Browsing by Author "Kao, Tsung Sheng"

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850/940-nm VCSEL for optical communication and 3D sensing
(2018-01-01)
Cheng, Chih-Hsien
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Shen, Chih-Chiang
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Kao, Hsuan-Yun
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Hsieh, Dan-Hua
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Wang, Huai-Yung
This paper is going to review the state-of-the-art of the high-speed 850/940-nm vertical cavity surface emitting laser (VCSEL), discussing the structural design, mode control and the related data transmission performance. InGaAs/AlGaAs multiple quantum well (MQW) was used to increase the differential gain and photon density in VCSEL. The multiple oxide layers and oxide-confined aperture were well designed in VCSEL to decrease the parasitic capacitance and generate single mode (SM) VCSEL. The maximal modulation bandwidth of 30 GHz was achieved with well-designed VCSEL structure. At the end of the paper, other applications of the near-infrared VCSELs are discussed.
Color-conversion efficiency enhancement of quantum dots via selective area nano-rods light-emitting diodes
(2016-08-22)
Liu, Che-Yu
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Chen, Tzu-Pei
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Kao, Tsung Sheng
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Huang, Jhih-Kai
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Kuo, Hao-Chung
A large enhancement of color-conversion efficiency of colloidal quantum dots in light-emitting diodes (LEDs) with novel structures of nanorods embedded in microholes has been demonstrated. Via the integration of nano-imprint and photolithography technologies, nanorods structures can be fabricated at specific locations, generating functional nanostructured LEDs for high-efficiency performance. With the novel structured LED, the color-conversion efficiency of the existing quantum dots can be enhanced by up to 32.4%. The underlying mechanisms can be attributed to the enhanced light extraction and nonradiative energy transfer, characterized by conducting a series of electroluminescence and time-resolved photoluminescence measurements. This hybrid nanostructured device therefore exhibits a great potential for the application of multi-color lighting sources. (C) 2016 Optical Society of America
Controllable lasing performance in solution-processed organic-inorganic hybrid perovskites
(2016)
Kao, Tsung Sheng
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Chou, Yu-Hsun
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Hong, Kuo-Bin
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Huang, Jiong-Fu
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Chou, Chun-Hsien
Solution-processed organic-inorganic perovskites are fascinating due to their remarkable photo-conversion efficiency and great potential in the cost-effective, versatile and large-scale manufacturing of opto-electronic devices. In this paper, we demonstrate that the perovskite nanocrystal sizes can be simply controlled by manipulating the precursor solution concentrations in a two-step sequential deposition process, thus achieving the feasible tunability of excitonic properties and lasing performance in hybrid metal-halide perovskites. The lasing threshold is at around 230 mu J cm(-2) in this solution-processed organic-inorganic lead-halide material, which is comparable to the colloidal quantum dot lasers. The efficient stimulated emission originates from the multiple random scattering provided by the micro-meter scale rugged morphology and polycrystalline grain boundaries. Thus the excitonic properties in perovskites exhibit high correlation with the formed morphology of the perovskite nanocrystals. Compared to the conventional lasers normally serving as a coherent light source, the perovskite random lasers are promising in making low-cost thin-film lasing devices for flexible and speckle-free imaging applications.
Controlling light emission performance with hybrid phase-change plasmonic crystals (Conference Presentation)
(2016-01-01)
Kao, Tsung Sheng
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交大名義發表
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National Chiao Tung University
Effect of Passivation Layer on the Thin Film Perovskite Random Lasers
(2020-05-01)
Mallick, Subha Prakash
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Hong, Yu-Heng
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Chen, Lih-Ren
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Kao, Tsung Sheng
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Lu, Tien-Chang
Novel functionalities of disorder-induced scattering effect in random lasers, attributed to low spatial coherence, draw remarkable attention in high-contrast to superior quality speckle-free imaging applications. This paper demonstrates perovskite-polystyrene (PS)-based random lasing action with robust optical performance at room temperature. Optical characterizations are carried out upon perovskite thin films addition with polystyrene of different mixing concentrations (wt.%). A low threshold lasing operation is achieved with an increasing concentration of polystyrene, accompanying a wavy surface texture with high surface roughness. The rough surface dominating multiple scattering effects leads to enhanced feedback efficiency. Moreover, this study also elucidates efficient fabrication process steps for the development of high quality and durable PS-based random lasers. With the advantages of reduced coherent artifacts and low spatial coherence, speckle free projection images of the USAF (U. S. Air Force MIL-STD-150A standard of 1951) resolution test chart are shown for different PS-based random lasers.
