Browsing by Author "Lee, C. Y."

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24-W cryogenically cooled Nd:YAG monolithic 946-nm laser with a slope efficiency > 70%
(2015-04-20)
Cho, C. Y.
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Lee, C. Y.
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Chang, C. C.
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Tuan, P. H.
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Huang, K. F.
A high-power efficient monolithic Nd: YAG 946-nm laser is demonstrated at the cryogenic temperature. By exploring the absorption and the fluorescence spectra of the Nd: YAG crystal, it reveals the fact that the absorption bandwidth at 808 nm is narrowing and the fluorescence intensity at 1061 nm is significant enhanced when the temperature is decreased. The temperature dependence of the lasing threshold at 946 nm is found to display a minimum value near a temperature of 170 K. At an incident pump power of 34.5 W, the local heating leads the optimum temperature to be approximately 120 K and the maximum output power can reach 24.4 W with the conversion efficiency of 71% as well as the slope efficiency up to 75%. (C)2015 Optical Society of America
Characterization of a burn-in failure caused by a defective source driver on TFT-LCD panel
(2006)
Wang, Fred S. C.
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Lin, Keh-La
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Tso, Ko-Yang
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Chao, Chin-Chieh
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Wang, Wai William
This paper describes a thorough investigation to identify the root cause of an LCD panel bum-in failure induced by an LCD source driver, which is observed in a large-scale LCD factory producing more than one million LCD panels per month. The investigation demonstrates the effectiveness of the circuit simulation to precisely locate the defective spot which is caused by a metal slice originated from outer rings of an LCD COG (chip-on-glass) source driver. With the aid of emission microscope (EMMI), Energy Dispersive Analysis X-Ray (EDAX), and Chip Probing (CP) tester, the root cause of the failure is well explained. The formation mechanism of metal slice from the outer rings is thoroughly studied. A solution to completely eliminate the source of metal slices from the outer rings during wafer processing is also proposed.
Characterizing the propagation evolution of wave patterns and vortex structures in astigmatic transformations of Hermite-Gaussian beams
(2018-01-01)
Chen, Y. F.
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Chang, C. C.
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Lee, C. Y.
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Tung, J. C.
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Liang, H. C.
Theoretical wave functions are analytically derived to characterize the propagation evolution of the Hermite-Gaussian (HG) beams transformed by a single-lens astigmatic mode converter with arbitrary angle. The derived wave functions are related to the combination of the rotation transform and the antisymmetric fractional Fourier transform. The derived formula is systematically validated by using an off-axis diode-pumped solid-state laser to generate various high-order HG beams for mode conversions. In addition to validation, the creation and evolution of vortex structures in the transformed HG beams are numerically manifested. The present theoretical analyses can be used not only to characterize the evolution of the transformed beams but to design the optical vortex beams with various forms.
Cryogenically monolithic self-Raman lasers: observation of single-longitudinal-mode operation
(2015-05-01)
Lee, C. Y.
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Chang, C. C.
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Tuan, P. H.
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Cho, C. Y.
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Huang, K. F.
A cryogenically monolithic Nd:YVO4 self-Raman laser is experimentally explored and theoretically analyzed. The variation of the stimulated Raman scattering (SRS) threshold on the temperature is found to be nonlinear because the reduction of thermal lensing enlarges the cavity mode size. In spite of the nonlinear variation of the SRS threshold on the temperature, the overall SRS output power can be efficiently increased from 0.78 to 1.36 W for temperature decreasing from 285 to 80 K at an absorbed power of 17.2 W. More interestingly, the single-longitudinal-mode operation is experimentally achieved when temperature is lower than 125 K. (C) 2015 Optical Society of America
EELS plasmon studies of silver/carbon core/shell nanocables prepared by simple arc discharge
(2007-04-01)
Wang, L. S.
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Buchholz, D. B.
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Li, Y.
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Li, J.
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Lee, C. Y.
