Browsing by Author "Hsieh, Wen-Feng"

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12 GHz passive harmonic mode-locking in a 1.06 mu m semiconductor optical amplifier-based fiber laser with figure-eight cavity configuration
(2013-03-15)
Chen, Hou-Ren
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Lin, Kuei-Huei
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Tsai, Chih-Ya
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Wu, Hsiao-Hua
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Wu, Chih-Hsuan
We report the generation of passively harmonic mode-locked pulses using a 1.06 mu m semiconductor optical amplifier (SOA) in a figure-eight laser configuration operated in the all-normal-dispersion regime. Different orders of harmonic mode-locking can be obtained from 30 MHz to 12.02 GHz by changing the injection current of the SOA from 80 to 660 mA together with the adjustment of polarization controllers. The highest pulse repetition rate increases almost linearly with the SOA current. As SOA current is set to 660 mA, we obtain the intracavity power of 46 mW at the highest repetition rate of 12.02 GHz, corresponding to the 1202th harmonic of the fundamental mode-locking frequency. To our best knowledge, this is the lowest intracavity power to generate the highest repetition rate with a passively mode-locked laser in the all-normal-dispersion regime. (C) 2013 Optical Society of America
Absolute frequency measurements of the molecular iodine hyperfine transitions at 535 nm
(2013-07-01)
Shie, Nang-Chian
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Chen, Shih-En
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Chang, Chun-Yu
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Hsieh, Wen-Feng
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Shy, Jow-Tsong
We report absolute frequency measurements of the alpha(1), alpha(10), and alpha(15) hyperfine components of molecular iodine P(28) 30-0 line at 535 nm. A frequency-doubled 1070 nm Nd:GdVO4 laser is frequency stabilized to a hyperfine component of I-2 using the third-harmonic demodulation technique. The frequency stability of 3 x 10(-12) is achieved at 10 s averaging time when its frequency is stabilized to the alpha(1) component. An optical frequency comb is used to measure its absolute frequency. The pressure shift is investigated to obtain the absolute frequency at zero pressure. The effect of pressure and power broadening of the a10 component are also investigated. This light source can be used for investigating parity nonconservation effect in atomic thallium. (C) 2013 Optical Society of America
Acoustic and optical phonon assisted formation of biexcitons
(2007-09-10)
Pan, Ching-Ju
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Lin, Kuo-Feng
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Hsieh, Wen-Feng
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光電工程學系
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Department of Photonics
Efficient exciton relaxation is required for bounding two cooled excitons to form biexciton. Acoustic and optical phonon scatterings playing key roles in exciton relaxation are responsible for formation of biexcitons at various temperatures. Using ZnO powders, the authors observed a sublinear dependence on excitation power at low temperature, in which the relaxation process involves only emission of acoustic phonons due to the excitons having kinetic energy lower than those of the optical phonons. However, the exponent comes near theoretical value of 2 for participation of optical phonons when the exciton kinetic energy approaches to the energy of the lowest optical phonon.
Acoustic Velocity and Optical Index Birefringence in A-Plane ZnO Thin Films
(2011-02-01)
Chen, Yi-Hsin
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Wen, Yu-Chieh
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Liu, Wei-Rein
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Hsieh, Wen-Feng
;
Sun, Chi-Kuang
The longitudinal acoustic velocity in the direction normal to the c-axis and the birefringence of refractive index of a-plane zinc oxide (ZnO) thin films were measured by ultrafast transient reflection measurement. Through Fourier analysis, the experimental data show that the acoustic velocity is about 6000 m/s and the measured refractive index near the band gap, which is higher than the previously reported results by 20 similar to 30%.
