Fig. 1. (a) LMA SCF reverse tapering diagram. (b) Dependence of theoretical and measured MFDs on reverse-tapered cladding diameter of the LMA SCF. (c) SEM image of the six-tube nested HC-ARF. (d) Measured and simulated transmission losses for six-tube nested HC-ARF in the near-IR (blue line) and mid-IR regions (red line). (e) Theoretical and measured coupled loss. Inset: cross sections of the HC-ARF after breaking the splice point.

Fig. 2. (a) Experimental setup of the coupled loss and back-reflection of LMA SCF onto nested HC-ARF chain. (b) Coupled loss and back-reflection dependence on cleave angle. (c) Output power of HC-ARF and transmission efficiency as functions of incident power. (d) Beam quality of pump laser before and after HC-ARF under different incident powers.

Fig. 3. (a) SEM image of the five-tube nested HC-ARF. (b) Measured and simulated transmission losses for five-tube nested HC-ARF in the near-IR (blue line) and mid-IR regions (red line). (c) Coupled loss of the LMA SCF and HC-ARF. Inset: transverse view of a broken splice point. (d) Output power of HC-ARF and transmission efficiency as functions of incident power. (e) Splice point temperature at 56 W incident power.

Fig. 4. Schematic of all-fiber-structure mid-IR gas-filled nested HC-ARF ASE source.

Fig. 5. (a) Absorption spectra of C2H2 from HITRAN database. (b) Schematic of C2H2 molecular energy-level transition.

Fig. 6. (a) Evolution of the 3.1 μm ASE light output power and (b) residual pump power with coupled pump power. (c) Evolution of the 3.1 μm ASE light output power with absorbed pump power. (d) Slope efficiencies of coupled and absorbed pump powers as functions of C2H2 gas pressure. (e) Long-term power stability of 3.1 μm ASE source at 6.59 W output power.

Fig. 7. (a) Spectrum of the mid-IR ASE source at 6.59 W. (b) Variation in the mid-IR ASE source output spectrum with changes in acetylene pressure under the coupled pump power of 13 W.

Fig. 8. (a) RF spectrum of the mid-IR ASE source at 6.59 W. (b) Relative intensity noise curve of the mid-IR ASE source at different output powers.

Fig. 9. Beam quality of the mid-IR ASE source. Inset: near-field pattern of the mid-IR ASE source.

Fig. 10. (a) Absorption spectra of CO2 from HITRAN database. (b) Schematic of CO2 molecular energy-level transition.

Fig. 11. (a) Signal light power of 4.3 μm and (b) residual pump power as functions of the coupled pump power under varying pressures. (c) Output power of 4.3 μm as a function of the absorbed pump power under varying pressures. (d) Variations in the slope efficiency and temperature with respect to the CO2 gas pressure.

Fig. 12. (a) Output spectrum at pressure of 4.1 mbar with 56.8 W pump power. Inset: near-field spot of the mid-IR ASE source. (b) Measured mid-IR ASE spectra varying with CO2 gas pressure.