We present a simple semianalytical model of thermally induced mode coupling in multimode rare-earth doped fiber amplifiers. The model predicts that power can be transferred from the fundamental mode to a higher-order mode when the operating power exceeds a certain threshold, and thus provides an explanation of recently reported mode instability in such fiber amplifiers under high average-power operation. We apply our model to a simple step-index fiber design, and investigate how the power threshold depends on various design parameters of the fiber.
© 2012 Optical Society of America
Fiber Optics and Optical Communications
Original Manuscript: February 29, 2012
Revised Manuscript: May 22, 2012
Published: June 12, 2012
Kristian Rymann Hansen, Thomas Tanggaard Alkeskjold, Jes Broeng, and Jesper Lægsgaard, "Thermally induced mode coupling in rare-earth doped fiber amplifiers," Opt. Lett. 37, 2382-2384 (2012)