BEAM DIAGNOSTICS AND FEEDBACK SYSTEM AND METHOD FOR SPECTRALLY BEAM-COMBINED LASERS

• US 20110249692A1
• Filed: 04/12/2011
• Published: 10/13/2011
• Est. Priority Date: 04/12/2010
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Madasamy, Pratheepan, Jander, Donald R., Honea, Eric C., Yilmaz, Tolga
• Granted Patent: US 8,411,712 B2
• Time in Patent Office: Days
• US Class Current: 372/29.011
• 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 6/32 having lens focusing means positioned between opposed fibre ends with lens being an integral part of the single fibre end G02B6/262
• 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 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/06783 Amplifying coupler
• CPC Class Codes: H01S 3/1001 by controlling the optical pumping
• CPC Class Codes: H01S 3/10015 by monitoring or controlling, e.g. attenuating, the input signal
• CPC Class Codes: H01S 3/1305 Feedback control systems

Abstract

Apparatus and method for control of lasers (which use an array of optical gain fibers) in order to improve spectrally beam-combined (SBC) laser beam quality along the plane of the SBC fiber array via spectral-to-spatial mapping of a portion of the spectrally beam-combined laser beams, detection of optical power in each of the spatially dispersed beams and feedback control of the lasers for wavelength-drift correction. The apparatus includes a diffractive element; a source of a plurality of substantially monochromatic light beams directed from different angles to a single location on the diffractive element, wherein the diffractive element spectrally combines the plurality of light beams into a single beam. A controller adjusts characteristics of the light beams if one of the light beams has become misadjusted. In some embodiments, the controller adjusts the wavelength tuning of the respective fiber laser.

Claims

1. An apparatus comprising:

an output diffractive element;

a source of a plurality of substantially monochromatic light beams directed from different angles to a single location on the output diffractive element, wherein the output diffractive element spectrally combines the plurality of light beams into a single beam, and wherein the plurality of light beams includes a first light beam having a first central wavelength and a second light beam having a second central wavelength different than the first central wavelength;

a first adjustment apparatus configured to set an adjustable characteristic of the first light beam;

a second adjustment apparatus configured to set an adjustable characteristic of the second light beam;

a detector configured to detect whether one of the light beams has become misadjusted, wherein the detector includes a plurality of light sensors and an imaging device that focuses the plurality of light beams onto the plurality of light sensors;

a diagnoser operatively connected to receive signals from the plurality of light sensors configured to determine whether the first light beam is the misadjusted one and if so, to control the first adjustment apparatus to adjust the adjustable characteristic of the first light beam in order that the first light beam becomes aligned relative to the single combined beam.

2. The apparatus of claim 1, wherein the source of a plurality of light beams includes a plurality of master-oscillator power-amplifier (MOPA) fiber lasers, each having a master-oscillator seed laser and a power amplifier, each seed laser tuned to a different wavelength.

3. The apparatus of claim 2, wherein the plurality of light sensors sense light from the seed lasers of the plurality of MOPA fiber lasers before that light is amplified by the power amplifiers of the plurality of MOPA fiber lasers.

4. The apparatus of claim 1, wherein the detector includes a diagnostic diffractive element configured to spatially separate a portion of the light from the plurality of substantially monochromatic light beams that was combined by the output diffractive element.

5. The apparatus of claim 1, further comprising a focussing mirror, wherein the source of the plurality of substantially monochromatic light beams includes a plurality of fiber lasers that emit light from an array of endcaps toward the focussing mirror, and wherein the focussing mirror collimates each one of the plurality of substantially monochromatic light beams into a substantially parallel beam of light that is non-parallel to the collimated light of the other ones of the plurality of substantially monochromatic light beams, such that the plurality of collimated substantially monochromatic light beams converge at different angles to a single area of the output diffractive element.

6. The apparatus of claim 1, further comprising a focussing mirror and an input diffractive element, and wherein the source of the plurality of substantially monochromatic light beams includes a plurality of fiber lasers that emit light from an array of endcaps toward the focussing mirror, and wherein the focussing mirror collimates each one of the plurality of substantially monochromatic light beams into a substantially parallel beam of light that is substantially parallel to the collimated light of the other ones of the plurality of substantially monochromatic light beams, such that the plurality of collimated substantially monochromatic light beams impinge at equal angles onto the input diffractive element, and the input diffractive element diffracts each beam at a different angle such that the plurality of collimated substantially monochromatic light beams converge at different angles to a single area of the output diffractive element.

7. The apparatus of claim 1, wherein the detector includes a diagnostic diffractive element configured to spatially separate a portion of the light from the plurality of substantially monochromatic light beams that was combined by the output diffractive element, the apparatus further comprising a focussing mirror, and wherein the source of the plurality of substantially monochromatic light beams includes a plurality of fiber lasers that emit light from an array of endcaps toward the focussing mirror, and wherein the focussing mirror collimates each one of the plurality of substantially monochromatic light beams into a substantially parallel beam of light that is non-parallel to the collimated light of the other ones of the plurality of substantially monochromatic light beams, such that the plurality of collimated substantially monochromatic light beams converge at different angles to a single area of the output diffractive element.

8. A method comprising:

providing a plurality of fiber lasers that generate laser beams at a plurality of substantially monochromatic light wavelengths including a first fiber that generates a first laser beam at a first wavelength and a second fiber that generates a second laser beam at a second wavelength;

spectrally combining the plurality of laser beams into a single output beam;

setting an adjustable characteristic of the first fiber to generate the first laser beam at a first wavelength;

setting an adjustable characteristic of the second fiber to generate the second laser beam at a second wavelength;

detecting that one of the laser beams has become misadjusted relative to the single combined beam;

determining that the first laser beam is the misadjusted one; and

changing the adjustable characteristic of the first fiber in order that the first laser beam is improved relative to the single combined beam.

