Browsing by Author "Chen, Chyong-Hua"

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1xN plasmonic power splitters based on metal-insulator-metal waveguides
(2013-02-25)
Chen, Chyong-Hua
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Liao, Kao-Sung
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光電工程學系
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Department of Photonics
Novel plasmonic power splitters constructed from a rectangular ring resonator with direct-connected input and output waveguides are presented and numerically investigated. An analytical model and systematic approach for obtaining the appropriate design parameters are developed by designing an equivalent lumped circuit model for the transmission lines and applying it to plasmonic waveguides. This approach can dramatically reduce simulation times required for determining the desired locations of the output waveguides. Three examples are shown, the 1 x 3, 1 x 4, and 1 x 5 equal-power splitters, with the design method being easily extended to any number of output ports. (C)2013 Optical Society of America
An Electrically Tunable Polarizer for a Fiber System Based on a Polarization-Dependent Beam Size Derived From a Liquid Crystal Lens
(2014-06-01)
Chen, Michael
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Chen, Chyong-Hua
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Lai, Yinchieh
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Lu, Yan-qing
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Lin, Yi-Hsin
A broadband electrically tunable variable polarizer for fiber systems based on a liquid crystal lens is proposed and demonstrated. The polarization selectivity is based on a polarization-sensitive coupling efficiency to the fiber in the fiber system. For an incident ordinary ray, the output beam size remains the same as that of the incident beam, which results in low coupling efficiency. For an incident extraordinary ray (e-ray), the output beam size is close to the size of the fiber core, giving rise to high coupling efficiency because of the lens effect. Moreover, the output beam size of the e-ray can be electrically controlled, thus allowing the optical attenuation to be manipulated. In our experiments, the polarizationdependent loss from the visible to the near-infrared spectral region was approximately 12 dB. Such a broadband electrically variable polarizer may be applied to various designs for fiberoptic sensing devices and polarization-sensitive optical instruments.
An Electrically Tunable Polarizer for a Fiber System Based on a Polarization-Dependent Beam Size Derived From a Liquid Crystal Lens
(2014-06-01)
Chen, Michael
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Chen, Chyong-Hua
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Lai, Yinchieh
;
Lu, Yan-qing
;
Lin, Yi-Hsin
A broadband electrically tunable variable polarizer for fiber systems based on a liquid crystal lens is proposed and demonstrated. The polarization selectivity is based on a polarization-sensitive coupling efficiency to the fiber in the fiber system. For an incident ordinary ray, the output beam size remains the same as that of the incident beam, which results in low coupling efficiency. For an incident extraordinary ray (e-ray), the output beam size is close to the size of the fiber core, giving rise to high coupling efficiency because of the lens effect. Moreover, the output beam size of the e-ray can be electrically controlled, thus allowing the optical attenuation to be manipulated. In our experiments, the polarizationdependent loss from the visible to the near-infrared spectral region was approximately 12 dB. Such a broadband electrically variable polarizer may be applied to various designs for fiberoptic sensing devices and polarization-sensitive optical instruments.
An electrically-tunable liquid crystal lens coupler for the fiber communication systems
(2015-01-01)
Chen, Chyong-Hua
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Chen, Michael
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Lin, Yi-Hsin
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光電工程學系
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Department of Photonics
In this study, we demonstrated an electrically tunable lens coupler for both variable optical attenuation (VOA) and polarization selection. This coupler consists of a liquid crystal (LC) lens sandwiched between two GRIN lens. A GRIN lens is used to couple the light into the single mode fiber, and a LC lens is used to electrically manipulate the beam size of light. It is known that the lens power of a LC lens is tunable with high polarization sensitivity. Then, as the applied voltage on the LC lens is zero, the incident light is focused due to GRIN lens and coupled into the fiber. On the other hand, the beam size of the transformed e-ray becomes larger because the lens power of a LC lens for the e-ray decreases with the increase of the applied voltage. This results in the decrease of the coupling efficiency, and the optical power coupled into the fiber is smaller. This lens coupler for the e-ray functions as a VOA due to a continuous optical attenuation. On the contrary, the lens power of this LC lens for the o-ray does not vary because of optical anisotropy of the LC layer, and then the coupling efficiency for the o-ray remains high. For an arbitrary polarized incidence, this tunable lens coupler acts as a broadband polarizer for the fiber systems. The polarization dependent loss is larger than 30 dB and the switching time is around 1 second.
