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Metasurfaces - from science to technology
Metallic or dielectric metasurfaces are ultra-thin and planar optical devices that promise not only to replace conventional optical components like lenses, mirrors, polarizers, waveplates, but also to be applied in practical photonic applications such as cloaking device, negative index device, metalens, metahologram, and color filter. We are designing and conducting experimental realization of those kinds of practical planar photonic devices such as 3D holographic display, multifunctional color filters and ultra-compact LiDAR. Furthermore, those two dimensional devices will revolutionize future display and sensing application such as reflective/projective displays and 3D object recognition (e.g. face ID and LiDAR).
Active Metaphotonics with Tunable Materials
To realize the 'real-time' active operations of optical metasurfaces, we utilize conventional and unconventional active medium such as liquid crystals, doped semiconductors and phase change materials. Particularly, dynamic meta-holographic displays with designer liquid crystal modulator are proposed. Such kind of approach will may open up new emerging applications such as smart hologram label for temperature/pressure/touch monitoring sensor, tangible holographic displays with touch sensing, and interactive holographic displays with haptic motion recognitions. Also, we propose a charge carrier-concentration controlled 'solid-state' tunable device based on a indium-gallium-zinc-oxide (IGZO) active layer. The IGZO-based devices are expected to be an important platform for electrically tunable solid-state devices operating at visible light. Also other intriguing active platforms have been investigated using diverse phase change materials such as VO2 and Ge2Sb2Te5.
Various exotic physics and applications of metasurfaces have been reported, but there are common issues of anisotropic and inhomogeneous characteristics such as narrow bandwidth operation, polarization dependency and incident angle dependency. Also, sometimes the function of single-layer metasurface are limited due to lack of degree of freedom. To overcome those obstacles and apply metamaterials to the device level applications, one should have to define truly three-dimensional metamaterials in the optical frequency range, or provide alternative ways to stack distinct metasurface layers to realize multifunctional devices. Therefore, the challenging tasks here are to develop new nanometer-scale 3D fabrication processes and to design novel stacked 3D structures.
Due to plasmonic mode excitation of high-k vector access in dispersion relation, light can be confined to deep sub-wavelength volume, and thereby increasing electric field dramatically. We are not only investigating the energy transportation mechanisms and applications at the nanometer length scale, but also studying various photonics devices such as nanolaser, single molecule sensor based on surface enhanced Raman spectroscopy (SERS), photocatalyst and metamaterial perfect absorber for ultrafast photothermal heating and solar energy harvesting applications.
Nanofabrication and Nanomanufacturing
Metamaterials provided a huge potential to realize scientific fictions and change the world. Current metamaterial demonstration relies on nanofabrication and nanomanufacturing techniques, so we are pursuing practical nanofabrication techniques useful for metamaterials structure realization such as ultra-high accurate electron beam lithography overlay and ultra-thin/smooth thin film deposition. However, nanofabrication is very low-throughput and high-cost technologies. Thus, we are trying to utilize conventional nanofabrication techniques for large scale fabrication such as (roll-to-roll) nanoimprinting and laser-interference lithography. Also to maximize light matter-interaction at the single-digit nanometer scale, we develop sub-10nm nanofabrication method using cascade domino patterning and atomic/molecular techniques.
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