Fig. 1. Spectral regions covered by Bi and rare earth elements in SiO₂ glass host^[4]

Fig. 2. Energy level diagram of Bi ions (Bi⁰, Bi⁺, Bi²⁺, Bi³⁺)^[10-11]

Fig. 3. Luminescence properties of Sr_2(1-x)B₅O₉Cl∶2xBi (x=1.0%)^[15]. (a) Excitation spectra; (b) decay fitting curves

Fig. 4. Luminescence properties of Bi∶PbF₂, Er∶PbF₂, and Bi/Er∶PbF₂^[18]. (a) Absorption spectra; (b) emission spectra

Fig. 5. Luminescence properties of Bi^2+[20]. (a) Absorption and emission spectra of SrBaB₄O₇ at different concentrations; (b) excitation and emission spectra of Bi-doped barium borate

Fig. 6. Luminescence properties and mechanism of Na₂Ca₃(Nb, Ta)₂O₉∶Bi^3+[24]. (a) PL and PLE spectra; (b) luminescence mechanism

Fig. 7. Optical fiber preparation process and cross-section using the molten core method. (a) Schematic diagram of preparing Bi-doped fibers using the molten core method^[30]; (b) optical and EPMA images of Bi-doped fiber cross-section^[32]

Fig. 8. Optical fiber preparation process and cross-section using the rod-in-tube approach. (a) Schematic diagram of preparing Bi-doped fibers by the rod-in-tube approach; (b) backscattered electron image and elements mapping of the fiber cross-section^[34]

Fig. 9. BDFA experimental setup diagrams^[49]. (a) Bi-doped fiber UL testing device; (b) schematic of S-band BDFA

Fig. 10. BDFA experimental results^[49]. (a) Measurement value of UL; (b) gain spectra of the BDFA in the E-, S-, and C-bands

Fig. 11. Experimental setup of the single mode BGSF continuous laser^[53]. (a) Tunable BDFL; (b) MOPA system

Fig. 12. Output performance of BDFL under two configurations^[53]. (a) Output power spectra from the tunable BDFL and MOPA; (b) variations of MOPA output power at 1450 nm with pump power in BDFA