Multi-mode fiber amplifier

• US 9,570,880 B2
• Filed: 02/06/2014
• Issued: 02/14/2017
• 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., Harter, Donald J.
• Primary Examiner(s): SAYADIAN, HRAYR
• Application Number:
  US14/174,269
• Publication Number:
  US 20140192403A1
• Time in Patent Office: 1,104 Days
• Field of Search: 372/6, 372/70, 359/341.3, 359/345
• 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. An optical apparatus comprising:

a length of multi-mode optical fiber comprising a gain medium and configured to propagate a fundamental mode;

a length of single mode optical fiber configured to propagate a single mode; and

a splice between the length of multi-mode optical fiber and the length of single-mode optical fiber,

wherein the single mode of the length of single mode optical fiber is matched to the fundamental mode of the length of multi-mode optical fiber.

2. The optical apparatus of claim 1, wherein an output end of the length of single mode optical fiber is spliced to an input end of the length of multi-mode optical fiber.

3. The optical apparatus of claim 1, wherein a tapered portion of the length of single mode optical fiber and the length of multimode optical fiber comprises the splice.

4. The optical apparatus of claim 3, wherein the tapered portion comprises an adiabatic taper.

5. The optical apparatus of claim 3, wherein the length of multi-mode optical fiber comprises a core, and a diameter of the core at an input end is sufficiently small to provide single mode operation of the length of multi-mode fiber at the tapered portion.

6. The optical apparatus of claim 1, wherein the length of multi-mode optical fiber comprises a core having a core diameter, and said gain medium is concentrated centrally within a fraction of the core diameter.

7. The optical apparatus of claim 6, wherein mode coupling into higher-order modes is reduced by gain guiding and the fundamental mode is preferentially amplified.

8. The optical apparatus of claim 1, wherein the length of multi-mode optical fiber comprises a fiber core having a total fiber core cross-sectional area, and the gain medium is confined in a cross-sectional area of the fiber core which is substantially smaller than the total fiber core cross-sectional area.

9. The optical apparatus of claim 1, wherein the optical apparatus is disposed in an optical cavity formed between a first mirror and a second mirror.

10. The optical apparatus of claim 9, wherein the optical cavity further comprises a pair of Faraday rotators.

11. The optical apparatus of claim 1, wherein the length of multi-mode optical fiber comprises a core having a diameter that is several tens of microns.

12. The optical apparatus of claim 1, wherein the optical apparatus is configured as a portion of a multi-mode fiber amplifier.

13. The optical apparatus of claim 1, wherein the splice is used to match the mode of the length single mode fiber to the fundamental mode of the length of multimode fiber.

14. The optical apparatus of claim 13, wherein the single mode of the length of single mode fiber is matched to the fundamental mode of the length of multimode fiber with an efficiency of approximately 90% or higher.

15. The optical apparatus of claim 1, wherein a core of the single mode fiber is thermally tapered to match the single mode of the length of single mode fiber to the fundamental mode of the length of multimode fiber.

16. An optical amplifier comprising the optical apparatus of claim 1, said optical amplifier configured to provide an amplified output substantially in a fundamental mode.

17. The optical amplifier of claim 16, wherein the length of multi-mode optical fiber comprises a double clad structure, the gain medium is cladding pumped, and the optical amplifier provides output power greater than 10 kW and a near diffraction limited output beam.

18. The optical amplifier of claim 17, wherein a core diameter of said length of multimode fiber is several tens of microns.

19. The optical amplifier of claim 17, wherein a core diameter of said length of multi-mode fiber is larger than a core diameter of said length of single mode fiber.

20. An optical apparatus for amplifying light, the apparatus comprising:

a length of multi-mode optical fiber, said multi-mode optical fiber including a gain medium;

an output for receiving amplified light from said length of multi-mode optical fiber;

an energy source for exciting said gain medium; and

an input for providing a beam of light to be amplified within said length of multi-mode fiber, said input comprising a near-diffraction limited laser source, said input optically coupled to said length of multi-mode fiber, said length of multi-mode fiber providing substantially single mode light at the output of said apparatus.

21. A light amplifier comprising:

a length of multi-mode optical fiber, said multi-mode optical fiber including a gain medium;

an energy source for exciting said gain medium; and

an input for providing a near-diffraction limited beam of light to be amplified within said length of multi-mode fiber, said input optically coupled to said length of multi-mode fiber to provide substantially diffraction limited light at the output of said amplifier, said input comprising a near-diffraction limited laser source.