Fig. 1. Cross-sectional structure of a dual-core PCF

Fig. 2. Variation of coupling energy with interaction length for initial structural parameters

Fig. 3. Variation curves of κ and δ for different structural parameters. (a) Aperture spacing; (b) refractive index difference of fiber core; (c) central air aperture diameter ratio; (d) fiber core diameter ratio; (e) air aperture diameter ratio; (f) air aperture symmetry

Fig. 4. Variation curves of δ and Δβ for different structural parameters. (a) δ; (b) Δβ

Fig. 5. Variation curves of κ²/δ² for different structural parameters. (a) Global view; (b) local zoomed-in view

Fig. 6. Variation of coupling ratio with core interaction length for different structural parameters. (a) Aperture spacing; (b) core refractive index difference; (c) central air pore diameter ratio; (d) core diameter ratio; (e) air pore diameter ratio; (f) air pore symmetry

Fig. 7. Variation of coupling ratio with core interaction length for different structural parameters at an incident light wavelength of 1310 nm. (a) Aperture spacing; (b) core refractive index difference; (c) central air pore diameter ratio; (d) core diameter ratio; (e) air pore diameter ratio; (f) air pore symmetry

Fig. 8. Broadband characteristics of the coupler for different d₀, d₂, and L

Fig. 9. Variation of coupling ratio and insertion loss and additional loss of straight through arm and coupling arm when L=3000 μm, d₂=1.8 μm, and d₀=0.51 μm. (a) Variation of coupling ratio; (b) insertion loss and additional loss