Fig. 1. Optimization of MMI. (a) MEP values under different input positions; (b) MEP values under different coupler maximum widths; (c) MEP values under different coupler lengths; (d) normalized output powers under different waveguide lengths

Fig. 2. C-band transmission spectra of MMI. (a) TE₀ mode; (b) TE₁ mode; (c) TE₂ mode

Fig. 3. Structure of mode insensitive thermo-optical switch.(a) Cross section of phase shifter; (b) effective refractive index versus waveguide width; (c) dneff/dT versus phase shifter width obtained by simulation; (d) schematic of mode insensitive switch

Fig. 4. C-band insertion loss and output power versus applied power. (a) C-band insertion loss; (b) inputting three modes separately; (c) inputting three modes together

Fig. 5. Influence of depth and width of air trench on power consumption

Fig. 6. Output power under trench assistance condition versus applied power. (a) Inputting three modes separately; (b) inputting three modes together

Fig. 7. Extinction ratios under two conditions. (a) With trench assistance; (b) without trench