Enhanced Lasing Performance in Solution-processed Lead Halide Perovskites Covered with PMMA and Ag
(2016)
Kao, Tsung Sheng
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Chou, Yu-Hsun
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Hong, Kuo-Bin
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Huang, Jiong-Fu
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Chen, Fang-Chung
We report the enhanced lasing performance in lead-halide perovskites covered with PMMA and Ag. Not only the perovskite can be protected from hydrolysis, but also the lasing thresholds can be greatly reduced resulting from the plasmonic effect.
Enhanced Light Extraction Efficiency of GaN-Based Hybrid Nanorods Light-Emitting Diodes
(2015-07-01)
Huang, Jhih-Kai
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Liu, Che-Yu
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Chen, Tzi-Pei
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Huang, Hung-Wen
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Lai, Fang-I
High light extraction GaN-based light-emitting diodes (LEDs) with a hybrid structure of straight nanorods located in an array of microholes have been successfully demonstrated. Via the nanoimprint lithography and photolithography techniques, high aspect-ratio light-guiding InGaN/GaN nanorods can be fabricated and regularly arranged in microholes, resulting in a great improvement of the light extraction for the GaN-based LED device. The light output power of the hybrid nanorods LED is 22.04 mW at the driving current standard of 25.4 A/cm(2), an enhancement of 38.7% to the conventional GaN-based LEDs. Furthermore, with a modification of the hybrid structures\' dimensions and locations, the emitted optical energy can be redistributed to obtain light-emitting devices with homogenueous optical field distributions.
Enhanced photoluminescence of DCJTB with ordered Ag-SiO2 core-shell nanostructures via nanosphere lithography
(2020-06-01)
Chau, Yuan-Fong Chou
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Lin, Chieh-Jen
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Kao, Tsung Sheng
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Wang, Ya-Chih
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Lim, Chee Ming
We have fabricated Ag-SiO2 core-shell nanostructure set in the hexagonally ordered Ag nanohole array by nanosphere lithography with reactive ion etching, and followed by Ag deposition. The resulting nanostructure includes the triangular-shaped plates with sharp edges on the top, the Ag-SiO2 core-shell nanospheres, the hexagonally arranged nanohole array, a SiO2 buffer layer and a DCJTB (4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran) fluorescent dye layer, respectively. Six patterns of substrates (i.e., Types 1-6) were fabricated and their photoluminescence enhancement performance was compared to substrate layered with pure DCJTB. The experimental results show that photoluminescence enhancement can be 15.69 times, and the lifetime can be shortened from 0.97 ns to 0.41 ns for Type 3 when compared to the pure DCJTB one. The finite element method revealed four structure conditions which are the effects of edge enhancement, gap plasmon resonance, hollow plasmon resonance, and core-shell hybridization plasmon resonance and can contribute to the photoluminescence enhancement factor. The proposed substrates provide a practical detecting platform with plasmon-enhanced photoluminescence, and the fabrication methods used are technically simple and low cost.
Flexible Organometal-Halide Perovskite Lasers for Speckle Reduction in Imaging Projection
(2019-05-01)
Wang, Yu-Chi
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Li, Heng
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Hong, Yu-Heng
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Hong, Kuo-Bin
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Chen, Fang-Chung
Disorder is emerging as a strategy for fabricating random laser sources with very promising materials, such as perovskites, for which standard laser cavities are not effective or too expensive. We need, however, different fabrication protocols and technologies for reducing the laser threshold and controlling its emission. Here, we demonstrate an effectively solvent-engineered method for high-quality perovskite thin films on a flexible polyimide substrate. The fractal perovskite thin films exhibit excellent optical properties at room temperature and easily achieve lasing action without any laser cavity above room temperature with a low pumping threshold. The lasing action is also observed in curved perovskite thin films on flexible substrates. The lasing threshold can be further reduced by increasing the local curvature, which modifies the scattering strengths of the bent thin film. We also show that the curved perovskite lasers are extremely robust with respect to repeated deformations. Because of the low spatial coherence, these curved random laser devices are efficient and durable speckle-free light sources for applications in spectroscopy, bioimaging, and illumination.
High Color-Conversion Efficiency CdSe Quantum Dots Hybrid Light Emitted Diode
(2016)
Liu, Che-Yu
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Kao, Tsung Sheng
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Chen, Tzu-Pei
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Chi, Gou-Chung
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Kuo, Hao-Chung
In this work, we have successfully demonstrated that the color-conversion efficiency in colloidal quantum dots can be greatly enhanced by light-emitting diodes (LEDs) with novel structures of nanorods embedded in microholes. Via an integrated technology of the nano-imprint and photolithography, nanorods structures can be fabricated at specific locations, generating functional nanostructured LEDs for high-efficiency light-emitting performance. With such a structured LED, the color-conversion efficiency of the existing quantum dots can be enhanced up to 12.5 %.
