Abstract

The study on mode instability (MI) in the large-mode-area fiber is generating great interest regarding the high-power applications of fiber lasers. To the best of our knowledge, we have investigated for the first time the dynamics of the output beam from a kilowatt-level all-fiber amplifier based on the low-numerical-aperture (<0.04) step-index (SI) fiber before and after the onset of the MI, including the temporal dynamics and mode evolution. The temporal power fluctuations indicate three evolution stages apart from the onset threshold of the MI, defined as stable, transition, and chaotic regions. In addition, the mode decomposition technique is utilized to accurately observe and investigate the mode evolution and relevant modal content corresponding to the transition and chaotic regions in the SI fiber laser for the first time. According to the mode decomposition results, the reduction of the extracted power can be explained by the high bending loss of the high-order mode excited in the MI process. Finally, the difference of MI dynamics between the fiber lasers based on the SI fiber and rod-type photonic crystal fiber is discussed.

© 2017 Optical Society of America

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Supplementary Material (3)

NameDescription
» Visualization 1: MOV (5662 KB)      The video of near-field beam-profile under different output power recorded by the HSC is shown in Visualization 1.
» Visualization 2: MOV (2093 KB)      The variations of the measured and corresponding reconstructed beam profiles with the output power of 585 W and 800 Ware shown in Visualization 2 and Visualization 3 respectively.
» Visualization 3: MOV (2157 KB)      The variations of the measured and corresponding reconstructed beam profiles with the output power of 585 W and 800 Ware shown in Visualization 2 and Visualization 3 respectively.

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Equations (1)

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