Browsing by Author "Chou, Yu-Hsun"

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Characteristic of UV Plasmonic Nanolasers with Different Spacer Thickness
(2016)
Chou, Yu-Hsun
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Chou, Bo-Tsun
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Lin, Sheng-Di
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Lin, Tzy-Rong
;
Lin, Chien-Chung
We report on plasmonic lasers with ZnO nanowire lying on single-crystalline silver film with different SiO2 thickness spacer. Spacer thickness were optimized to adjust the surface plasmon dispersion curve and resulting different group index.
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.
Crossover from polariton lasing to exciton lasing in a strongly coupled ZnO microcavity
(2016-02-03)
Lai, Ying-Yu
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Chou, Yu-Hsun
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Lan, Yu-Pin
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Lu, Tien-Chang
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Wang, Shing-Chung
Unlike conventional photon lasing, in which the threshold is limited by the population inversion of the electron-hole plasma, the exciton lasing generated by exciton-exciton scattering and the polariton lasing generated by dynamical condensates have received considerable attention in recent years because of the sub-Mott density and low-threshold operation. This paper presents a novel approach to generate both exciton and polariton lasing in a strongly coupled microcavity (MC) and determine the critical driving requirements for simultaneously triggering these two lasing operation in temperature <140 K and large negative polariton-exciton offset (<-133 meV) conditions. In addition, the corresponding lasing behaviors, such as threshold energy, linewidth, phase diagram, and angular dispersion are verified. The results afford a basis from which to understand the complicated lasing mechanisms in strongly coupled MCs and verify a new method with which to trigger dual laser emission based on exciton and polariton.
Engineering radiative coupling of excitons in 2D semiconductors
(2019-11-20)
Horng, Jason
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Chou, Yu-Hsun
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Chang, Tsu-Chi
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Hsu, Chu-Yuan
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Lu, Tien-Chang
The resonance energy and the transition rate of atoms, molecules, and solids were understood as their intrinsic properties in classical electromagnetism. It was later realized that these quantities are linked to the radiative coupling between the transition dipole and photon modes. Such effects can be greatly amplified in macroscopic many-body systems from virtual photon exchange between dipoles, but are often masked by inhomogeneity and pure dephasing, especially in solids. Here, we observe in both absorption and emission spectroscopy the renormalization of the exciton resonance and the radiative decay rate in transition metal dichalcogenides monolayers due to their radiative interactions. Tuning the photon mode density near the monolayer, we demonstrate control of cooperative Lamb shift, radiative decay, and valley polarization of the excitons as well as control of the charged exciton emission. Our work establishes a technologically accessible and robust experimental system for engineering cooperative matter-light interactions. (c) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
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.
Fabrication and characteristics of a GaN-based microcavity laser with shallow etched mesa
(2014-06-01)
Lai, Ying-Yu
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Chou, Yu-Hsun
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Wu, Yu-Sheng
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Lan, Yu-Pin
;
Lu, Tien-Chang
In this work, we have developed a simple GaN-based microcavity (MC) with an intracavity shallow etched mesa. The textured GaN-based MC incorporated two high-reflectivity dielectric Bragg mirrors and an InGaN/GaN multiple quantum well with a shallow etched mesa as an optical confined structure. Lasing and transverse optical confinement characteristics have been verified by measuring devices with different mesa diameters. A quality factor (Q) of 2600 and a threshold energy of 30 nJ have been observed in a 10-mu m-diameter device. Such a cavity structure could be implanted into electrically pumped GaN vertical-cavity surface-emitting lasers for supporting efficient transverse confinement. (C) 2014 The Japan Society of Applied Physics
Fabrication and characteristics of a GaN-based microcavity laser with shallow etched mesa
(2014-06-01)
Lai, Ying-Yu
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Chou, Yu-Hsun
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Wu, Yu-Sheng
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Lan, Yu-Pin
;
Lu, Tien-Chang
In this work, we have developed a simple GaN-based microcavity (MC) with an intracavity shallow etched mesa. The textured GaN-based MC incorporated two high-reflectivity dielectric Bragg mirrors and an InGaN/GaN multiple quantum well with a shallow etched mesa as an optical confined structure. Lasing and transverse optical confinement characteristics have been verified by measuring devices with different mesa diameters. A quality factor (Q) of 2600 and a threshold energy of 30 nJ have been observed in a 10-mu m-diameter device. Such a cavity structure could be implanted into electrically pumped GaN vertical-cavity surface-emitting lasers for supporting efficient transverse confinement. (C) 2014 The Japan Society of Applied Physics
High-operation-temperature Aluminum-based SPP Nanolasers
(2016)
Chou, Yu-Hsun
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Hong, Kuo-Bin
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Chou, Bo-Tsun
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Wu, Yen-Mo
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Shih, Jheng-Hong
Metal-insulator-semiconductor structures has widely adopted in plasmonics lasers. However, we found that the insulator is not necessary if permittivity combination of laser structures is properly designed. Single-mode laser operation was demonstrate in devices without artificial insulator layers. Moreover, the operation temperature can achieve to 353 K.