High-performance InGaN-based green light-emitting diodes with quaternary InAlGaN/GaN superlattice electron blocking layer
(2016-05-30)
Tzou, An-Jye
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Lin, Da-Wei
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Yu, Chien-Rong
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Li, Zhen-Yu
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Liao, Yu-Kuang
In this study, high-performance InGaN-based green light-emitting diodes (LEDs) with a quaternary InAlGaN/GaN superlattice electron blocking layer (QSL-EBL) have been demonstrated. The band structural simulation was employed to investigate the electrostatic field and carriers distribution, show that the efficiency and droop behavior can be intensively improved by using a QSL-EBL in LEDs. The QSL-EBL structure can reduce the polarization-related electrostatic fields in the multiple quantum wells (MQWs), leading to a smoother band diagram and a more uniform carriers distribution among the quantum wells under forward bias. In comparison with green LEDs with conventional bulk-EBL structure, the light output power of LEDs with QSL-EBL was greatly enhanced by 53%. The efficiency droop shows only 30% at 100 A/cm(2) comparing to its peak value, suggesting that the QSL-EBL LED is promising for future white lighting with high performance. (C) 2016 Optical Society of America
High-Performance Ultraviolet 385-nm GaN-Based LEDs With Embedded Nanoscale Air Voids Produced Through Atomic Layer Deposition and Al2O3 Passivation
(2016-04)
Liu, Che-Yu
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Huang, Chia-Yen
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Wu, Pei-Yu
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Huang, Jhih-Kai
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Kao, Tsung Sheng
This letter developed the high-performance GaN-based light-emitting diodes (LEDs) for ultraviolet (UV) light emission at 385 nm with the light output power enhanced by up to 52% compared with that of the conventional UV-LEDs. The high-power-efficiency UV-LEDs include sidewall-passivated Al2O3 dielectric nanoscale air voids, which were created using the atomic layer deposition method and act as intermediate media for improving the internal quantum efficiency, reducing threading dislocation, and relaxing strain. The fabricated air void nanostructure also enhanced the light extraction efficiency by similar to 32.7%, resulting in a high-power UV light-emitting device.
Laser-patterned Array with Aerosol-jet Printing Quantum-dots for Novel White Light Source
(2016)
Wang, Sheng-Wen
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Lin, Huang-Yu
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Lin, Chien-Chung
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Kao, Tsung Sheng
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Chen, Kuo-Ju
Through the laser-ablation and aerosol-jet printing techniques, a novel photoluminescent quantum-dots device with microscale patterns has been demonstrated as a white-light emitting source with stable emission at different driving currents and larger color productivity domain.
Lasing behaviors upon phase transition in solution-processed perovskite thin films
(2014-12-08)
Kao, Tsung Sheng
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Chou, Yu-Hsun
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Chou, Chun-Hsien
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Chen, Fang-Chung
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Lu, Tien-Chang
In this paper, the temperature dependent lasing characteristics of solution-processed organic-inorganic halide perovskite CH3NH3PbI3 films have been demonstrated. The lasing temperature can be sustained up to a near room temperature at 260 K. Via the temperature dependent photoluminescence (PL) measurements, an emerged phase-transition band can be observed, ascribing to the crystalline structures changed from the orthorhombic to tetragonal phase states in the perovskites as a function of a gradual increase in the ambient temperature. The optical characteristics of the PL emission peaks and the anomalous shifts of the peak intensities are highly correspondent with the phase states in perovskites at different temperatures, showing a low-threshold lasing behavior at the phase transition. The laser cavities may be formed under multiple random scattering provided by the polycrystalline grain boundary and/or phase separation upon the phase transition. Since the threshold gain is potentially high in the random cavities, the large material gain exhibited by the solution-processed perovskite would be very promising in making practical laser devices. (C) 2014 AIP Publishing LLC.
Light emission characteristics of nonpolar a-plane GaN-based photonic crystal defect cavities
(2015-01-01)
Kao, Tsung Sheng
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Wu, Tzeng-Tsong
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Tsao, Che-Wei
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Lin, Jyun-Hao
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Lin, Da-Wei
In this paper, nonpolar a-plane GaN-based photonic crystals (PCs) with different defect cavities have been demonstrated. By using a micro-photoluminescence (mu-PL) system operated at 77 K, the dominant resonant modes of the GaN-based PC defect cavities show high quality factor (Q) values in the light emission performance which can be up to 4.3x10(3). Moreover, the degree of polarization (DOP) of the light emission from the nonpolar GaN-based PC defect cavities was measured to achieve around 64 % along the m crystalline direction.