Band gap engineering and stimulated emission of ZnMgO nanowires
(2006-07-03)
Hsu, Hsu-Cheng
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Wu, Chun-Yi
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Cheng, Hsin-Ming
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Hsieh, Wen-Feng
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光電工程學系
We report a simple method for fabricating heterostructured ZnMgO nanowires by annealing the preformed ZnO/MgO core-shell structure. Photoluminescence from the alloy nanowires shows strong near-band-edge (NBE) emission, reflecting good material quality. A blueshift of the NBE emission at room temperature after the annealing treatment is attributed to the diffusion of Mg from the shell into the core ZnO of the nanowires to form a ternary ZnMgO alloy. Band gap engineering and stimulated emissions of ZnMgO nanowires with different Mg doping concentrations are also demonstrated. (c) 2006 American Institute of Physics.
Build-up of supercontinuum in heated and unheated photonic crystal fibers using a chirped femtosecond laser
(2006-09-15)
Lin, Ja-Hon
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Hsu, Chih-Chang
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Hsieh, Wen-Feng
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Lin, Kuel-Huei
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光電工程學系
The build-up of supercontinuum in a photonic crystal fiber (PCF) has been investigated experimentally as a function of pump power using chirped 100-fs pulses from a Ti:sapphire laser. As compared with the PCF at room temperature, a new blue-shifted spectral component is observed in the initial steps of supercontinuum (SC) generation when the central part of PCF is heated to 120 degrees C by a hot plate. In addition, the slope efficiency of SG is slightly improved with the slightly extension of supercontinuum spectrum in blue edge at high pump powers. The change in dispersion property as well as the effective cascading of nonlinear photonic crystal fibers for heated PCF would be the main attributions. (c) 2006 Elsevier B.V. All rights reserved.
Calculation of quasi dispersion curves and quality factors of coupled resonator optical waveguides in photonic-crystal slabs
(2012-09-01)
Huang, Chih-Hsien
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Li, Wei-Shuo
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Wu, Jing-Nuo
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Hsieh, Wen-Feng
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Chang, Yia-Chung
We propose a stabilization method to numerically calculate the dispersion relations and quality factors of optically confined finite structures. For the coupled resonator optical waveguide (CROW) made in a photonic-crystal slab (PCS) used as an example, the dispersion curve is normally not well defined due to the appearance of discontinuities, which do not occur in a two-dimensional CROW with infinite slab height. Therefore, there is less effort devoted to the calculation of quasi dispersion curves of the CROW in a slab. The dispersion relation of the PCS CROW can only be obtained by theoretical fitting to the experimental data under the tight-binding approximation. Here, we demonstrate the use of a stabilization method to calculate the quasi dispersion relation of a PCS CROW accurately. From the stabilization graph, we can calculate the quality factor for an eigenfrequency and properly choose the size of the simulation cell to avoid coupling the CROW modes with the unconfined modes and to accurately calculate the dispersion curve of the PCS CROW using the plane-wave expansion method. The proposed method and results not only provide important information for designing practical photonic devices such as slow-light optical waveguides and nonlinear photonic devices for the PCS CROWs but also can be applied to compute the quality factors and resonance frequencies of microcavities or nanocavities. (c) 2012 Optical Society of America
Calculation of spontaneous emission from a V-type three-level atom in photonic crystals using fractional calculus
(2011-07-05)
Huang, Chih-Hsien
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Wu, Jing-Nuo
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Li, Yen-Yin
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Cheng, Szu-Cheng
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Hsieh, Wen-Feng
Fractional time derivative, an abstract mathematical operator of fractional calculus, is used to describe the real optical system of a V-type three-level atom embedded in a photonic crystal. A fractional kinetic equation governing the dynamics of the spontaneous emission from this optical system is obtained as a fractional Langevin equation. Solving this fractional kinetic equation by fractional calculus leads to the analytical solutions expressed in terms of fractional exponential functions. The accuracy of the obtained solutions is verified through reducing the system into the special cases whose results are consistent with the experimental observation. With accurate physical results and avoiding the complex integration for solving this optical system, we propose fractional calculus with fractional time derivative as a better mathematical method to study spontaneous emission dynamics from the optical system with non-Markovian dynamics.
