Mode-locked multi-mode fiber laser pulse source

• US 9,153,929 B2
• Filed: 10/17/2014
• Issued: 10/06/2015
• 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:
  US14/517,107
• Publication Number:
  US 20150036702A1
• Time in Patent Office: 354 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 length of doped multimode fiber having a first end;

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

a first length of 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 exits said multimode fiber from a second end of said multimode fiber opposite said first end; and

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

2. The laser system according to claim 1, further comprising a second length of single mode fiber optically connected to said second end of said multimode fiber, said second single mode fiber disposed opposite said first end of said multimode fiber and in said laser cavity.

3. The laser system according to claim 1, wherein matching of the fundamental mode of the multi-mode fiber to the mode of the single-mode fiber is carried out with a splice formed between the multi-mode fiber and the single-mode fiber.

4. 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%.

5. The laser system according to claim 1, where an M² value of said nearly diffraction limited output beam is approximately 1.2.

6. The laser system according to claim 1, wherein at least one of the reflectors comprises a fiber Bragg grating or mirror.

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

8. The laser system according to claim 1, wherein said pump source is arranged for side pumping said doped multimode fiber.

9. The laser system according to claim 1, wherein the single- mode fiber excites the fundamental mode of the multi-mode fiber with an efficiency of approximately 90% to nearly 100%.