Fiber- or rod-based optical source featuring a large-core, rare-earth-doped photonic-crystal device for generation of high-power pulsed radiation and method

• US 7,391,561 B2
• Filed: 05/26/2006
• Issued: 06/24/2008
• Est. Priority Date: 07/29/2005
• Status: Active Grant

• Current Assignee: Lockheed Martin Aculight Corp. (Martin Marietta Corporation)
• Original Assignee: Aculight Corporation (Martin Marietta Corporation)
• Inventors: Di Teodoro, Fabio, Brooks, Christopher D.
• Primary Examiner(s): Hughes; Deandra M
• Application Number:
  US11/420,729
• Publication Number:
  US 20070041083A1
• Time in Patent Office: 760 Days
• Field of Search: 385/126, 359/341.1
• US Class Current: 359/341.1
• CPC Class Codes: C03B 37/10 Non-chemical treatment surface treatment of fibres or filaments made from glass, minerals or slags C03C25/00
• CPC Class Codes: G02B 6/02328 Hollow or gas filled core
• 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 6/02376 Longitudinal variation along fibre axis direction, e.g. tapered holes
• CPC Class Codes: G02B 6/02385 Comprising liquid, e.g. fluid filled holes
• CPC Class Codes: G02B 6/3826 characterised by form or shape
• CPC Class Codes: G02B 6/3853 Lens inside the ferrule lensed connectors G02B6/32
• CPC Class Codes: H01S 3/005 Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping shaping laser beam for working metal or other materials B23K26/06; optical elements, systems or apparatus in general G02B
• CPC Class Codes: H01S 3/0064 Anti-reflection devices, e.g. optical isolaters absorbing layers for marking or protecting purposes in laser working B23K26/50; magneto-optical non-reciprocal devices G02F1/093, G02F1/0955
• CPC Class Codes: H01S 3/0078 Frequency filtering
• 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 3/06729 Peculiar transverse fibre profile
• CPC Class Codes: H01S 3/06741 Photonic crystal fibre, i.e. the fibre having a photonic bandgap
• CPC Class Codes: H01S 3/06745 Tapering of the fibre, core or active region
• CPC Class Codes: H01S 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/06758 Tandem amplifiers
• CPC Class Codes: H01S 3/094007 Cladding pumping, i.e. pump light propagating in a clad surrounding the active core

Abstract

A method and apparatus use a photonic-crystal fiber having a very large core while maintaining a single transverse mode. In some fiber lasers and amplifiers having large cores problems exist related to energy being generated at multiple-modes (i.e., polygamy), and of mode hopping (i.e., promiscuity) due to limited control of energy levels and fluctuations. The problems of multiple-modes and mode hopping result from the use of large-diameter waveguides, and are addressed by the invention. This is especially true in lasers using large amounts of energy (i.e., lasers in the one-megawatt or more range). By using multiple small waveguides in parallel, large amounts of energy can be passed through a laser, but with better control such that the aforementioned problems can be reduced. An additional advantage is that the polarization of the light can be maintained better than by using a single fiber core.

Claims

1. An apparatus comprising:

a first photonic-crystal optical device that includes a first waveguide that has a diameter of about 40 microns or more within a pump cladding and maintains a single transverse mode with operation at a peak power of at least about one megawatt (1 MW) and a beam quality M² of less than 1.5.

2. The apparatus of claim 1, wherein the first core of the first photonic-crystal device is capable of operation with an output beam quality M² of less than 1.2 to generate linearly polarized pulses with a peak power of about 100 kW or more.

10. The apparatus of claim 1, wherein the first photonic-crystal device further includes a second waveguide that maintains a single transverse mode and has a diameter of about 40 microns or more and is located parallel to the first waveguide and within the pump cladding.

32. The apparatus of claim 1, wherein an output optical signal pulse of the device has a spectral linewidth of less than 13 GHz.

33. The apparatus of claim 1, wherein an output optical signal pulse of the device has a spectral linewidth of less than 20 GHz.

34. The apparatus of claim 1, wherein an output optical signal pulse of the device is linearly polarized and has a linewidth of less than 50 GHz.

35. The apparatus of claim 1, wherein an output optical signal pulse of the device has a spectral linewidth of about 9 GHz.

36. The apparatus of claim 1, wherein an output optical signal pulse of the device has a spectral linewidth of less than 35 GHz.

37. The apparatus of claim 1, wherein an output optical signal pulse of the device has an energy of greater than 0.6 mJ, a peak-power of greater than 600 kW, an average-power of greater than 6 W, a 1.06-μ

m-wavelength, a pulse duration of about 1 ns, a linear polarization having a degree of polarization of 99%, an M2 of less than 1.3, and a spectral linewidth of about 10 GHz.

