Fig. 1. Schematic of mid-infrared passively Q-switched all-fiber laser

Fig. 2. Energy-level diagram of Er³⁺ and Dy³⁺and transitions related to 2.8 μm laser

Fig. 3. Simulation results without 3.1 μm fiber Bragg gratings (R₃×R₄ is 0.0001) at pump power of 1 W. (a) Normalized pulse photon density of 2.8 μm radiation, Er³⁺ population of ⁴I_11/2 energy level, and Dy³⁺ population of ⁶H_13/2 energy level as functions of time; (b) single pulse profile of 2.8 μm laser

Fig. 4. Simulation results without 3.1 μm fiber Bragg gratings (R₃×R₄ is 0.0001) at pump power of 3 W. (a) Normalized 2.8 μm pulse photon density; (b) Er³⁺ population of ⁴I_11/2 energy level; (c) Dy³⁺ population of ⁶H_13/2 energy level

Fig. 5. Normalized 2.8 μm pulse photon density, Er³⁺ population of ⁴I_11/2 energy level, and Dy³⁺ population of ⁶H_13/2 energy level as functions of time with 3.1 μm fiber Bragg gratings (the R₃×R₄ is 0.85) at pump powers of 1 W and 3 W. (a)(b) Pump power of 1 W; (c)(d) pump power of 3 W

Fig. 6. PRF of 2.8 μm laser as a function of pump power when length of saturable absorber is 3 m and R₃×R₄ is 0.85

Fig. 7. PRF of 2.8 μm laser as a function of saturable absorber length when pump power is 3 W and R₃×R₄ is 0.85

Fig. 8. PRF of 2.8 μm laser as a function of reflectivity of FBG4 when pump power is 3 W and length of saturable absorber is 3 m