Fig. 1. Schematic of heterogeneously-integrated EOM based on thin film lithium niobate. (a) Overall device structure; (b) cross-sectional view of modulation region; (c) side view of proposed EOM

Fig. 2. Effect of different filling layer thicknesses on V_πL and α_op. (a) Parameters of V_πL and α_op versus filling layer thicknesses H for the materials of BCB and SiO₂; electric field patterns of TE modes under the conditions of (b) H=0 nm, (c) H=100 nm, and (d) H=300 nm, where the filling material is BCB

Fig. 3. SiO₂ filling layer thickness h between modulation electrode and thin film lithium niobate affecting on optical loss α_op and modulation parameter V_πL. (a) Change curves of optical loss α_op; (b) change curves of modulation parameter V_πL

Fig. 4. Electrode gap width G of the proposed device affecting on modulation parameter V_πL and optical loss α_op

Fig. 5. Microwave loss versus electrode thickness. (a) Electrode thickness h_Au of the proposed device affecting on the microwave loss α_m; (b) microwave field distribution of the modulation waveguide as electrode thickness h_Au is 1.0 μm

Fig. 6. Relation between signal electrode width W_S and electrode gap G for different SiO₂ filling layer thicknesses when the impedance matching condition is satisfied

Fig. 7. Mode effective index n_RF of the microwave as a function of electrode gap width G and SiO₂ filling layer thickness h. (a) n_RF changed with G; (b) n_RF changed with h

Fig. 8. Electrode gap width G of proposed device affecting on EO response and modulation parameter V_πL. (a) Change of EO response;(b) change of modulation parameter V_πL

Fig. 9. Influence of different waveguide widths on optical loss and TE mode field of waveguide cross-sections at different positions. (a) Comparison of coupling loss between proposed structure and butt coupling structure; (b) schematic of proposed coupling structure; (c)-(f) TE mode distributions of the waveguide cross-section at four key positions along the propagation direction

Fig. 10. Fabrication process of the inverted stepped thin-film LN: (Ⅰ) a 120 nm chromium layer is sputtered on X-cut LN thin film with the thickness of 300 nm as a hard mask, then transfer the pattern on the photoresist to the hard mask layer; (Ⅱ) the pattern is transferred to LN thin film using etching, then transfer the second layer structure on the photoresist to the hard mask layer; (Ⅲ) the second and third layers of inverted stepped thin film structure are etched by using etching; (Ⅳ) filling the vacancy of inverted stepped thin film structure with SiO₂ layer grown by PECVD method