Comparison of transverse mode instability in Yb, Tm and Ho doped bent high-power fiber amplifiers

Abstract

In this paper, the transverse mode instability of three different high power silica fiber amplifiers doped with rare earth ions, Ytterbium, Thulium and Holmium is compared. Mode instability in these amplifiers has been investigated using the normalizedpropagation constant model in straight and bent fibers. The behavior of three amplifiers with different signal and pump wavelengths, though with the same V-number, refractive index of cladding, core diameter, cladding diameter and the thermophysical constants, were analyzed. In this model, we investigated the role of fiber amplifiers parameters, and the result was higher mode instability threshold for Holmium amplifier, which used at lower frequency and for Thulium amplifier was lower mode instability threshold due to high quantum defect heating, in comparison with Ytterbium amplifier. Nevertheless, bending in Thulium and Holmium amplifiers with higher signal wavelength (in compare of Ytterbium), does not have significant effect on increasing the mode instability threshold. To analyze the effect of higher order modes on mode instability, we considered two different V-numbers in our simulations.