Introduction

Metasurfaces, a two-dimensional (2D) version of metamaterials1,2,3,4 composed of subwavelength planar meta-atoms, possess the ability to freely manipulate electromagnetic (EM) waves. Unlike traditional metamaterials, metasurfaces harness the abrupt phase changes at the interfaces through the interaction between EM waves and meta-atoms. This mechanism, which differs from the phase accumulation in bulk media typical of metamaterials, simplifies fabrication and enhances the flexibility of applications. Owing to the versatile design capabilities of metasurfaces, a variety of ultrathin planar optical devices have been rapidly developed. These are now widely employed in many fields, including frequency filtering5, holographic displays6,7, beam steering8, meta-lenses9,10, and others11,12,13.

However, the functionality of most metasurfaces is intrinsically linked to their structures, becoming fixed once fabrication is complete, thus limiting their functionalities and applications. Dynamic tuning is thus expected in metasurfaces to significantly enhance their wave manipulation flexibility. Such reconfigurability enables independent or simultaneous manipulations of phase, amplitude, and polarization, as well as the temporal and spatial response in the spectrum. Commonly, it is achieved by integrating static metasurfaces with active materials and/or tunable mechanisms, allowing the EM waves to be controlled through external stimuli.

In recent years, extensive efforts have been focused on developing reconfigurable metasurfaces through the use of adaptable materials and innovative triggering approaches14,15,16,17. Well-known materials used for tunability include liquid crystals (LCs)18,19, transparent conducting oxides (TCOs)20,21, 2D materials22, and phase change materials (PCMs)23,24,25,26, etc. The principal mechanisms for tuning these metasurfaces encompass mechanical, thermal, and electrical control, as well as micro/nano-electromechanical systems and nonlinear optical control27,28,29. Therein, mechanically reconfigurable metasurfaces, which are defined as metasurfaces capable of converting external stimuli into physical structural changes, have attracted significant interest from researchers in a wide variety of fields. Mechanically reconfigurable metasurfaces can be triggered by a variety of external stimulations, such as physical stretching, electrostatic force, temperature change, etc., which are potentially compatible with different application environments. Compared with other reconfigurable schemes that are only applicable to specific materials, such as LC, phase change materials (VO2, GST), 2D materials (graphene), and transparent conducting oxides (ITO), one advantage of the mechanically reconfigurable metasurfaces is the broad material applicability. For refs. 16,28, a comparison of several representative reconfiguration mechanisms is summarized in Table 1. In this article, we briefly review the key advancements in this rapidly evolving field, with a specific focus on the tuning mechanisms and practical applications of mechanically reconfigurable metasurfaces.

Table 1 A comparison of several representative reconfiguration mechanisms
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Mechanical reconfiguration from different external stimuli

The geometric pattern of metasurfaces is critical for the functionality of optical devices. Reconfigurable metasurfaces can be achieved by mechanically altering the geometric structures of constituent meta-atoms or by adjusting the spacing between adjacent meta-atoms and between meta-atoms and their substrates. Changes in the distance can manipulate near-field interactions among the meta-atoms, leading to significant alterations in the EM properties of the entire meta-system. In this section, we summarize different dynamic control methods and mechanisms of mechanical reconfiguration based on different external stimuli such as pre-stressing force, electrostatic interaction, thermal effect, photo-mechanics and so on.

Mechanical reconfiguration based on stretch-pressed flexible substrates

Flexible substrates can serve as a direct platform for realizing reconfigurable meta-devices. By stretching or compressing these flexible photonic materials, the functional nanostructures on elastic substrates undergo geometric deformation. This leads to a tunable enhancement of the EM field. In 2010, Pryce et al.30 reported a compliant metasurface with a tunability of ∆λ ~400 nm, utilizing the elasticity of a flexible substrate. Such a substrate enabled the tuning of resonant frequency in the near-infrared region by altering the distances and, consequently, the coupling strength between pairs of resonator elements. As illustrated in Fig. 1a, stretching the substrate increases the gaps between metallic resonators, modulating both the capacitance of the split-ring-resonator (SRR) gap between resonators, thereby achieving significant resonant-frequency tuning. Subsequently, Philipp Gutruf et al.31 proposed a mechanically tunable metasurface design based on dielectric resonators, operating at visible wavelengths. With a mere 6% applied strain, there was a measured shift of the resonance peak by 5.08% towards the red under y-polarization and by 0.96% towards the blue under x-polarization. Besides lateral stretching, the elastic deformation in z-direction can introduce a controllable chiroptical response in the metasurfaces. Zhiguang Liu et al.32 successfully achieved a wide-range reconfiguration of circular dichroism (CD) at optical wavelengths through reversible vertical compression of the stereo metasurfaces using a fiber tip. When the fiber tip touches and compresses the sample, the height of the stereo structures decreases, leading to a significant alteration in the twisted geometries and then the CD response, as shown in Fig. 1b. Additionally, Xiaoyu Hou et al.33 developed a novel multichannel information encryption strategy based on structural color. The strategy employs the orientations of one-dimensional gratings, as illustrated in Fig. 1c. Initially, the patterns are entirely concealed when the sample is in a relaxed state. However, when the sample is progressively stretched, the patterns ‘BR’ and ‘river’ become visible as the square units rotate to 15° and 30°, respectively.

