Mode-locked multi-mode fiber laser pulse source

• US 9,450,371 B2
• Filed: 09/14/2015
• Issued: 09/20/2016
• Est. Priority Date: 11/25/1998
• Status: Expired due to Fees

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Fermann, Martin E.
• Primary Examiner(s): Park, Kinam
• Application Number:
  US14/853,135
• Publication Number:
  US 20160006208A1
• Time in Patent Office: 372 Days
• Field of Search: 372/6
• US Class Current: 1/1
• 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 system, 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, said multimode optical fiber comprising a multimode core, and a cladding;

a pump source for exciting said gain medium, said pump source arranged for cladding pumping said gain medium of said multimode optical fiber, wherein a numerical aperture of the cladding exceeds a numerical aperture of the multimode core; and

a single mode fiber positioned in said cavity which confines the light amplified by said multi-mode optical fiber to preferentially the fundamental mode of said multi-mode optical fiber; and

a splice joining said multimode fiber and said single mode fiber.

2. The laser system according to claim 1, wherein said single mode fiber comprises a single-mode mode-filter fiber.

3. The laser system according to claim 2, wherein said single mode mode-filter fiber is operably arranged to excite the fundamental mode of said multi-mode fiber.

4. The laser system according to claim 2, wherein said single mode mode-filter fiber is operably arranged to excite the fundamental mode of said multi-mode fiber with an efficiency of at least 90%.

5. The laser system according to claim 2, wherein said single-mode mode-filter fiber is fusion spliced to one end of said multi-mode optical fiber.

6. The laser system according to claim 5, wherein said multi-mode fiber is tapered at said fusion splice.

7. The laser system according to claim 5, wherein said single-mode mode-filter fiber is tapered at said fusion splice.

8. The laser system according to claim 5, wherein both said single-mode mode-filter fiber and said multi-mode fiber are tapered at said fusion splice.

9. The laser system according to claim 1 wherein said pump source is coupled to said multi-mode fiber along said cavity axis.

10. The laser system according to claim 1 wherein said pump source is coupled to the side of said multi-mode fiber.

11. The laser system according to claim 10, comprising a v-groove on said multi-mode optical fiber for coupling said pump to said multi-mode fiber.

12. The laser system according to claim 1, wherein said cavity comprises a pair of reflectors at its opposite ends, and wherein one of said pair of reflectors is partially reflecting and provides the output for said cavity.

13. The laser system according to claim 1, further comprising a linear polarization transformer on said cavity axis.

14. The laser system according to claim 1, further comprising a frequency converter disposed downstream from said single mode fiber and said multimode fiber, and operably arranged to provide a frequency converted beam.

15. The laser system according to claim 1 wherein said multi-mode optical fiber is polarization-maintaining.

16. The laser system according to claim 1, wherein multimode fiber comprises a low-index polymer producing a numerical aperture for the cladding which exceeds the numerical aperture of the multimode fiber core.

17. The laser system according to claim 1, wherein said single mode fiber is arranged with respect to said multimode fiber in such a way that a single mode of said single mode fiber is matched to a fundamental mode of said multimode fiber.

18. The laser system according to claim 1, wherein matching a single mode of said single mode fiber to a fundamental mode of said multimode fiber produces an excitation of the fundamental mode in the multi-mode fiber with an efficiency of 99%.

19. The laser system according to claim 1, wherein said laser system is operably arranged to produce optical pulses.

20. The laser system according to claim 19, wherein said optical pulses comprise ultrashort optical pulses.

21. The laser system according to claim 1, further comprising a mode locking mechanism positioned on said cavity axis;

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

22. The laser system according to claim 1, wherein said single mode fiber is disposed at a first end of said multimode fiber, and said laser system comprises a second single mode fiber optically connected to said multimode fiber, said second single mode fiber disposed at a second end of said multimode fiber opposite said first end and in said laser cavity.

23. The laser system according to claim 1, wherein said multimode fiber comprises a bent portion with a bend radius as small as 1.5 cm.

24. A laser system, comprising:

a doped multimode fiber having a first end;

a pump source to pump said doped multimode fiber, said pump source arranged for cladding pumping of said doped multimode fiber;

a first single mode fiber; and

reflectors disposed to form a laser cavity, said cavity comprising said doped multimode fiber and said first single mode fiber,

wherein one end of said first single mode fiber is arranged with respect to said first end of said multimode fiber in such a way that a single mode of said single mode fiber is matched to a fundamental mode of said multimode fiber,

wherein an output beam of said laser system is nearly diffraction limited and propagates toward an output of said laser system after exiting a second end of said multimode fiber opposite said first end; and

a splice joining said first end of said multimode fiber and said one end of said first single mode fiber.

25. The laser system according to claim 24, further comprising a second single mode fiber optically connected between said second end of said multimode fiber and said output of said laser system.

26. A laser system, 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, said multimode optical fiber comprising a multimode core, and a cladding;

a pump source for exciting said gain medium, said pump source arranged for cladding pumping said gain medium of said multimode optical fiber, wherein a numerical aperture of the cladding exceeds a numerical aperture of the multimode core; and

a single mode fiber positioned in said cavity, said single mode fiber and said multimode optical fiber being arranged so that light passing from said single mode fiber into said multimode fiber preferentially excites the fundamental mode of said multi-mode optical fiber; and

a splice joining said multimode fiber and said single mode fiber,

wherein an output beam of said laser system is nearly diffraction limited.

27. The laser system according to claim 26, wherein said single mode fiber comprises a single-mode mode-filter fiber.

28. The laser system according to claim 26, wherein said single mode fiber is spliced to said multimode fiber in such a way that a single mode of said single mode fiber is matched to a fundamental mode of said multimode fiber.

29. The laser system according to claim 26, wherein said multimode fiber comprises a bent portion with a bend radius as small as 1.5 cm.