9. The method of claim 8, wherein the plurality of fiber lasers includes a plurality of master-oscillator power-amplifier (MOPA) fiber lasers, each having a master-oscillator seed laser and a power amplifier, each seed laser tuned to a different wavelength.

10. The method of claim 9, wherein detecting that one of the laser beams has become misadjusted relative to the single combined beam includes sensing light from the seed lasers of the plurality of MOPA fiber lasers before that light is amplified by the power amplifiers of the plurality of MOPA fiber lasers.

11. The method of claim 8, wherein the detecting that one of the laser beams has become misadjusted relative to the single combined beam includes diffracting to spatially separate a portion of the light from the single output beam into a spatially separated plurality of substantially monochromatic diagnostic light beams.

12. The method of claim 8, further comprising:

providing an output diffractive element,

wherein the spectrally combining of the plurality of laser beams into the single output beam further comprises;

emitting light from an array of endcaps of the plurality of fiber lasers; and

reflectively focussing and collimating each one of the plurality of substantially monochromatic laser beams into a substantially parallel beam of light that is non-parallel to the collimated light of the other ones of the plurality of substantially monochromatic light beams, such that the plurality of collimated substantially monochromatic light beams converge at different angles to a single area of the output diffractive element.

13. The method of claim 8, further comprising:

providing an input diffractive element and an output diffractive element,

wherein the spectrally combining of the plurality of laser beams into the single output beam further comprises;

emitting light from an array of endcaps of the plurality of fiber lasers;

reflectively focussing and collimating each one of the plurality of substantially monochromatic laser beams into a substantially parallel beam of light that is substantially parallel to the collimated light of the other ones of the plurality of substantially monochromatic light beams, such that the plurality of collimated substantially monochromatic light beams impinge at equal angles onto the input diffractive element; and

diffracting each beam at a different angle from the input diffractive element such that the plurality of collimated substantially monochromatic light beams converge at different angles onto a single area of the output diffractive element.

14. The method of claim 8, further comprising:

providing a diagnostic diffractive element and an output diffractive element,

wherein the spectrally combining of the plurality of laser beams into the single output beam further comprises reflectively focussing and collimating each one of the plurality of substantially monochromatic laser beams into a substantially parallel beam of light that is non-parallel to the collimated light of the other ones of the plurality of substantially monochromatic light beams, such that the plurality of collimated substantially monochromatic light beams converge at different angles to a single area of the output diffractive element; and

wherein the detecting that one of the laser beams has become misadjusted relative to the single combined beam further comprises using the diagnostic diffractive element, spatially separating a portion of the light from the plurality of substantially monochromatic light beams that was combined by the output diffractive element.

15. An apparatus comprising:

a plurality of fiber lasers that generate laser beams at a plurality of substantially monochromatic light wavelengths including a first fiber that generates a first laser beam at a first wavelength and a second fiber that generates a second laser beam at a second wavelength;

means for spectrally combining the plurality of laser beams into a single output beam;

means for setting an adjustable characteristic of the first fiber to generate the first laser beam at a first wavelength;

means for setting an adjustable characteristic of the second fiber to generate the second laser beam at a second wavelength;

means for detecting that one of the laser beams has become misadjusted relative to the single combined beam;

means for determining that the first laser beam is the misadjusted one; and

means for changing the adjustable characteristic of the first fiber in order that the first laser beam is improved relative to the single combined beam.

16. The apparatus of claim 15, wherein the plurality of fiber lasers includes a plurality of master-oscillator power-amplifier (MOPA) fiber lasers, each having a master-oscillator seed laser and a power amplifier, each seed laser tuned to a different wavelength.

17. The apparatus of claim 16, wherein the means for detecting that one of the laser beams has become misadjusted relative to the single combined beam includes means for diffracting to spatially separate a portion of the light from the single output beam into a spatially separated plurality of substantially monochromatic diagnostic light beams.

18. The apparatus of claim 15, wherein the means for detecting that one of the laser beams has become misadjusted relative to the single combined beam includes means for diffracting to spatially separate a portion of the single output beam into a spatially separated plurality of substantially monochromatic diagnostic light beams.

19. The apparatus of claim 15, further comprising:

an output diffractive element,

wherein the means for spectrally combining of the plurality of laser beams into the single output beam further comprises;

means for emitting light from an array of endcaps of the plurality of fiber lasers; and

means for reflectively focussing and collimating each one of the plurality of substantially monochromatic laser beams into a substantially parallel beam of light that is non-parallel to the collimated light of the other ones of the plurality of substantially monochromatic light beams, such that the plurality of collimated substantially monochromatic light beams converge at different angles to a single area of the output diffractive element.

20. The apparatus of claim 15, further comprising:

an output diffractive element,

wherein the means for spectrally combining of the plurality of laser beams into the single output beam further comprises reflectively focussing and collimating each one of the plurality of substantially monochromatic laser beams into a substantially parallel beam of light that is non-parallel to the collimated light of the other ones of the plurality of substantially monochromatic light beams, such that the plurality of collimated substantially monochromatic light beams converge at different angles to a single area of the output diffractive element; and

wherein the means for detecting that one of the laser beams has become misadjusted relative to the single combined beam further comprises means for spatially separating a portion of the light from the plurality of substantially monochromatic light beams that was combined by the output diffractive element.