Fig. 1: Mechanical control based on a stretch-pressed flexible substrate.
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a Dynamic resonant-frequency tuning achieved with mechanically switchable metasurfaces based on a flexible substrate in IR regime30. b Mechanical compression and release of a three-arm pinwheel array change the height of the pinwheels, enabling reversible switching between chiral transmission and non-chiral transmission32. c Grating patterns with different azimuth angles (illustrated by code patterns) and the process of reading encrypted patterns by stretching33. d 3D morphable meso-structures formed by mechanically guided buckling and twisting on elastomeric kirigami substrates. (i) pre-stretching a substrate with engineered kirigami cuts to 100% biaxial strain; (ii) bonding of a 2D precursor onto the pre-stretched kirigami substrate at selected regions (circular pads); (iii) releasing of the substrate pre-strain to 40%, thereby causing the structure to buckle; (iv) further releasing of the substrate pre-strain to 0%, thereby causing the structure to twist99.

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Furthermore, pre-stretched elastic substrates can help the assembly of three-dimensional (3D) nanostructures from 2D precursors34,35,36. In 2018, Wenjie Liu et al.37 developed a ‘metal-assisted transfer’ technique, achieving mechanical buckling and twisting of meso-structures on elastomeric kirigami substrates. As shown in Fig. 1d, by adhering the 2D precursor to the pre-stretched kirigami substrate and then progressively releasing the pre-strain from 100% to 0%, the structures show prominent buckle at 40% pre-strain and twisting at 0% pre-strain.

Despite the limited modulation rate of switchable metasurfaces based on elastic materials, Flexible substrates integrated with functional components provide rich deformability, broad tunability, and biocompatibility38. This mechanically tuned approach has been widely applied in a range of stretchable photonic applications, encompassing flexible electronics, mechano-sensing, and camouflage39.

Mechanical reconfiguration based on electrostatic interaction

As the main challenge of metasurfaces based on flexible substrates, the setups that offer stretching or pressing increases the complexity of integration and miniaturization. To improve the integrability, dynamic tunability of metasurfaces in response to electrical stimuli, along with their tuning mechanisms, has been extensively studied. One primary approach is integrating meta-atoms with various electrically sensitive materials, such as LCs40, doped semiconductors41, 2D materials42, and others. In addition to altering the material properties of metasurface structures and their environments, the micro-electro-mechanical systems (MEMS) technique also provides significant inspiration for researchers. In MEMS, structures can be dynamically reconfigured under the electrostatic force induced by voltage input, thus altering the morphology or adjusting the distances between meta-atoms and their substrates. For instance, the electrostatic field-based reconfigurable nano-kirigami metasurfaces, as shown in Fig. 2a, constitute a nano-electromechanical system built on an Au/SiO2/Si substrate. When there is a potential difference between the top gold nanostructure and the bottom silicon substrate, the generated attractive electrostatic force will induce vertical displacement of the transformable units. As a result, a high modulation contrast of 494% at near-infrared wavelengths and reconfigurable optical chirality is successfully achieved in this deformable metasurfaces system43. Other optical functionalities achieved using reconfigurable nano-kirigami metasurfaces, such as beam focusing, holographic imaging, and deflection conversion, have been reported44. Longqing Cong et al.45 introduced a multifunctional operation plate, where the cantilever angle, controlled by MEMS-voltage, reconfigures the resonance and radiation phase of each dipolar element. As shown in Fig. 2b, the device involves a suspended metasurface composed of Si antenna arrays, with each antenna functioning as an individual Mie resonator for manipulating light. By applying actuation voltages ranging from 0 to 2.75 V, the gap between the suspended metasurfaces and the Si substrate varies, resulting in changes to the Fabry-Perot modes and, consequently, a visible color shift. More importantly, continuous dynamic beam steering and light focusing can be realized through complete phase control, enabled by micro-electro-mechanical movement in silicon antenna arrays46. Similarly, Xinyu Liu et al. demonstrated a room-temperature dynamic metamaterial IR emitter47. The metamaterial is designed for low emissivity in its free-standing state, but upon applying bias voltages, the top layer is pulled down by electrostatic forces, resulting in high emissivity near 9 μm wavelength, as illustrated in Fig. 2c. Furthermore, mechanical reconfiguration-based on electrostatic interactions offers a platform for opto-electro-mechanical (OEM) switches. Figure 2d shows how the bending of a gold membrane (dz) causes a resonance shift (Δλres) by altering the mode index. This modification allows incident light in the through port to switch between the drop state and through state, depending on the resonant wavelength (λres) encountered.

