Modal instability induced by stimulated Raman scattering in high-power Yb-doped fiber amplifiers

Hejaz, Kamran; Shayganmanesh, Mahdi; Rezaei-Nasirabad, Reza; Roohforouz, Ali; Azizi, Saeed; Abedinajafi, Ali; Vatani, Vahid

doi:10.1364/ol.42.005274

Cited by 58 publications

(27 citation statements)

References 16 publications

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“…The TMI emerges in this fiber oscillator may relate to the strong SRS effect, which is similar to the previous research in the fiber amplifier [18], [19]. As revealed in [19], with the increasing the intensity ratio of the Raman stokes light, the quantum defect between the signal light and the Raman light results in a thermally-induced refractive index grating, which may lead to the onset of TMI.…”

Section: Laser Performance With External Feedbacksupporting

confidence: 87%

“…We can see that the backward power in the fiber oscillator with external feedback is remarkably higher than that of the oscillator without external feedback, which indicates that a strong SRS effect in the fiber oscillator with the 4% facet reflection. According to the recent understanding of the relationship between the TMI and SRS effect in the fiber amplifier [18], [19], [22], the TMI will be triggered by the stronger Raman power inducing by the quantum defect from Raman power conversion. In the present of the external feedback, the SRS effect is stronger, and the Raman power is above 280 W near the TMI threshold.…”

Section: Discussionmentioning

confidence: 99%

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Experimental Study of 5-kW High-Stability Monolithic Fiber Laser Oscillator With or Without External Feedback

Shi

et al. 2019

IEEE Photonics J.

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In this paper, we construct a high power monolithic fiber laser oscillator based on a commercial ytterbium-doped fiber with core/inner cladding diameter of 25/400 µm. The output performances of the fiber oscillator are experimentally investigated in the conditions of either with or without an external feedback. In the presence of external feedback, a very strong stimulated Raman scattering (SRS) (∼9 dB below the signal light) emerges at the output power of ∼3.56 kW, where the onset of the transverse mode instability (TMI) limits further power scaling. By large angle cleaving the signal arm of the forward combiner to avoid external feedback, the maximum output power of 5.07 kW is achieved with no sign of TMI. The Raman stokes light is ∼35 dB below the signal light and the M 2 factor is measured to be ∼1.6. To directly characterize its power stability and engineering capability, the fiber oscillator is tested for continuous 5-h operation at ∼5.07 kW with power fluctuation less than 0.42%. During the test process, the output power, spectrum, beam quality, and temporal signal perform excellent stability. The experimental results reveal that thresholds of SRS and TMI strongly depend on the external feedback in high power fiber oscillators.

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Section: Laser Performance With External Feedbacksupporting

confidence: 87%

Section: Discussionmentioning

confidence: 99%

Experimental Study of 5-kW High-Stability Monolithic Fiber Laser Oscillator With or Without External Feedback

Shi

et al. 2019

IEEE Photonics J.

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“…noted that our simulation does not consider the stimulated Raman scattering effect, which may also result in the onset of the TMI [27] . This will be improved in our future work.…”

Section: Discussionmentioning

confidence: 99%

“…In order to solve the coupled-mode equations given by Equation (27), the pump power distribution along the active fiber as well as the signal gain is required. Therefore, we introduce the rate equation and the pump propagation equation as shown below: where A clad is the area of the inner cladding, σ e p , σ a p and Γ p are the emission/absorption cross section and filling factor for the pump light, respectively.…”

Section: Numerical Simulation Of the Ticll In Co-pumped Step-index 20mentioning

confidence: 99%

Numerical modeling of the thermally induced core laser leakage in high power co-pumped ytterbium doped fiber amplifier

Kong

Leng

Zhang

et al. 2018

High Pow Laser Sci Eng

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We propose a novel model to explain the physical process of the thermally induced core laser leakage (TICLL) effect in a high power co-pumped ytterbium doped fiber (YDF) amplifier. This model considers the thermally induced mode bending loss decrease and the thermally induced mode instability (TMI) in the coiled YDF, and is further used to reproduce the TICLL effect in the high power co-pumped step-index $20/400$ fiber amplifier. Besides, the TICLL effect in the co-pumping scheme and counter-pumping scheme is compared. The result proves that the TICLL effect is caused by the combined effect of the thermally induced mode bending loss decrease and the TMI, and could be mitigated by adopting the counter-pumping scheme. To our best knowledge, this is the first theoretical explanation of the TICLL effect in high power fiber amplifier.

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“…Then the system-based ones referred to shifting pump or signal wavelength [39], [47], changing the linewidth of the signal laser or pump laser [48], [49], controlling the excitation of mode content at injection end of the amplifier [22], adapting the cooling condition [20], [49], and so on. The recent research even disclosed that TMI was related to the occurrence of the nonlinear effects such as the stimulated Brillouin scattering (SBS) [50] and the stimulated Raman scattering (SRS) [51], [52], which provided new cognitions to suppress the TMI in terms of optimizing the system configuration to prevent the nonlinear effects. Furthermore, some latest in-depth research targeting the physical origin of the phase shift between the refractive index grating and the modes interference pattern has proven that the active control of the phase shift by the pump modulation was feasible to mitigate the TMI [30], [53].…”

Section: Introductionmentioning

confidence: 99%

Towards the Enhancement of the TMI Threshold in Monolithic High-Power Fiber System by Controlling the Pump Distribution and the Seed Power

Huang¹,

Tao²,

Shi³

et al. 2018

IEEE Photonics J.

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In recent years, the transverse mode instability (TMI) has been a main limiting factor of average power scalability of high-power fiber lasers with near-diffraction-limited beam quality. A number of strategies in experimental or theoretical scopes have been proposed to mitigate the TMI, especially in the bulk-optic systems. In this paper, the enhancement of the TMI threshold is to be systematically investigated in a monolithic high-power large-modearea (LMA) Yb-doped fiber laser system, by all-optical strategies including optimizing the pump distribution as well as adapting the seed power during operation. It is demonstrated that the TMI threshold can be dramatically increased under counter-pump and bi-directional pump regime compared with the co-pump regime. Further enhancement of the TMI threshold is achieved via optimizing the ratio of the forward pump power to the total pump power under bi-directional pump regime. As a result, a ∼3 kW TMI-free high-power output is realized. Moreover, the systematical study on the effect of the seed laser on the TMI threshold reveals a rising trend of the TMI threshold with the seed power increased. At the same time, a semi-analytical model considering both the gain saturation and the photo-darkening effect is set to theoretically analyze the TMI threshold, manifesting good agreements with the experimental data. This paper provides a valuable reference for the construction of monolithic high-power LMA fiber-based laser system in terms of effectively mitigating the TMI threshold.

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Modal instability induced by stimulated Raman scattering in high-power Yb-doped fiber amplifiers

Cited by 58 publications

References 16 publications

Experimental Study of 5-kW High-Stability Monolithic Fiber Laser Oscillator With or Without External Feedback

Experimental Study of 5-kW High-Stability Monolithic Fiber Laser Oscillator With or Without External Feedback

Numerical modeling of the thermally induced core laser leakage in high power co-pumped ytterbium doped fiber amplifier

Towards the Enhancement of the TMI Threshold in Monolithic High-Power Fiber System by Controlling the Pump Distribution and the Seed Power

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