3. An apparatus comprising:

a first photonic-crystal optical device that includes a first waveguide that has a diameter of about 40 microns or more within a pump cladding and maintains a single transverse mode with operation at a peak power of at least about one megawatt (1 MW) and a beam quality M² of less than 1.5, and one or more wavelength-conversion optical media operable to receive high-peak-power input radiation having a first wavelength from the first waveguide of the first photonic-crystal device, and to generate radiation having a peak power of about 100 kW or more and of a shorter second wavelength through wavelength conversion.

4. The apparatus of claim 3, wherein the second-wavelength radiation includes visible light having a wavelength between about 400 nm and about 700 nm.

5. The apparatus of claim 3, wherein the second-wavelength radiation includes ultraviolet light having a wavelength of about 400 nm or shorter.

6. The apparatus of claim 3, wherein the second-wavelength radiation includes wavelength longer than the first wavelength.

7. An apparatus comprising:

a first photonic-crystal optical device that includes a first waveguide that has a diameter of about 40 microns or more within a pump cladding and maintains a single transverse mode with operation at a peak power of at least about one megawatt (1 MW) and a beam quality M² of less than 1.5,

wherein the first optical device is a first photonic-crystal rod and the first waveguide is a first core of the first photonic-crystal device that supports a mode area having a diameter of about 50 microns or larger and a cladding having a diameter of about 1,000 microns or larger.

8. An apparatus comprising:

a first photonic-crystal optical device that includes a first waveguide that has a diameter of about 40 microns or more within a pump cladding and maintains a single transverse mode with operation at a peak power of at least about one megawatt (1 MW) and a beam quality M² of less than 1.5, wherein the first optical device is a first photonic-crystal fiber and the first waveguide is a first core of the first photonic-crystal device;

a first optical isolator;

a first narrow-bandwidth filter; and

a first master-oscillator seed laser operable to generate a narrow-linewidth seed-laser signal of a first wavelength operably coupled to the first core of the first photonic-crystal fiber through the first optical isolator and the first narrow-bandwidth filter.

9. The apparatus of claim 8, further comprising

a second optical isolator;

a second narrow-bandwidth filter;

a second photonic-crystal fiber optical amplifier having a core; and

a second master-oscillator seed laser operable to generate a seed-laser signal of a second wavelength different than the first wavelength, and operably coupled to the core of the second photonic-crystal fiber through the second optical isolator and the second narrow-bandwidth filter, wherein the second photonic-crystal fiber outputs the narrow-linewidth seed-laser signal.

26. The apparatus of claim 8, wherein the first waveguide of the first photonic-crystal device is surrounded by a plurality of longitudinal holes that define a transverse extent of the first waveguide, and wherein the holes are closed for a first length at a first end of the first photonic-crystal fiber to form an endcap.

27. The apparatus of claim 26, wherein the closed holes at the first end of the first photonic-crystal fiber are melted shut for the first length.

28. The apparatus of claim 26, wherein the closed holes at the first end of the first photonic-crystal fiber are filled with an index-matching material for the first length.

29. The apparatus of claim 26, wherein the endcap of the first photonic-crystal fiber is tapered to a diameter smaller than a diameter of the first fiber away from the endcap, and has a facet at an end of the endcap.

30. The apparatus of claim 29, further comprising

a third photonic-crystal fiber having an endcap on an end of the third fiber, wherein the endcap is tapered to a diameter smaller than a diameter of the third fiber away from the endcap, and wherein the endcap has a facet at an end of the endcap of the third fiber, wherein the endcap of the first fiber is located side-by-side to the endcap of the third fiber such that the end facet of the first fiber and the end facet of the second fiber are placed at a center-to-center distance smaller than the diameter of the first fiber away from the endcap of the first fiber.

31. The apparatus of claim 8, wherein the first waveguide of the first photonic-crystal fiber constitutes a core, and wherein the first photonic-crystal fiber further includes a plurality of other cores arranged side-by-side generally along a line transverse to a length of the first fiber, wherein the fiber includes an inner pump cladding surrounding the plurality of cores to provide pump light into the inner pump cladding surrounding the cores in order to provide pump light into the cores over a length of the fiber, and an outer cladding surrounding the inner cladding in order to contain the pump light inside an outer-extent radius of the inner cladding, and wherein the cores each have a diameter of about 40 microns or more and maintain a single transverse mode in each of the plurality of cores.

11. A method comprising:

providing a first photonic-crystal device that includes a first waveguide having a diameter of about 40 microns or more; and

optically amplifying light in the first waveguide in a single transverse mode to a peak power of about 1 MW or more.

23. The method of claim 11, wherein the first photonic-crystal device further includes a second waveguide that has a diameter of about 40 microns or more and which extends alongside the first waveguide along a substantially lengthwise direction of the first waveguide;

the method further comprising

optically amplifying light in the second waveguide with a single transverse mode.

