Theoretical treatment of modal instability in high-power cladding-pumped Raman amplifiers

Naderi, Shadi; Dajani, Iyad; Grosek, Jacob; Madden, Timothy J.

doi:10.1117/12.2083038

Cited by 6 publications

(5 citation statements)

References 12 publications

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“…The maximal coupling frequency as a function of seed power has also been calculated in figure 10, and the curves corresponding to the cases without photodarkening have also been plotted for comparison. The photodarkening in the calculations is set to be the same as in figure (9). It reveals that the frequency detuning between the maximal coupling frequency with or without photodarkening increases as seed power increases, and then decreases, which is more obvious for fiber with a higher ratio of pump cladding diameter to core diameter, e.g.…”

Section: Theoretical Results With Photodarkeningmentioning

confidence: 99%

“…This often implies laser beams with near diffraction limited beam quality, the power scaling of which is currently hampered by the sudden onset of mode instabilities [4][5][6]. Mode instabilities in various fiber laser systems have been under extensive investigation during recent years [6][7][8][9][10][11], and considerable attention has been diverted to it by different research groups to investigate the physical mechanisms related to mode instabilities [12][13][14][15][16][17][18]. Several approaches to improve mode instability threshold have also been reported including dynamic mode excitation [19], tailoring the Yb-ion distribution [20,21], shifting the pump or signal wavelength [22][23][24][25][26], increasing the ratio of pump cladding diameter to core diameter [26,27], increasing the loss of high-order mode [28][29][30][31], employing different pump configurations [32][33][34][35], and so on.…”

Section: Introductionmentioning

confidence: 99%

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Seed power dependence of mode instabilities in high-power fiber amplifiers

Tao

Wang

Zhang

et al. 2017

J. Opt.

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Abstract:We use a semi-analytical model of stimulated thermal Rayleigh scattering to present theoretical study of seed power on mode instability with the presence of photodarkening. The behavior of mode instabilities as a function of seed power has been investigated. The nonlinear dependence of the threshold with lower seed powers is ascribed to the influence of gain saturation while the reduction behavior of the threshold with higher seed powers is put down to the effects of photodarkening, which agrees well with the experimental results. IntroductionMode instabilities have been under intense investigation during the past few years, and several research groups have carried out much work to investigate the underlying physical mechanisms [1,2]. So far a common agreement on the thermal origin of the mode instabilities has been achieved, while the required phase shift is still a subject of discussion. Essentially two different assumptions have been proposed in the literature, and models for both assumptions have been developed, which can be used to explain and predict the experiments [3][4][5]. However, the dependence of mode instabilities on the seed power, experimentally reported in Refs.[5] and [6], has not been explained or investigated in details from the perspective of the stimulated thermal Rayleigh scattering assumption. In this paper, based on a semi-analytical model of the stimulated thermal Rayleigh scattering, the behavior of threshold power and maximal coupling frequency as a function of seed power has also been investigated, and good agreement with experimental results has been achieved. Theoretical studyIn this section, we first study the threshold behavior as a function of seed power without considering the effects of photodarkening. To model mode instability thresholds and the maximal coupling frequency, we use our semianalytical STRS model (detailed in [7,8]). The co-pumped cladding pumped amplifiers are unbent, step-index fibers with uniform doping across the full core. We define threshold as the signal output or pump power at which LP 11 content reaches 5%. We assume that mode instabilities are induced by the quantum noise, which is a minimum seed level and yields the highest thresholds. Even though the simulations are exemplified for the particular case of the quantum noise induced mode instabilities, the qualitative behavior of the threshold will be similar for other cases [4,9,10]. The fiber parameters used are listed in Table 1. These parameters are typical of high power ytterbium doped amplifiers.

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Section: Theoretical Results With Photodarkeningmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Seed power dependence of mode instabilities in high-power fiber amplifiers

Tao

Wang

Zhang

et al. 2017

J. Opt.

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“…The underlying physical mechanism responsible for MI is generally thought to be a form of stimulated thermal Rayleigh scattering, which is widely employed in the theoretical study of MI [7,18,20,[22][23][24][25][26]. Based on the aforementioned physical principle, the coupled-mode equations for high order mode (HOM) (LP 11 in the article) near the threshold can be expressed as [13,17]…”

Section: Theoretical Model In Briefmentioning

confidence: 99%

Theoretical study of pump power distribution on modal instabilities in high power fiber amplifiers

Tao

Wang

et al. 2016

Laser Phys. Lett.

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Influence of pump power distribution on modal instabilities (MI) is studied numerically, which reveals that the MI threshold is dependent on the pump power distribution in fiber amplifiers and can be increased by optimizing the pump power distribution without any adjustment of other amplifier parameters. It shows that amplifiers with backward or bi-direction pump schemes have a higher threshold than those employing forward pump schemes. For backward pumped amplifiers employing fiber with core/clad diameter being 20/400 µm, the MI threshold yields a 42% increase compared to the forward pumped ones. For bi-direction pumped amplifiers, there exists an optimal power ratio between forward and backward pump power, which results in the highest threshold power. When amplifiers with core/clad diameter being 20/400 µm employ a bi-direction pump scheme at the optimal backward pump power fraction, the threshold can be increased by a factor of approximately 60% with respect to the forward pump configuration. The threshold increment factor reduces as the gain saturation effect weakens. It also shows that the MI threshold can be increased by employing multi-point side pump schemes.

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“…In the 2-kW amplifier, we found it challenging to remove the heat load generated in the coiled Raman fiber and pigtailed passive fiber of end cap, resulting in serious thermal effects in the RFA at high power level. The similar thermal-induced instability associated with SRS has also been studied by other research groups [43][44][45][46], which not only influence the stable output performance of laser, but also would ultimately limit the power scaling and BE in RFLs. Thus, the approaches to the more efficient thermal management in the high-power Raman laser is urged.…”

Section: Introductionmentioning

confidence: 87%

3 kW Passive-Gain-Enabled Metalized Raman Fiber Amplifier With Brightness Enhancement

Chen

Yao

et al. 2021

J. Lightwave Technol.

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Raman fiber lasers (RFLs) are currently promising and versatile light sources for a variety of applications. So far, operations of high power and brightness-enhanced RFLs have absorbed enormous interests along with rapid progress. Nevertheless, the stable Raman lasing at high power levels remains challenged by the thermal effects. In an effort to realize more effective thermal management in high power RFLs, here we demonstrate, for the first time, an all-fiberized RFA employing metal-coated passive fiber enabling high power lasing. By employing aluminum to the cladding of graded-index (GRIN) passive fiber, the thermal abstraction of the laser devices is more sufficient to support low-temperature operation. The maximum output power reaches 3.083 kW at 1130 nm with a conversion efficiency of 78.7%. To the best of our knowledge, this is the first Raman laser generation based on metal-coated passive fiber. Meanwhile, it is also the highest power attained in the fields of all kinds of Raman lasers based on merely nonlinear gain.

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Theoretical treatment of modal instability in high-power cladding-pumped Raman amplifiers

Cited by 6 publications

References 12 publications

Seed power dependence of mode instabilities in high-power fiber amplifiers

Seed power dependence of mode instabilities in high-power fiber amplifiers

Theoretical study of pump power distribution on modal instabilities in high power fiber amplifiers

3 kW Passive-Gain-Enabled Metalized Raman Fiber Amplifier With Brightness Enhancement

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