Mode Instabilities in High-Power Fiber-Laser

Fiber lasers are well known for their power scalability, robustness and high efficiency [1]. Nevertheless, the performance of pulsed fiber lasers is hindered by nonlinear effects, which degrade the pulse quality. The most beneficial approach to overcome these limitations is mode field area scaling. State of the art fiber laser systems use main amplifiers with 80 µm mode field diameter in a few-mode regime (see subfigure c to get an impression of the size of very large mode area fibers exemplified by the large-pitch fiber (LPF) ) [2]. However, by pushing the limits for the occurrence of unwanted nonlinear effects to higher average output power levels, a new limiting effect becomes observable for the first time (the intensity profile below the threshold is shown in figure a and above threshold is shown in figure b ) [3]. This effect is related to a rapid degradation of the beam quality after a specific average output power level is reached. At the same time, the former stable beam profile starts to fluctuate and several fiber higher order modes can be excited for a short period (a time series of the intensity evolution at four different times is shown in figure d) [4,5]. Thus, the effect is called mode instabilities. The scope of this project is to study in great detail the effect of mode instabilities with the goal to understand, to explain and finally to develop mitigation strategies.


  1. D. J. Richardson, J. Nilsson, and W. A. Clarkson, “High power fiber lasers: current status and future perspectives,“ J. Opt. Soc. Am. B 27, B63-B92 (2010).
  2. J. Limpert, F. Stutzki, F. Jansen, H.-J. Otto, T. Eidam, C. Jauregui, and A. Tünnermann, "Yb-doped large-pitch fibres: effective single-mode operation based on higher-order mode delocalisation," Light: Science & Applications 1, e8 (2012).
  3. T. Eidam, C. Wirth, C. Jauregui, F. Stutzki, F. Jansen, H.-J. Otto, O. Schmidt, T. Schreiber, J. Limpert, and A. Tünnermann, "Experimental observations of the threshold-like onset of mode instabilities in high power fiber amplifiers.," Optics express 19, 13218–24 (2011).
  4. C. Jauregui, T. Eidam, H. Otto, F. Stutzki, F. Jansen, J. Limpert, and A. Tünnermann, "Physical origin of mode instabilities in high- power fiber laser systems," Optics Express 20, 10180–10192 (2012).
  5. H.-J. Otto, F. Stutzki, F. Jansen, T. Eidam, C. Jauregui, J. Limpert, A. Tünnermann, and H. Jena, "Temporal dynamics of mode instabilities in high- power fiber lasers and amplifiers," 20, 10180–10192 (2012).