High-Operation-Temperature Plasmonic Nanolasers on Single-Crystalline Aluminum
(2016-05)
Chou, Yu-Hsun
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Wu, Yen-Mo
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Hong, Kuo-Bin
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Chou, Bo-Tsun
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Shih, Jheng-Hong
The recent development of plasmonics has overcome the optical diffraction limit and fostered the development of several important components including nanolasers, low-operation-power modulators, and high-speed detectors. In particular, the advent of surface-plasmon-polariton (SPP) nanolasers has enabled the development of coherent emitters approaching the nanoscale. SPP nanolasers widely adopted metal insulator semiconductor structures because the presence of an insulator can prevent large metal loss. However, the insulator is not necessary if permittivity combination of laser structures is properly designed. Here, we experimentally demonstrate a SPP nanolaser with a ZnO nanowire on the as-grown single-crystalline aluminum. The average lasing threshold of this simple structure is 20 MW/cm(2), which is four-times lower than that of structures with additional insulator layers. Furthermore, single-mode laser operation can be sustained at temperatures up to 353 K. Our study represents a major step toward the practical realization of SPP nanolasers.
High-Performance Plasmonic Nanolasers with a Nanotrench Defect Cavity for Sensing Applications
(2018-07-01)
Cheng, Pi-Ju
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Huang, Zhen-Ting
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Li, Jhu-Hong
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Chou, Bo-Tsun
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Chou, Yu-Hsun
Recent developments in small footprint plasmonic nanolasers show promise for active optical sensing with potential applications in various fields, including real-time and label-free biochemical sensing, and gas detection. In this study, we demonstrate a novel hybrid plasmonic crystal nanolaser that features a ZnO nanowire placed on Al grating surfaces with a nanotrench defect nanocavity. The lasing action of gain-assisted defect nanocavity overcomes the ohmic loss parasitically in the plasmonic nanostructures. Therefore, the plasmonic nanolaser exhibits an extremely small mode volume, a narrow linewidth Delta lambda, and a high Purcell factor that can facilitate the strong interaction between light and matter. This can be used as a refractive index sensor and is highly sensitive to local changes in the refractive indices of ambient materials. By careful design, the near-ultraviolet nanolaser sensors have significant sensing performances of glucose solutions, revealing a high sensitivity of 249 nm/RIU and high resolution, with a figure of merit of 1132, at the resonant wavelength of 373 nm.
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.
Lasing in a ZnO membrane microcavity with designable shape fabricated by focused ion beam milling
(2015)
Chang, Tsu-Chi
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Lai, Ying-Yu
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Chou, Yu-Hsun
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Lu, Tien-Chang
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照明與能源光電研究所
We show a three-dimensional membrane cavity fabrication technique and corresponding lasing characteristics of the fabricated rectangular ZnO membrane microcavity (MC) using optical injection. The ZnO membrane was cut from a single crystalline ZnO substrate by using a focused ion beam, and was then placed onto a SiO2 substrate by using a glass tip. The micro-photoluminescence measurement performed on the fabricated ZnO membrane MC at 77 K showed an obvious feature of lasing action including non-linear increasing of intensity and linewidth narrowing. By using this fabrication approach, various MCs with desired shapes can be made.
