Large-mode-area fibers operating near singlemode regime Fanting Kong,* Christopher Dunn, Joshua Parsons, Monica T. Kalichevsky-Dong, Thomas W. Hawkins, Maxwell Jones, and Liang Dong ECE/COMSET, Clemson University, AMRL Building, 91 Technology Drive, Anderson, South Carolina 29625, USA *
[email protected]
Abstract: Lower NA in large-mode-area fibers enables better single-mode operation and larger core diameters. Fiber NA has traditionally been limited to 0.06, mostly due to the control tolerance in the fabrication process. It has been recognized recently that transverse mode instability is a major limit to average power scaling in fiber lasers. One effective method to mitigate this limit is to operate nearer to the single-mode regime. Lower fiber NA is critical in this since it allows relatively larger core diameters which is the key to mitigate the limits imposed by nonlinear effects. We have developed a fabrication process of ytterbium-doped silica glass which is capable of highly accurate refractive index control and sufficient uniformity for LMA fibers. This process is also capable of large-volume production. It is based on a significant amount of post-processing once the fiber preforms are made. We have demonstrated 30/400 and 40/400 LMA fibers with a NA of ~0.028 operating very close to the single-mode regime. The second-order mode cuts off at ~1.2μm and ~1.55µm respectively. We have also studied issues related to bend losses due to the low NA and further optimization of LMA fibers. ©2016 Optical Society of America OCIS codes: (060.2280) Fiber design and fabrication; (060.3510) Lasers, fiber; (140.3615) Lasers, ytterbium.
References and links 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
M. E. Fermann, “Single-mode excitation of multimode fibers with ultrashort pulses,” Opt. Lett. 23(1), 52–54 (1998). J. P. Koplow, D. A. V. Kliner, and L. Goldberg, “Single-mode operation of a coiled multimode fiber amplifier,” Opt. Lett. 25(7), 442–444 (2000). “Laser Marketplace 2015,” Laser Focus World (2015). D. Larcombe, “Fiber versus CO2 laser cutting,” Industrial Laser Solutions, November 2013. T. Eidam, S. Hanf, E. Seise, T. V. Andersen, T. Gabler, C. Wirth, T. Schreiber, J. Limpert, and A. Tünnermann, “Femtosecond fiber CPA system emitting 830 W average output power,” Opt. Lett. 35(2), 94–96 (2010). A. V. Smith and J. J. Smith, “Mode instability in high power fiber amplifiers,” Opt. Express 19(11), 10180– 10192 (2011). B. Ward, C. Robin, and I. Dajani, “Origin of thermal modal instabilities in large mode area fiber amplifiers,” Opt. Express 20(10), 11407–11422 (2012). K. R. Hansen, T. T. Alkeskjold, J. Broeng, and J. Lægsgaard, “Thermally induced mode coupling in rare-earth doped fiber amplifiers,” Opt. Lett. 37(12), 2382–2384 (2012). L. Dong, “Stimulated thermal Rayleigh scattering in optical fibers,” Opt. Express 21(3), 2642–2656 (2013). V. Khitrov, J. D. Minelly, R. Tumminelli, V. Petit, and E. S. Pooler, “3kw single-mode direct diode pumped fiber laser,” Proc. SPIE 8961, 89610V (2014). V. Fomin, M. Abramov, A. Ferin, A. Abramov, D. Mochalov, N. Platonov, and V. Gapontsev, “10 kW singlemode fiber laser,” in 5th International Symposium on High-Power Fiber Lasers and Their Applications, St. Petersburg, June 28-July 1, (2010). K. Brar, M. Savage-Leuchs, J. Henrie, S. Courtney, C. Dilley, R. Afzal, and E. Honea, “Threshold power and fiber degradation induced modal instabilities in high power fiber amplifiers based on large mode area fibers,” Proc. SPIE 8961, 89611R (2014). C. Hupel, S. Kuhn, S. Hein, N. Haarlammert, J. Nold, F. Beier, B. Sattler, T. Schreiber, R. Eberhardt, and A. Tünnermann, “MCVD Based Fabrication of Low-NA Fibers for High Power Fiber Laser Application,” in Advanced Solid State Lasers, OSA Technical Digest (online) (Optical Society of America, 2015), paper AM4A.2.
#260150 © 2016 OSA
Received 1 Mar 2016; revised 22 Apr 2016; accepted 22 Apr 2016; published 3 May 2016 16 May 2016 | Vol. 24, No. 10 | DOI:10.1364/OE.24.010295 | OPTICS EXPRESS 10295
14. D. Jain, Y. Jung, P. Barua, S. Alam, and J. K. Sahu, “Demonstration of ultra-low NA rare-earth doped step index fiber for applications in high power fiber lasers,” Opt. Express 23(6), 7407–7415 (2015). 15. V. Petit, R. P. Tumminelli, J. D. Minelly, and V. Khitrov, “Extremely low NA Yb doped preforms (