Highly rare-earth-doped optical fibers for fiber lasers and amplifiers

• US 8,498,046 B2
• Filed: 12/03/2009
• Issued: 07/30/2013
• Est. Priority Date: 12/04/2008
• Status: Active Grant

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Dong, Liang, Fermann, Martin E., McKay, Hugh, Fu, Libin, Suzuki, Shigeru
• Primary Examiner(s): Hellner, Mark
• Assistant Examiner(s): Diacou, Ari M
• Application Number:
  US12/630,550
• Publication Number:
  US 20110069723A1
• Time in Patent Office: 1,335 Days
• Field of Search: 359/341.5
• US Class Current: 359/341.5
• CPC Class Codes: C03C 13/046 Multicomponent glass compositions
• CPC Class Codes: G02B 2006/12038 Glass (SiO2 based materials)
• CPC Class Codes: G02B 2006/1209 Multimode
• CPC Class Codes: G02B 6/02347 Longitudinal structures arranged to form a regular periodic lattice, e.g. triangular, square, honeycomb unit cell repeated throughout cladding
• CPC Class Codes: G02B 6/02366 Single ring of structures, e.g. "air clad"
• CPC Class Codes: G02B 6/02371 Cross section of longitudinal structures is non-circular
• CPC Class Codes: G02B 6/036 core or cladding comprising multiple layers multicore optical fibres G02B6/02042; microstructured properties G02B6/02295; omniguide fibres G02B6/023
• CPC Class Codes: H01S 2301/03 Suppression of nonlinear conversion, e.g. specific design to suppress for example stimulated brillouin scattering [SBS], mainly in optical fibres in combination with multimode pumping
• 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 3/1603 rare earth
• CPC Class Codes: H01S 3/1616 thulium
• CPC Class Codes: H01S 3/1618 ytterbium
• CPC Class Codes: H01S 3/163 characterised by a crystal matrix
• CPC Class Codes: H01S 3/1691 characterised by additives / sensitisers / promoters as further dopants
• CPC Class Codes: H01S 3/1693 aluminium
• CPC Class Codes: H01S 3/175 phosphate glass
• CPC Class Codes: H01S 3/176 silica or silicate glass
• CPC Class Codes: H04B 10/2507 for the reduction or elimination of distortion or dispersion

Abstract

Various embodiments described herein comprise a laser and/or an amplifier system including a doped gain fiber having ytterbium ions in a phosphosilicate glass. Various embodiments described herein increase pump absorption to at least about 1000 dB/m-9000 dB/m. The use of these gain fibers provide for increased peak-powers and/or pulse energies. The various embodiments of the doped gain fiber having ytterbium ions in a phosphosilicate glass exhibit reduced photo-darkening levels compared to photo-darkening levels obtainable with equivalent doping levels of an ytterbium doped silica fiber.

Claims

1. An optical fiber comprising:

a rare earth doped glass comprising silica, a rare-earth dopant, phosphorus, and aluminum, wherein the concentration of the rare-earth dopant is at least about 0.5 mol %;

said optical fiber configured to have a peak absorption greater than about 3000 dB/m at a pump wavelength and a gain greater than about 0.5 dB/cm at an emission wavelength, and

wherein the phosphorus in the rare-earth doped glass has a concentration such that a saturated value of photo-darkening loss in the optical fiber is less than about 10 dB/m at said emission wavelength.

2. The optical fiber of claim 1, wherein said concentration of phosphorous in said rare-earth doped glass comprises at least about 10 mol % P₂O₅.

3. The optical fiber of claim 1, said rare-earth doped glass comprising about 10-30 mol % of phosphorus, less than about 25 mol % of boron, and about 0.5-15 mol % aluminum.

4. The optical fiber of claim 1, wherein said rare-earth doped glass comprises about 0.5-15 mol % of ytterbium.

5. The optical fiber of claim 1, wherein said rare-earth doped glass comprises about 0.5-15 mol % ytterbium, and about 0.5-1 mol % erbium.

6. The optical fiber of claim 1, wherein said rare-earth doped glass comprises about 0.5-15 mol % thulium.

7. The optical fiber of claim 1, wherein said rare-earth doped glass comprises about 0.5-1 mol % erbium.

8. The optical fiber of claim 1, wherein the gain is in a range from about 0.5 dB/cm to about 10 dB/cm.

9. The optical fiber of claim 1, wherein the peak absorption is in a range from about 3000 dB/m to about 9000 dB/m.

10. The optical fiber of claim 1, wherein the saturated value of the photo-darkening loss in the optical fiber is less than about 10 dB/m and greater than about 1 dB/m.

11. The optical fiber of claim 1, wherein said silica has a refractive index and wherein said rare earth doped glass has a refractive index within approximately ±

0.003 or less of the refractive index of silica.

12. The optical fiber of claim 1, wherein the optical fiber is configured to have a gain greater than about 100 dB/m.

13. A laser-based system, comprising:

at least one multimode pump diode;

a large core fiber configured to receive energy from said pump diode and emit a single-mode or few-mode pump output; and

an optical system configured to receive said pump output,

wherein at least one of said large core fiber or said optical system comprises the optical fiber of claim 1.

14. A laser-based system, comprising:

a source of optical pulses;

a fiber amplifier, comprising the optical fiber of claim 1; and

a non-linear fiber configured to spectrally broaden pulses emitted from said fiber amplifier, said non-linear fiber comprising a stress-guided fiber configured to guide a mode within said fiber using stress-optic effect.

15. The laser-based system of claim 14, further comprising a pulse compressor configured to receive pulses from said non-linear fiber and compress said pulses to a pulse width in a range of about 10 fs to about 1 ps.