Fig. 2: Mechanical control based on electrostatic interaction.
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a Modulation contrast and optical chirality of the electrostatic field-based reconfigurable nano-kirigami metasurfaces43. b Spatial control over the reflection phase based on metasurface with MEMS46. c An IR emitter that can be spatially and temporally controlled in real-time based on electrically actuated MEMS metamaterials47. d A hybrid photonic–plasmonic disc resonator with a vertical gap tuned by electrostatic forces. The resonant spectra can be tuned with a speed of 12 MHz93.

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Electrostatic reconfiguration strategy, as one of the friendliest to integrate with prior art, has the characteristics of fast response time, wide response range, and no special requirements for the use environment. Although electrostatic force may not induce large deformations, it is frequently utilized in MEMS actuation, especially when integrating metasurfaces onto silicon-on-insulator, which is crucial in recently integrated optoelectronic systems. Combining MEMS with metasurfaces paves the way for developing applications in CMOS integration, such as dynamic reconfigurability for light detection and ranging (LiDAR), imaging, and other specialized applications.

Mechanical reconfiguration based on thermal effects

Beyond electrostatic actuation that requires well-organized circuits, thermal effect is another approach to introduce mechanical deformation with relatively simple designs. Such thermally reconfigurable metasurfaces rely on the differential expansion of materials48,49,50,51. These metasurfaces are typically composed of two material layers with differing coefficients of thermal expansion (CTE). One layer, often made of materials like Al or Cu, exhibits a higher CTE, while the other layer, made of materials such as SiO2 or W, has a relatively lower CTE. As temperature varies, the layer with the higher CTE undergoes more pronounced shape changes due to thermal expansion and/or contraction, compared to the layer with the lower CTE. This differential expansion results in the structure gradually bending towards the side with smaller shape change, significantly altering the structure and morphology of the metasurfaces. As illustrated in Fig. 3a, the 3D split-ring resonators (SRRs), made of a substrate-free silicon nitride/gold composite film, can reversibly switch between closed and split states. This change is due to the deformation of the double-layer film caused by Joule heating, which directly alters the gap width. Consequently, the interaction between incident light and the structure can be modulated by the gap width-governed LC model. As a result, the resonant dip in the reflection spectra can shift within the range of 10.4 and 6.3 μm, with a reflection change reaching up to 95%52. Similarly, Fig. 3b depicts a switchable winding-shaped cantilever material (WCM) used for active logical modulation. By applying a DC bias voltage, the released WCM bends downwards towards the Si substrate under Joule heat, enabling logical modulation bits to represent ‘on’ and ‘off’ states by alternating the position of the WCM53. In addition, as illustrated in Fig. 3c, d, PCMs, particularly VO2, can serve as electrothermal mechanical actuators, diverging from the conventional VO2-based optical devices that rely primarily on VO2’s optical properties. Xi Wang et al. developed a multifunctional micro-electro-optomechanical systems (MEOMS) platform, consisting of a cantilever array made of VO2, chromium, and gold nanolayers. Notably, these devices exhibit over 50% light modulation efficiency across a broad wavelength range54. Kai Liu et al. demonstrated micro bimorph coils functioning as efficient torsion muscles, utilizing the metal-insulator phase transition in VO2 thin films that were actuated by increasing the temperature of the entire chip (global heating), more conveniently, by Joule heating of current flowing through the coil itself, as shown in Fig. 3d55.