A method for the fabrication of large quantities of high quality silver nanocables encapsulated in carbon nanotubes (Ag@C) using a hydrogen arc is presented. A growth mechanism based on the generation of poly-aromatic hydrocarbons by the hydrogen arc is proposed. The size-dependent electronic structures of the resultant materials are investigated using electron energy loss spectroscopy (EELS). The surface plasmon and bulk-excitation character observed by EELS are discussed. As the diameter of Ag@C nanocable decreases, the surface and bulk plasmons of the silver core shift to lower energy and the peaks broaden. Measurements of electrical conductivity exhibits a liner current-voltage character with a conductivity of 0.5x10(4) S/cm for the nanocable structure.
Efficiency and Droop Improvement in GaN-Based High-Voltage Light-Emitting Diodes
(2011-08-01)
Wang, C. H.
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Lin, D. W.
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Lee, C. Y.
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Tsai, M. A.
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Chen, G. L.
The efficiency and electrical characteristics of GaN-based high-voltage light-emitting diodes (HV-LEDs) are investigated in detail. The spatial distribution of light output and simulation results showed that 100-V HV-LED with smaller microchips had superior current spreading. As a result, under 1-W operation, the luminous efficiency of 100-V HV-LED with smaller microchips was enhanced by 7.8% compared to that of 50-V HV-LED, while the efficiency droop behaviors were reduced from 28% in 50-V HV-LED to 25.8% in 100-V HV-LED. Moreover, smaller microchips exhibited lower series resistance and forward voltage, leading to higher wall-plug efficiency.
Excellent Color Rendering Index Quantum Dots White Light-Emitting Diode with Distributed Bragg Reflector Structure
(2014)
Chen, K. J.
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Lin, B. C.
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Han, H. V.
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Lin, C. C.
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Lee, C. Y.
This study demonstrated the high CRI and excellent uniformity colloidal quantum dot white-light-emitting diodes with the DBR structure at different correlated color temperature from 2500 K to 4500K.
Experimental study of R-134a evaporation heat transfer in a narrow annular duct
(2010-04-01)
Chen, C. A.
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Lee, C. Y.
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Lin, T. F.
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機械工程學系
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Department of Mechanical Engineering
An experiment is carried out here to investigate the evaporation heat transfer and associated evaporating flow pattern for refrigerant R-134a flowing in a horizontal narrow annular duct The gap of the duct is fixed at 1.0 and 2 0 mm. In the experiment, the effects of the duct gap, refrigerant vapor quality, mass flux and saturation temperature and imposed heat flux on the measured evaporation heat transfer coefficient h, are examined in detail. For the duct gap of 2.0 mm, the refrigerant mass flux G is varied from 300 to 500 kg/m(2) s, imposed heat flux q from 5 to 15 kW/m(2), vapor quality x(m) from 0.05 to 0.95, and refrigerant saturation temperature T(sat) from 5 to 15 degrees C. While for the gap of 1.0 mm, G is varied from 500 to 700 kg/m(2)s with the other parameters varied in the same ranges as that for delta = 2 0 mm The experimental data clearly show that the evaporation heat transfer coefficient increases almost linearly with the vapor quality of the refrigerant and the increase is more significant at a higher G. Besides, the evaporation heat transfer coefficient also rises substantially at increasing q. Moreover, a significant increase in the evaporation heat transfer coefficient results for a rise in T,,,. but the effects are less pronounced in the narrower duct at a low imposed heat flux and a high refrigerant mass flux. Furthermore, the evaporation heat transfer coefficient increases substantially with the refrigerant mass flux except at low vapor quality. We also note that reducing the duct gap causes a significant increase in h(r). In addition to the heat transfer data, photos of R-134a evaporating flow taken from the duct side show the change of the dominant two-phase flow pattern in the duct with the experimental parameters. Finally, an empirical correlation for the present measured heat transfer coefficient for the R-134a evaporation in the narrow annular ducts is proposed. (C) 2009 Elsevier Ltd. All rights reserved
Exploiting concave-convex linear resonators to design end-pumped solid-state lasers with flexible cavity lengths: application for exploring the self-mode-locked operation
(2016-11-14)
Tuan, P. H.
