Browsing by Author "Yu, Cheng-Li"

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Circular Polarized Lasing Characteristics in Metal/GaN Double-Spiral Nanowire Cavity
(2017-01-01)
Yu, Cheng-Li
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Liao, Shu-Wei
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Hsiao, Yu-Hao
;
Kuo, Hao-Chung
;
Shih, Min-Hsiung
Room temperature highly circular polarized laser was demonstrated with a compact metal/GaN double-spiral nanowire cavity. The lasing action was observed with a UV wavelength of 363 nm and a high dissymmetry factor of +1.05.
Circularly-polarized lasing of ultraviolet plasmonic gammadion nanocavity
(2019-01-01)
Cheng, Pi-Ju
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Lai, Ming-Sheng
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Hsiao, Yu-Hao
;
Yu, Cheng-Li
;
Chang, Chiao-Yun
In this work, we present the model of plasmonic chrial nanolasers composed of aluminum-coated gallium-nitride (GaN) gammadions, which may lase with a high degree of circular polarization at room temperatures. Using the finite-element method, we examine resonant modes of the four-fold rotationally symmetric cavities of gammadions whose resonant frequencies lie in the gain spectrum of GaN. We find a degenerate doublet of resonant modes which can couple to plane waves in the far-field zone above gammadions. Their near-field profiles exhibit localized distribution in the arms of gammadions and a Fabry-Perot standing-wave pattern along the post. In practice, fabrication imperfections would inevitably spoil the four-fold rotation symmetry of gammadions. Typical perturbation could lift the degeneracy of doublet and leads to mixing of the two degenerate modes which may still output signals with observable handedness above gammadions. Considering a gammadion cavity with a single elongated arm, we show that the magnitude of dissymmetry factor of its resonant mode can be larger than unity. Our calculations are consistent with the experimental results, indicating that the right-handed gammadion cavities lase with a magnitude of dissymmetry factors near 1 at a wavelength of 364 nm. The dimensionless effective mode volume scaled by the cube of effective wavelength is 2.62, reflecting a modal distribution remarkably confined in the plasmonic structures and the capability of enhancing the spontaneous-emission rate noticeably. These chiral nanolasers with an ultrasmall footprint could be potentially utilized as future circularly-polarized photon source at the chip level.
High Circular Polarized Nanolaser with Chiral Gammadion Metal Cavity
(2020-05-12)
Yu, Cheng-Li
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Hsiao, Yu-Hao
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Chang, Chiao-Yun
;
Cheng, Pi-Ju
;
Lin, Hsiang-Ting
We demonstrate a circularly polarized laser with the metal-gallium-nitride gammadion nanocavities. The ultraviolet lasing signal was observed with the high circular dichroism at room temperature under pulsed optical pump conditions. Without external magnetism which breaks the time-reversal symmetry to favor optical transitions of a chosen handedness, the coherent outputs of these chiral nanolasers show a dissymmetry factor as high as 1.1. The small footprint of these lasers are advantageous for applications related to circularly polarized photons in future integrated systems, in contrast to the bulky setup of linearly-polarized lasers and quarter-wave plates.
Hybrid Composites of Quantum Dots, Monolayer WSe2, and Ag Nanodisks for White Light-Emitting Diodes
(2020-07-24)
Chang, Chiao-Yun
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Yu, Cheng-Li
;
Lin, Chen-An
;
Lin, Hsiang-Ting
;
Lee, Andrew Boyi
We investigated hybrid zero-dimensional core-shell CdSe/ZnS quantum dot (QD)/two-dimensional monolayer WSe2 semiconductors with an Ag nanodisk (ND) for manipulating plasmonic-enhanced photoluminescence (PL) and color conversion efficiency. The absorption spectrum of the local surface plasmon resonance (LSPR) effectively overlaps with that of QDs or monolayer WSe2 to considerably enhance PL. The broad absorption spectrum of the LSPR simultaneously overlapped with the emission spectrum of QDs and the absorption spectrum of excitons in WSe2 to enhance the color conversion efficiency. The highest efficiency of color conversion from QDs to WSe2 with Ag ND was 53%. In the future, hybrid QD/transition metal dichalcogenide light emitters could be further integrated with GaN-based white light-emitting diodes to manipulate the color temperature and expand the color gamut to develop a miniature white light-emitting diode.
Large-Area and Strain-Reduced Two-Dimensional Molybdenum Disulfide Monolayer Emitters on a Three-Dimensional Substrate
(2019-07-24)
Chang, Chiao-Yun
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Lin, Hsiang-Ting
;
Lai, Ming-Sheng
;
Yu, Cheng-Li
;
Wu, Chong-Rong
Atomically thin membranes of two-dimensional (2-D) transition-metal dichalcogenides (TMDCs) have distinct emission properties, which can be utilized for realizing ultrathin optoelectronic integrated systems in the future. Growing a large-area and strain-reduced monolayer 2-D material on a three-dimensional (3-D) substrate with microstructures or nanostructures is a crucial technique because the electronic band structure of TMDC atomic layers is strongly affected by the number of stacked layers and strain. In this study, a large-area and strain-reduced MoS2 monolayer was fabricated on a 3D substrate through a two-step growth procedure. The material characteristics and optical properties of monolayer TMDCs fabricated on the nonplanar substrate were examined. The growth of monolayer MoS2 on a cone-shaped sapphire substrate effectively reduced the tensile strain induced by the substrate by decreasing the thermal expansion mismatch between the 2-D material and the substrate. Monolayer MoS2 grown on the nonplanar substrate exhibited uniform strain reduction and luminescence intensity. The fabrication of monolayer MoS2 on a nonplanar substrate increased the light extraction efficiency. In the future, large-area and strain-reduced 2-D TMDC materials grown on a nonplanar substrate can be employed as novel light-emitting devices for applications in lighting, communication, and displays for the development of ultrathin optoelectronic integrated systems.
Strain-reduced and Photoluminescence Enhanced of MoS2 Emitters on Three-Dimensional Substrate
(2020-01-01)
Lee, Andrew Boyi
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Chang, Chiao-Yun
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Lin, Hsiang-Ting
;
Lai, Ming-Sheng
;
Yu, Cheng-Li
Two-dimensional (2D) atomic transition metal dichalcogenides (TMDCs) have distinct emission properties, which can be applied for ultrathin detectors and light-emitters in the future. In this study, strain and photoluminescence of MoS2 monolayer on a 3D substrate through a two-step growth procedure was analyzed. The structural of materials and those optical properties of monolayer TMDCs fabricated on the planar and nonplanar substrate were examined. Monolayer MoS2 grown on the nonplanar substrate exhibited uniform strain reduction and luminescence intensity. The fabrication of monolayer MoS2 on a nonplanar substrate increased the light extraction efficiency. In the future, strain-reduced 2D TMDC materials grown on a nonplanar substrate can be employed as novel light-emitting devices for applications in light-emitters, communication, and displays for ultrathin optoelectronic integrated systems.
Using Planar Hyperbolic Metamaterials to Enhance Spontaneous Emission in Two-dimensional Transition Metal Dichalcogenides
(2018-01-01)
Lin, Chen-An
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Yu, Cheng-Li
;
Lin, Hsiang-Ting
;
Chang, Chiao-Yun
;
Kuo, Hao-Chung
We designed one-dimensional planar hyperbolic metamaterials (P-HMMs) which supported high k modes and had better coupling compared to multilayers HMMs. Therefore, spontaneous emission enhancement and the strong coupling between P-HMMs and 2D materials were achieved.