Fig. 3: Mechanical control based on thermal effects.
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a Reversible switching of an electrothermal tunable 3D SRR metasurface in the infrared (IR) wavelength region52. b Schematic drawings of MEMS-based WCM used as an electrothermal actuator as well as resonator in THz wavelength region53. c The MEOMS multifunctional platform with curved cantilevers at room temperature (T < TC) and flat cantilevers at temperature above TC (T > TC), showing greater than 50% optical modulation depths over a broad wavelength range54. d Micro bimorph coils that function as powerful torsional muscle55. e Various plasmonic paintings (butterfly and temple symbols) based on sodium-based plasmonic color-manipulation strategy by direct heating56. f A temperature-dependent optical response of ordered lattices of noninteracting gold-core/PNIPAM57.

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Additionally, a select few materials can directly exhibit a volumetric morphological response to temperature changes. For instance, sodium metasurfaces, being an alkali metal with active physicochemical properties and a low melting point of 97 °C, can transition from anti-dome to dome structures through direct heating and continuous filling, resulting in a resonance shift, as illustrated in Fig. 3e. Moreover, an innovative thermosensitive ‘invisible ink’ device was shown to transition from a mirror state to a metasurface state56. Michele Magnozzi et al. explored the temperature-dependent optical response of ordered lattices of noninteracting gold-core/poly(N-isopropylacrylamide)-shell nanoparticles (PNIPAM). PNIPAM, a thermoresponsive polymer, undergoes a volume phase transition (VPT) in an aqueous environment above its critical solution temperature of ~32 °C, as shown in Fig. 3f57.

Temperature can be modulated by various methods, such as global heating, Joule heating, and photothermal excitation. While the operational speed is typically low due to the gradual nature of temperature increases in direct heating or electrothermal methods, the photothermal effect under ultrafast optical excitation has been demonstrated to facilitate phase transition processes within a timescale of approximately picoseconds58. Meanwhile, the differential expansion-based mechanism asks for the deformation to be proportional to the functional unit, which limits the modulation depth in microscale, especially in the visible wavelength range.

Mechanical reconfiguration based on other responses

In order to enhance the modulation speed on thermally sensitive metasurfaces and other tunable metasurfaces, the fastest modulation scheme in reconfigurable metasurfaces relies so far on ultrafast light pulses, capable of achieving modulation speeds at the picosecond or even femtosecond scale59,60,61. Additionally, optical forces at the sub-micron scale can be comparable to or larger than elastic forces, offering a potential approach for achieving reconfigurable mechanical deformations in metasurfaces with rapid modulation speeds. Artemios Karvounis et al. developed an all-dielectric metasurface featuring sharp near-infrared optical resonances, constructed from a 100 nm thick polycrystalline silicon membrane within a silicon frame. This metasurface demonstrates strong optical nonlinearity due to light-induced nano-mechanical oscillations, altering the physical configuration and resonant response of its constituent metamolecules. As shown in Fig. 4a, the optomechanical resonance intensifies with increasing pump intensity, reaching a peak modulation depth of 0.2% at a central frequency of 152 MHz62.

Fig. 4: Mechanical control based on other interactions.
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a Intensity-dependent optical force-actuated nano-optomechanical systems (NOMS) reconfiguration in a dielectric metamateria62. b Displacement of the spiral structure with respect to the applied pressure, which deformed the planar spiral to a left-handed or right-handed helix63. c Principle of pneumatically reconfigurable nano-kirigami metasurfaces and the modulation contrast of reflection based on the tunable metasurfaces64. d Active polarization conversion of microwaves achieved by a liquid-metal-incorporated metasurface realized with micro-fluidics technology66.

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Pneumatic force is a unique actuate method that provides large deformations with substantial modulation contrast. In 2015, Tetsuo Kan et al. showcased a vertical deformation of a planar spiral by introducing pneumatic force. Figure 4b illustrates the displacement of the spiral structure with respect to the applied pressure. The deformation direction can be reversed by alternating the pressure between the upper and lower chambers, allowing the selection of handedness for the 3D deformed spiral63. Similarly, but on a much smaller scale, Shanshan Chen et al. employed the pneumatic force to reconfigure the nano-kirigami metasurface on a free-standing gold/silicon nitride nanofilm. This 2D-to-3D transformation leads to a striking and reversible shift in plasmonic quadrupole modes, achieving a significant 137% modulation in reflection64.

