The impact of core size scaling on the transverse mode instability threshold in fiber laser amplifiers

Kholaif, Sobhy; Bahri, Mehran; Klenke, Arno; Jáuregui, César; Nold, Johannes; Haarlammert, Nicoletta; Kühn, Stefan; Thomas, Sabu; Limpert, Jens

doi:10.1117/12.2651074

Cited by 4 publications

(1 citation statement)

References 8 publications

(8 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A comparison of the measured mode field diameters with the simulated ones based on the measured dimensions of the fibers proves a high accuracy of the refractive index match between core and cladding of <1E-5. The fiber was tested in a high power amplifier setup and showed excellent laser performance with single mode beam quality which was reported earlier [4]. Powers up to 570W could be extracted.…”

Section: Manufacturing Of Precisly Index-matched Large Pitch Fibersmentioning

confidence: 56%

High-precision adjustment of the refractive Index in high-power laser fibers

Haarlammert,

Nold,

Palma-Vega

et al. 2024

Fiber Lasers XXI: Technology and Systems

Self Cite

View full text Add to dashboard Cite

A manufacturing chain that revolutionizes the production of fibers with highly precise refractive index matching is presented. By integrating iterative refractive index adjustments using reference fibers, a remarkable improvement in homogeneity, reaching 1E-5, was achieved. Conventional methods, such as the MCVD process, are limited to ~1E-4. This enhanced precision was demonstrated through meticulous measurements of core materials and validated in the final fiber. Importantly, the presented manufacturing method considers that the refractive index of fused silica is not a fixed property of the material. It depends on the thermal treatment history and the exact conditions during fiber drawing. This breakthrough manufacturing process ensures the reproducible manufacturing of fibers with fundamental mode guiding properties and mode field diameters exceeding 100µm. These specialized fibers play a pivotal role in scaling the power of fiber lasers for ultrashort pulse applications.

show abstract

Section: Manufacturing Of Precisly Index-matched Large Pitch Fibersmentioning

confidence: 56%

High-precision adjustment of the refractive Index in high-power laser fibers

Haarlammert,

Nold,

Palma-Vega

et al. 2024

Fiber Lasers XXI: Technology and Systems

Self Cite

View full text Add to dashboard Cite

show abstract

Theory of transverse mode instability in fiber amplifiers with multimode excitations

Wisal,

Chen,

Cao

et al. 2024

APL Photonics

View full text Add to dashboard Cite

Transverse Mode Instability (TMI) that results from dynamic nonlinear thermo-optical scattering is the primary limitation to power scaling in high-power fiber lasers and amplifiers. It has been proposed that TMI can be suppressed by exciting multiple modes in a highly multimode fiber. We derive a semi-analytic frequency-domain theory of the threshold for the onset of TMI in narrowband fiber amplifiers under arbitrary multimode input excitation for general fiber geometries. Our detailed model includes the effect of gain saturation, pump depletion, and mode-dependent gain. We show that TMI results from the exponential growth of noise in all the modes at downshifted frequencies due to the thermo-optical coupling. The noise growth rate in each mode is given by the sum of signal powers in various modes weighted by pairwise thermo-optical coupling coefficients. We calculate thermo-optical coupling coefficients for all ∼104 pairs of modes in a standard circular multimode fiber and show that modes with large transverse spatial frequency mismatch are weakly coupled, resulting in a banded coupling matrix. This short-range behavior is due to the diffusive nature of the heat propagation, which mediates the coupling and leads to a lower noise growth rate upon multimode excitation compared to a single mode, resulting in significant TMI suppression. We find that the TMI threshold scales linearly with the number of modes that are excited asymptotically, leading to roughly an order of magnitude increase in the TMI threshold in an 82-mode fiber amplifier.

show abstract

Impact of thermal lensing on the TMI threshold powers in rod-type Yb-doped fiber amplifiers

Mermelstein

2024

Appl. Opt.

View full text Add to dashboard Cite

The impact of thermal lensing (TL) on the transverse mode instability (TMI) threshold power in rod-type fiber amplifiers is investigated. Simulations are conducted with a 3D coupled mode analysis on a set of five scaled large pitch fiber (LPF) amplifiers. The LPF fibers are represented by surrogate step-index fibers (SIFs) with scaled cladding diameters, core diameters, and numerical apertures for a fixed normalized frequency V equal to 3.0 and scaled modal field overlap integrals with the core and cladding. It is found that thermal lensing decreases the TMI threshold powers due to increases in the TMI nonlinear gain. This gain increase is attributed to an increase in the nonlinear gain overlap integrals that occurs with the reduction in the fundamental mode effective area. Estimates for the TMI threshold power are in good agreement with measurements; however, the simulations overestimate the mode shrinkage factor. This discrepancy is tentatively attributed to the representation of the LPF by an effective SIF. These results may offer opportunities for fiber designs that increase the TMI threshold powers.

show abstract

The impact of core size scaling on the transverse mode instability threshold in fiber laser amplifiers

Cited by 4 publications

References 8 publications

High-precision adjustment of the refractive Index in high-power laser fibers

High-precision adjustment of the refractive Index in high-power laser fibers

Theory of transverse mode instability in fiber amplifiers with multimode excitations

Impact of thermal lensing on the TMI threshold powers in rod-type Yb-doped fiber amplifiers

Contact Info

Product

Resources

About