Pre-compensation of thermally induced refractive index changes in a depressed core Fully-Aperiodic Large-Pitch-Fiber for high average power operation

Marie-Alicia Malleville (1) , Baptiste Leconte (1) , Romain Dauliat (1) , Raphaël Jamier (1) , Anka Schwuchow (2) , Katrin Wondraczek (2) , Philippe ROY (1)

1 XLIM-PHOT - Photonique Fibre et Sources Cohérentes
2 Leibniz IPHT - Leibniz Institute of Photonic Technology

To prevent the thermally induced spatial beam degradation occurring in high-power fibre lasers and amplifiers, a depressed core "Fully Aperiodic Large-Pitch Fibers" (FA-LPFs) has been designed and fabricated. In contrast to standard LPF structure, in which the active core and the surrounding cladding material are index-matched, the core refractive index is in slight depression comparing to the surrounding material (∆n≈-3×10-5). Thus, the indexdepressed fibre core tends first to behave as an anti-guide, preventing light from being properly guided into it. However, by increasing the pump power coupled in the fiber, the thermal load induces a parabolic refractive index change sufficient to exceed the-3×10-5 index depression in the core, enabling a robust single-mode amplification at high average power. As a proof of concept, M² values of 1.3 were demonstrated in an amplifier configuration from 60 W of emitted power to a maximal value of 170 W only limited by the available pump power.

Domaines: Sciences de l'ingénieur [physics]; Physique [physics]

Marie-Alicia Malleville, Baptiste Leconte, Romain Dauliat, Raphaël Jamier, Anka Schwuchow, et al.. Pre-compensation of thermally induced refractive index changes in a depressed core Fully-Aperiodic Large-Pitch-Fiber for high average power operation. Optics Letters, 2021, ⟨10.1364/OL.424743⟩. ⟨hal-03857919⟩