Beyond optical forces and pneumatic pressure, microfluidic methods offer another avenue for metasurface configuration control. By varying the filling factors of metal liquids or solvents within microfluidic channels, precise and continuous modulation of each meta-atom’s EM response can be achieved65,66. For example, in 2015, Liu’s group developed a reconfigurable metalens by embedding resonators in microfluidic channels, subsequently demonstrating its dynamically switchable focusing effect. Additionally, P. C. Wu et al. reported a broadband, wide-angle, multifunctional polarization converter which utilizes L-shaped galinstan resonators, as shown in Fig. 4d66.

Applications from mechanically reconfigurable metasurfaces

Reconfigurable metasurfaces hold great promise for broadening the functionality of optical devices and facilitating the development of photonics. In this section, we summarize recent advances in common applications such as dynamic focusing, image display, beam steering, polarization manipulator, radiative cooling, and so on.

Dynamic beam focusing

Traditional lens imaging typically changes the thickness of glass or plastic lenses to alter the phase delay, thus controlling the focal length. However, in accordance with the Generalized Snell’s law67, metasurfaces can induce complete phase change (0 ~ 2π) in subwavelength scale. Such “metalens” offers a new approach for miniaturized imaging. A range of external stimuli has been investigated to introduce tunability into metalens, thus expanding the capabilities of imaging technology. For example, Ho-Seok et al. demonstrated an ultrathin, 1.7× zoom lens operating at 632.8 nm. As shown in Fig. 5a, they mechanically altered the lattice constant of the metal micro/nanostructures, which are placed on a soft PDMS substrate68. Figure 5b features a strain-based tunable metalens operating at 915 nm, with focal distances ranging from 600 μm to 1400 μm69. Figure 5c presents a moiré metalens with a tunable focal length from negative to positive at 900 nm, achieved by rotating the angle between layers70. In Fig. 5d, we observe the photo-responsive bending, which facilitates the adjustment of the focal distance. By modulating the incident laser intensity, the deformation of silicon materials can be rapidly altered in the order of 10 ms, with a focal length modulation exceeding 5%71. As shown in Fig. 5e, Faraon et al. employed MEMS to change the interspace between two distinct layers of metasurfaces. This design yields a tunable lens characterized by an extensive focal length range and an expansive field of view (~40 degrees), which is particularly advantageous for 3D imaging applications72. Moreover, Alan Sha and colleagues pioneered a technique for manipulating the strain field of a substrate through the application of an electrical bias to dielectric elastomer actuators. This approach affords meticulous control over various optical parameters, including focal length, astigmatism, and lateral shift73.

Fig. 5: Imaging applications of several typical mechanical tunable meta-lenses.
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a A mechanically reconfigurable metalens through mechanically controlling geometries of nanostructures on the PDMS substrate68. b Highly tunable dielectric metasurface devices based on subwavelength-thick silicon nano-posts encapsulated in a thin, transparent elastic polymer69. c A moiré metalens with wide focal length tunability from negative to positive by mutual angle rotation at the wavelength of 900 nm70. d An ultrathin tunable metalens whose focal distance can be changed through optomechanical control with moderate continuous-wave intensities71. e MEMS-controllable gap between two substrates with metasurface nanostructures72.

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Image display

The advancement of high-performance and multifunctional color displays is an important direction in the field of image display. Aiming to align closely with the human visual experience, the accurate transmission and reproduction of color information are highly desired. Holography emerges as an exemplary 3D display methodology, primarily due to its capability to capture both intensity and complex phase information of the light field. However, the development of holographic technology is impeded by changes such as limited field of view and constrained information capacity. Metasurfaces, as innovative optical field control devices, hold the key to driving significant advancements, attributed to their minute pixel size and robust control capabilities. Especially, the exploration of dynamic holographic displays remains critically important.

