical pulses as defined in

claim 37

wherein said mode filter excites the fundamental mode of said multi-mode fiber.

39. A laser for generating ultra-short optical pulses as defined in

claim 38

wherein said mode filter excites the fundamental mode of said multi-mode fiber with an efficiency of at least 90%.

40. A laser for generating ultra-short optical pulses as defined in

claim 1

wherein said cavity additionally comprises a positive dispersion element.

41. A laser for generating ultra-short optical pulses as defined in

claim 40

wherein said positive dispersion element comprises a length of single-mode positive dispersion fiber positioned along said cavity axis.

42. A laser for generating ultra-short optical pulses as defined in

claim 41

additionally comprising an output coupler for limiting the light energy at said single-mode positive dispersion fiber to less than 10% of the peak power in said cavity.

43. A laser for generating ultra-short optical pulses as defined in

claim 42

additionally comprising a frequency converter for compressing pulses generated by said cavity.

44. A laser for generating ultra-short optical pulses as defined in

claim 43

wherein said frequency converter comprises a frequency doubler.

45. A laser for generating ultra-short optical pulses as defined in

claim 44

wherein said frequency doubler comprises chirped periodically poled LiNbO₃.

46. A laser for generating ultra-short optical pulses as defined in

claim 1

wherein said multi-mode fiber includes a core, and wherein said gain medium in said multi-mode optical fiber is concentrated centrally within the core of said multi-mode fiber.

47. A laser for generating ultra-short optical pulses as defined in

claim 1

wherein said multi-mode optical fiber is polarization-maintaining.

48. A laser for generating ultra-short optical pulses as defined in

claim 47

wherein said polarization-maintaining multi-mode fiber has an elliptical core.

49. A laser for generating ultra-short optical pulses as defined in

claim 47

wherein said polarization maintaining multi-mode fiber comprises stress-producing regions.

50. A laser for generating ultra-short optical pulses as defined in

claim 1

wherein said cavity additionally comprises a fiber grating written onto said multi-mode fiber, said grating primarily reflecting the fundamental mode of said multi-mode fiber.

51. A method of generating ultra-short pulses, comprising:

providing a length of optical fiber doped with a gain medium;

repeatedly passing signal light through said length of optical fiber to produce said ultra-short pulses; and

providing sufficient stored energy within said gain medium to amplify said pulses to a peak power above 1 KW.

52. A method of generating ultra-short pulses as defined in

claim 51

additionally comprising:

environmentally stabilizing said optical fiber.

53. A method of generating ultra-short pulses as defined in

claim 51

additionally comprising modelocking said optical fiber.

54. A method of generating ultra-short pulses as defined in

claim 51

wherein said providing step comprises providing a multi-mode fiber doped with a gain medium.

55. A method of generating ultra-short optical pulses, comprising:

circulating light energy within a cavity;

amplifying said light energy within said cavity in a multi-mode fiber; and

confining said light energy within said cavity substantially to the fundamental mode of said multi-mode fiber.

56. A method of generating ultra-short optical pulses as defined in

claim 55

additionally comprising mode locking said light energy.

57. A method of generating ultra-short optical pulses as defined in

claim 55

wherein said confining comprises mode filtering said light energy.

58. A mode-locked laser for generating high power ultra-short optical pulses, comprising:

A multi-mode optical fiber doped with gain material for amplifying optical energy;

means for pumping said optical fiber; and

means for confining the optical energy amplified by said multi-mode optical fiber to substantially the fundamental mode of said multi-mode optical fiber.