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RISS 인기검색어
- 검색키워드
- 저자 : Johan Nilsson (검색결과 3 건)
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Multi-kilowatt Single-mode Ytterbium-doped Large-core Fiber Laser
정윤찬,Johan Nilsson,David N. Payne,Alexander J. Boyland,Jayanta K. Sahu,정승환 한국광학회 2009 Current Optics and Photonics Vol.13 No.4
We have demonstrated a highly efficient cladding-pumped ytterbium-doped fiber laser, generating >2.1 kW of continuous-wave output power at 1.1 μm with 74% slope efficiency with respect to launched pump power. The beam quality factor (M2) was better than 1.2. The maximum output power was only limited by available pump power, showing no evidence of roll-over even at the highest output power. We present data on how the beam quality depends on the fiber parameter, based on our current and past fiber laser developments. We also discuss the ultimate power-capability of our fiber in terms of thermal management, Raman nonlinear scattering, and material damage, and estimate it to 10 kW.
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Park Kyoungyoon,Harish Achar V.,Nilsson Johan,Jeong Yoonchan 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.80 No.1
We theoretically study stimulated Brillouin scattering (SBS) in a standard single-mode fiber (SMF), taking Brillouinenhanced four-wave-mixing (BEFWM) effects into account. In particular, we investigate the case when there is non-negligible back-reflection of the forward-pump field at the rear fiber end although such reflection is typically weak and undesired. We first justify that BEFWM can be treated as a steady-state process under an undepleted pump approximation as long as the nominal SBS gain remains as low as 40 dB unless the pump, Stokes, anti-Stokes fields interact under near-perfect phase-matching condition, which hardly happens in normal circumstances with a standard SMF. Under the steady-state and undepleted-pump condition, we find analytical solutions to the Stokes and anti-Stokes fields generated by the forward and backward-pump fields, and also derive their asymptotic formulae in both infinitesimal and infinite limits in terms of the phase-mismatch parameter of |ΔkL| , assuming that both seeding Stokes and anti-Stokes fields arise from white background noise components. When |ΔkL| ≪ 1 , the acoustic fields driven by SBS and BEFWM tend to interfere destructively, and thus, SBS and BEFWM are anti-resonant to each other, thereby eventually resulting in both Stokes and anti-Stokes scatterings minimized at Δk = 0 . When |ΔkL| ≫ 1 , all the asymptotic curves for the amplification ratios and extra gain factor obey the inverse square law with respect to |ΔkL| , irrespective of the level of the back-reflection at the rear fiber. In particular, when |ΔkL| is in the intermediate range where the FWM gain remains relatively large, SBS and BEFWM can be cooperative via the phase-pulling effect by the FWM gain, thereby leading to quasi-resonant growths of both Stokes and anti-Stokes fields. However, the extra gain by BEFWM reduces significantly if the level of the back-reflection remains below one percent, irrespective of the value of |ΔkL|. Since the interplay between SBS and BEFWM is inherently phase-dependent whilst it can still happen with white noise seeding with random phases, the related mechanism can further be exploited for all-optical switching functionality. We expect our theoretical modeling and formulation will be useful for designing and analyzing a variety of fiber systems that incorporate high-power narrow-linewidth light undergoing non-negligible back-reflection under various conditions.
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