CC BY
20LS-I-4
LASER SYSTEMS AND MATERIALS
^l^.ALT'22
Recent Progress in Cladding-Pumped Bismuth-Doped Fiber Lasers and Amplifiers
Sergei V. Firstov*
Prokhorov General Physics Institute of the Russian Academy of Sciences, Dianov Fiber Optics Research Center, 38
Vavilov str., 119333 Moscow, Russia *E-mail:fir@fo.gpi.ru
Bismuth-doped fibers exhibit broadband amplification in the near IR range, where efficient active silica-based fibers are not available. Recently, a bismuth-doped laser (BDFL) at a wavelength of 1.46 ^m with a slope efficiency of 72% [1], compact [2] and broadband amplifiers (BDFAs) [3] in the O+E+S bands with very promising characteristics interested for telecom industry were developed using new types of bismuth-doped fibers. All the existing Bi-doped fiber devices are core-pumped that notably reduces potential for power scalability.
This report reviews recent progress in cladding-pumped BDFLs and BDFAs. In this regard, the output characteristics of a series of the BDFLs and BDFAs pumped into the active fiber cladding by multimode laser diodes operating at wavelengths of 793 and 808 nm are presented and discussed. The active media for these devices were Bi-doped phospho- and germanosilicate glass core fibers having a circular inner cladding coated by a polymer with low refractive index of 1.396 that allows to provide a light-guiding structure in the inner cladding. Developed BDFLs were assembled in a simple linear scheme consisting of a pump and signal combiner for coupling of pump radiation into the active fiber, a ~100%-reflection fiber Bragg grating and a right-cleaved fiber end as mirrors. A family of BDFAs for the O-, E-, S-telecom bands was implemented using various types of Bi-doped fibers. Length of the active fiber per a device varies in range of 80-200 m.
Input pump power, W Wavelength, nm
Fig. 1. (a) Output power of the clad-pumped BDFL at ~1360 nm versus the input pump power of 793 nm (inset: output emission spectrum); (b) gain spectrum of BDFA pumped into the cladding by multimode laser diodes at 793 nm with a summarized power of 15 W.
The slope efficiency of the clad-pumped BDFLs operating at a wavelength range of 1.3-1.5 ^m was 1-1.5% at a low power threshold of about 1 W. For instance, Fig. 1(a, inset) shows the output power and emission characteristics of the laser operating at ~1360 nm. Figure 1(b) shows the BDFA with a gain spectrum having a width of ~135 nm (at a -3 dB level), a peak gain of 28 dB, a flatness of ~1.5 dB. The minimum noise figure of the BDFA presented was lower than 7 dB.
The progress achieved in this direction opens up previously inaccessible possibilities of devices based on bismuth-doped fibers and their possible practical prospects.
This research was supported by the Russian Science Foundation (22-19-00708).
[1] A. S. Vakhrushev, et al.,W-type and Graded-index bismuth-doped fibers for efficient lasers and amplifiers operating in E-band, Opt. Express 30, pp. 1490-1498 (2022).
[2] S.V. Firstov, et al. Compact and efficient O-band bismuth-doped phosphosilicate fiber amplifier for fiber-optic communications, Sci Rep 10, 11347 (2020).
[3] Y.Wang, et al., Ultra-broadband Bismuth-Doped Fiber Amplifier Covering a 115-nm Bandwidth in the O and E Bands, J. Lightwave Technol., vol.39, pp.795 - 800 (2021).
