Electrically tunable metasurfaces: from direct to indirect mechanisms

Abstract

Developments of nanofabrication process open a new window to control electromagnetic waves using subwavelength nanostructures array, named metasurfaces. Although the metasurfaces have succeeded in achieving unprecedented functionality by arranging various shapes of nanostructures to modulate the properties of the incident light, inherent passive characteristics make it impossible to alter the engraved functions after it is fabricated. To give tunability to metasurfaces, various methods have been proposed by using a thermal, chemical, optical and physical stimulus. In particular, electrically tunable metasurfaces are attractive in that they are easy to control precisely and could be integrated into electronic devices. In this review, we categorize the representative electrical tuning mechanisms and research into three; voltage-operated modulation, electrochemical-driven modulation, and externally mediated modulation. Voltage-operated modulation uses materials that could be directly reorganized by an electric field, including liquid crystals and Drude materials. Electrochemical-driven modulation adjusts the optical properties of metasurfaces through electrochemical responses such as electrochromism and electrodeposition. Lastly, externally mediated modulation causes a change in the geometric parameters of metasurfaces or in the phase of the constituent materials by converting electrical energy into thermal or mechanical stimulation. This paper concludes after explaining the pros and cons of each mechanism and the new possibilities that electrically-responsive metasurfaces could bring about.

Recent Advances and Prospects of Optical Metasurfaces

“…In addition to the combination mode, the displacement and rotation between the two cascaded metasurfaces can also be regarded as novel degrees of freedom for dynamic modulation (Figure d). At the same time, holographic multiplexing schemes based on active metasurfaces have been proposed, including phase-change property, , electro-optic effect, , chemical tuning, − mechanical tuning, and immersive tuning. , Combining Micro-Electro-Mechanical System (MEMS), liquid crystals, and other modulation devices, dynamic metasurfaces with high resolution and large FOV are promising for wide applications. Several reviews have been published on active metasurfaces, providing comprehensive summaries and valuable prospects. ,− …”

Dynamic Chiral Metasurfaces for Broadband Phase‐Gradient Holographic Displays

“…The degree of freedom includes multiple information specifically for metadisplays into a single metasurface with dynamic optical response and integration with external stimuli. [45][46][47] Such dynamic responses are accomplished by phase-change materials (PCMs), [48] such as Vanadium dioxide (VO 2 ) [49,50] and germanium antimony tellurium (GST). [51] However, these materials offer tunability by changing their state from crystalline to amorphous upon applying various electrical and thermal stimuli that eventually vary the material's refractive index (n).…”

Comparison of Electrodeposited and Sputtered Tungsten Trioxide Films for Inorganic Electrochromic Nanostructures

“…The combination of solid electrochromic materials and structural colors has been the subject of intense research in recent years with many potential applications. − The main motivation is to develop energy-saving displays that reflect ambient light instead of relying on emissive pixels (as in ordinary liquid crystal displays or light-emitting diode displays). Although combinations of electrochromic materials can provide a full color range, the integration with structural coloration in ultrathin layers is viewed as a possibility for more vibrant colors and higher contrast.…”