Fig. 1. TM mode of (a) SiO₂ waveguide; (b) SOI waveguide; (c) Si₃N₄ waveguide; (d) LRSPP waveguide

Fig. 2. (a) Schematic diagram of temperature insensitive structure based on Si₃N₄ waveguide and LRSPP waveguide; (b) Cross-section of the Si₃N₄ waveguide; (c) Cross-section of the LRSPP waveguide

Fig. 3. (a) Coupling efficiencies of the Si₃N₄ waveguide and LRSPP waveguide with different core heights. Inset: the zoom of the coupling efficiency; (b) Coupling efficiencies of the Si₃N₄ waveguide and LRSPP waveguide with different core widths. Inset: optimal coupling efficiency with different core heights; (c) Mode area differences of the Si₃N₄ waveguide and LRSPP waveguide with different core heights; (d) Coupling losses of the Si₃N₄ waveguide and LRSPP waveguide with different core heights

Fig. 4. (a) Offset between the Si₃N₄ waveguide and LRSPP waveguide in horizontal (x) and vertical (y) direction; (b) Transmission field of the Si₃N₄ waveguide and LRSPP waveguide with lateral offset; (c)-(g) Properties of the Si₃N₄ waveguide and LRSPP waveguide with longitudinal offset: (i) mode distribution in P₁, (ii) mode distribution in P₂, (iii) transmission field

Fig. 5. (a) Effective mode refractive index of the Si₃N₄ waveguide and LRSPP waveguide under different temperatures; (b) Phase change of the Si₃N₄ waveguide and LRSPP waveguide under different length ratios

Fig. 6. (a) Temperature of the LRSPP waveguide under different voltages, inset: the temperature field distribution of the LRSPP waveguide under different voltages; (b) Heating curve of the LRSPP waveguide, inset: zoom in the heating curve; (c) Cooling curve of the LRSPP waveguide, inset: the temperature field distribution of the LRSPP waveguide

Fig. 7. (a) Experimental setup of the LRSPP waveguide; (b) Output spot of the LRSPP waveguide at TM polarization state; (c) Output of the LRSPP waveguide under the TE polarization state