Fig. 1. Parameters of lithium niobate waveguide. (a) Structural parameters of crossing waveguide; (b) lithium niobate refractive index ellipsoid

Fig. 2. Numerical calculation results of effective refractive index and beat length. (a) Effective refractive index and (b) beat length versus multimode waveguide width for X-cutting Y-propagating; (c) effective refractive index and (d) beat length versus multimode waveguide width for X-cutting Z-propagating

Fig. 3. Relationships among device performance and structural parameters. (a) Insertion loss versus width and length of multimode waveguide; (b) crosstalk versus width and length of multimode waveguide

Fig. 4. Relationships among device performance and structural parameters of multimode waveguide for X-cutting Z-propagating. (a) Insertion loss and (b) crosstalk versus width and length of multimode waveguide when light is incident from port 1; (c) insertion loss and (d) crosstalk versus width and length of multimode waveguide when light is incident from port 4

Fig. 5. Device performance of crossing waveguide in different cases. (a) Insertion loss and (b) crosstalk versus multimode waveguide length; (c) insertion loss and (d) crosstalk versus wavelength

Fig. 6. Device processing process

Fig. 7. Optical microscope pictures of crossing waveguide. (a) Single crossing waveguide; (b)(c) cascaded crossing waveguides;

Fig. 8. Test performance of crossing waveguide device. (a) Insertion loss spectra of single crossing waveguide; (b) crosstalk spectra of single crossing waveguide

Fig. 9. Relationship between device performance and process error. (a) Insertion loss and (b) crosstalk of crossing waveguide versus multimode waveguide width; (c) insertion loss and (d) crosstalk of crossing waveguide versus device angle