Fig. 1. Schematic of the generalized Snell's law^[20]. (a) Schematic of Fermat principle; (b) schematic of wavefront shaping of metasurface

Fig. 2. Schematic of molecular arrangement for three typical LCs^[50]. (a) Cholesteric LC; (b) smectic LC; (c) nematic LC

Fig. 3. LC based tunable metasurface for beam steering and zoom lens. (a) LC based metasurface for beam steering^[33]; (b) LC based tunable bifocal lens^[54]; (c) LC based metalens with a continuously tunable focal length^[55]

Fig. 4. LC-plasmon hybrid device. (a) Electrically tuned dynamic plasma color filter^[58]; (b) a hexagonal gold nanodot array in a LC matrix^[47]; (c) LC-based electrically tunable negative permeability metasurface^[59]; (d) optically controlled LC-based metasurface switch^[45]

Fig. 5. All dielectric LC-based metasurface. (a) Transmission modulation by heating^[40]; (b) thermally induced beam deflection^[32]; (c) vector vortex beam generator^[60]; (d) electrically tunable full-color reflective displays^[61]

Fig. 6. Chalcogenide glass-plasmon hybrid device. (a) Metasurface electro-optic switch^[76]; (b) GST-based bidirectional, all-optical switch^[74]; (c) GST-based perfect absorber^[77]; (d) electrically tunable second-harmonic generator^[78]

Fig. 7. All-dielectric chalcogenide glass metasurface. (a) Dolmen metamolecule structure^[27]; (b) planar dielectric nano-grating metasurface^[79]; (c) GSST-based reconfigurable non-volatile metasurface^[28]

Fig. 8. Electrically controlled VO₂ metasurface; (a) Terahertz VO₂ memory metasurface^[85]; (b) beam deflection through VO₂-based metasurface^[86]; (c) VO₂‑based switchable terahertz metasurface^[87]

Fig. 9. Thermally-controlled VO₂ metasurface. (a) Self-aligned Ag/VO₂ metasurface^[88]; (b) VO₂-based perfect absorber^[89]; (c) thermal tuning of mid-infrared plasmonic antenna arrays^[90]; (d) VO₂-based tunable absorber^[91]; (e) VO₂-based plasmonic color generator^[92]

Fig. 10. Flexible and stretchable materials-based tunable metasurface. (a) PDMS-based tunable structural color metasurface^[98]; (b) full-spectrum stretchable plasmonic device^[99]; (c) tunable elastic dielectric zoom lens^[100]

Fig. 11. Example 1 of MEMS-based tunable metasurface. (a) MEMS-based metasurface dynamic waveplate^[106]; (b) MEMS-based dynamic metasurface lens^[37]; (c) MEMS-based dielectric zoom lens^[107]; (d) MEMS-actuated metasurface Alvarez lens^[108]

Fig. 12. Example 2 of MEMS based tunable metasurface. (a) MEMS-based Maltese-cross metasurface^[109]; (b) mirrorlike T-shape terahertz metasurface^[110]; (c) MEMS dynamic waveplate^[111]