Fig. 1. Procedure of LNTF fabrication. (a) He⁺ implantation; (b) SiO₂ deposition and polishing; (c) crystal bonding; (d) annealing, splitting, and polishing

Fig. 2. LN waveguides and integrated photonic chips. (a) Proton exchanged LN waveguide; (b) LNOI ridge waveguides; (c) scalar production of PIC on LNOI using ultraviolet lithography and dry etching^[8]

Fig. 3. Special phase matching mechanism. (a) Periodically grooved LN ridge waveguide^[18]; (b) metasurface assisted phase matching ^[19]; (c) phase matching in semi-nonlinear waveguides^[21]

Fig. 4. SHG in PPLNOI ridge waveguides and their fabrication procedures^[22-23]

Fig. 5. cTHG in a LNTF microdisk^[24]. (a) Simulated results of mode effective index; (b)-(d) distribution of different order modes; (e) experimentally observed SHG and cTHG in the LNOI microdisk

Fig. 6. QPM schemes in LNOI WGM microresonators. (a) Cyclic variation of d_eff of a TE-polarized mode^[25]; (b)(c) direct use of QPM in racetrack and circular microrings^[26-27]

Fig. 7. PhC cavity and SHG on the LNOI platform^[28]. (a) PhC cavity obtained by microscope; (b) PhC cavity obtained by SEM; (c) SHG in PhC cavity

Fig. 8. The χ⁽²⁾ nonlinear processes in the LNOI microdisk. (a) SFG spectrum diagram^[31]; (b) DFG spectrum diagram^[32]; (c) schematic of modal-PM SFG/DFG

Fig. 9. Cascade four-wave mixing (FWM) effect in the LNOI microdisk^[30]. (a) Spectrum of cascaded FWM; (b) relationship between output power and pump energy

Fig. 10. Electro-optical coupling in PPLNOI ridge waveguide^[34-35]. (a) Cascade process of SH and electro-optic polarization coupling in PPLNOI ridge waveguide; (b) optical field distribution of FW light and SH light

Fig. 11. LN microring resonator and mode-locked Kerr solitons^[43]. (a) Experimental schematic diagram; (b) SEM of LNOI microring; (c) cross-section diagram of waveguide mode; (d)-(h) experimental results

Fig. 12. Frequency comb generation in LNTF microresonators from electro-optic modulation^[44]. (a) Schematic of LNOI microcavity and electrodes; (b) spectrum of electro-optic modulation optical frequency comb in LNOI microcavity