Fig. 1. Illustration of the proposed mode selective switch，and air-trenched waveguide structure

Fig. 2. Relationship between waveguide width and effective refractive index when the core thickness is 4 μm（λ=1 550 nm），schematic diagram of two-mode（E₀₀，E₁₀）multiplexer（MUX）and mode field transmission from E₀₀ mode to E₁₀ mode

Fig. 3. Operation principle of the mode selecting switch

Fig. 4. When light is input from Input₁，the transmittance of output varies with driving powers

Fig. 5. Light propagating along the silica waveguide switch，when the E₀₀ mode output from Output₁，Output₂，and Output₃，respectively

Fig. 6. Transmittance versus wavelength from Output₁，Output₂，and Output₃

Fig. 7. Prepared partial light microscope images of MSS

Fig. 8. Side view of the active arm with air trench structure

Fig. 9. Measurement device for characterizing output power，mode pattern and time response

Fig. 10. The transmission of Output₁，Output₂ and Output₃ as a function of electric drive power

Fig. 11. Optical bandwidth characterization

Fig. 12. Response time of the prepared mode selector switch

Fig. 13. Thermal field distribution of traditional planar heater plan，and the case air trenches are introduced