Light Emission Characteristics of Nonpolar a-Plane GaN-Based Photonic Crystal Defect Cavities
(2016-09)
Kao, Tsung Sheng
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Wu, Tzeng-Tsong
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Tsao, Che-Wei
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Lin, Jyun-Hao
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Lin, Da-Wei
In this paper, the light emission performance from nonpolar a-plane gallium nitride (GaN)-based photonic crystal (PC) slabs with line-type defect cavities has been investigated. Via the focused ion beam milling technique, thin membrane structures of the nonpolar GaN PC defect cavities were engineered, exhibiting one dominated resonant mode occurred at 419.3 nm with a high quality factor of 1.9 x 10(3) in the photoluminescence emission characterizations. In the far-field region, light emission performance shows a high polarization degree of 50% with the beam direction perpendicular to the defect cavity. Compared with the PC defect cavity patterns fabricated on c-axial oriented GaN materials, the a-plane PC defect cavities display not only the linear light output-input power dependence, but also an invariant resonant mode of constant light emission behavior with increasing the injection carriers, therefore providing a new perspective for the future development of promising optoelectronic devices.
Light energy transformation over a few nanometers
(2017-09-20)
Huang, Hung Ji
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Liu, Bo-Heng
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Su, James
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Chen, Po-Jui
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Lin, Chun-Ting
Continuous platinum (Pt) thin film was fabricated via the plasma-enhanced atomic layer deposition method for a study of light energy transformation over a few nanometers. Light-to-heat experiments were used to determine the oscillating size effects on electromagnetic energy transformation in quantum wells of smooth and condensed Pt thin films. For Pt-film thicknesses of around 4 nm, 7 nm and 12 nm, electromagnetic heating presented unexpectedly high energy conversion efficiency. An empirical equation acquired from the fitting of the experimental data from various thicknesses of Pt thin films was suggested to describe the oscillating electromagnetic heating and quantized energy transformation. The experimental results show that size control of the nanostructures is extremely important for future applications involving quantum effects in nano devices.
Localized surface plasmon for enhanced lasing performance in solution-processed perovskites
(2016-09-05)
Kao, Tsung Sheng
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Hong, Kuo-Bin
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Chou, Yu-Hsun
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Huang, Jiong-Fu
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Chen, Fang-Chung
A promising method to promote the lasing performance of solution-processed organic-inorganic lead-halide perovskites has been demonstrated. With the adding Ag and PMMA thin films, the threshold excitation power for low-temperature lasing action in perovskites can be greatly reduced by over two orders of magnitude than that acquired in bare perovskite layers, ascribing to the strong exciton-plasmon coupling between the Ag and perovskite films. Also, the PMMA layer can be exploited to prevent the perovskite degradation from the hydrolysis in ambient environment, achieving long-lasting light-emitting performance. The advantages exhibited by the hybrid perovskite configuration would be very promising in making practical laser devices. (C) 2016 Optical Society of America
Planar Metal-GaN Spiral Nanowire Cavities for High Circular Dichroism Lasing Action
(2016)
Hsiao, Yu-Hao
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Kao, Tsung Sheng
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Liao, Shu-Wei
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Liao, Wei-Chun
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Chen, Kuo-Lu
The compact and energy-efficient planar metal-GaN spiral nanowire cavity lasing device has been demonstrated with high circularly polarized UV laser light at 364 nm and the circular dichroism performance enhanced to dissymmetry factor of + 1.4.
Pulsed-laser micropatterned quantum-dot array for white light source
(2016-03-23)
Wang, Sheng-Wen
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Lin, Huang-Yu
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Lin, Chien-Chung
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Kao, Tsung Sheng
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Chen, Kuo-Ju
In this study, a novel photoluminescent quantum dots device with laser-processed microscale patterns has been demonstrated to be used as a white light emitting source. The pulsed laser ablation technique was employed to directly fabricate microscale square holes with nano-ripple structures onto the sapphire substrate of a flip-chip blue light-emitting diode, confining sprayed quantum dots into well-defined areas and eliminating the coffee ring effect. The electroluminescence characterizations showed that the white light emission from the developed photoluminescent quantum-dot light-emitting diode exhibits stable emission at different driving currents. With a flexibility of controlling the quantum dots proportions in the patterned square holes, our developed white-light emitting source not only can be employed in the display applications with color triangle enlarged by 47% compared with the NTSC standard, but also provide the great potential in future lighting industry with the correlated color temperature continuously changed in a wide range.