Fig. 1. (a) Refractive index distribution and the cross-sectional image (inset), (b) absorption spectrum, (c) excitation–emission spectra, and (d) fluorescence decay curves of the BELDF.

Fig. 2. (a) Fluorescence spectrum pumped by 980 nm laser and (b) the gain coefficient at different signal light powers as a function of pump power of the BELDF.

Fig. 3. Schematic of the 1596 nm fiber laser and optical amplification.

Fig. 4. Laser characteristics. (a) Laser output powers as a function of input pump powers with different lengths of BELDF1, (b) slope efficiency and maximum output power as functions of the BELDF1 length, (c) output spectra of the laser with a 6-m-long BELDF1 under maximum output power, (d) laser stability monitored within 6.5 h, (e) laser stability monitored within 65 min, and (f) fluctuation of the lasing center wavelength.

Fig. 5. (a) Amplified laser output power as a function of input pump power with different lengths of BELDF2 and (b) spectral characteristics of the amplified laser with BELDF2 length of 6 m.