Fig. 1. Overview of electrically tunable optical metasurfaces: materials, configurations, and applications.

Fig. 2. Electrically tunable LC metasurfaces based on homogeneous meta-atoms. (a) LC-integrated tunable full-color plasmonic display. The LC-plasmonic system produces the RGB color basis set as a function of voltage. The letters appear and gradually become darker when the voltage increases from 0 to 20 V. Adapted with permission from Ref. [164] © Springer Nature. (b) LC-integrated Si metasurface for electrically tunable transparent display. Adapted with permission from Ref. [169] © American Chemical Society (ACS). (c) Electrically tunable transmissive metasurface SLM with three-level phase modulation for reversing deflection angles. Adapted with permission from Ref. [174] © the American Association for the Advancement of Science (AAAS). (d) Electrically tunable reflective metasurface SLM with continuous and full-phase modulation programmable beam steering. The incident light is diffracted preferentially into the $+1$ order when applied with a three-level voltage to create a supercell. Adapted with permission from Ref. [175] © ACS. (e) Tunable LC metasurface for computational spectropolarimetry. The reconstructed wavelengths and polarization states of the incident monochromatic light from 1420 to 1479 nm perfectly match the ground truth. Adapted with permission from Ref. [62] © Springer Nature. (f) Electrically switchable nonlocal metasurfaces for SHG. The second-harmonic intensity varies with applied voltages. Adapted with permission from Ref. [181] © AAAS.

Fig. 3. Electrically tunable LC metasurfaces based on inhomogeneous meta-atoms. (a) Superperiodic LC metasurfaces for electrically controlled anomalous refraction. The device switches from anomalous refraction to direct transmission with an applied voltage of 3 V. Adapted with permission from Ref. [182] © ACS. (b) Inverse-designed LC metasurfaces for high-efficiency, large-angle, and tunable deflection. Adapted with permission from Ref. [183] © ACS. (c) LC-integrated varifocal metalens. The focal length continuously varies from 4.5 to 9 mm with an applied voltage. Adapted with permission from Ref. [184] © ACS. (d) Electrically controlled 4-bit DMSD for programmable displays. The programmable information sequence is dynamically generated by the DMSD. Adapted with permission from Ref. [191] © Springer Nature.

Fig. 4. Electrically tunable LC metasurfaces with independent LCs positioned before metasurfaces. (a) Electrically tunable structural color by combining an LC cell and an elliptical meta-atom array hosting enhanced Mie scattering via lattice-induced quasi-GMRs. The color is gradually modulated from green to magenta by adjusting the applied voltages to the LC cell. Adapted with permission from Ref. [193] © Springer Nature. (b) LC-driven metagrating FP color filter. Adapted with permission from Ref. [194] © the Electromagnetics Academy. (c) Polarization-multiplexed tunable achromatic metalens using twisted nematic LCs. The focal length shifts from 50 to 100 µm once the applied voltage changes from 0 to 5 V. Adapted with permission from Ref. [197] © ACS. (d) LC-integrated metalens for electrically switchable bright-field and edge-enhanced imaging. Adapted with permission from Ref. [198] © ACS. (e) Stimuli-responsive dynamic meta-holographic displays enabled by an LC modulator. The voltage-dependent display was realized in different polarization states. Adapted with permission from Ref. [199] © John Wiley and Sons. (f) Electrically driven LC meta-optics for simultaneous near-/far-field multiplexing display. Nanoprinting and meta-holography can be switched by changing the applied voltage. Adapted with permission from Ref. [202] © John Wiley and Sons. (g) Dynamic hyperspectral holography enabled by inverse-designed metasurfaces with LCs. Multicolor holographic images were realized by varying the applied electric field. Adapted with permission from Ref. [204] © John Wiley and Sons.

