ALL-FIBER INTEGRATED HIGH POWER COHERENT BEAM COMBINATION

• US 20110032602A1
• Filed: 08/07/2009
• Published: 02/10/2011
• Est. Priority Date: 08/07/2009
• Status: Active Grant

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Space & Mission Systems Corporation (Northrop Grumman Corporation)
• Inventors: Rothenberg, Joshua Elliott
• Granted Patent: US 8,184,363 B2
• Time in Patent Office: Days
• US Class Current: 359/341.1
• CPC Class Codes: G02B 6/02042 Multicore optical fibres
• CPC Class Codes: G02B 6/04 formed by bundles of fibres G02B6/24 takes precedence
• 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 3/005 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 3/06729 Peculiar transverse fibre profile
• 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 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/082 defining a plurality of resonators, e.g. for mode selection or suppression
• CPC Class Codes: H01S 3/1003 tunable optical elements, e.g. acousto-optic filters, tunable gratings
• CPC Class Codes: H01S 3/1307 Stabilisation of the phase
• CPC Class Codes: H01S 3/2308 Amplifier arrangements, e.g. MOPA
• CPC Class Codes: H01S 3/2383 Parallel arrangements
• CPC Class Codes: H01S 3/2391 emitting at different wavelengths

Abstract

A fiber laser amplifier system including a master oscillator that generates a signal beam. A splitter splits the signal beam into a plurality of fiber beams where a separate fiber beam is sent to a fiber amplifier for amplifying the fiber beam. A tapered fiber bundle couples all of the output ends of all of the fiber amplifiers into a combined fiber providing a combined output beam. An end cap is optically coupled to an output end of the tapered fiber bundle to expand the output beam.

Claims

1. A fiber amplifier system comprising:

a master oscillator generating a signal beam;

a splitter splitting the signal beam into a plurality of fiber beams;

a plurality of phase modulators each receiving one of the fiber beams, said phase modulators providing phase modulation;

a plurality of fiber amplifiers each receiving a fiber beam from one of the phase modulators, said fiber amplifiers amplifying the fiber beam, said fiber amplifiers each including an output end;

a tapered fiber bundle including an input end and an output end, said input end being coupled to the output end of all of the fiber amplifiers, said output end of the tapered fiber bundle being a combined fiber including portions of all of the fiber amplifiers with fiber cores in a single fiber mass, said tapered fiber bundle outputting a combined output beam;

an end cap optically coupled to the output end of the taper fiber bundle, said end cap expanding the output beam from the tapered fiber bundle; and

a beam sampler for sampling a portion of the output beam from the end cap and providing a sample beam.

2. The system according to claim 1 further comprising a phase detector and a synchronous phase processor, said phase detector detecting the phase of the fiber beams in the sample beam and providing phase measurement signals to the phase processor, said phase processor controlling the phase modulators to control the optical phase of the fiber beams in the fiber amplifiers in response to the phase measurement signals.

3. The system according to claim 2 wherein the phase detector detects the phase of the fiber beams by detecting a unique dither on the fiber beams in phase or amplitude using distinct frequencies for frequency modulation or amplitude modulation or a distinct code for code division multiple access or time division multiple access.

4. The system according to claim 1 further comprising a polarization detector, a synchronous polarization processor and a plurality of polarization controllers each receiving one of the fiber beams, said polarization detector detecting the polarization of the fiber beams in the sample beam and providing polarization measurement error signals to the polarization processor, said polarization processor controlling the polarization controllers to control the polarization of the fiber beams in the fiber amplifiers in response to the polarization measurement error signals to make the orientation of the polarization of the fiber beams the same.

5. The system according to claim 4 wherein the polarization detector detects the polarization of the fiber beams by detecting a unique dither on the fiber beams in phase or amplitude using distinct frequencies for frequency modulation or amplitude modulation or a distinct code for code division multiple access or time division multiple access.

6. The system according to claim 1 further comprising a collimating and magnifying telescope receiving the output beam from the end cap before the beam sampler, said collimating and magnifying telescope expanding and collimating the output beam.

