Axicons for mode conversion in high peak power, higher-order mode, fiber amplifiers

Optics Express
J W NicholsonD DiGiovanni

Abstract

Higher-order mode fiber amplifiers have demonstrated effective areas as large as 6000 μm<sup>2</sup>, allowing for high pulse energy and peak power amplification. Long-period gratings are used to convert the fundamental mode to the higher-order mode at the entrance to the amplifier, and reconvert back to the fundamental at the exit, to achieve a diffraction limited beam. However, long period gratings are susceptible to nonlinearity at high peak power. In this work, we propose and demonstrate axicons for linear bulk-optic mode conversion at the output of higher order mode amplifiers. We achieve an M<sup>2</sup> of less than 1.25 for 80% mode conversion efficiency. Experiments with pulsed amplifiers confirm that the mode conversion is free from nonlinearity. Furthermore, chirp pulse amplifier experiments confirm that HOM amplifiers plus axicon mode convertors provide energy scalability in femtosecond pulses, compared to smaller effective area, fundamental mode fiber amplifiers. We also propose and demonstrate a route towards fiber integration of the axicon mode convertor by fabricating axicons directly on the tip of the fiber amplifier end-cap.

References

May 27, 2006·Optics Letters·S RamachandranF V Dimarcello
Mar 7, 2007·Optics Letters·John M Fini, Siddharth Ramachandran
Aug 7, 2007·Applied Optics·Norbert LindleinSiddharth Ramachandran
Sep 4, 2007·Optics Letters·J W NicholsonC Headley
Feb 21, 2005·Optics Express·J LimpertC Jakobsen
Sep 18, 2010·Optics Letters·J W NicholsonD J DiGiovanni
Dec 6, 2011·Optics Letters·Paul SteinvurzelSiddharth Ramachandran
Nov 29, 2012·Optics Express·J W NicholsonD J DiGiovanni
Nov 29, 2012·Optics Express·Fanting KongLiang Dong
Feb 8, 2013·Optics Express·Deepak JainJayanta Kumar Sahu
Feb 12, 2014·Optics Express·Xiang PengDavid J Digiovanni
Jun 13, 2014·Optics Express·He HuangX Wu

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