An ultra-broadband nano-plasmonic reflector with an asymmetric nano-ring resonator
(2014-01-01)
Chang, Yuhsin
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Chen, Chyong-Hua
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光電工程學系
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Department of Photonics
We propose a broadband nano-plasmonic reflector by using an asymmetric nano-ring resonator directly connected to the input and output waveguides based on metal-insulator-metal waveguides. Due to direct connection, both clockwise and counterclockwise traveling modes propagate inside the ring resonator, giving rise to resonator resonances and Mach Zehnder interference. Ultra-broad bandwidth is realized by adjusting the lengths of the ring to manipulate the resonant wavelengths and varying its widths to minimize the low-transmission ripples. An example of the plasmonic reflector with the dimensions of 200x522 nmxnm and the bandwidth of 1000 nm is numerically accomplished
Breakthrough to Non-Vacuum Deposition of Single-Crystal, Ultra-Thin, Homogeneous Nanoparticle Layers: A Better Alternative to Chemical Bath Deposition and Atomic Layer Deposition
(2017-04-01)
Liao, Yu-Kuang
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Liu, Yung-Tsung
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Hsieh, Dan-Hua
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Shen, Tien-Lin
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Hsieh, Ming-Yang
Most thin-film techniques require a multiple vacuum process, and cannot produce high-coverage continuous thin filmswith the thickness of a fewnanometers on rough surfaces. We present a new "paradigm shift" non-vacuum process to deposit high-quality, ultra-thin, single-crystal layers of coalesced sulfide nanoparticles (NPs) with controllable thickness down to a few nanometers, based on thermal decomposition. This provides high-coverage, homogeneous thickness, and large-area deposition over a rough surface, with little material loss or liquid chemical waste, and deposition rates of 10 nm/min. This technique can potentially replace conventional thin-film deposition methods, such as atomic layer deposition (ALD) and chemical bath deposition (CBD) as used by the Cu(In, Ga) Se2 (CIGS) thin-film solar cell industry for decades. We demonstrate 32% improvement of CIGS thin-film solar cell efficiency in comparison to reference devices prepared by conventional CBD deposition method by depositing the ZnS NPs buffer layer using the new process. The new ZnS NPs layer allows reduction of an intrinsic ZnO layer, which can lead to severe shunt leakage in case of a CBD buffer layer. This leads to a 65% relative efficiency increase.
Broadband Plasmonic Bandstop Filters With a Single Rectangular Ring Resonator
(2014-10-01)
Chang, Yuhsin
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Chen, Chyong-Hua
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交大名義發表
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光電工程學系
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National Chiao Tung University
A broadband plasmonic bandstop filter with a single directly connected rectangular ring resonator is proposed. Inside this resonator, which is constructed using two nonidentical branches, both ring resonance and Mach-Zehnder interference occurred. A broad stopband can be realized by appropriately adjusting the resonant wavelengths of these two interferences. An equivalent circuit model is established to analytically describe the performance of this structure and to systematically target its design parameters to achieve the minimal transmittance in the stopband. An example of the plasmonic bandstop filter with its dimensions of 200 nm x 522 nm and stopband edge wavelengths of 1300 and 1800 nm is numerically demonstrated.