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
Manipulation of exciton and photon lasing in a membrane-type ZnO microcavity
(2015-03-30)
Lai, Ying-Yu
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Chen, Jee-Wei
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Chang, Tsu-Chi
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Chou, Yu-Hsun
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Lu, Tien-Chang
We report on the fabrication and characterization of a membrane-type ZnO microcavity (MC). The ZnO membrane was cut from a single crystalline ZnO substrate by using focused ion beam milling, and was then placed onto a SiO2 substrate by using glass microtweezers. Through changing the pumping regime, manipulation of P-band exciton lasing and whispering-gallery mode (WGM) photon lasing could be easily achieved. P-band exciton lasing was observed only when the pumping laser was focused at the center of the ZnO MC with a small pumping size because of the innate ring-shaped WGM distribution. Furthermore, the lasing threshold of the ZnO MC could be reduced to an order lower by using a larger pumping spot because of the more favorable spatial overlap between the optical gain and WGM. (C) 2015 AIP Publishing LLC.
Metal for Plasmonic Ultraviolet Laser: Al or Ag?
(2017-11-01)
Chou, Yu-Hsun
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Hong, Kuo-Bin
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Chung, Yi-Cheng
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Chang, Chun-Tse
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Chou, Bo-Tsun
Surface plasmon polariton (SPP) nanolasers have recently emerged as promising candidates for generating a coherent light source in nanophotonic integration circuits. The properties of SPP nanolasers, such as group velocity, mode area, modulation speed, and threshold performance, can be manipulated using a dispersion relation. In this study, we investigated the characteristics of SPP nanolasers operated near and far from the SP frequency. Our results indicated that SPP nanolaser performance can be significantly influenced by manipulating the dispersion relation.
Perfect Absorption by an Atomically Thin Crystal
(2020-08-05)
Horng, Jason
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Martin, Eric W.
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Chou, Yu-Hsun
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Courtade, Emmanuel
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Chang, Tsu-chi
Optical absorption is one of the most fundamental processes in light-matter interactions. The ability to achieve and control high absorption is crucial for a broad range of modern photonic technologies. In nanomaterials of length scales much smaller than a wavelength, optical absorption is typically a weak perturbation. To achieve high absorption, exquisite techniques and structures have been developed, such as coherent interference of multiple laser beams and plasmonic metasurfaces. Here, we show that a robust critical-coupling condition exists to allow perfect absorption of light by a subnanometer-thick two-dimensional semiconductor, when the radiative-decay rate of the exciton resonance balances with its loss rate. We measure an absorption up to 99.6% in a monomolecular MoSe2 crystal placed in front of a flat mirror. We furthermore demonstrate control of the perfect absorption by tuning the exciton-phonon, exciton-exciton, and exciton-photon interactions with temperature, pulsed laser excitation, and a movable mirror, respectively. Our work suggests a mechanism to achieve and control critical coupling in two-dimensional excitonic systems, enabling photonic applications including ultrafast low-power light modulators and sensitive optical sensing.
Realization of UV Plasmonic Nanolasers With Extremely Small Mode Volume
(2015-11-01)
Chou, Bo-Tsun
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Chou, Yu-Hsun
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Chiang, Chih-Kai
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Wu, Yen-Mo
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Lin, Tzy-Rong
It is difficult to operate plasmonic nanolasers on silver films in the ultraviolet regime owing to the bending-back effect of surface plasmon dispersion. In this paper, we report on plasmonic lasers comprised of a ZnO nanowire lying on a single-crystalline silver film with a SiO2 spacer layer. The silver can strongly shrink the mode volume, thereby boosting the Purcell factor. Meanwhile, the SiO2 spacer thickness is optimized to adjust the surface plasmon dispersion curve so that the lasing wavelength can be located at a large dispersion region, thereby achieving a large group index of 55, an ultra-small effective mode volume of 3.5 x 10(-3)lambda(3), and low-threshold of 11 MW/cm(2).
