Build up and decay of mode instability in a high power fiber amplifier

Haarlammert, Nicoletta; Vries, Oliver de; Liem, A.; Kliner, A.; Peschel, Thomas; Thomas, Sabu; Eberhardt, Ramona; Tünnermann, Andreas

doi:10.1364/oe.20.013274

Cited by 61 publications

(41 citation statements)

References 14 publications

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“…The sudden degradation from 94% to 90% above 1.2kW was caused by MI while the slowly degradation of PER as lasing power increases may be caused by the temperature increase of the fiber. An InGaAs photo detector (150 MHz, 700-1800 nm, Thorlabs) with a pinhole of 1.5mm diameter was put in the center of the collimated beam to monitor the onset of MI [10,11,19]. Time traces at different output power are shown in Fig.…”

Section: Experimental Setup and Resultsmentioning

confidence: 99%

13 kW monolithic linearly polarized single-mode master oscillator power amplifier and strategies for mitigating mode instabilities

Tao¹,

Ma²,

Wang³

et al. 2015

Photon. Res.

111

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Abstract:We report on the high power amplification of 1064nm linearlypolarized laser in all-fiber polarization-maintained MOPA, which can operate at output power level of 1.3kW. The main amplifier was pumped with six 915nm laser diodes, and the slope efficiency is 65.3%. The beam quality (M 2 ) was measured to be <1.2 at full power operation. The polarization extinction rate of the fiber amplifier was measured to be above 94% before mode instabilities (MI) sets in, which reduced to about 90% after the onset of MI. Power scaling capability of strategies for suppressing MI is analyzed based on a novel semi-analytical model, the theoretical results of which agree with the experimental results. It shows that mitigating MI by coiling the gain fiber is an effective and practical way in standard double-cladding large mode area fiber, and, by tight coiling of the gain fiber to the radius of 5.5cm, the MI threshold can be increased to 3 times higher than that without coiling or loose coiling. Experimental study has been carried out to verify the idea, which has proved that MI was suppressed successfully in the amplifier by tight coiling.

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Section: Experimental Setup and Resultsmentioning

confidence: 99%

13 kW monolithic linearly polarized single-mode master oscillator power amplifier and strategies for mitigating mode instabilities

Tao¹,

Ma²,

Wang³

et al. 2015

Photon. Res.

111

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“…In recent years modal instabilities (MI) have been reported in a number of high power fiber lasers and amplifiers, typically manifested as a sharp power threshold for the onset of higher order mode output with degraded beam quality and pointing stability [1][2][3][4]. A number of descriptions and models have been proposed to explain these Threshold Power Modal Instabilities (TPMI) in Large Mode Area (LMA) fibers [5][6][7][8][9] along with experimental evidence of the role of thermal effects [10,11]. Of particular interest is in refining our understanding of TPMI and in particular how TPMI vary with fiber properties and thermal properties.…”

Section: Introductionmentioning

confidence: 99%

Threshold power and fiber degradation induced modal instabilities in high-power fiber amplifiers based on large mode area fibers

et al. 2014

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We report on two types of modal instabilities observed in high power Yb amplifiers based on Large Mode Area Fibers. The first is observed to occur at a Threshold Power, which we refer to as Threshold Power Modal Instabilities (TPMI). The modal instability is observed as a decrease in beam quality or reduced core light output as higher order modes leak into the fiber cladding. In PM 25/400 fiber amplifiers, we observe the threshold for the modal instability to vary depending on pump wavelength detuning, with the onset occurring at approximately 15 W/m peak heat load. In PM 20/400 and 25/400 fiber amplifiers without stress rods or other polarization control, we can achieve 1 kW output, limited by available pump power, without modal instabilities. The second type of modal instability is observed for certain cases where the fiber initially operates without any sign of MI but then degrades over an extended operating time, leading to a similar behavior as the TPMI. We refer to the second class as Fiber Degradation Modal Instabilities (FDMI). For these degraded fibers, we observe that fiber performance is unchanged below the critical power for modal instabilities. Experiments on degraded fiber show a wavelength dependent permanent change in the degraded fiber with a memory of the original operating wavelength.

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“…4 shown, the beam quality factor was measured to be ∼1.732 and ∼1.779 in the x and y directions, respectively, for the laser beam with >5000 W laser power using a beam profile analyzer (M2-200S, Ophir Photonics) based on 4-sigma method; near diffraction-limited beam quality was achieved. Mode instability is a phenomenon of beam quality degradation for high power fiber laser systems [16], [17]. The >5000 W laser beam was monitored and no mode instability was observed.…”

Section: -Kw Near-diffraction-limited Cw Monolithic Fiber Lasermentioning

confidence: 99%

5 kW Near-Diffraction-Limited and 8 kW High-Brightness Monolithic Continuous Wave Fiber Lasers Directly Pumped by Laser Diodes

Fang

Shi

et al. 2017

IEEE Photonics J.

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Tandem pumping technique are traditionally adopted to develop >3-kW continuous-wave (cw) Yb 3+ -doped fiber lasers, which are usually pumped by other fiber lasers at shorter wavelengths (1018 nm e.g.). Fiber lasers directly pumped by laser diodes have higher wall-plug efficiency and are more compact. Here we report two high brightness monolithic cw fiber laser sources at 1080 nm. Both lasers consist of a cw fiber laser oscillator and one laser-diode pumped double cladding fiber amplifier in the master oscillator-power amplifier configuration. One laser, using 30-µm-core Yb 3+ -doped fiber as the gain medium, can produce >5-kW average laser power with near diffraction-limited beam quality (M 2 <1.8). The slope efficiency of the fiber amplifier with respect to the launched pump power reached 86.5%. The other laser utilized 50-µm-core Yb 3+ -doped fiber as the gain medium and produced >8-kW average laser power with high beam quality (M 2 : ∼ 4). The slope efficiency of the fiber amplifier with respect to the launched pump power reach 83%. To the best of our knowledge, this is the first detailed report for >5-kW near-diffraction-limited and >8-kW high-brightness monolithic fiber lasers directly pumped by laser diodes.

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Build up and decay of mode instability in a high power fiber amplifier

Cited by 61 publications

References 14 publications

13 kW monolithic linearly polarized single-mode master oscillator power amplifier and strategies for mitigating mode instabilities

13 kW monolithic linearly polarized single-mode master oscillator power amplifier and strategies for mitigating mode instabilities

Threshold power and fiber degradation induced modal instabilities in high-power fiber amplifiers based on large mode area fibers

5 kW Near-Diffraction-Limited and 8 kW High-Brightness Monolithic Continuous Wave Fiber Lasers Directly Pumped by Laser Diodes

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