Fig. 5. Electrically tunable LC metasurfaces with directly pixelated LC cells. (a) High-resolution multispectral SLMs with continuous $2\pi$ phase modulation based on LC-coupled FP nanocavities. Programmable beam steering was achieved by selectively applying voltage patterns (top panel) to the electrodes to create linear phase profiles. Adapted with permission from Ref. [212] © Springer Nature. (b) Pixelated LC superstructures for generating vectorial holographic images with spatially varied amplitudes and phase differences. The LC-holographic video of a football match was addressed by both the electric field and polarization keys. Adapted with permission from Ref. [213] © Springer Nature.

Fig. 6. Electrically tunable ${\mathrm{VO}}_2$ metasurfaces. (a) A hybrid metasurface absorber consisting of two continuous Au layers sandwiching a thin ${\mathrm{VO}}_2$ layer for electrically triggered reflection control in the mid-infrared range. A continuous spectral tuning is achieved before saturation when the applied electrical current increases. Adapted with permission from Ref. [235] © Springer Nature. (b) Dynamically reconfigurable metadevice for reflection modulation in the near-infrared range by positioning nanostructured ${\mathrm{VO}}_2$ patches within the feed gap of Au bow-tie antennas. The absorption spectra vary with the device temperature. Adapted with permission from Ref. [236] © ACS. (c) Electrically tunable ${\mathrm{VO}}_2$ metasurface for continuous phase modulation of reflected light in the near-infrared range. A reversible voltage-dependent hysteresis loop is shown in the phase shift when the applied voltage varies between 0 and 13 V. Adapted with permission from Ref. [241] © ACS. (d) Electrically driven ${\mathrm{VO}}_2$ metasurface for broadband dynamic polarization control. When ${\mathrm{VO}}_2$ transits from the insulating to the metallic phase through the applied current, the metasurface transforms from a broadband HWP or QWP to a mirror. Adapted with permission from Ref. [244] © John Wiley and Sons. (e) Electrically tunable ${\mathrm{VO}}_2$-Au metasurface for transmission switching and optical isolation in the mid-infrared regime. The OPEN (transmitting) and CLOSED (non-transmitting) states are switched by electrical Joule heating from electrical bias and/or photothermal heating from incident light. Adapted with permission from Ref. [245] © Springer Nature. (f) Electrically programmable nanophotonic matrix consisting of ${\mathrm{VO}}_2$ cavities on pixelated microheaters. Each unit spectral pixel ($2\times 2$${\mathrm{VO}}_2$ cavities) can be individually controlled for spectrum detection. Adapted with permission from Ref. [249] © Springer Nature.

Fig. 7. Electrically tunable PCC metasurfaces. (a) GST metasurface emerging as an integrated optoelectronic framework for high-resolution electronic display, in which a nanoscale conductive tip is used to locally switch color pixels by applying a voltage between the two ITO layers. Adapted with permission from Ref. [257] © Springer Nature. (b) Electrically actuated GST-Ag metasurface for reflection modulation in the visible range. The absorption spectra vary with the device temperature. Reset and set pulses are applied through the Ag strip, heating the metasurface to facilitate a reversible transition between the amorphous and crystalline phases. Adapted with permission from Ref. [260] © Springer Nature. (c) Electrically reconfigurable metasurface beam deflector based on GSST meta-atoms on a metal heater. The deflection efficiencies are redistributed at the design wavelength of 1550 nm by switching the phase of GSST meta-atoms. Adapted with permission from Ref. [261] © Springer Nature. (d) Electrically reconfigurable heterostructure metadevice for non-volatile, reversible, multilevel, fast, and remarkable optical modulation in the near-infrared spectrum by integrating a robust resistive microheater with an $\mathrm{Au}\text{-}{\mathrm{Al}}_2{\mathrm{O}}_3\text{-}\mathrm{GST}\text{-}{\mathrm{Al}}_2{\mathrm{O}}_3$-Au metasurface. An absolute reflectance contrast reaching 80% can be achieved between the reflective and absorptive states during multiple electrical sets and reset pulses. Adapted with permission from Ref. [262] © Springer Nature. (e) GSST fishnet metasurface for electrically tunable transmission modulation. Low- and high-transmission states with a contrast ratio of 5.5 dB can be consistently switched using electrical pulses for 1250 cycles. Adapted with permission from Ref. [264] © John Wiley and Sons. (f) Electrically switchable $\mathrm{W}\text{-}{\mathrm{Sb}}_2{\mathrm{S}}_3$ color filter. Adapted with permission from Ref. [266] © John Wiley and Sons. (g) Electrically tunable ${\mathrm{Sb}}_2{\mathrm{S}}_3$ SNOC pixels. Individual ${\mathrm{Sb}}_2{\mathrm{S}}_3$ SNOC pixels are controlled with a DC voltage of 10 V. Adapted with permission from Ref. [270] © ACS. (h) Electrically programmable ${\mathrm{Sb}}_2{\mathrm{Se}}_3$ metasurface as a phase-only transmissive SLM by independently controlling individual meta-molecules. Tunable focusing with different focal lengths is observed by selectively transitioning the phase of 2 (i), 4 (ii), and 6 (iii) central meta-molecules to the amorphous state while maintaining the rest in the crystalline state. Adapted with permission from Ref. [271] © ACS.

