Experimental study on the impact of signal bandwidth on the transverse mode instability threshold of fiber amplifiers

Abstract

In this work, we conduct a detailed experimental study on the impact of signal bandwidth on the TMI threshold of fiber amplifiers. Both the filtered superfluorescent fiber sources and the phase-modulated single-frequency lasers are employed to construct seed lasers with different 3 dB spectral linewidths ranging from 0.19 nm to 7.97 nm. The TMI threshold of the fiber amplifier employing those seed lasers are estimated through the intensity evolution of the signal laser, and different criteria have been utilized to characterize the spectral linewidth of the seed lasers. Notably, the experimental results reveal that the TMI threshold of fiber amplifiers grows, keeps constant, and further grows as a function of spectral linewidth of seed lasers. Our experimental results could provide a well reference to understand the mechanism of the TMI effect and optimize the TMI effect in high-power fiber amplifiers.

Transverse mode instability mitigation in a high-power confined-doped fiber amplifier with good beam quality through seed laser control

“…However, in the current study, the impact of the seed laser's power seems very significant. Since the TMI threshold could be affected by a series of factors, such as: a. the seed laser power [32,33]; b. the temporal stability/noise of the seed laser [34]; c. the linewidth of the seed laser [35]; d. the mode purity of the seed laser [10], in order to find the dominant influencing factor, comparative investigations are systematically carried out.…”

New avenues for high-power high-brightness tandem-pumped fiber lasers

“…Narrow linewidth fiber lasers are greatly demanded in many applications, including coherent/spectral beam combination, nonlinear frequency conversion, etc. However, the power scaling of narrow linewidth fiber lasers is more challenging than its broadband counterpart owing to the SBS effect and the lower TMI threshold [48]. Previously, by comprehensively suppressing these detrimental effects, the output power of the LD-pumped narrow-linewidth fiber laser has reached ~5 kW using active fiber with a core diameter of 20/25 μm, where further power scaling was limited by the SRS and TMI effect [39,49].…”

Six kilowatt record all-fiberized and narrow-linewidth fiber amplifier with near-diffraction-limited beam quality

“…Nevertheless, the power scaling of narrow-linewidth fiber lasers always lags behind that of broad-linewidth fiber lasers [ 12 – 17 ] , because extra design is required to maintain narrow-linewidth operation. Furthermore, recent experimental results reveal that narrower signal bandwidth generally means a lower TMI threshold for the same fiber amplifier [ 18 ] . Accordingly, compared to broad-linewidth fiber amplifiers, the TMI effect is a more critical issue in designing high-power narrow-linewidth fiber amplifiers.…”