Metasurface holograms fabricated on stretchable substrates exhibit the capability for dynamic reconfiguration through isotropic stretching, facilitating the multiplexing of two or more distinct holographic images. As demonstrated in Fig. 6a, gold nanorods, arranged under the guidance of the Pancharatnam-Berry phase principle, were integrated onto PDMS substrates to realize strain-multiplexed metasurface holograms. The stretching of the metasurface results in an increase in the hologram image size and a corresponding shift of the hologram image plane away from the metasurface. This design enables the transition between different holographic images74. To mitigate the effects of anisotropic deformation caused by stretching, Zhang et al. introduced a novel approach with a polarization-insensitive, stretchable TiO2 metasurface. This was achieved by harnessing two distinct mechanisms: near-field mutual interaction and grating effects75. Electrically tunable metasurfaces are increasingly recognized as a leading approach for realizing interactive holographic displays, primarily due to their compatibility with conventional electrical equipment. In their research, Yu Han and colleagues provided a proof of concept exhibiting a reprogrammable metasurface. This advanced design, based on the cutting-edge electromechanical nano-kirigami, enables the independent manipulation of individual pixels at visible wavelengths through the mechanical deformation of nanostructures. As depicted in Fig. 6b, the application of a programmable voltage distribution facilitates the independent control of out-of-plane deformation for each pixel, along with its corresponding phase retardation, which supports the functionality of the reprogrammable metasurface holograms76.

Fig. 6: Dynamically tunable displays.
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a Optical metasurfaces holograms based on a flexible substrate: optical holograms at unstretched and stretched states (right)74. b Pixelated voltage-controllable nano-kirigami patterns for holographic displays76. c Schematic of improving the performance of structural color of the Si metasurfaces by covering a refractive index matching layer11. d A flexible, high-contrast meta-structure (HCM) whose color can be varied by stretching the membrane78.

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Structural color originates from the interaction of light with resonant units through interference, diffraction, or scattering, with the resultant color being determined by the physical feature sizes and shapes of these resonant units. Achieving a wide color gamut, high brightness, and high resolution has long been a primary objective in display technology. The capability to actively modulate the perceived color of objects holds immense potential for a variety of applications, including camouflage, sensing, and dynamic displays. In 2018, Shang Sun et al. demonstrated the feasibility of real-time tunable colors employing microfluidic reconfigurable all-dielectric metasurfaces. This was achieved by varying the refractive index within the microfluidic channels, significantly altering the Mie resonances of the dielectric nanostructures, thereby enabling control over the reflection spectra and corresponding colors of the metasurface77. Additionally, they suggested that the incorporation of a refractive index matching layer could prominently enhance both the brightness and color purity, as shown in Fig. 6c. Figure 6d illustrates a flexible, high-contrast structural color design, composed of silicon meta-structures embedded in a flexible membrane. The color properties of this arrangement can be dynamically altered by stretching78.

Beam steering and other optical reconfigurations

Dynamic steering of optical beams is critical in various domains, including radar, optical communication, laser processing, 3D printing, and other emerging technologies. Reconfigurable metasurface is considered to be a promising approach for comprehensive control over the characteristics of light. Chao Meng et al. developed an innovative, electrically driven dynamic MEMS optical metasurfaces (MEMS-OMS) platform, enabling both phase and amplitude modulation of reflected light. As shown in Fig. 7a, for a predetermined minimum air gap, the gap-surface plasmon (GSP)-based OMS is designed to exhibit specific functionalities, which can be activated or deactivated by adjusting the MEMS mirror toward or away from the OMS surface. This platform allows for dynamic polarization-independent beam steering and reflective 2D focusing, presenting high efficiency (~50%), broadband capability (~20%), and rapid response (<0.4 ms)79. Figure 7b demonstrates a monolithic MEMS integrated with a metalens that can focus light at the mid-infrared wavelength. The 2D angular rotation of metalens can be electrically controlled, altering the position of the focal spot by approximately 9° 80. Furthermore, Lizhi Xu et al. demonstrated that kirigami sheets composed of stiff/strong nanocomposites can function as tunable diffraction gratings, producing wide-angle diffraction, as shown in Fig. 7c81. The angular range for beam steering achievable with these sheets can extend up to 6.5° for a 635 nm laser beam, a significant improvement compared to the ∼1° and ∼0.02° ranges achieved with surface-grooved elastomer gratings and MEMS gratings, respectively.

Fig. 7: Applications in other optical reconfigurations.
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a An electrically driven dynamic MEMS-OMS platform that offers controllable phase and amplitude modulation of the reflected light by finely actuating the MEMS mirror79. b A 2D scanning MEMS platform controls the angle of the lens along two orthogonal axes by ±9°, thus enabling dynamic beam steering80. c Kirigami nanocomposites as wide-angle diffraction gratings81. d Close-loop nano-kirigami with giant optical chirality in 3D state84. e A dynamic and multifunctional thermal emitter based on deformable nano-kirigami structures82.