Fig. 8. Electrochemically activated metasurfaces based on inorganic materials. (a) Electrically controlled $\mathrm{Al}/{\mathrm{Li}}_x{\mathrm{WO}}_3/\mathrm{Al}$ gap plasmon resonators for tunable structural color generation, where ${\mathrm{Li}}^{+}$ ions are reversibly inserted and removed under specific voltages. The color changes from blue to red/purple upon lithiation, corresponding to a blue shift of 58 nm in the reflection spectrum. Adapted with permission from Ref. [276] © ACS. (b) Asymmetric $\mathrm{W}\text{-}{\mathrm{WO}}_3$-PET FP nanocavity for tunable structural colors. By electrically adjusting the amount of Li injected into the ${\mathrm{WO}}_3$ layer, subtle color modulation from red to green was achieved. Adapted with permission from Ref. [278] © Springer Nature. (c) Electrochemically actuated $\mathrm{Ag}\text{-}{\mathrm{TiO}}_2$-Al plasmonic metasurfaces for dynamic color tuning. The metasurface exhibited a significant color change from gold to green when anatase ${\mathrm{TiO}}_2$ transitions to LTO. Adapted with permission from Ref. [279] © ACS. (d) Compositionally and mechanically dual-altered rechargeable Si metasurfaces integrated into an LIB cell for dynamic color display. Under a low voltage, lithiation and delithiation processes occur dynamically to control the phase transformation from Si to $\mathrm{Li}{}_x\mathrm{Si}$, enabling high-contrast colorization and decolorization with long cyclic stability. Adapted with permission from Ref. [280] © AAAS. (e) Switchable plasmonic color generation by integrating an electrically controlled local proton source. When a positive bias of 5 V is applied, hydrogen ions split from moisture travel through a proton-conducting ${\mathrm{GdO}}_x$ layer and transform Mg to ${\mathrm{MgH}}_2$, resulting in color changes. Adapted with permission from Ref. [288] © Springer Nature.

Fig. 9. Electrochemically activated metasurfaces based on conducting polymer PEDOT. (a) Electrochemically activated PEDOT:Sulf nanoantennas for tunable extinction. Extinction spectra of a nanodisk array with a thickness of 65 nm, a diameter of 145 nm, and an array period of 600 nm on the counter ITO electrode, where on and off plasmonic resonance was switched at the electrical bias of 0 and 5 V. Adapted with permission from Ref. [292] © John Wiley and Sons. (b) Electrode-free PEDOT:Sulf INR arrays for electrically tunable extinction. Plasmon resonance of an INR array was switched OFF and ON by applying voltages of $-5$ and 0 V repeatedly. Adapted with permission from Ref. [293] © Royal Society of Chemistry. (c) Electrically switchable PEDOT:PSS nanoantennas. Plasmonic resonance of fabricated PEDOT:PSS antennas was completely tuned ON and OFF with applied voltages of $+1$ and $-1\mathrm{V}$, respectively, with a modulation frequency of up to 30 Hz. Adapted with permission from Ref. [294] © AAAS. (d) Electrically switchable metaobjective comprising two PEDOT:PSS metalenses. The metaobjective allows for four different states depending on the individual voltage applied to the polymer metalens. Adapted with permission from Ref. [297] © Springer Nature. (e) Electrically controlled near-infrared optical modulator by coupling Tamm plasmon to PEDOT:PSS. Optical modulation depth exceeding 88% was achieved under low voltages of $\pm 1\mathrm{V}$. Adapted with permission from Ref. [298] © John Wiley and Sons.

