Fig. 1. Summary of reported maximum incident CW laser damage threshold of ChG fibers^[7-12]

Fig. 2. Comparison of maximum resistable peak power density of silica, fluoride, fluorotellurite, and ChG fibers under irradiation of pulsed laser with various pulse durations^[28-36]

Fig. 3. Fabrication flow of ULMA ChG PCF. (a)(c) Extruded chalcogenide glass rod and tubes for PCF fabrication; (d) preform composed by low-index rod and high-index tube using rod-in-tube method; (e) stacked ChG preform for ULMA PCF; (f) schematic of drawing all-solid ChG PCF

Fig. 4. Measured optical properties of host materials for ULMA ChG PCF and numerical simulations of single-mode ULMA ChG PCF. (a) Measured transmission and (b) refractive index curves of prepared Ge₁₀As₂₄S₆₆ and Ge₁₂As₂₄Se₆₄ glasses; (c) schematic of ULMA ChG PCF with two rings of low-index filling rods; calculated mode profiles of (d) LP₀₁ and (e) LP₁₁; calculated confinement losses (CL) of all-solid Ge-As-Se/Ge-As-S ULMA PCF with core diameter of 80 μm at the wavelength of 2 μm and 4 μm of the PCFs with (f) 2-ring structure and (g) 1-ring structure

Fig. 5. Measured guiding performances of fabricated single-mode ULMA ChG PCF. (a) Scanning electron microscope (SEM) photograph of single-mode ULMA ChG PCF; (b) near-field and (c) far-field mode profiles observed from ULMA ChG PCF output end at 4 μm; (d) measured loss spectra of unclad Ge₁₂As₂₄Se₆₄ glass fiber in 29 μm and ULMA ChG PCF at 4 μm

Fig. 6. Origin of bending loss in PCF with ultra-low NA. (a) Straight fiber; (b) bent fiber

Fig. 7. Microstructure and numerical simulation of dual-moded ULMA ChG PCF. (a) Schematic of dual-moded ULMA ChG PCF; (b) SEM image of fabricated dual-moded ULMA ChG PCF;（c）calculated CLs of LP₀₁ and LP₁₁ modes of the fabricated fiber (Λ=90 μm, d₁/Λ=0.40, and d₂/Λ=0.55) in the range of 28 μm, in comparison with the PCF with uniform d/Λ=0.40 (d₁=d₂) and Λ=90 μm;（d）calculated A_eff of LP₀₁ and LP₁₁ modes of the fabricated fiber (Λ=90 μm, d₁/Λ=0.40, and d₂/Λ=0.55) in the range of 28 μm, in comparison with the PCF with uniform d/Λ=0.40 (d₁=d₂) and Λ=90 μm

Fig. 8. Measured bending loss and fitting with exponential decay function of dual-moded ULMA ChG PCF with bending radius under different diameters of the incident 2-μm laser spot. (a) ~75 μm; (b) ~100 μm

Fig. 9. Measured optical homogeneity of Ge-As-Se chalcogenide glass with 100-mm aperture

Table 1. Reported maximum resisted mid-IR power of ChG fibers

Table 2. Damage threshold of various glass fibers, including silica, fluoride, fluorotellurite, and ChG fibers under CW laser irradiation