Fig. 1. Model of Bragg fiber. (a) Cross-sectional diagram; (b) refractive index distribution; (c) light guiding principle (n₁>n₂) ^[17]

Fig. 2. PBG structure when d₁/d₂=1 and dn=0.8

Fig. 3. Variation of photonic bandgap with structural parameters R and M. (a) C versus R (d₁/d₂=1,Λ=6.72 μm, M=3); (b) C versus M (d₁/d₂=1,Λ=6.72 μm, R=90 μm)

Fig. 4. Loss of Bragg fiber when Λ=6.72 μm, d₁/d₂=1, R=90 μm, and M=3

Fig. 5. Thermal and optical properties of Ge₂₀As₂₀Se₁₅Te₄₅ and As₂S₃ glass. (a) Glass samples; (b) transmittance spectra; (c) thermal expansion curves; (d) refractive index distribution

Fig. 6. Glass and prepared fiber preform used in experiment. (a) Glasses; (b) preform

Fig. 7. Cross sections of different Bragg fibers. (a)‒(c) Based on equal thickness glass; (d)‒(f) based on non-equal thickness glass

Fig. 8. Layer thicknesses and T_i/D values of different Bragg fibers. (a) Based on equal thickness glass; (b) based on non-equal thickness glass

Fig. 9. Comparison of fiber loss before and after optimization of cladding glass. (a) Fiber loss based on equal thickness glass with light spot pattern shown in inset; (b) fiber loss based on non-equal thickness glass with light spot pattern shown in inset; (c) loss obtained by simulation based on structural parameters of actual prepared fiber with electric field distribution shown in inset