Fig. 1. Schematic of the energy levels relevant to the 3.5 μm Er3+∶ZBLAN fiber laser

Fig. 2. Comparison between experimental results and simulations. (a) H2016 experimental results and simulations in this paper; (b) M2017 experimental results and simulations in this paper

Fig. 3. Simulation results of a typical 3.5 μm laser oscillating generation process

Fig. 4. Particle density, signal and pump power at different fiber positions. (a) Particle density of each energy level when continuous oscillation is steady; (b) signal and pump power at each fiber element

Fig. 5. Influence of overlap factor on the 3.5 μm laser power. (a) Γp1; (b) Γp2

Fig. 6. 3.5 μm laser power as a function of 975 nm pump power. (a) With ESA2; (b) without ESA2; (c) comparison between with and without ESA2 when P2=6 W

Fig. 7. 3.5 μm laser power as a function of 1975 nm pump power

Fig. 8. Impact of output coupler reflectivity on 3.5 μm laser power

Fig. 9. 3.5 μm laser output power and efficiencies with different fiber lengths and output coupler reflectivities. (a) Roc=20%; (b) Roc=30%; (c) Roc=40%; (d) slope efficiencies and pump thresholds

Fig. 10. Impacts of interionic interaction on 3.5 μm laser power. (a) W1103; (b) W2206; (c) W4251; (d) W5031