ENVIRONMENTALLY STABLE PASSIVELY MODELOCKED FIBER LASER PULSE SOURCE

• US 20120219020A1
• Filed: 02/16/2012
• Published: 08/30/2012
• Est. Priority Date: 12/20/1993
• Status: Active Grant

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Fermann, Martin E., Harter, Donald J.
• Granted Patent: US 8,548,014 B2
• Time in Patent Office: Days
• US Class Current: 372/6
• CPC Class Codes: H01S 3/067 Fibre lasers
• CPC Class Codes: H01S 3/08059 Constructional details of the reflector, e.g. shape mirrors in general G02B5/08; mountings for mirrors G02B7/18
• CPC Class Codes: H01S 3/1112 Passive mode locking
• CPC Class Codes: H01S 3/1115 using intracavity saturable absorbers
• CPC Class Codes: Y10T 29/49826 Assembling or joining

Abstract

The present invention is directed to providing an environmentally stable, ultra-short pulse source. Exemplary embodiments relate to passively modelocked ultra-short fiber lasers which are insensitive to temperature variations and which possess only negligible sensitivity to pressure variations. Further, exemplary embodiments can be implemented in a cost-effective manner which render them commercially practical in unlimited applications. Arbitrary fiber lengths (e.g., on the order of 1 millimeter to 1 kilometer, or greater) can be used to provide an ultra-short pulse with a cost-effective architecture which is commercially practical.

Claims

1. A passively modelocked laser comprising:

a laser energy generator that produces laser energy at a laser wavelength, the laser energy generator having a cavity which includes;

a fiber gain medium for amplifying energy in the cavity, said gain medium comprising at least a section of highly-birefringent doped fiber;

a pair of reflectors which define an optical axis which passes through the fiber gain medium and supports a plurality of longitudinal modes;

a mode-locking mechanism that locks said longitudinal modes in phase to produce optical pulses at a laser wavelength, wherein said modelocking mechanism comprises a semiconductor saturable absorber in said cavity arranged to at least initiate mode locking; and

an output for laser energy generated within said cavity, said output generating ultra-short pulses,

wherein said passively modelocked laser is capable of generating output pulses at GHz repetition rates.

2. The passively modelocked laser according to claim 1, wherein said cavity further comprises one or more sections of low birefringent fiber.

3. The passively modelocked laser according to claim 1, wherein said modelocking mechanism operates with a non-linear phase delay and is arranged in such a way that a non-linear phase difference between polarization states is determined by the relative power between said polarization states.

4. The passively modelocked laser according to claim 1, further comprising a compensator which reduces the effects of linear phase drifts of the gain medium.

5. The passively modelocked laser according to claim 1, further comprising a tuning element located in said cavity and configured to change either the optical length of said cavity or a wavelength of the laser energy generated within said cavity.

6. The passively modelocked laser according to claim 5, wherein said tuning element comprises a fiber stretcher located in said cavity and is operable to change a repetition rate of said ultra-short pulses.

7. The passively modelocked laser according to claim 1, wherein said cavity comprises multiple sections of fiber having different magnitudes of group-velocity dispersion, said multiple sections of fiber, in combination, providing for increased energy of oscillating pulses.

8. The passively modelocked laser according to claim 7, wherein at least a portion of said multiple sections of fiber are concatenated.

9. A passively modelocked laser comprising:

a laser energy generator that produces laser energy at a laser wavelength, the laser energy generator having a cavity which includes;

a fiber gain medium for amplifying energy in the cavity, said gain medium comprising at least a section of highly-birefringent doped fiber and at least a section of low-birefringent fiber, wherein the total length of birefringent fiber is relatively long in comparison with the low birefringent sections;

a pair of reflectors which define an optical axis which passes through the fiber gain medium and supports a plurality of longitudinal modes;

a mode-locking mechanism that locks said longitudinal modes in phase to produce optical pulses at said laser wavelength, wherein said modelocking mechanism comprises a semiconductor saturable absorber in said cavity arranged to at least initiate mode locking; and

an output for laser energy generated within said cavity, said output generating ultra-short pulses.

10. The passively modelocked fiber laser according to claim 9, wherein said passively modelocked laser is capable of generating output pulses having GHz repetition rates.

11. The passively modelocked fiber laser according to claim 9, wherein the total length of fiber within said cavity is on the order of 1 mm to 1 km.

12. The passively modelocked fiber laser according to claim 9, wherein the total length of low birefringent fiber is on the order of eight to ten times shorter than the highly-birefringent fiber.

13. The passively modelocked laser according to claim 9, wherein said modelocking mechanism operating with a non-linear phase delay and arranged in such a way that a non-linear phase difference between polarization states is determined by the relative power between said polarization states.

