Browsing by Author "Sun, Mao-Guo"

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Electrically tunable transmission of gold binary-grating metasurfaces integrated with liquid crystals
(2016-07-25)
Chen, Kuo-Ping
;
Ye, Shi-Cheng
;
Yang, Chi-Yin
;
Yang, Zong-Han
;
Lee, Wei
Planar photonics using metasurfaces is of great interest because a metasurface can control the flow of light beyond that attainable with natural materials. The resonance wavelength of a binary-grating metasurface is adjustable by changing the width and thickness of the nanostructure. We propose a novel combination of nematic liquid crystals and a binary-grating metasurface with which the diffraction efficiency can be controlled by adjusting the applied voltage. (C) 2016 Optical Society of America
Narrowband Wavelength Selective Thermal Emitters by Confined Tamm Plasmon Polaritons
(2017-09-01)
Yang, Zih-Ying
;
Ishii, Satoshi
;
Yokoyama, Takahiro
;
Thang Duy Dao
;
Sun, Mao-Guo
This study experimentally demonstrates infrared wavelength selective thermal emission based on Tamm plasmon polaritons (TPPs). Unlike conventional TPP structures, which have a thin metal layer on a distributed Bragg reflector (DBR), the proposed structure has a thick metal under a DBR that is more robust for thermal radiation. The number of DBR pairs is a critical factor in maximizing the narrowband emission needed to satisfy the impedance matching condition, which varies with the choice of metal film. Optimum designs for four different metals, aluminum, gold, molybdenum, and tungsten, are presented. The temporal coupled-mode theory was introduced to explain the origin of the high Q-factor of the proposed structure, which can achieve a twice higher Q factor for the measured emissivity compared to typical plasmonic thermal emitters. The structure is one-dimensional, consisting of only multilayers and free from nanopatterning, offering a practical design in applications such as gas sensing, narrowband IR sources, and thermophotovoltaics.
Nonradiating Silicon Nanoantenna Metasurfaces as Narrowband Absorbers
(2018-07-01)
Yang, Chi-Yin
;
Yang, Jhen-Hong
;
Yang, Zih-Ying
;
Zhou, Zhong-Xing
;
Sun, Mao-Guo
High-refractive-index (HRI) nanostructures support optically induced electric dipole (ED) and magnetic dipole (MD) modes that can be used to control scattering and achieve narrowband absorption. In this work, a high-absorptance device is proposed and realized by using amorphous silicon nanoantenna (a-Si NA) arrays that suppress backward and forward scattering with engineered structures and in particular periods. The overlap of ED and MD resonances, by designing an array with a specific period and exciting lattice resonances, is experimentally demonstrated. The absorptance of a-Si NA arrays increases 3-fold in the near-infrared range in comparison to unpatterned silicon films. Nonradiating a-Si NA arrays can achieve high absorptance with a small resonance bandwidth (Q = 11.89) at a wavelength of 785 nm. The effect is observed not only due to the intrinsic loss of material but by overlapping the ED and MD resonances.