Fig. 10. Electrochemically activated metasurfaces based on conducting polymer PANI. (a) Electrochemically controlled visible metasurfaces with high-contrast switching through in-site optimization. A maximum intensity contrast was achieved by selectively and locally coating PANI on Au antennas with 36 cycles. Adapted with permission from Ref. [301] © AAAS. (b) Active Huygens’ metasurface based on in-situ grown PANI. Intermediate PANI states with gradually varied refractive indices could be addressed via voltage tuning, enabling the continuous modification of the intensity distributions between the $+1$st and zeroth diffraction orders. Adapted with permission from Ref. [308] © De Gruyter.

Fig. 11. Electrically tunable metasurfaces with continuous graphene layers. (a) Tunable metasurface absorber composed of a metasurface on graphene, an ${\mathrm{Al}}_2{\mathrm{O}}_3$ layer, and an Al substrate at the wavelength of 6.5 µm. Adapted with permission from Ref. [311] © ACS. (b) Reflective intensity modulator based on a Fano-resonant metasurface integrated with graphene at the wavelength of 7 µm. Adapted with permission from Ref. [313] © ACS. (c) Reflective phase modulator based on gate-tunable graphene-Au nanoantenna array at the wavelength of 8.5 µm. Adapted with permission from Ref. [315] © ACS. (d) Transmissive intensity modulator by coupling extraordinary optical transmission resonances to electro-statically tunable graphene plasmonic ribbons. Adapted with permission from Ref. [323] © Springer Nature. (e) Metamolecule composed of a pair of independently controlled gate-tunable graphene plasmonic meta-atoms for complete complex amplitude modulation at the wavelength of 7 µm. Adapted with permission from Ref. [325] © ACS. (f) Tunable mid-infrared multi-resonant graphene-metal hybrid metasurfaces. Adapted with permission from Ref. [327] © John Wiley and Sons.

Fig. 12. Electrically tunable metasurfaces with directly patterned graphene meta-atoms. (a) Reflective graphene plasmonic metasurfaces comprising subwavelength-patterned graphene ribbons on a dielectric/metal substrate for dynamic control over reflective wavefronts by modulating the plasmonic resonance through adjustment of graphene’s Fermi level at the wavelength of around 20 µm. Adapted with permission from Ref. [337] © Springer Nature. (b) Transmissive graphene nano-cross metasurfaces for dynamically tunable broadband MIR anomalous refraction, operating at the wavelength of around 17 µm. Adapted with permission from Ref. [339] © John Wiley and Sons. (c) Reflective graphene metasurface for high-order anomalous reflection switching. Adapted with permission from Ref. [341] © John Wiley and Sons. (d) Reflective diagonal nano-cross graphene metasurfaces for tunable polarization-preserving vortex beam generation at the wavelength of 8 µm. Adapted with permission from Ref. [344] © John Wiley and Sons.

Fig. 13. Electrically tunable metasurfaces with other 2D materials. (a) Tunable Fano resonances by coupled plasmons and infrared-active optical phonon in back-gated b-PC nanoribbon arrays. Adapted with permission from Ref. [350] © ACS. (b) Tunable ${\mathrm{WS}}_2$ zone plate metalens in transmission using excitonic resonance tuning effect. Adapted with permission from Ref. [348] © Springer Nature. (c) Exciton-based ${\mathrm{MoSe}}_2$ metasurface for dynamic reflective beam steering. Adapted with permission from Ref. [349] © ACS. (d) TLBP-integrated FP cavity for dynamic polarization control in reflection. Adapted with permission from Ref. [352] © AAAS.