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Chang, C. C.
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Lee, C. Y.
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Cho, C. Y.
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Liang, H. C.
The characteristics of a convex-concave linear resonator under the thermal lensing effect are theoretically analyzed to find an analytical model for designing end-pumped solid-state lasers with flexible cavity lengths. By exploiting the design model, the power scaling for continuous-wave operation under strong thermal lensing can be easily achieved in the proposed resonator with different cavity lengths. Furthermore, the proposed resonator is applied to explore the exclusive influence of cavity length on the self-mode-locked (SML) operation. It is discovered that the lasing longitudinal modes will split into multiple groups in optical spectrum to lead to a multi-pulse mode-locked temporal state when the cavity length increases. Finally, a theoretical model is derived to reconstruct the experimental results of SML operation to deduce a simple relationship between the group number of lasing modes and the cavity length. (C) 2016 Optical Society of America.
Frequency comb expansion in a monolithic self-mode-locked laser concurrent with stimulated Raman scattering
(2014-09-01)
Lee, C. Y.
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Chang, C. C.
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Liang, H. C.
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Chen, Y. F.
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交大名義發表
The discovery of a novel phase-locked frequency comb generated from a monolithic laser with the concurrent processes of self-mode locking (SML) and stimulated Raman scattering (SRS) is reported. It is experimentally shown that the width of the Raman gain can be exploited to considerably expand the frequency comb of a monolithic SML crystal laser via the SRS process. At a pump power of 6.5 W, an output power of 140 mW in the Stokes wave with a pulse width as narrow as 2.9 ps at a pulse repetition rate of 6.615 GHz is obtained. The present finding not only provides useful insights into the monolithic intracavity SRS process but also paves the way for generating mode-locked pulses based on monolithic self-Raman crystals.
GaN-Based LEDs Grown on HVPE Growth High Crystalline Quality Thick GaN Template
(2011)
Lin, D. W.
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Lin, C. C.
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Chiu, C. H.
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Lee, C. Y.
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Yang, Y. Y.
In this study, high crystalline quality 30 mu m thick gallium nitride (GaN) films were grown by hydride vapor phase epitaxy (HVPE) on sapphire substrate, and the thick GaN films were used for developing high performance light-emitting diodes (LEDs). By using high-resolution X-ray diffraction, the full width at half-maximum (FWHM) of the rocking curve shows that this 30 mu m thick GaN template had high crystalline quality. In addition, the transmission electron microscopy (TEM) images suggest that threading dislocation densities (TDDs) are almost free in multiple quantum wells (MQWs) for LEDs grown on 30 mu m thick GaN template. Compared with conventional LEDs grown on sapphire, LEDs grown on 30 mu m thick GaN template exhibit 26% enhancement of light output at 20 mA. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.003111jes] All rights reserved.
Generating high-peak-power structured lights in selectively pumped passively Q-switched lasers with astigmatic mode transformations
(2017-12-01)
Chang, C. C.
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Hsieh, Y. H.
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Lee, C. Y.
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Sung, C. L.
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Tuan, P. H.
Various high-order Hermite-Gaussian (HG) modes with high repetition rates and high peak powers are systematically generated by designing the cavity configuration to satisfy the criterion of the passive Q-switching. For the HG(m,0) modes with the order m = 1-9, the pulse repetition rate can exceed 100 kHz with peak power higher than 0.3 kW. For the HG(m,m) modes with the order m = 1-10, the pulse repetition rate can be up to 37 kHz with peak power higher than 0.35 kW. Furthermore, the high-order HG beams is transformed by using an astigmatic mode converter to generate various structured lights with optical vortices. Experimental patterns of the transformed high-order HG beams in the propagation are theoretically analyzed and the phase structures are numerically manifested.
Generation of orthogonally polarized self-mode-locked Nd:YAG lasers with tunable beat frequencies from the thermally induced birefringence
(2016-04-15)
Sung, C. L.
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Cheng, H. P.
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Lee, C. Y.
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Cho, C. Y.
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Liang, H. C.
