Fig. 1. Schematic diagram of lithium niobate film ridge waveguide structure

Fig. 2. Structural diagram of spot size converter

Fig. 3. Variation of waveguide mode with ridge waveguide width

Fig. 4. TE₀ distribution of LN ridge waveguide

Fig. 5. Mode field distribution of single-mode fiber

Fig. 6. Waveguide parameters of SiO₂ waveguide under single mode condition and x-y cross sectional TE₀ mode field distribution of SiO₂ waveguide with 6 µm×6 µm waveguide size

Fig. 7. Single mode condition and x-y cross sectional TE₀ mode field distribution of SiON waveguide

Fig. 8. Relation curve between taper waveguide lengthL₁ and conversion efficiency under different SiON taper waveguide tip width W₁

Fig. 9. The influence of W₅ and L₂ on the conversion efficiency in Zone III

Fig. 10. Relation curve between taper length L₃ and conversion efficiency in Zone IV under different taper tip width W₆

Fig. 11. （a） Structure diagram, （b） optical field transmission diagram and （c） cross section optical field distribution diagrams of designed spot size converter

Fig. 12. Relationship between transverse dislocation and coupling loss