Calculations of electronic structure and density of states in the wurtzite structure of Zn(1) (-) (x)Mg(x)O alloys using sp(3) semi-empirical tight-binding model
(2009-01-01)
Lin, Kuo-Feng
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Pan, Ching-Ju
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Hsieh, Wen-Feng
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光電工程學系
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Department of Photonics
Calculating the electronic structure and the density of states in the wurtzite structure of Zn(1) (-) (x)Mg(x)O(ZMO) alloys using sp(3) semi-empirical tight-binding model, we observed increases of both band gap and electron effective mass that agree with the experimental results as increasing Mg composition up to x = 0.3. From the calculated total density of states, the increasing electron effective mass is a result of less orbital overlap of cation sites due to extra density of modes coming from Mg3s and Mg3p orbitals as introducing more Mg composition. Additionally, reducing electronegative characteristic of oxygen was caused by that the O2p was less localized around the oxygen atom.
Capabilities of time-resolved X-ray excited optical luminescence of the Taiwan Photon Source 23A X-ray nanoprobe beamline
(2020-01-01)
Lin, Bi-Hsuan
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Wu, Yu-Hao
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Li, Xiao-Yun
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Hsu, Hsu-Cheng
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Chiu, Yu-Cheng
Time-resolved X-ray excited optical luminescence (TR-XEOL) was developed successfully for the 23A X-ray nanoprobe beamline located at the Taiwan Photon Source (TPS). The advantages of the TR-XEOL facility include (i) a nano-focused X-ray beam (<60 nm) with excellent spatial resolution and (ii) a streak camera that can simultaneously record the XEOL spectrum and decay time. Three time spans, including normal (30 ps to 2 ns), hybrid (30 ps to 310 ns) and single (30 ps to 1.72 mu s) bunch modes, are available at the TPS, which can fulfil different experimental conditions involving samples with various lifetimes. It is anticipated that TR-XEOL at the TPS X-ray nanoprobe could provide great characterization capabilities for investigating the dynamics of photonic materials.
Carrier dynamics of thin ZnO epifilm above band-gap states
(2009)
Ou, Po-Chi
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Lin, Ja-Hon
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Chang, C. A.
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Liu, W. R.
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Hsieh, Wen-Feng
Ultrafast carrier dynamics of ZnO epifilm were investigated by the pump probe meausrement Relative fast occruring and recovery of band gap renormalizaion following the band filling effect will result in transmission change at 362 nm.
Characteristics of exciton-polaritons in ZnO-based hybrid microcavities
(2011-02-28)
Chen, Jun-Rong
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Lu, Tien-Chang
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Wu, Yung-Chi
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Lin, Shiang-Chi
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Hsieh, Wen-Feng
Wide bandgap semiconductors are promising materials for the development of polariton-based optoelectronic devices operating at room temperature (RT). We report the characteristics of ZnO-based microcavities (MCs) in the strong coupling regime at RT with a vacuum Rabi splitting of 72 meV. The impact of scattering states of excitons on polariton dispersion is investigated. Only the lower polariton branches (LPBs) can be clearly observed in ZnO MCs since the large vacuum Rabi splitting pushes the upper polariton branches (UPBs) into the scattering absorption states in the ZnO bulk active region. In addition, we systematically investigate the polariton relaxation bottleneck in bulk ZnO-based MCs. Angle-resolved photoluminescence measurements are performed from 100 to 300 K for different cavity-exciton detunings. A clear polariton relaxation bottleneck is observed at low temperature and large negative cavity detuning conditions. The bottleneck is suppressed with increasing temperature and decreasing detuning, due to more efficient phonon-assisted relaxation and a longer radiative lifetime of the polaritons. (C) 2011 Optical Society of America
Coherent acoustic phonon oscillation accompanied with backward acoustic pulse below exciton resonance in a ZnO epifilm on oxide-buffered Si(111)
(2016-08-17)
Lin, Ja-Hon
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Shen, Yu-Kai
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Liu, Wei-Rein
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Lu, Chia-Hui
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Chen, Yao-Hui
Unlike coherent acoustic phonons (CAPs) generated from heat induced thermal stress by the coated Au film, we demonstrated the oscillation from c-ZnO epitaxial film on oxide buffered Si through a degenerate pump-probe technique. As the excited photon energy was set below the exciton resonance, the electronic stress that resulted from defect resonance was used to induce acoustic wave. The damped oscillation revealed a superposition of a high frequency and long decay CAP signal with a backward propagating acoustic pulse which was generated by the absorption of the penetrated pump beam at the Si surface and selected by the ZnO layer as the acoustic resonator.