25. The method of claim 11, wherein the first optical device is a first photonic-crystal fiber and the first waveguide is a first core of the first photonic-crystal fiber, wherein the first photonic-crystal fiber further includes a plurality of other cores arranged side-by-side generally along a straight line transverse to a length of the first fiber, wherein the fiber includes an inner pump cladding surrounding the plurality of cores and an outer cladding surrounding the inner cladding, and wherein the cores each have a diameter of about 40 microns or more, the method further comprising maintaining a single transverse mode in each of the plurality of cores;

providing pump light into the inner pump cladding surrounding the cores in order to provide pump light into the cores over a length of the fiber; and

containing the pump light inside an outer-extent radius of the inner cladding.

12. A method comprising:

providing a first photonic-crystal device that includes a first waveguide having a diameter of about 40 microns or more;

optically amplifying light in the first waveguide in a single transverse mode to a peak power of about 1 MW or more; and

converting high-peak-power light having a first wavelength from the first waveguide of the first photonic-crystal device to generate light having a peak power of about 100 kW or more of a shorter second wavelength through non-linear wavelength conversion.

13. The method of claim 12, wherein the second-wavelength radiation includes visible light having a wavelength between about 400 nm and about 700 nm.

14. The method of claim 12, wherein the second-wavelength radiation includes ultraviolet light having a wavelength of about 400 nm or shorter.

15. A method comprising:

providing a first photonic-crystal device that includes a first waveguide having a diameter of about 40 microns or more; and

optically amplifying light in the first waveguide in a single transverse mode to a peak power of about 1 MW or more,

wherein the first core of the first photonic-crystal device supports a mode area having a diameter of about 50 microns or larger and has a cladding having a diameter of about 1000 microns or larger.

16. A method comprising:

providing a first photonic-crystal device that includes a first waveguide having a diameter of about 40 microns or more; and

optically amplifying light in the first waveguide in a single transverse mode to a peak power of about 1 MW or more, wherein the first optical device is a first photonic-crystal fiber and the first waveguide is a first core of the first photonic-crystal device;

generating a narrow-linewidth seed-laser signal;

optically isolating the narrow-linewidth seed-laser signal;

narrow-bandwidth filtering the narrow-linewidth seed-laser signal; and

amplifying the isolated filtered narrow-linewidth seed-laser signal using the first waveguide of the first photonic-crystal device.

17. The method of claim 16, the generating of the narrow-linewidth seed-laser signal further comprising:

generating an original seed-laser signal;

optically isolating the original seed-laser signal;

narrow-bandwidth filtering the original seed-laser signal;

providing a second photonic-crystal fiber optical amplifier having a core; and

amplifying the isolated filtered original seed-laser signal using the core of the second photonic-crystal fiber, wherein the second photonic-crystal fiber outputs the narrow-linewidth seed-laser signal.

18. The method of claim 16, wherein the first waveguide of the provided first photonic-crystal device is surrounded by a plurality of longitudinal holes that define a transverse extent of the first waveguide, the method further comprising:

closing the holes for a first length at a first end of the first photonic-crystal fiber to form an endcap.

19. The method of claim 18, wherein the closing of the holes of the first waveguide of the first photonic-crystal fiber comprises melting the holes shut for the first length.

20. The method of claim 18, wherein the closing of the holes of the first waveguide of the first photonic-crystal fiber comprises filling the holes with an index-matching material for the first length.

21. The method of claim 18, wherein the first optical device is a first photonic-crystal fiber and the first waveguide is a first core of the first photonic-crystal device, the method further comprising:

forming the endcap of the first photonic-crystal fiber to a diameter smaller than a diameter of the first fiber away from the endcap, and

forming a facet at an end of the endcap of the first fiber.

22. The method of claim 21, further comprising

providing a third photonic-crystal fiber;

forming an endcap on an end of the third fiber to a diameter smaller than a diameter of the third fiber away from the endcap;

forming a facet at an end of the endcap of the third fiber; and

placing the endcap of the first fiber side-by-side to the endcap of the third fiber such that the end facet of the first fiber and the end facet of the second fiber are placed at a center-to-center distance smaller than the diameter of the first fiber away from the endcap of the first fiber.

24. A method comprising:

providing a first photonic-crystal device that includes a first waveguide having a diameter of about 40 microns or more; and

optically amplifying light in the first waveguide in a single transverse mode to a peak power of about 1 MW or more,

wherein the first photonic-crystal fiber further includes a plurality of other waveguides that each have a diameter of about 40 microns or more;

the method further comprising

maintaining a single transverse mode in each of the plurality of waveguides.

38. An apparatus comprising:

a first photonic-crystal optical device that includes a first waveguide that has a diameter of about 40 microns or more within a pump cladding and maintains a single transverse mode with operation at a peak power of at least about one megawatt (1 MW) and a beam quality M² of less than 1.5, further comprising beam-expanding endcaps.

39. An apparatus comprising:

a first photonic-crystal optical device that includes a first waveguide that has a diameter of about 40 microns or more within a pump cladding and maintains a single transverse mode with operation at a peak power of at least about one megawatt (1 MW) and a beam quality M² of less than 1.5, and

means for passing pulses of one megawatt (1 MW) out of the first photonic-crystal optical device.