CC BY
5Multimode-diode-pumped watt-level bismuth-doped fiber lasers
and amplifiers
S.V. Alyshev1*, M.A. Melkumov1, S.V. Firstov1
1-Prokhorov General Physics Institute of the Russian Academy of Sciences, Dianov Fiber Optics Research
Center, 38 Vavilov str., 119333 Moscow, Russia
Bismuth-doped laser-active fibers have come a long way since the first Bi-doped fiber laser was reported in 2005 [1]. The unique properties of these media allowed researchers to demonstrated lasers and optical amplifiers operating in a broad range starting from around 1270 nm and going up to 1775 nm. The next logical step in the development of the Bi-Doped Fiber Lasers and Amplifiers (BDFLs, BDFAs) would be the scaling up the output power, which goes hand in hand with the utilization of more powerful pump sources. This would necessitate the usage of multimode high aperture diodes, which only can be used if pumping into the cladding of a fiber is possible. The realization of cladding pumped Bi-doped devices is met with difficulties stemming from the fact that that the addition of Bi into the core leads not only to the creation of Bismuth-related active centers (BACs) but also to the increase of the background loss, which grows faster than linearly with the increase of the total Bi concentration. Thus, doping with Bi beyond a certain limit is counterproductive, and results in very inefficient devices. On the other hand, this meant that cladding absorption of pump radiation at wavelengths suitable for pumping in the metastable level, which had been utilised for core-pumped devices, would unlikely be at an acceptable level.
Those difficulties notwithstanding, the solution was found, which entailed the utilization of pumping into a higher-laying pump layer. This approach provides two advantages. First, the pump wavelengths conveniently fall into the 800-nm range, where high-power multimode diodes are commercially available. Secondly, the BACs' absorption at these wavelengths is much higher. These two factors allowed us to develop cladding pumped amplifiers, which at very least have performance on par with their core-pumped counterparts, while having slight improvements on noise performance due to the possibility of achieving higher inversion levels [2]. On the lasers side, it was also possible to achieve lasing, albeit, with very small efficiency. After optimization of inner cladding geometry, the efficiency of the lasers reached a level of 3 to 5% with the output power of 260 mW [3].
At the conference we are going to present our further improvements on the matter, which allowed us to reach 0.8 W (and more) of output power.
This work was supported by The Russian Science Foundation (Grant # 22-19-00708).
[1] E. Dianov, V. Dvoyrin, V. Mashinsky, A. Umnikov, M. Yashkov, A. Gur'yanov, CW bismuth fibre laser, Quantum Electron. 35(1), 10831084 (2005).
[2] A. Vakhrushev, A. Khegai, S. Alyshev, K. Riumkin, A. Kharakhordin, E. Firstova, A. Umnikov, A. Lobanov, F. Afanasiev, A. Guryanov, M. Melkumov, S. Firstov, Cladding pumped bismuth-doped fiber amplifiers operating in O-, E-, and S-telecom bands, Opt. Lett. 48, 13391342 (2023).
[3] A. Vakhrushev, Y. Ososkov, S. Alyshev, A. Khegai, A. Umnikov, F. Afanasiev, K. Riumkin, E. Firstova, A. Guryanov, M. Melkumov, S. Firstov, Output Power Saturation Effect in Cladding-Pumped Bismuth-Doped Fiber Lasers, Journal of Lightwave Technology, 41(2), 709715, (2023).
