Fig. 1. (a) Design of the electrically switchable GMR-filter element. The ITO layer serves as resistive heating element underneath the VO₂ grating, which itself forms the waveguide structure. (b) Cross-sectional profile of GMR-filter element with dimensions.

Fig. 2. (a) Refractive index n and (b) extinction coefficient k of prepared VO₂ film below and above the SMT.

Fig. 3. SEM images of a cross-section of a VO₂ thin film on silicon substrate, (a) before annealing and (b) after annealing, indicating the growth of thickness. Image (c) shows an etched VO₂ grating with additional layers above and below. ITO is the thin bright layer above the substrate.

Fig. 4. Raman spectra of VO₂ films on Silicon: after deposition, after annealing and after etching (lines from bottom to top).

Fig. 5. Transmitted amplitude of the optical element in relation to the calculated temperature from heating power inserted into the resistive heating film. Each measurement was taken after thermal equilibrium was reached.

Fig. 6. Reflection of the guided mode resonance grating at 30 °C and 90 °C, respectively. The dashed lines show the results of RCWA simulation. The calculated reflection switching ratio c_r is shown in black.