Collective excitations, Nambu-Goldstone modes, and instability of inhomogeneous polariton condensates
(2013-11-08)
Chen, Ting-Wei
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Cheng, Szu-Cheng
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Hsieh, Wen-Feng
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光電工程學系
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Department of Photonics
We study nonequilibrium polariton condensates in a harmonic potential trap. After finding the steady-state density and supercurrent distributions of nonequilibrium condensates, we calculate the collective excitations of the system. From collective excitation spectra, we can identify the bifurcation of the stable and unstable modes in terms of the pumping spot size and power. There exist Nambu-Goldstone modes that reveal the pattern of the spontaneous symmetry breaking of the system. Moreover, the unstable mechanism associated with the inward supercurrent flow is characterized by the existence of a supersonic region within the condensate.
Complex Oxide-Noble Metal Conjugated Nanoparticles
(2013-04-11)
Guo, Jun-Ling
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Chiou, Yao-De
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Liang, Wen-I
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Liu, Heng-Jui
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Chen, Ying-Jiun
Hybrid nanoparticles (NPs) composed of multiple components offer new opportunities for next-generation materials. In this study, a paradigm for the noble metal/ternary complex oxide hybrid NPs is reported by adopting pulsed laser ablation in liquids. As model hybrids, gold-spinel heterodimer (Au-CoFe2O4) and gold-pervoskite heterodimer (Au-SrTiO3) NPs are investigated. This work has demonstrated the diverse playgroup of NP conjugation enlarged by complex oxides.
Controlling electromagnetic wave through dual heights micro-lens array of a CMOS image sensor
(2016-05-15)
Lin, Kuo-Feng
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Hsiao, Yu-Kun
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Hsieh, Chin-Chuan
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Hsin, Shui-Chuan
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Hsieh, Wen-Feng
We demonstrate control of electromagnetic (EM) wave through dual heights micro-lens (DHML) array in 1.1 mu m pixel size complementary metal oxide semiconductor image sensor. The sensitivity and signal-to-noise ratio (SNR) are significantly improved ( > 10%) using the DHML structure. This DHML structure acts as an array of fundamental waveguides to enhance the optical throughput and to suppress the spatial crosstalk that is confirmed by evaluating the pixel performance in terms of the confinement factor of fundamental mode in this DHML structure. (C)) 2016 Published by Elsevier B.V.
Correlation between photoluminescence and varied growth pressure of well-aligned ZnO nanorods on fused silica substrate
(2007-11-01)
Yang, Song
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Hsu, Hsu-Cheng
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Liu, Wei-Ren
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Cheng, Hsin-Min
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Hsieh, Wen-Feng
Well-aligned ZnO nanorods with variable diameters were fabricated on fused silica substrates by the simple physical vapor deposition method with and without pre-deposited NiO particles. The diameter control of ZnO nanorods on the fused silica substrates was achieved by varying the growth pressure. The room-temperature photoluminescence spectra of the ZnO nanorods exhibit strong exciton emission at 3.25 eV that reveals good crystal quality. The exciton emission peak shifts toward 3.22 eV for the samples made at the larger growth pressure that is attributed to the influence of the electron-acceptor-level transition. The ZnO nanorods were examined by high resolution transmission electron microscopy and X-ray diffraction to show single crystal quality and preferentially c-axis alignment. Furthermore, we used scanning electron microscope to verify not only the size but also the growth mechanisms of ZnO nanorods. The results show a ZnO buffer layer formed between the flat top-facet nanorods and the substrate. In comparison with the samples without pre-deposited NiO particles on the substrate, the pre-deposited NiO particles act as nucleation centers for Zn vapor during the deposition process that improves the quality of the buffer layer. (C) 2007 Elsevier B.V. All rights reserved.