Single-crystalline aluminum film for ultraviolet plasmonic nanolasers
(2016-01-27)
Chou, Bo-Tsun
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Chou, Yu-Hsun
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Wu, Yen-Mo
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Chung, Yi-Cheng
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Hsueh, Wei-Jen
Significant advances have been made in the development of plasmonic devices in the past decade. Plasmonic nanolasers, which display interesting properties, have come to play an important role in biomedicine, chemical sensors, information technology, and optical integrated circuits. However, nanoscale plasmonic devices, particularly those operating in the ultraviolet regime, are extremely sensitive to the metal and interface quality. Thus, these factors have a significant bearing on the development of ultraviolet plasmonic devices. Here, by addressing these material-related issues, we demonstrate a low-threshold, high-characteristic-temperature metal-oxide-semiconductor ZnO nanolaser that operates at room temperature. The template for the ZnO nanowires consists of a flat single-crystalline Al film grown by molecular beam epitaxy and an ultrasmooth Al2O3 spacer layer synthesized by atomic layer deposition. By effectively reducing the surface plasmon scattering and metal intrinsic absorption losses, the high-quality metal film and the sharp interfaces formed between the layers boost the device performance. This work should pave the way for the use of ultraviolet plasmonic nanolasers and related devices in a wider range of applications.
Surface plasmon polariton nanolasers: Coherent light sources for new applications
(2018-11-01)
Chou, Yu-Hsun
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Chang, Chia-Jui
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Lin, Tzy-Rong
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Lu, Tien-Chang
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光電工程學系
The invention of the Internet and mobile devices has caused tremendous changes in human lives over the past two decades. Information technology has broken through limitations of geospatial space, enabling extremely high-speed data transmission and new types of data services. In recent years, demands for data processing have shown an increasing trend. Furthermore, data generated from internet-related applications such as cloud services and self-driving technology are likely to grow exponentially over the coming years. Currently, data transmission inside integrated circuits mainly relies on metal wires. However, the substantial resistive-capacitive delay and energy loss that are caused by metal wires limit data transmission speeds. Optical interconnection has been regarded as a major solution to efficiently reduce energy consumption and increase data transmission speeds. The size of conventional semiconductor laser devices, which are the key component in optical interconnection, cannot be smaller than the wavelength of light, which is a fundamental physical obstacle to lasers integrating with current electronic integrated circuits in reasonable volumes. To realize optical interconnection, the volume of the laser device must match the existing electronic components. Recently, the use of diffraction-unlimited plasmonic lasers has been successfully demonstrated, and these have great potential in different applications. In this paper, we discuss the recent progress toward surface plasmon polariton lasers and provide practical insights into the challenges in realizing these novel devices.
Surface roughness effects on aluminium-based ultraviolet plasmonic nanolasers
(2017-01-03)
Chung, Yi-Cheng
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Cheng, Pi-Ju
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Chou, Yu-Hsun
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Chou, Bo-Tsun
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Hong, Kuo-Bin
We systematically investigate the effects of surface roughness on the characteristics of ultraviolet zinc oxide plasmonic nanolasers fabricated on aluminium films with two different degrees of surface roughness. We demonstrate that the effective dielectric functions of aluminium interfaces with distinct roughness can be analysed from reflectivity measurements. By considering the scattering losses, including Rayleigh scattering, electron scattering, and grain boundary scattering, we adopt the modified Drude-Lorentz model to describe the scattering effect caused by surface roughness and obtain the effective dielectric functions of different Al samples. The sample with higher surface roughness induces more electron scattering and light scattering for SPP modes, leading to a higher threshold gain for the plasmonic nanolaser. By considering the pumping efficiency, our theoretical analysis shows that diminishing the detrimental optical losses caused by the roughness of the metallic interface could effectively lower (-33.1%) the pumping threshold of the plasmonic nanolasers, which is consistent with the experimental results.