Fig. 14. Electrically tunable metasurfaces with single-gated TCOs. (a) ITO-integrated plasmonic absorber for amplitude modulation at $\lambda =3.8\mathrm{\mu m}$. Adapted with permission from Ref. [360] © Springer Nature. (b) ITO-integrated nanostrip metasurfaces for dynamic phase and polarization control at $\lambda =5.94\mathrm{\mu m}$. Adapted with permission from Ref. [363] © ACS. (c) Individually addressable nanostrip metasurfaces for 1D reconfigurable wavefront shaping at $\lambda =1.55\mathrm{\mu m}$. Adapted with permission from Ref. [368] © ACS. (d) Tunable multifunctional metasurfaces consisting of individually addressable fishbone nanoantennas for 1D dynamic wavefront shaping at $\lambda =1.522\mathrm{\mu m}$. Adapted with permission from Ref. [369] © ACS. (e) Transmission-type tunable ITO-integrated metasurface employing hybrid plasmonic waveguide mode at $\lambda =1.5\mathrm{\mu m}$. Adapted with permission from Ref. [371] © John Wiley and Sons. (f) Pixelated ITO-integrated GSP metasurface for 2D beam steering at $\lambda =1.3\mathrm{\mu m}$. Adapted with permission from Ref. [374] © De Gruyter.

Fig. 15. Electrically tunable metasurfaces with multi-gated TCOs. (a) Multi-gated all-dielectric metasurfaces for dynamic polarization and 1D wavefront shaping at $\lambda =1.4\mathrm{\mu m}$. Adapted with permission from Ref. [386] © John Wiley and Sons. (b) Dual-gated MIM metasurfaces with opposite top and bottom biases for enhanced ($>300°$) phase tunability at $\lambda =1.55\mathrm{\mu m}$. Adapted with permission from Ref. [392] © ACS. (c) Dual-gated ITO-integrated MIM metasurface with different top and bottom biases for independent phase and amplitude control. A 3D depth image was produced using the ITO metasurface SLM. Adapted with permission from Ref. [393] © Springer Nature.

Fig. 16. Electrically tunable metasurfaces based on thin-film inorganic Pockels materials. (a) Near-infrared active Fresnel lens in reflection. Adapted with permission from Ref. [401] © ACS. (b) Reflective metasurface intensity modulator at $\lambda =1550\mathrm{nm}$ based on a MIM configuration. Adapted with permission from Ref. [404] © ACS. (c) Transmissive metasurface intensity modulator by tuning hybrid LSPR/FP resonances. Adapted with permission from Ref. [405] © Optical Society of America (OSA). (d) Transmissive metasurface intensity modulator with structured LN meta-atoms on a ${\mathrm{SiO}}_2/\mathrm{LN}$ substrate. Adapted with permission from Ref. [411] © ACS. (e) Programmable plasmonic phase modulator consisting of a Si prism, an Ag thin film for surface plasmon polaritons, an EO dielectric modulation layer of SRN or AlN, and a $4\times 4$ electrode matrix on a sapphire wafer, operating at $\lambda =1550\mathrm{nm}$. A tunable phase shift between $[0,\pi ]$ was achieved with [0 V, 18 V] applied voltages, which can be implemented for polarization contrast imaging. Adapted with permission from Ref. [399] © Springer Nature.

Fig. 17. Electrically tunable metasurfaces based on EO polymers. (a) Reflective EO-polymer-activated metasurface intensity modulator. Adapted with permission from Ref. [418] © AIP Publishing. (b) Plasmonic meta-fiber EO modulators with nanoeye plasmonic metasurfaces for dual-band operation. Adapted with permission from Ref. [424] © Springer Nature. (c) Hybrid Si-organic metasurfaces comprising a Mie-resonance Si metasurface layer, Au interdigitated electrode array, and JRD1 layer for high-speed intensity modulation in transmission. Adapted with permission from Ref. [426] © Springer Nature. (d) Hybrid Si-organic slot metasurfaces comprising a Si slot metasurface, Au interdigitated electrode array, and HLD layer for intensity modulation in reflection with CMOS-level voltages. Adapted with permission from Ref. [427] © Springer Nature.