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In addition to beam steering capabilities, mechanically reconfigurable metasurfaces also play an important role in manipulating nonlinearity, polarization conversion, thermal radiation, etc82,83. For example, the nano-kirigami structure developed by Zhiguang Liu et al. exhibited a tremendous chiral transformation, attributed to the nanoscale 3D twisting features generated from the 2D-to-3D transition, as shown in Fig. 7d84. Given the scarcity of such extensive on-chip reconfigurable CD applications, this unique structure presents a valuable platform for advancing research in CD reconstruction85,86. Additionally, Xing Liu et al. reported a design that achieves broadband (covering 870 nm) and high-efficiency (>90%) linear polarization conversion in the near-infrared wavelength range, enabled by the transformation of structures from 2D-to-3D87. Yinghao Zhao et al. proposed a dynamic and multifunctional thermal emitter based on deformable nano-kirigami structures, which can be actuated by electronic bias or mechanical compression, as shown in Fig. 7e. By applying an electric bias, the helical structure will deform downward, causing the decrease of emittance and radiation intensity. Particularly, this article theoretically and experimentally verified that a composite structure of nano-kirigami and PDMS thin film could work as a thermal management device, which can dynamically switch the state of cooling and heating by simply pressing the device82.

Conclusion and outlook

In conclusion, dynamically reconfigurable metasurfaces, with their advantageous properties over traditional optics, have witnessed rapid development in the past decade. This advancement has catalyzed a variety of applications in the next generation of nanophotonics, including augmented reality/virtual reality (AR/VR) display, LiDAR, autonomous vehicles, etc. On the other hand, the growing demands of these innovative domains for complete control of the interaction between EM waves and meta-atoms have further stimulated the research of dynamically reconfigurable metasurfaces. Among various approaches, mechanically configurable metasurfaces stand out as a particularly effective method, which enables direct modification of the geometrical parameters of the cells, and, thus, fundamentally determines the properties of the metasurfaces.

In this review, we have comprehensively summarized the methodologies for realizing mechanically reconfigurable metasurfaces, including mechanical engineering, electrostatic actuation, thermal control, and photo-mechanics, along with their appealing applications. The use of elastic deformation in flexible substrates emerges as a straightforward and convenient approach to alter the geometrical parameters of structures, offering a large response range and a simple fabrication process. However, this method encounters limitations, such as the challenges in integration with other systems, which limit its further advancement. Electrical tuning methods currently dominate the field in the development of tunable metasurfaces. Electrostatic actuation, in particular, is distinguished by its rapid response time, broad response range, and versatility across various application environments. Most importantly, electrically tunable metasurfaces are compatible with mature CMOS technologies, presenting significant potential for mass production. Nevertheless, metasurfaces based on electrostatic actuation that incorporate MEMS typically exhibit limited control ranges and require complicated structural systems. There is a pressing need to miniaturize movable structures to the nanometer scale, which will extend the working wavelength to IR and/or visible range. Thermal control presents unique advantages in specific scenarios, yet their response speed could be enhanced through the design and development of materials with high thermal conductivity and low specific heat capacity. Such optimization targets the improvement of heat transfer efficiency by refining the heat transfer path. Optomechanical methods, benefiting from their non-contact nature, show promising prospects for practical applications. The primary challenge here is to develop materials that have a broad responsive spectrum and low activation thresholds. Additionally, pneumatically reconfigurable metasurfaces, microfluidic techniques, and other strategies with distinct advantages and are well-suited for specific operating scenarios.

In summary, the field of dynamically reconfigurable metasurfaces continues to pursue advancements in rapid response speeds, user-friendly control mechanisms, easy integration, and multifunctionality, envisioning significant potential for further exploration and development. Especially as one important development trend, addressable optical metasurfaces capable of pixelated reconfiguration that make the dynamical reconfiguration more flexible and powerful is highly desirable for practical applications88,89. Nevertheless, the addressable optical metasurfaces without complex additional designs remain challenging, building up novel opportunities and challenges for the development of tunable ultrathin meta-devices at the nanoscale. It is predictable that meta-devices will replace conventional optical elements, particularly in specialized domains such as radar systems, virtual reality displays, and photonic neuromorphic computing90,91.