Bettina Sattler

Bio: Bettina Sattler is an academic researcher from Fraunhofer Society. The author has contributed to research in topics: Single-mode optical fiber & Fiber. The author has an hindex of 7, co-authored 15 publications receiving 303 citations.

Single mode 4.3 kW output power from a diode-pumped Yb-doped fiber amplifier.

Abstract: We investigate the average power scaling of two diode-pumped Yb-doped fiber amplifiers emitting a diffraction-limited beam. The first fiber under investigation with a core diameter of 30 µm was able to amplify a 10 W narrow linewidth seed laser up to 2.8 kW average output power before the onset of transverse mode instabilities (TMI). A further power scaling was achieved using a second fiber with a smaller core size (23µm), which allowed for a narrow linewidth output power of 3.5 kW limited by stimulated Brillouin scattering (SBS). We mitigated SBS using a spectral broadening mechanism, which allowed us to further increase the output power to 4.3 kW only limited by the available pump power. Up to this power level, a high slope efficiency of 90% with diffraction-limited beam quality and without any sign of TMI or stimulated Raman scattering for a spectral dynamic range of higher than -80 dB was obtained.

Narrow linewidth, single mode 3 kW average power from a directly diode pumped ytterbium-doped low NA fiber amplifier

Abstract: We report on a newly designed and fabricated ytterbium-doped large mode area fiber with an extremely low NA (~0.04) and related systematic investigations on fiber parameters that crucially influence the mode instability threshold. The fiber is used to demonstrate a narrow linewidth, continuous wave, single mode fiber laser amplifier emitting a maximum output power of 3 kW at a wavelength of 1070 nm without reaching the mode-instability threshold. A high slope efficiency of 90 %, excellent beam quality, high temporal stability, and an ASE suppression of 70 dB could be reached with a signal linewidth of only 170 pm.

Experimental investigations on the TMI thresholds of low-NA Yb-doped single-mode fibers

Abstract: In this contribution we investigate the transversal mode instability behavior of a ytterbium-doped commercial 20/400 fiber and obtain 2.9 kW of output power after optimizing the influencing parameters. In this context, we evaluate the influence of the bend diameter and the pump wavelength within the scope of the absorption length and the length of the fiber. Furthermore, with a newly developed fiber we report on 4.4 kW of single-mode output power at 40 cm bend diameter.

Optimizing mode instability in low-NA fibers by passive strategies.

Abstract: Systematic experimental investigations toward the mode instability (MI) threshold in low-NA fibers are performed. By testing several fibers with varying V-parameters drawn from the same preform, a high degree of reproducibility of the experimental conditions could be achieved. This allows for systematic investigations on isolated parameters influencing the complex behavior of MI. A maximum MI threshold of 2 kW could be demonstrated for the tested fibers, which represents a new record output power for narrow linewidth fiber amplifiers. The MI threshold was found to sensitively depend on the V-parameter for large V-parameters (>2), but to be robust for smaller V-parameters. Furthermore, the fiber bending diameter and the seed excitation conditions were identified to sensitively influence the MI threshold.

Measuring thermal load in fiber amplifiers in the presence of transversal mode instabilities.

Abstract: We report on detailed in situ distributed temperature measurements inside a high power fiber amplifier. The deducted thermal load and the transversal mode instability (TMI) threshold of a commercial large mode area fiber with 25 μm core and 400 μm cladding were measured at various seed wavelengths. By matching these results with detailed simulations we show that photodarkening has a negligible impact on the thermal load and, therefore, on the TMI threshold in this fiber.

Single mode 4.3 kW output power from a diode-pumped Yb-doped fiber amplifier.

Abstract: We investigate the average power scaling of two diode-pumped Yb-doped fiber amplifiers emitting a diffraction-limited beam. The first fiber under investigation with a core diameter of 30 µm was able to amplify a 10 W narrow linewidth seed laser up to 2.8 kW average output power before the onset of transverse mode instabilities (TMI). A further power scaling was achieved using a second fiber with a smaller core size (23µm), which allowed for a narrow linewidth output power of 3.5 kW limited by stimulated Brillouin scattering (SBS). We mitigated SBS using a spectral broadening mechanism, which allowed us to further increase the output power to 4.3 kW only limited by the available pump power. Up to this power level, a high slope efficiency of 90% with diffraction-limited beam quality and without any sign of TMI or stimulated Raman scattering for a spectral dynamic range of higher than -80 dB was obtained.

Materials for optical fiber lasers: A review

Abstract: Over the past two decades, fiber laser technologies have matured to such an extent that they have captured a large portion of the commercial laser marketplace. Yet, there still is a seemingly unquenchable thirst for ever greater optical power to levels where certain deleterious light-matter interactions that limit continued power scaling become significant. In the past decade or so, the industry has focused mainly on waveguide engineering to overcome many of these hurdles. However, there is an emerging body of work emphasizing the enabling role of the material. In an effort to underpin these developments, this paper reviews the relevance of the material in high power fiber laser technologies. As the durable material-of-choice for the application, the discussion will mainly be limited to silicate host glasses. The discussion presented herein follows an outward path, starting with the trivalent rare earth ions and their spectroscopic properties. The ion then is placed into a host, whose impact on the spectroscopy is reviewed. Finally, adverse interactions between the laser lightwave and the host are discussed, and novel composition glass fiber design and fabrication methodologies are presented. With deference to the symbiosis required between material and waveguide engineering in active fiber development, this review will emphasize the former. Specifically, where appropriate, materials-based paths to the enhancement of laser performance will be underscored.

Transverse mode instability

Abstract: This work presents a review on the effect of transverse mode instability in high-power fiber laser systems and the corresponding investigations led worldwide over the past decade. This paper includes a description of the experimental observations and the physical origin of this effect, as well as some of the proposed mitigation strategies.

High power fibre lasers

Abstract: Recent progress in the development of high power fibre lasers will be reviewed, and the prospects for scaling output powers to well beyond the hundred watt level, whilst maintaining diffraction-limited beam quality will be discussed

1.89 kW all-fiberized and polarization-maintained amplifiers with narrow linewidth and near-diffraction-limited beam quality.

Abstract: In this manuscript, we demonstrate high power, all-fiberized and polarization-maintained amplifiers with narrow linewidth and near-diffraction-limited beam quality by simultaneously suppressing detrimental stimulated Brillouin scattering (SBS) and mode instability (MI) effects. Compared with strictly single frequency amplification, the SBS threshold is scaled up to 12 dB, 15.4 dB, and higher than 18 dB by subsequently using three-stage cascaded phase modulation systems. Output powers of 477 W, 1040 W, and 1890 W are achieved with full widths at half maximums (FWHMs) of within 6 GHz, ~18.5 GHz, and ~45 GHz, respectively. The MI threshold is increased from ~738 W to 1890 W by coiling the active fiber in the main amplifier. Both the polarization extinction ratio (PER) and beam quality (M2 factor) are maintained well during the power scaling process. To the best of our knowledge, this is the first demonstration of all-fiberized amplifiers with narrow linewidth, near linear polarization, and near-diffraction-limited beam quality at 2 kW power-level.