Compact waveguide crossings with a cascaded multimode tapered structure
(2015-02-01)
Chen, Chyong-Hua
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光電工程學系
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Department of Photonics
A compact waveguide crossing constructed by a cascaded multimode tapered structure is numerically presented. By using an eigenmode expansion method, we observe that the phase difference between the two lowest guided modes can be changed after a multimode waveguide junction because of the coupling between these two guided modes. Accordingly, we propose a fourfold symmetric waveguide crossing composed of three cascaded tapered structures with Gaussian profiles on each branch. Analyzed by the finite difference time domain method, this waveguide crossing has the size of 4160 nm x 4160 nm, insertion loss of 0.13 dB, cross talk of -43.5 dB, and backreflection of -33.6 dB at the wavelength of 1550 nm and broad transmission spectrum at the wavelength range of 1500-1600 nm. (C) 2015 Optical Society of America
Design of a Broadband Plasmonic Unequal-Power Splitter with a Rectangular Ring Resonator
(2015-06-01)
Chang, Yuhsin
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Chen, Chyong-Hua
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光電工程學系
;
Department of Photonics
We proposed a novel method to design a broadband plasmonic unequal-power splitter with a rectangular ring resonator directly connected to the input and output waveguides. By properly assigning the locations of the input and output waveguides, the splitting ratio is controlled by manipulating the output waveguide widths while the reflectance is eliminated by adjusting the input waveguide width without varying any other design parameters. To obtain the design parameters of the input and output waveguide widths, analytical expressions of the splitting ratio and the reflectance are established by using the equivalent circuit based on the transmission line model. Design examples of unequal-power splitters with splitting ratio of 0.5 are numerically demonstrated. The analysis based on equivalent circuit is well confirmed by the finite difference time domain simulation. The simulated results show that the unequal-power splitters have a flat and wide band over the wavelength range from 1500 nm to 1600 nm by using a compact rectangular ring resonator with the dimensions of 550 nm x 275 nm.
Device Modeling of the Performance of Cu(In,Ga)Se-2 Solar Cells with V-Shaped Bandgap Profiles
(2014)
Kuo, Shou-Yi
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Hsieh, Ming-Yang
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Hsieh, Dan-Hua
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Kuo, Hao-Chung
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Chen, Chyong-Hua
The effect of Cu(In,Ga)Se-2 (CIGS) with V-shaped bandgap on device performance is investigated in detail. A series of Ga/(In+Ga) ratio are set to study the influence of V-shaped bandgap profile on the electricity of CIGS thin film solar cells. The modeling of device current density-voltage (J-V) curve and bandgap grading profile corresponded well to measurement results. Detailed characteristic and modeling results show that an increased gradient of bandgap from valley to the buffer layer CdS will result in a barrier and lead to an enhanced recombination in the valley. This phenomenon can be modified by the back electric field resulting from a gradient bandgap from valley (bandgap minimum) to the Mo back contact. These results indicate CIGS-based solar cells can achieve higher performance by optimizing the V-shaped bandgap profile.
Effective algorithm for high-channel-count multichannel fiber Bragg grating designs
(2012-09-01)
Chang, Yuhsin
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Chen, Chyong-Hua
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光電工程學系
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Department of Photonics
We present an efficient approach to design a high-channel-count multichannel fiber Bragg grating by assigning optimal sets of delay coefficients and constant phases to the corresponding channel responses. Based on approximate Fourier transform, the delay coefficients are chosen to separate all the single-channel gratings into several groups spatially in the grating structure, and the constant phases in each group are optimized to minimize the maximum index modulation to be approximately the square root of the maximum of the number of the channels in all groups times larger than that of the one-channel grating. Design examples demonstrate that the proposed method has advantages of low index modulation, low algorithmic complexity, and suitability for multichannel fiber Bragg grating designs with either identical or nonidentical spectral responses. (c) 2012 Optical Society of America
Efficient and stable polymer solar cells prepared using plasmonic graphene oxides as anode buffers
(2015-08-01)
Chen, Chung-Lei
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Chuang, Ming-Kai
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Chen, Chyong-Hua
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Chu, Chih-Wei
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Keshtov, Muchamed L.
