We present a time dependent computer model for modal instabilities (MI) in high power fiber amplifiers based on beam propagation method. Three regimes of temporal dynamics that are characteristic of the transfer of energy between the fundamental mode and higher order mode are captured and applied to predicting the threshold of these instabilities in absence of any frequency offset between the interfering modes. Simulation results show an increase of the instabilities threshold by a factor of approximately %30 in the case of bi-directional pump scheme with respect to the forward pump configuration. Furthermore, we estimated the MI threshold applying a coupled-mode model of thermally induced instabilities which also takes account of gain saturation to its first order approximation, and obtained reasonably good agreement with respect to our beam propagation simulation results.

Date Published: 4 March 2015
PDF: 5 pages
Proc. SPIE 9344, Fiber Lasers XII: Technology, Systems, and Applications, 93442G (4 March 2015); doi: 10.1117/12.2080536

Published in SPIE Proceedings Vol. 9344:
Fiber Lasers XII: Technology, Systems, and Applications
L. Brandon Shaw, Editor(s)