To suppress high order modes and improve the beam quality, an active self-imaging mode filter based on multimode interference and self-imaging effect is proposed in large mode area (LMA) fiber amplifier. With this filter structure, transverse mode competition and individual transverse mode power distributions in strongly pumped fiber amplifiers are theoretically demonstrated. Employing this mode selection technique in 30/400 LMA strongly pumped fiber amplifier, the percentage of the fundamental mode rises from 27.8% (without filter) to 96.3%. By the modal power decomposition, the M² parameter of beam quality decrease dramatically from 2.24 to 1.11 (0 relative phase) and from 3.01 to 1.24 (π/2 relative phase). This study provides a new method to achieve single mode in LMA fiber amplifier and this filter would be extended to larger mode area fiber amplifier to improve the beam quality.

Date Published: 24 October 2017
PDF: 7 pages
Proc. SPIE 10457, AOPC 2017: Laser Components, Systems, and Applications, 104572Q (24 October 2017); doi: 10.1117/12.2284934

Published in SPIE Proceedings Vol. 10457:
AOPC 2017: Laser Components, Systems, and Applications
Shibin Jiang; Lijun Wang; Lan Jiang; Long Zhang, Editor(s)