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Timestamp: 2019-04-25 12:58:38+00:00

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The effect of thermal annealing on the luminescent and laser properties of high-germania-core silicate fibers doped with bismuth was investigated. We studied the behavior of optical absorption assigned to the bismuth-related active centers associated with germanium as well as the behavior of unsaturable absorption in annealed fibers with respect to the Bi content. The dependence of the increment of the active center content on the Bi concentration in the annealed fibers was obtained. We achieved laser oscillations near a wavelength of 1700 nm with a slope efficiency of 18% using a 8.5 m long Bi-doped fiber. The comparison of the output parameters of the laser based on an annealed Bi-doped fiber with the ones of a pristine Bi-doped fiber laser is given. The performance of the obtained bismuth-doped fiber lasers was modeled using the propagation and rate equations of a homogeneous quasi-two-level laser medium. Theoretical results are compared with experimental ones.
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Fig. 1 Contour plots of luminescence intensity versus emission and excitation wavelengths of Bi-doped fiber: a) pristine; b) after annealing. (Fiber # 232).
Fig. 2 Typical absorption spectrum of a Bi-doped fiber (Fiber #217). The experimentally defined UA are shown by ball-shaped points. The blue-shaded region indicates the extrapolation of the UA.
Fig. 3 Absorption of the BACs-Ge and UA as a function of total Bi concentration. Linear and non-linear functions are indicated by dashed and solid lines, respectively.
Fig. 4 Increment of relative concentration of the BACs during annealing versus total Bi content.
Fig. 5 Setup of laser experiments.
Fig. 6 Output power of the laser versus absorbed pump power (empty squares – experimental data for low-Bi-content and annealed fiber, filled squares – data for high-Bi-content fiber; dashed lines – calculation). Inset: The calculated dependence of the slope efficiency of the Bi-doped laser on the ratio between the total absorption at 1650 nm and the UA. The total absorption was kept equal to ~1 dB/m and the UA was varied so the ratio was changed in a broad range.
Table 2 Parameters used for the modeling of the laser operation.
Parameters used for the modeling of the laser operation.

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