Origin and evolution of phase-shifts in high-power fiber laser systems: detailed insights into TMI

Cesar Jauregui; Christoph Stihler; Andreas Tünnermann; Jens Limpert

doi:10.1117/12.2508854

7 March 2019 Origin and evolution of phase-shifts in high-power fiber laser systems: detailed insights into TMI

Cesar Jauregui, Christoph Stihler, Andreas Tünnermann, Jens Limpert

Proceedings Volume 10897, Fiber Lasers XVI: Technology and Systems; 1089704 (2019) https://doi.org/10.1117/12.2508854
Event: SPIE LASE, 2019, San Francisco, California, United States

Abstract

In this work, we study the generation and evolution of phase-shifts between the modal interference pattern and the thermally-induced index grating due to pump-power changes. This study is not only important to understand new mitigation strategies based on controlling such phase-shifts, but also to comprehend how pump/signal noise can trigger TMI. Understanding how such a phase-shift can develop from a pump/signal change is not trivial, since the movement of both the MIP and the RIG are thermally driven and, therefore, should have similar time constants. Our simulations show unequivocally that a change of the pump power will lead to the generation of a phase-shift and the physical reason for this behavior is unveiled. The main reason is an increased sensitivity of the MIP to temperature variations because the local beat-length changes of the MIP are accumulated along the whole fiber length. Therefore, the further downstream the fiber a MIP maximum is (i.e. closer to the pump end in a counter-pumped configuration), the stronger and faster its position shift will be. This insight shows a way to obtain more TMI-resilient fiber designs and may help understanding the core area dependence of TMI.

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Cesar Jauregui, Christoph Stihler, Andreas Tünnermann, and Jens Limpert "Origin and evolution of phase-shifts in high-power fiber laser systems: detailed insights into TMI", Proc. SPIE 10897, Fiber Lasers XVI: Technology and Systems, 1089704 (7 March 2019); https://doi.org/10.1117/12.2508854

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KEYWORDS

Phase shifts

Laser systems engineering

Energy transfer

High power fiber lasers

Fiber lasers

Refractive index

Frequency modulation

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