14. The passively modelocked laser according to claim 9, further comprising a compensator which reduces the effects of linear phase drifts of the gain medium.

15. The passively modelocked laser according to claim 9, further comprising a tuning element located in said cavity and configured to change either the optical length of said cavity or a wavelength of the laser energy generated within said cavity.

16. The passively modelocked laser according to claim 15, wherein said tuning element comprises a fiber stretcher located in said cavity and is operable to change a repetition rate of said ultra-short pulses.

17. The passively modelocked laser according to claim 9, wherein said cavity comprises multiple sections of fiber having different magnitudes of group-velocity dispersion, said multiple sections of fiber, in combination, providing for increased energy of oscillating pulses.

18. A passively modelocked laser comprising:

a laser energy generator having a cavity which includes;

a fiber gain medium for amplifying energy in the cavity, wherein said cavity comprises multiple sections of fiber having different magnitudes of group-velocity dispersion, said multiple sections of fiber, in combination, providing for increased energy of oscillating pulses;

a pair of reflectors which define an optical axis which passes through the fiber gain medium and supports a plurality of longitudinal modes;

a mode-locking mechanism that locks said longitudinal modes in phase to produce optical pulses at said laser, wherein said modelocking mechanism comprises a semiconductor saturable absorber in said cavity arranged to at least initiate mode locking; and

an output for laser energy generated within said cavity, said output generating ultra-short pulses.

19. The passively modelocked laser according to claim 18, wherein said gain medium comprises a section of highly-birefringent doped fiber.

20. The passively modelocked laser according to claim 19, wherein said modelocking mechanism operates with a non-linear phase delay and is arranged in such a way that a non-linear phase difference between polarization states is determined by the relative power between said polarization states.

21. The passively modelocked laser according to claim 18, wherein said passively modelocked laser is capable of generating output pulses at GHz repetition rates.

22. A fiber laser having a linear optical resonator, comprising:

a fiber gain medium having optical transitions operable to absorb optical carriers at a pump wavelength of a specified wavelength range and to emit optical carriers at a laser wavelength that is different from said pump wavelength;

first and second reflective elements disposed relative to said fiber gain medium to form a linear optical resonator that encloses said fiber gain medium and supports a plurality of longitudinal modes;

a saturable absorber disposed in said optical resonator and configured to exhibit an intensity-dependent absorption, said saturable absorber operable to effect a mode-locking mechanism that locks said longitudinal modes in phase to produce optical pulses at said laser wavelength;

a pump light source, operable to produce a pump beam at said pump wavelength which optically excites said fiber gain medium;

an optical coupler, disposed relative to said fiber gain medium to couple said pump beam into said fiber gain medium; and

a tuning element located in said optical resonator and configured to change either the optical length of said optical resonator or said laser wavelength.

23. A fiber laser as in claim 22, wherein said fiber gain medium is formed of a polarization-maintaining fiber having one polarization axis that defines the polarization of said optical pulses.

24. A fiber laser as in claim 22, wherein said fiber gain medium is doped with rare-earth ions.

25. A fiber laser as in claim 24, wherein said rare-earth ions include Er ions, said laser wavelength is about 1.55 μ

m.

26. A fiber laser as in claim 22, wherein said saturable absorber includes one or more semiconductor compounds each having a bandgap equal to or less than a photon energy corresponding to said laser wavelength.

27. A fiber laser as in claim 22, wherein said optical coupler is positioned in an optical path between said fiber gain medium and said saturable absorber to couple said pump beam into said fiber gain medium by propagating from said optical coupler to said fiber gain medium.

28. A fiber laser as in claim 22, wherein said tuning element includes a fiber stretcher engaged to said fiber gain medium, said fiber stretcher operable to change a repetition rate of said optical pulses.

29. A fiber laser as in claim 22, further comprising an output optical coupler disposed in said resonator to produce an output.

30. A fiber laser as in claim 29, wherein said output optical coupler includes a fiber segment to carry said output.

31. A fiber laser as in claim 30, wherein said output optical coupler includes an optical isolator to reduce a feedback to said optical resonator.

32. A method of constructing and operating a fiber laser, comprising:

forming a linear optical resonator by using two reflective elements;

disposing a fiber gain medium in an optical path linking said two reflective elements to provide a gain equal to or greater than a total optical loss in said resonator, wherein said fiber gain medium is formed of polarization-maintaining fiber;

using a saturable absorber in said resonator to mode lock multiple oscillating longitudinal modes to produce optical pulses; and

configuring a linear absorption of said saturable absorber and a total group velocity dispersion inside said resonator to make said optical pulses as soliton pulses.