Fig. 1. Structure of transformation thin-film lithium niobate photonic crystal waveguide. (a) Structure of photonic crystal waveguide with nanoporous; (b) cross-section structure of waveguide; (c) longitudinal section of photonic crystal unit

Fig. 2. Dispersion of lithium niobate photonic crystals. (a) Dispersion curves of lithium niobate nanoporous photonic crystal waveguides; (b) eigenmode field distribution of four photonic crystals with different periods and the eigenfrequency is 299.79 THz; (c) for light with a frequency of 299.79 THz, group velocity of photonic crystal varies with the period

Fig. 3. Design of the transformation photonic crystal waveguides. (a) Group velocity vg varying along z; (b) period a of transforming optical photonic crystal waveguide as a function of z

Fig. 4. Rainbow trapping effect simulation after light with different wavelengths enters the transforming optical photonic crystal waveguide. (a) 1000 nm; (b) 990 nm; (c) 980 nm; (d) 970 nm

Fig. 5. Analysis of four-wave mixing in the transformation photonic crystal waveguide. (a) For the signal light of 299.19THz, the pump light of 294.19THz, and the corresponding idle light of 289.19THz, relationship between phase mismatch Δk and coordinate z; (b) variation of effective nonlinear coefficient γ of photonic crystal waveguide with the coordinate z; (c)-(h) when frequency of signal light remains unchanged, and idle light frequency changes to 291.19, 293.19, 295.19 THz, respectively, phase mismatch Δk and effective nonlinear coefficient γ of photonic crystal waveguide vary with coordinate z