16. A fiber laser oscillator, comprising:

a gain fiber comprising the optical fiber of claim 1, said gain fiber having a first length;

a pump source for pumping said gain fiber;

a first reflector optically connected to a first output end of said gain fiber, wherein the reflector is configured to control intra-cavity dispersion, said reflector having a reflectivity of at least about 40%;

an undoped fiber optically coupled to a second output end of the gain fiber and configured to receive energy emitted from the second output end of the gain fiber, said undoped fiber having a second length, the second length greater than the first length;

a saturable absorber configured as a highly reflective cavity end mirror, said saturable absorber having a reflectivity of at least about 40% and operable to mode-lock said fiber oscillator, said saturable absorber configured to receive and reflect energy emitted from the second output end of the gain fiber; and

an intra-cavity polarizer optically coupled to said gain fiber and said undoped fiber, the polarizer configured as a first output coupler to emit a first set of output pulses.

17. The fiber laser oscillator of claim 16, wherein said first reflector comprises a chirped Bragg grating.

18. The fiber laser oscillator of claim 16, wherein said oscillator further comprises a polarization controller, said polarization controller comprising a quarter-wave plate, wherein said quarter-wave plate is configured to be adjustable to control output coupling of said first set of output pulses.

19. The fiber laser oscillator of claim 18, wherein said polarization controller is configured for output coupling of at least about 50%.

20. The fiber laser oscillator of claim 16, wherein said oscillator is configured to support solitons.

21. The fiber laser oscillator of claim 16, wherein said oscillator is configured to limit non-linear phase delay of the output pulses to less than π

.

22. A system comprising:

a fiber amplifier comprising an amplifier material configured to amplify radiation in a first wavelength range having a signal wavelength, the amplifier material comprising rare-earth dopant, phosphorus, and aluminum, wherein the phosphorus in the amplifier material has a concentration such that a saturated value of photo-darkening loss in the amplifier material is less than about 10 dB/m at the signal wavelength; and

a fiber pump laser comprising a laser material configured to produce radiation in a second wavelength range having a pump wavelength, said fiber pump laser configured to core pump the fiber amplifier,

wherein an emission cross section of the pump laser material at the pump wavelength is about 10% greater than an emission cross section of the amplifier material at the pump wavelength.

23. The system of claim 22, wherein the fiber amplifier comprises an Yb aluminosilicate fiber.

24. The system of claim 22, wherein the fiber pump laser comprises an Yb phosphosilicate fiber.

25. The system of claim 22, wherein the emission cross section of the pump laser material at the pump wavelength is in a range from about 25% to about 50% greater than the emission cross section of the amplifier material at the pump wavelength.

26. The system of claim 22, wherein the saturated value of the photo-darkening loss in the amplifier material is less than about 10 dB/m and greater than about 1 dB/m.

27. An optical amplifier, comprising:

a pump source; and

a gain fiber, said gain fiber comprising;

a cladding comprising silica;

a core comprising a rare-earth dopant, phosphorus, and aluminum,

wherein the concentration of the rare-earth dopant is at least about 0.5 mol %, and said gain fiber has a peak absorption greater than about 3000 dB/m at a pump wavelength and a gain greater than about 0.5 dB/cm at an emission wavelength, and

wherein the phosphorus in the gain fiber has a concentration such that a saturated value of photo-darkening loss of the gain fiber is less than about 10 dB/m at the emission wavelength.

28. The optical amplifier of claim 27, wherein said pump source is configured to core pump said gain fiber, and said pump source comprises a large-core fiber amplifier.

29. The optical amplifier of claim 27, wherein said pump source is configured to cladding pump said gain fiber.

30. A fiber laser comprising the optical amplifier of claim 27, said gain fiber configured as a gain medium within an optical resonator.

31. The optical amplifier of claim 27, wherein the concentration of the rare-earth dopant is less than about 15 mol %.

32. The optical amplifier of claim 27, wherein the gain is in a range from about 0.5 dB/cm to about 10 dB/cm.

33. The optical amplifier of claim 27, wherein the peak absorption is in a range from about 3000 dB/m to about 9000 dB/m.

34. The optical amplifier of claim 27, wherein the saturated value of the photo-darkening loss in the optical fiber is less than about 10 dB/m and greater than about 1 dB/m.

35. An optical fiber comprising:

a rare earth doped core having a core radius ρ

;

a first cladding disposed about said core; and

a second cladding disposed about said first cladding,

said first cladding having an outer radius ρ

₁, said core and said first cladding having a difference in index of refraction Δ

n, and said first cladding and said second cladding having a difference in index of refraction Δ

n₁,

wherein (i) less than 10 modes are supported in said core, (ii) the first cladding radius, ρ

₁, is greater than about 1.1ρ and

less than about 2ρ

, and (iii) the refractive index difference between said first cladding and said second cladding, Δ

n₁, is greater than about 1.5 Δ

n and less than about 50 Δ

n,

wherein said optical fiber comprises silica, a rare-earth dopant, phosphorus, and aluminum, and the concentration of the rare-earth dopant is at least about 0.5 mol %, said optical fiber having a peak absorption greater than about 3000 dB/m to about 9000 dB/m at a pump wavelength, and

wherein the phosphorus in the rare-earth doped core has a concentration such that the saturated value of the photo-darkening loss of the optical fiber is less than about 10 dB/m at an emission wavelength.

36. The optical fiber of claim 35, wherein the concentration of the rare-earth dopant is less than about 15 mol %.

37. The optical fiber of claim 35, wherein a gain of the optical fiber is in a range from about 0.5 dB/cm to about 10 dB/cm at the emission wavelength.

38. The optical fiber of claim 35, wherein the saturated value of the photo-darkening loss of the optical fiber is less than about 10 dB/m and greater than about 1 dB/m.