Coupling theory of asymmetric photonic-crystal waveguides
(2008)
Huang, Chih-Hsien
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Hsieh, Wen-Feng
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Cheng, Szu-Cheng
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光電工程學系
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Department of Photonics
The physical properties of asymmetric photonic-crystal directional couplers axe studied by using the tight-binding theory, which considers that the field distributions of photonic-crystal waveguides (PCWs) are localized around the periodic defects. From this model, the analytic formulas which describe the dispersion of the coupler and the eigenmode patterns were derived. By considering coupling up to the third nearest-neighboring between two PCWs, analytic expressions of the dispersion relations of asymmetric photonic crystal coupler are consistent with the results from the plane wave expansion method (PWEM). Due to the broken symmetry, two dispersion curves will never cross. Nevertheless, the eigenmode patterns switch their parity as the symmetric coupler does when wavevector k passes over the decoupling point.
Dark solitons in a spinor microcavity-polariton condensate
(2016-10)
Chen, Ting-Wei
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Jheng, Shih-Da
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Hsieh, Wen-Feng
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Cheng, Szu-Cheng
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物理研究所
Dark solitons of a two-component condensate occurring in nonresonantly-pumped microcavity polaritons (spinor MPCs) with integer vorticities, referred to as integer dark solitons (IDSs), can be excited by a laser beam with tunable polarization and power. We investigate the physical properties of stationary IDSs in a pure spinor MPCs without defects. From the excitations of a IDS, we show that the soliton is stable when the pump power is higher than a critical value. When the pump polarization is in favor of one component, we find that the critical pump power for the stabilization becomes higher. The stable IDS exists below a critical pump polarization. A stable phase diagram of IDSs in terms of the pump condition, i.e., pump polarization and power, is thus obtained. (C) 2016 Elsevier Ltd. All rights reserved.
Defect induced ferromagnetic ordering in epitaxial Zn0.95Mn0.05O films on sapphire (0001)
(2019-12-04)
Liu, Wei-Rein
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Pao, Chih-Wen
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Yu, Doris Weijyun
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Chin, Yi-Ying
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Wu, Wen-Bin
We report the influence of Mn dopant on magnetic properties of Zn0.95Mn0.05O (ZMO)/Al2O3(0001) hetero-epitaxial systems grown by using pulsed-laser deposition. The room temperature (RT) intrinsic ferromagnetic (FM) ordering verified by superconducting quantum interference device magnetometer and x-ray magnetic circular dichroism spectrum of Mn L-2(,3) edges is ascribed to the substitutional Mn atoms in the Zn site of ZnO. Mn in ZMO has a tetrahedral local symmetry instead of the octahedral symmetry of MnO, after verifying the absence of the Mn-related impurities or clusters in ZMO epitaxial film by Mn K-edge and Zn K-edge x-ray absorption spectroscopy spectrum, as well as the analysis of long-range structural ordering on Renninger scan of forbidden (0005) reflection in x-ray diffraction, transmission electron microscopy and Raman spectrum. Comparison of x-ray absorption spectra of ZMO with those of ZnO epilayers at O K-, Zn K-, and L-3-edges indicates that the substitution of the Zn site with Mn enhances the charge-transfer (CT) transition and the presence of Zn vacancies (V-Zn) also dominate the photoluminescence (PL) spectrum, implying that the formation of numerous V-Zn defects plays an important role in activating FM interactions. The strong CT effect and the existence of high-density V-Zn suggest that the intrinsic RT FM ordering of insulating ZMO is a result of the formation of the bound magnetic polarons (BMPs) that interact with each other via intermediate magnetic impurities.