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“Crypto-Display” in Dual-Mode Metasurfaces by Simultaneous Control of Phase and Spectral Responses
Yoon, Gwanho,Lee, Dasol,Nam, Ki Tae,Rho, Junsuk American Chemical Society 2018 ACS NANO Vol.12 No.7
<P>Although conventional metasurfaces have demonstrated many promising functionalities in light control by tailoring either phase or spectral responses of subwavelength structures, simultaneous control of both responses has not been explored yet. Here, we propose a concept of dual-mode metasurfaces that enables simultaneous control of phase and spectral responses for two kinds of operation modes of transmission and reflection, respectively. In the transmission mode, the dual-mode metasurface acts as conventional metasurfaces by tailoring phase distribution of incident light. In the reflection mode, a reflected colored image is produced under white light illumination. We also experimentally demonstrate a crypto-display as one application of the dual-mode metasurface. The crypto-display looks a normal reflective display under white light illumination but generates a hologram that reveals the encrypted phase information under single-wavelength coherent light illumination. Because two operation modes do not affect each other, the crypto-display can have applications in security techniques.</P> [FIG OMISSION]</BR>
Electrically tunable metasurface perfect absorber for infrared frequencies
Yoon Gwanho,So Sunae,Kim Minkyung,Mun Jungho,Ma Ren-Min,노준석 나노기술연구협의회 2017 Nano Convergence Vol.4 No.36
We theoretically investigate a metasurface perfect absorber based on indium-tin-oxide as active material. Our design scheme relies on conventional metal–oxide–semiconductor model and the Drude model. Inducing a voltage into the device causes a blue-shift of 50 nm in the reflectance spectrum in the infrared region. The total thickness of the device is only 3.5% of the working wavelength λ = 2.56 μm, and the rate of reflectance change reaches 5.16 at λ = 2.56 μm. Because the material that we use has advantages of easy fabrication and fast response, our design approach can be used for numerous applications on active plasmonic sensors and filters.
윤관호(Gwanho Yoon),이다솔(Dasol Lee),노준석(Junsuk Rho) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
Dual-mode metasurfaces enabling simultaneous control of phase and spectral responses have been demonstrated. Conventional metasurfaces have shown many promising functionalities such as super-lensing, negative refraction and optical cloaking, but their operation is restricted by spatial coherence of light sources. In this work, we have exploited typical geometric metasurfaces to manipulate phase responses while reflection spectrum is also controlled by specific shape of each nanostructure. Two functionalities can be independently controlled, so the dual-mode metasurface can work as not only a hologram under coherent light, but also a colored reflective display under white light illumination.
Facile Nanocasting of Dielectric Metasurfaces with Sub-100 nm Resolution
Kim, Kwan,Yoon, Gwanho,Baek, Seungho,Rho, Junsuk,Lee, Heon American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.29
<P>This work presents a facile nanocasting technique to fabricate dielectric metasurfaces at low cost and high throughput. A flexible polymer mold is replicated from a master mold, and then the polymer mold is used to shape particle-embedded UV-curable polymer resin. The polymer mold is compatible with flexible and curved substrates. A hard-polydimethylsiloxane improves mechanical stability of the polymer mold providing sub-100 nm patterning resolution. The patterned resin itself can work as a metasurface without secondary operations because dielectric particles sufficiently increase the refractive index of the resin. The absence of the secondary operations allows our method to have higher productivity and cost competitiveness than those of typical nanoimprint lithography. Experimental demonstration verifies the feasibility of our method, and the replicated metasurface exhibits a conversion efficiency of 46% in the visible, which is comparable to metasurfaces based on low-loss dielectrics. Given that conventional dielectric metasurfaces have been fabricated by electron beam lithography at formidable cost due to low throughput, our method will be a promising nanofabrication platform and thereby facilitate commercialization of dielectric metasurfaces.</P> [FIG OMISSION]</BR>
Complete amplitude and phase control of light using broadband holographic metasurfaces
Lee, Gun-Yeal,Yoon, Gwanho,Lee, Seung-Yeol,Yun, Hansik,Cho, Jaebum,Lee, Kyookeun,Kim, Hwi,Rho, Junsuk,Lee, Byoungho The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.9
<P>Reconstruction of light profiles with amplitude and phase information, called holography, is an attractive optical technology with various significant applications such as three-dimensional imaging and optical data storage. Subwavelength spatial control of both amplitude and phase of light is an essential requirement for an ideal hologram. However, traditional holographic devices suffer from their restricted capabilities of incomplete modulation in both amplitude and phase of visible light; this results in sacrifice of optical information and undesirable occurrences of critical noises in holographic images. Herein, we have proposed a novel metasurface that is capable of completely controlling both the amplitude and phase profiles of visible light independently with subwavelength spatial resolution. The full, continuous, and broadband control of both amplitude and phase was achieved using X-shaped meta-atoms based on the expanded concept of the Pancharatnam-Berry phase. The first experimental demonstrations of the complete complex-amplitude holograms with subwavelength definition at visible wavelengths were achieved, and excellent performances with a remarkable signal-to-noise ratio as compared to those of traditional phase-only holograms were obtained. Extraordinary control capability with versatile advantages of our metasurface paves a way to an ideal holography, which is expected to be a significant advancement in the field of optical holography and metasurfaces.</P>