V.E. Ustimchik - Ph.D. (Phys.-Math.), Junior Research Scientist, Kotelnikov IRE RAS (Moscow). E-mail: ustimchikv@gmail.com Yu.K. Chamorovskii - Ph.D. (Phys.-Math.), Leading Research Scientist, Kotelnikov IRE RAS (Moscow) V.N. Filippov - Ph.D. (Phys.-Math.), Research Scientist, Optoelectronic Research Center, Tampere University of Technology (Finland) K.M. Golant - Dr.Sc. (Phys.-Math.), Senior Research Scientist, Kotelnikov IRE RAS (Moscow) S.A. Nikitov - Dr.Sc. (Phys.-Math.), Director, Head of Laboratory, Kotelnikov IRE RAS (Moscow)

We consider mode instability in both irregular tapered and regular cylindrical double-clad Yb-doped optical fibers. Appearance of mode instability was investigated experimentally in linear CW-laser scheme based on each type of fibers. Comparison of experimental results shows that mode instability occurs with much less output power in regular fibers.

 

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