Gold nanoparticle-decorated graphene oxides (AuNP-GOs) have been incorporated into inverted organic photovoltaic devices (OPVs) as anode interlayers. The OPVs fabricated with AuNP-GOs exhibited significant improvement in both the short-circuit current and fill factor compared to a reference device fabricated with neat GOs. We attribute the improvement in the efficiency of the device to the plasmonic effects of the AuNP-GO nanocomposites, which induced local enhancement of the electromagnetic field. More importantly, the inverted OPVs also exhibited better reliability after the use of AuNP-GO nanocomposites.
Growth and characterization of Cu(In,Ga)Se-2 thin films by nanosecond and femtosecond pulsed laser deposition
(2014-06-02)
Chen, Shih-Chen
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Hsieh, Dan-Hua
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Jiang, Hsin
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Liao, Yu-Kuang
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Lai, Fang-I
In this work, CuIn1-xGaxSe2 (CIGS) thin films were prepared by nanosecond (ns)- and femtosecond (fs)-pulsed laser deposition (PLD) processes. Different film growth mechanisms were discussed in perspective of the laser-produced plasmas and crystal structures. The fs-PLD has successfully improved the inherent flaws, Cu-2 (-) Se-x, and air voids ubiquitously observed in ns-PLD-derived CIGS thin films. Moreover, the prominent antireflection and excellent crystalline structures were obtained in the fs-PLD-derived CIGS thin films. The absorption spectra suggest the divergence in energy levels of radiative defects brought by the inhomogeneous distribution of elements in the fs-PLD CIGS, which has also been supported by comparing photoluminescence (PL) spectra of ns- and fs-PLD CIGS thin films at 15 K. Finally, the superior carrier transport properties in fs-PLD CIGS were confirmed by fs pump-probe spectroscopy and four-probe measurements. The present results indicate a promising way for preparing high-quality CIGS thin films via fs-PLD.
High-Efficiency InGaN/GaN Core-Shell Nanorod Light-Emitting Diodes With Low-Peak Blueshift and Efficiency Droop
(2017-03)
Tzou, An-Jye
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Hsieh, Dan-Hua
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Hong, Kuo-Bin
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Lin, Da-Wei
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Huang, Jhih-Kai
In this study, novel three-dimensional (3-D) nanoscale structures and methodology are demonstrated for application in high-efficiency core-shell nanorod (NR) light-emitting diodes (LEDs). The key to our successful growth of the structures is the introduction of passivation, which can be used to selectively grow active layers in desired structures. Through the fabrication methodology, core-shell NR green LEDs exhibiting large nonpolar active region and homogeneous indium distributions without a point tip shape were achieved. Stable light emission at a central wavelength of 518 nm was achieved as the injected current increased to more than 40 mA. The improved NR LEDs exhibited a stable luminescence emission wavelength (blueshift of 62 nm) and low-efficiency droop (18.1%) at 200 mA. Our scheme is scalable and compatible with current technologies, which provides a new perspective for developing high-performance, 3-D nanoscale optoelectronic devices.