7. The system according to claim 1 wherein the tapered fiber bundle includes a plurality of coreless cladding fibers positioned around the fiber amplifiers.

8. The system according to claim 1 wherein the tapered fiber bundle includes a low index of refraction glass tube provided around the fiber amplifiers.

9. The system according to claim 1 wherein the fiber amplifiers are coupled together into a multi-core fiber where each fiber in the multi-core fiber includes an air cladding layer, said multi-core fiber being chemically etched at one end to separate constituent fibers, and where the individual fiber amplifiers are coupled to the multi-core fiber by splices to said constituent fibers, and the other end of said multi-core fiber is tapered to form the tapered fiber bundle.

10. The system according to claim 1 wherein the end cap includes a negative gradient index lens and a uniform glass rod optically coupled together where the negative gradient index lens is coupled to the output end of the tapered fiber bundle.

11. The system according to claim 1 wherein the end cap includes an anti-reflective coating provided on an output end of the end cap and a positive gradient index lens coupled to an output end of the end cap or a positive lens formed by a curved surface at an output end of the end cap.

12. The system according to claim 11 wherein the positive lens is part of a collimating and magnifying telescope.

13. The system according to claim 1 wherein a face of the end cap is curved to form a surface lens.

14. A fiber amplifier system comprising:

a master oscillator generating a signal beam;

a splitter splitting the signal beam into a plurality of fiber beams;

a plurality of phase modulators each receiving one of the fiber beams, said phase modulators providing phase modulation;

a plurality of polarization controllers each receiving one of the fiber beams, said polarization controllers providing polarization orientation control;

a plurality of fiber amplifiers each receiving a fiber beam after the phase modulator and polarization controller, said fiber amplifiers amplifying the fiber beam, said fiber amplifiers each including an output end;

a tapered fiber bundle including an input end and an output end, said input end being coupled to the output end of all of the fiber amplifiers, said output end of the tapered fiber bundle being a combined fiber including portions of all of the fiber amplifiers with fiber cores in a single fiber mass, said tapered fiber bundle outputting a combined output beam;

an end cap optically coupled to the output end of the tapered fiber bundle, said end cap expanding the output beam from the tapered fiber bundle;

a beam sampler for sampling a portion of the output beam from the end cap and providing a sample beam;

a polarization detector detecting the polarization in the fiber beams in the sample beam and providing polarization error measurement signals;

a synchronous polarization processor receiving the polarization error measurement signals and controlling the polarization controllers to control the orientation of the polarization of the fiber beams in the fiber amplifiers in response to the polarization measurement signals; and

a collimating and magnifying telescope receiving the output beam from the end cap before the beam sampler, said collimating and magnifying telescope expanding and collimating the output beam.

15. The system according to claim 14 wherein the tapered fiber bundle includes a plurality of coreless cladding fibers positioned around the fiber amplifiers.

16. The system according to claim 14 wherein the tapered fiber bundle includes a low index of refraction glass tube provided around the fiber amplfiers.

17. The system according to claim 14 wherein the fiber amplifiers are coupled together into a multi-core fiber where each fiber in the multi-core fiber includes an air cladding layer, said multi-core fiber being chemically etched at one end to separate constituent fibers, and where the individual fiber amplifiers are coupled to the multi-core fiber by splices to said constituent fibers, and the other end of said multi-core fiber is tapered to form the tapered fiber bundle.

18. The system according to claim 14 wherein the polarization detector detects the polarization of the fiber beams by detecting a unique dither on the fiber beams in phase or amplitude using distinct frequencies for frequency modulation or amplitude modulation or a distinct code for code division multiple access or time division multiple access.

19. The system according to claim 14 further comprising a phase detector and a synchronous phase processor, said phase detector detecting the phase of the fiber beams in the sample beam and providing phase measurement signals to the phase processor, said phase processor controlling the phase modulators to control the optical phase of the fiber beams in the fiber amplifiers in response to the phase measurement signals.

20. The system according to claim 19 wherein the phase detector detects the phase of the fiber beams by detecting a unique dither on the fiber beams in phase or amplitude using distinct frequencies for frequency modulation or amplitude modulation or a distinct code for code division multiple access or time division multiple access.