Helical fiber amplifier

• US 6,496,301 B1
• Filed: 03/10/2000
• Issued: 12/17/2002
• Est. Priority Date: 03/10/2000
• Status: Expired due to Term

• Current Assignee: National Technology & Engineering Solutions Of Sandia LLC (Honeywell International Inc.), The United States of America As Represented By The Secretary of Agriculture, The United States of America Represented by The Department of Veterans Affairs
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Koplow, Jeffrey P., Kliner, Dahy, Goldberg, Lew
• Primary Examiner(s): Moskowitz, Nelson
• Application Number:
  US09/523,215
• Time in Patent Office: 1,012 Days
• Field of Search: 357/337, 357/341, 357/885, 357/337.1, 357/337.2, 357/341.1, 385/1, 385/104
• US Class Current: 359/337
• CPC Class Codes: G02B 6/03622 having 2 layers only
• CPC Class Codes: G02B 6/14 Mode converters
• CPC Class Codes: G02B 6/4214 the intermediate optical element having redirecting reflective means, e.g. mirrors, prisms for deflecting the radiation from horizontal to down- or upward direction toward a device G02B6/4246 takes precedence
• CPC Class Codes: H01S 3/06704 Housings; Packages
• CPC Class Codes: H01S 3/06712 Polarising fibre; Polariser
• CPC Class Codes: H01S 3/06729 Peculiar transverse fibre profile
• CPC Class Codes: H01S 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/08045 Single-mode emission

Abstract

A multi-mode gain fiber is provided which affords substantial improvements in the maximum pulse energy, peak power handling capabilities, average output power, and/or pumping efficiency of fiber amplifier and laser sources while maintaining good beam quality (comparable to that of a conventional single-mode fiber source). These benefits are realized by coiling the multimode gain fiber to induce significant bend loss for all but the lowest-order mode(s).

Claims

1. A multimode fiber amplifier system providing discrimination between a fundamental mode and undesired higher-order modes, said amplifier system comprising:

a light source for producing a light beam, and

a linear multimode fiber amplifier for receiving said light beam and comprising a multimode doped optical fiber having a V-number equal to or higher than 4 with respect to an input signal, capable of supporting a fundamental mode and higher-order modes, having a radius of curvature such that the higher-order modes of said input signal experience substantially increased bend losses as compared with the fundamental mode of said input signal.

2. An amplifier system according to claim 1 wherein said fiber comprises a coiled fiber.

3. An amplifier system according to claim 2 wherein said coiled fiber has a constant radius of curvature.

4. An amplifier system according to claim 2 wherein said coiled fiber has a non-constant radius of curvature.

5. An amplifier system according to claim 1 wherein said light source comprises a continuous wave light source.

6. An amplifier system according to claim 1 wherein said light source comprises a pulsed light source.

7. An amplifier system according to claim 1 wherein said multimode optical fiber comprises a double-cladding structure.

8. An amplifier system according to claim 1 wherein said multimode optical fiber comprises a core having a diameter of between 3 microns and 100 microns.

9. An amplifier system according to claim 1, further comprising a first mandrel and a second mandrel, wherein said first mandrel has a vertically extending longitudinal axis and second mandrel has a horizontally extending longitudinal axis, and wherein said multimode optical fiber is wound respectively onto each of said first and second mandrels.

10. An amplifier system according to claim 1 wherein said multimode fiber amplifier has an M² value less than 1.2, where M²=1 denotes diffraction-limited beam quality.

11. An amplifier system according to claim 1 wherein the fiber amplifier is side pumped.

12. A linear multimode fiber amplifier comprising:

a cylindrical support member, and

a doped multimode optical fiber having a V-number equal to or higher than 4 with respect to an input signal, capable of supporting a fundamental mode and a plurality of higher-order modes, said fiber being wound onto said support with a radius such that said higher-order modes of said input signal experience substantially increased bend loss as compared with the fundamental mode of said input signal.

13. An amplifier system according to claim 12 wherein said wound fiber has a constant radius of curvature.

14. An amplifier system according to claim 12 wherein said wound fiber has a non-constant radius of curvature.

15. A multimode fiber amplifier according to claim 12 wherein said multimode optical fiber comprises a double-cladding structure.

16. A multimode fiber amplifier according to claim 12 wherein said multimode optical fiber comprises a core having a diameter of between 3 μ

m and 100 μ

m.

17. A multimode fiber amplifier according to claim 12 wherein said multimode fiber amplifier has an M² value less than 1.2, where M²=1 denotes diffraction-limited beam quality.

18. A multimode fiber amplifier according to claim 12 further comprising a second cylindrical support member having a diameter about equal to that of the first-mentioned cylindrical support member, and said second support member having a longitudinal axis extending perpendicular to that of said first support member, and wherein a portion of said fiber is wound onto said second support member.

19. An amplifier system as in claim 12, wherein each of said first and second mandrels is of a comparable radius and wherein a length of fiber wound onto each said mandrel is comparable.

20. An amplifier system as in claim 12, further comprising a seed beam having a controlled launch condition for preferential excitation of the fundamental mode.