Modal instability of rod fiber amplifiers: a semi-analytic approach

Mette Marie Jørgensen, Kristian Rymann Hansen, Marko Laurila, Thomas Tanggaard Alkeskjold, Jesper Lægsgaard

Research output: Contribution to journalConference articleResearchpeer-review


The modal instability (MI) threshold is estimated for four rod fiber designs by combining a semi-analytic model with the finite element method. The thermal load due to the quantum defect is calculated and used to numerically determine the mode distributions on which the expression for the onset of MIs is highly dependent. The relative intensity noise of the seed laser in an amplifier setup is used to seed the mode coupling between the fundamental and higher order mode, and lead to MI threshold values of 174 W – 348 W of extracted output power for the four rod fibers having core diameters in the range 53 μm – 95 μm.
Original languageEnglish
JournalProceedings of SPIE, the International Society for Optical Engineering
Pages (from-to)860123
Number of pages8
Publication statusPublished - 2013
EventSPIE Photonics West : Fiber Lasers X: Technology, Systems, and Applications: Technology, Systems, and Applications - San Francisco, CA, United States
Duration: 4 Feb 20137 Feb 2013
Conference number: 10


ConferenceSPIE Photonics West : Fiber Lasers X: Technology, Systems, and Applications
CountryUnited States
CitySan Francisco, CA


  • Fiber amplifiers
  • Modal instability
  • Microstructured fibers
  • High power amplifiers
  • Thermal effects

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