A time-dependent analytical model is rigorously derived which shows that the thermally induced modal instability in high power rare-earth doped fiber amplifiers is fundamentally a two-wave mixing between fundamental and higher-order modes through a thermally-induced grating imprinted by beating between these modes. We show that previously postulated movement of this grating to phase-match the coupling between the modes naturally occurs due to a finite thermal-response time of a fiber. This theory is consistent with experimental observations in that it accurately predicts the onset-like threshold and temporal instabilities in the kilohertz-frequency range.

Date Published: 22 March 2013
PDF: 9 pages
Proc. SPIE 8601, Fiber Lasers X: Technology, Systems, and Applications, 860109 (22 March 2013); doi: 10.1117/12.2002732

Published in SPIE Proceedings Vol. 8601:
Fiber Lasers X: Technology, Systems, and Applications
Sami T. Hendow, Editor(s)