Fig. 1. （a）The schematic diagram of the TFLN PM，（b）the cross section of the TFLN PM

Fig. 2. （a）The V_π of conditional bulk PM various G at different modulation length，where Γ = 0.5，（b）the V_π of TFLN PM various b₂ at different modulation length， where Γ = 0.9，b₁=5 μm

Fig. 3. （a）The sketch of Y-junction waveguide，（b）the W of Y-junction waveguide versus L₂ at different α

Fig. 4. （a）The results of BPM simulation，（b）the refractive index profile of waveguide section，（c）the power distribution of Y-junction waveguide

Fig. 5. The results of simulation modulator insertion loss，where L₁=1 000 μm，L₂=9 000 μm，L₃=10 000 μm，α=0.6°

Fig. 6. The microscope image of the cross-section of the TFLN slab bonded on the LN substrate