The simultaneous self-mode-locking of two orthogonally polarized states in a Nd:YAG laser is demonstrated by using a short linear cavity. A total output power of 3.8 W can be obtained at an incident pump power of 8.2 W. The beat frequency Delta f(c) between two orthogonally polarized mode-locked components is observed and measured precisely. It is found that the beat frequency increases linearly with an increase in the absorbed pump power. The origin of the beat frequency can be utterly manifested by considering the thermally induced birefringence in the Nd: YAG crystal. The present result offers a promising approach to generate orthogonally polarized mode-locked lasers with tunable beat frequency. (C) 2016 Optical Society of America
Generation of terahertz optical beating from a simultaneously self-mode-locked Nd: YAG laser at 1064 and 1123 nm
(2017-01-15)
Sung, C. L.
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Lee, C. Y.
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Chang, C. C.
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Liang, H. C.
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Chen, Y. F.
The reflectivity of the output coupler is designed to achieve the synchronously self-mode-locked operation at 1064 and 1123 nm in a diode-end-pumped Nd:YAG laser. Numerical analyses are performed to confirm that the designed output coupler can lead the emission lines to be predominant at 1064 and 1123 nm. Moreover, the crossover of the threshold pump powers for the 1064 and 1123 nm emission lines can be exploited to obtain the single central wavelength of 1064 nm or the single central wavelength of 1123 nm or, simultaneously, dual-central-wavelength self-mode-locked operation by finely adjusting the cavity alignment. For the dual-central-wavelength mode-locked emissions, the pulse repetition rate and the pulse duration are 4.5 GHz and 50.8 ps, respectively. The maximum output power can be up to 2.47 W at a pump power of 7.5 W. The synchronization of the 1064 and 1123 nm mode-locked pulses generates the optical beating pulse trains with repetition rates up to 14.7 THz. (C) 2017 Optical Society of America
Growth and characterization of Ge nanostructures selectively grown on patterned Si
(2008-11-03)
Cheng, M. H.
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Ni, W. X.
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Luo, G. L.
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Huang, S. C.
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Chang, J. J.
By utilizing different distribution of strain fields around the edges of oxide, which are dominated by a series of sizes of oxide-patterned windows, long-range ordered self-assembly Ge nanostructures, such as nano-rings, nano-disks and nano-dots, were selectively grown by ultra high vacuum chemical vapor deposition (UHV-CVD) on Si (001) substrates. High-resolution double-crystal symmetrical omega/2 theta scans and two-dimensional reciprocal space mapping (2D-RSM) technologies employing the triple axis X-ray diffractometry have been used to evaluate the quality and strain status of as-deposited as well as in-situ annealed Ge nanostructures. Furthermore, we also compare the quality and strain status of Ge epilayers grown on planar unpatterned Si substrates. It was found that the quality of all Ge epitaxial structures is improved after in-situ annealing process and the quality of Ge nano-disk structures is better than that of Ge epilayers; on planar unpatterned Si substrates, because oxide sidewalls are effective dislocation sinks. We also noted that the degree of relaxation for as-deposited Ge epilayers on planar unpatterned Si substrates is less than that for as-deposited Ge nano-disk structures. After in-situ annealing process,all Ge epitaxial structures are almost at full relaxation whatever Ge epitaxial structures grew on patterned or unpatterned Si substrates. (c) 2008 Published by Elsevier B.V.
Growth and Field Emission Characteristics of Pillar-like Carbon Nanotubes Using Co-Ti/Al Co-deposited Catalysts at Low Temperature
(2010)
Chang, C. T.
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Lee, C. Y.
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Lin, K. C.
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Lai, R. L.
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Tsai, Wan-Lin
In this essay, the pillar-like CNT field emission arrays synthesis with co-deposited catalysts at low temperature (550 degrees C) was proposed. Pillar-like CNT has been successfully synthesized by thermal CVD system. The current density of this proposed pillar like CNTs was as high as 1272 mu A/cm(2) at 6 V/mu m and the turn-on field was 3.6 V/mu m. Additionally, the reliability was more stable as lower than 7% degradation of initial current density.