Fig. 18. MEMS/NEMS-integrated homogeneous metasurfaces. (a) Electrically reconfigurable plasmonic metamaterial for modulating reflected and transmitted telecom light using in-plane electrostatic forces between parallel strings on a flexible SiN membrane. Adapted with permission from Ref. [443] © Springer Nature. (b) Broadband tunable Si metasurfaces for intensity modulation in the visible spectrum using out-plane electrostatic forces. Adapted with permission from Ref. [445] © ACS. (c) Tunable plasmonic metasurfaces for intensity modulation at telecom wavelengths, activated by out-of-plane electrothermal actuation. Adapted with permission from Ref. [446] © AIP Publishing. (d) Birefringent reconfigurable metasurfaces for visible wavelengths utilizing MEMS-integrated Au nanogratings. Adapted with permission from Ref. [447] © AIP Publishing. (e) NEMS integrated metasurfaces for dynamic amplitude and phase modulation at telecom wavelengths with nanostructures meticulously designed for high-order Mie resonances. Adapted with permission from Ref. [449] © Springer Nature. (f) NEMS integrated metasurfaces for dynamic amplitude and phase modulation at telecom wavelengths with nanostructures meticulously designed for high-$Q$ slot resonance modes. Adapted with permission from Ref. [450] © ACS. (g) NEMS modulation of a strongly coupled plasmonic dimer for high-speed ($\sim 10\mathrm{MHz}$) light-intensity modulator. Adapted with permission from Ref. [452] © Springer Nature.

Fig. 19. MEMS-mirror-integrated dynamic metasurfaces. (a) Suspended Si metasurfaces for dynamic wavefront shaping in the visible spectrum via voltage-controlled electrostatic forces between the suspended metasurfaces and the underlying Si substrate. Adapted with permission from Ref. [453] © AAAS. (b) MEMS-mirror-integrated phase-gradient GSP metasurfaces for broadband polarization-independent dynamic wavefront shaping. Adapted with permission from Ref. [454] © AAAS. (c) MEMS-mirror-integrated plasmonic metasurfaces for dynamic wavefront shaping through tunable hybrid plasmonic/FP resonances. Adapted with permission from Ref. [455] © ACS. (d) MEMS-mirror-integrated tunable waveplate with full $2\pi$ birefringence coverage. Adapted with permission from Ref. [456] © Springer Nature. (e) MEMS-mirror-integrated tunable linear polarizer. Adapted with permission from Ref. [457] © OSA. (f) MEMS-mirror-integrated chiral metasurfaces for voltage-controllable topological phase transitions and tunable CP light filtering. Adapted with permission from Ref. [458] © AAAS.

Fig. 20. MEMS-integrated tunable metalenses. (a) Transmissive silicon metasurface integrated with dielectric elastomer actuators for controlling focal length, astigmatism, and shift. Adapted with permission from Ref. [470] © AAAS. (b) Reflective plasmonic metalens directly transferred to a MEMS mirror for angled MIR focusing. Adapted with permission from Ref. [471] © AIP Publishing. (c) MEMS-tunable varifocal transmissive Si metasurface doublet with adjustable separation controlled by out-of-plane electrostatic forces between the substrates supporting the two metalenses. Adapted with permission from Ref. [472] © Springer Nature. (d) MEMS-actuated varifocal transmissive Alvarez metalens by introducing lateral displacement between two static metalenses using comb-drive actuators. Adapted with permission from Ref. [475] © Springer Nature.

Fig. 21. MEMS-activated metasurfaces with 2D-to-3D transformations. (a) Optical nano-kirigami with pinwheel and spiral arrays for reflective intensity modulation and tunable circular dichroism. Adapted with permission from Ref. [476] © Springer Nature. (b) MEMS cantilever-controlled plasmonic color filter demonstrating dynamic plasmonic colors with adjustable transmittance, designed for sustainable optical displays. Adapted with permission from Ref. [480] © AAAS.