High-peak-power large-angular-momentum beams generated from passively Q-switched geometric modes with astigmatic transformation
(2017-12-01)
Chen, Y. F.
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Chang, C. C.
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Lee, C. Y.
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Sung, C. L.
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Tung, J. C.
The criterion of achieving efficient passive Q-switching is analyzed to design an off-axis pumped Nd:YVO4/Cr4+ : YAG laser with a degenerate cavity. Experimental results reveal that pure high-order HG(0,m) or HG(m,0) eigenmodes with the order m between 0 and 14 can be generated, depending on the off-axis displacement along the y axis or the x axis. On the other hand, lasing modes naturally turn into planar geometric modes when the off- axis displacement is larger than the value for exciting the HG(0,m) or HG(m,0) eigenmodes with m > 14. The overall peak powers for high- order eigenmodes or geometric modes can exceed 140 W. Furthermore, the high- order eigenmodes and geometric modes are employed to generate vortex beams with large orbital angular momentum by using an external cylindrical mode converter. Theoretical analyses are performed to confirm experimental results and to manifest the phase structures of the generated vortex beams. (C) 2017 Chinese Laser Press
Hole injection and efficiency droop improvement in InGaN/GaN light-emitting diodes by band-engineered electron blocking layer
(2010-12-27)
Wang, C. H.
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Ke, C. C.
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Lee, C. Y.
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Chang, S. P.
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Chang, W. T.
A graded-composition electron blocking layer (GEBL) with aluminum composition increasing along the [0001] direction was designed for c-plane InGaN/GaN light-emitting diodes (LEDs) by employing the band-engineering. The simulation results demonstrated that such GEBL can effectively enhance the capability of hole transportation across the EBL as well as the electron confinement. Consequently, the LED with GEBL grown by metal-organic chemical vapor deposition exhibited lower forward voltage and series resistance and much higher output power at high current density as compared to conventional LED. Meanwhile, the efficiency droop was reduced from 34% in conventional LED to only 4% from the maximum value at low injection current to 200 A/cm(2). (C) 2010 American Institute of Physics. [doi:10.1063/1.3531753]
Intracavity continuous-wave multiple stimulated-Raman-scattering emissions in a KTP crystal pumped by a Nd:YVO4 laser
(2015-08-24)
Lee, C. Y.
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Chang, C. C.
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Sung, C. L.
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Chen, Y. F.
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電子物理學系
Intracavity continuous-wave (CW) multiple stimulated-Raman-scattering emissions have been successfully demonstrated in a KTP crystal pumped by a Nd:YVO4 1064-nm laser for the first time. Three different output couplers (OCs) with high-reflection (HR) coating in the range of 1-1.1, 1-1.13, and 1-1.15 mu m are employed in the experiment to generate lasing wavelengths at 1095 (the first-Stokes emission of the 266 cm(-1) Raman shift), 1095 + 1128 (the first-and second-Stokes emission of the 266 cm-1 Raman shift), and 1095 + 1128 + 1149 nm (the first two Stokes emissions of the 266 cm-1 Raman shift and the first-Stokes emission of the 694 cm-1 Raman shift), separately. This Raman laser paves a way to produce more-closely spaced set of CW emission in the green-yellow region. (C) 2015 Optical Society of America
Investigating the temporal dynamics of continuously pumped Nd:YVO4 self-Raman lasers: observation of self-mode-locking
(2013-09-01)
Lin, Y. C.
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Lee, C. Y.
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Zhuang, W. Z.
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Su, K. W.
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Chen, Y. F.
We experimentally investigate the temporal dynamics of continuously pumped Nd:YVO4 self-Raman lasers. In the single-transverse-mode operation, it is found that the temporal behavior of the self-Raman laser exhibits a regular pulse train similar to the phenomenon of self-mode-locking. In the multi-transverse-mode operation, the average output power can be scaled up to 1.1 W and the temporal feature displays a complex dynamics that is numerically reconstructed with simultaneous longitudinal and transverse mode-locking.