High-power passively continuous-wave and Q-switching mode-locked Nd:LuVO4 laser by few-layer graphene-oxide films
(2016-12-01)
Chen, Hou-Ren
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Tsai, Chih-Ya
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Cheng, Hsin-Ming
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Lin, Kuei-Huei
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Chen, Chyong-Hua
Using a series of different concentration polymer-free graphene oxide (GO) films as saturable absorbers (SAs), we demonstrate high-power passively continuous-wave modelocking (CW-ML) and Q-switching mode-locking (QS-ML) for a Nd: LuVO4 laser at 1 mu m. CW-ML pulses of 6.62 ps with maximum output power of 3.89 W have been achieved to give the highest pulse peak power of 4.85 kW and pulse energy of 32.14 nJ under 15-W pumping by using SAs of 84.4% transmittance. Using SAs with a lower transmittance having a larger modulation depth of 75.9% and 63.4%, we obtain both the CW-ML pulses of 4.85-ps and QSML pulses with 2.73 W and 1.92 W output powers, respectively. (C) 2016 Optical Society of America
High-quality and Large-size Topological Insulator Bi2Te3-Gold Saturable Absorber Mirror for Mode-Locking Fiber Laser
(2016-12-05)
Chen, Hou-Ren
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Tsai, Chih-Ya
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Cheng, Hsin-Ming
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Lin, Kuei-Huei
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Yen, Po-Hsiu
A novel high-quality, large-size, reflection-type topological insulator Bi2Te3-Gold (BG) film-based nonlinear optical modulator has been successfully fabricated as a two-dimensional saturable absorber mirror (SAM) by pulsed laser deposition (PLD). This BG-SAM possesses saturation fluence of 108.3 mu J/cm(2), modulation depth (Delta R) of 6.5%, non-saturable loss of 38.4%, high damage threshold above 1.354 mJ/cm(2) and excellent uniformity providing for the generation of passive mode-locked (ML) pulses for erbium-doped fiber lasers (EDFLs) on a large sample area. Under 124 mW 976 nm pumping, We obtained 452-fs continuous-wave ML pulses with pulse energy of 91 pJ and full width at halfmaximum (FWHM) of 6.72-nm from this EDFL. The results clearly evidence that the PLD is an efficient method for fabricating BG-SAM that is suitable for a compact ultrafast ML fiber laser system.
Highly Efficient Flexible Hybrid Nanocrystal-Cu(In,Ga)Se-2 (CIGS) Solar Cells
(2015-01-21)
Liao, Yu-Kuang
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Brossard, Mael
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Hsieh, Dan-Hua
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Lin, Tzu-Neng
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Charlton, Martin D. B.
A novel scheme for hybridizing inkjet-printed thin film Cu(In,Ga)Se-2 (CIGS) solar cells with self-assembled clusters of nanocrystal quantum dots (NQDs), which provides a 10.9% relative enhancement of the photon conversion efficiency (PCE), is demonstrated. A non-uniform layer of NQD aggregates is deposited between the transparent conductive oxide and a CdS/CIGS p-n junction using low cost pulsed-spray deposition. Hybridization significantly improves the external quantum efficiency of the hybrid devices in the absorption range of the NQDs and in the red to near-IR parts of the spectrum. The low wavelength response enhancement is found to be induced by luminescent down-shifting (LDS) from the NQD layer, while the increase at longer wavelengths is attributed to internal scattering from NQD aggregates. LDS is demonstrated using time-resolved spectroscopy, and the morphology of the NQD layer is investigated in fluorescence microscopy and cross-sectional transmission electron microscopy. The influence of the NQD dose on the PCE of the hybrid devices is investigated and an optimum value is obtained. The low costs and limited material consumptions associated with pulsed-spray deposition make these flexible hybrid devices promising candidates to help push thin-film photovoltaic technology towards grid parity.
In Situ Regeneration of Si-based ARROW-B Surface Plasmon Resonance Biosensors
(2015-06-01)
Hsu, Hsin-Feng
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Lin, Yen-Ting
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Huang, Yang-Tung
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Lu, Ming-Feng
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Chen, Chyong-Hua
Si-based antiresonant reflecting optical waveguide type B (ARROW-B) surface plasmon resonance (SPR) biosensors allow label-free high-sensitivity detection of biomolecular interactions in real time. The ARROW-B waveguide, which has a thick guiding layer, provides efficient coupling with a single-mode fiber. The Si-based ARROW-B SPR biosensors were fabricated by using the standard semiconductor fabrication processes with a single-step lithography. A fluid flow system was designed to transport samples or analytes. The waveguide consists of propagation and SPR sensing regions. The propagation regions in the front and rear of the SPR sensing region have a symmetric cladding structure to isolate them from environmental changes. A high-index O-ring is used to seal the liquid flow channel. The intensity interrogation method was used to characterize the sensors. The sensitivity of the biosensors was 3.0 x 10(3) A mu W/RIU (refractive index unit) with a resolution of 6.2 x 10(-5) RIU. An in situ regeneration process was designed to make the sensors reusable and eliminate re-alignment of the optical measurement system. The regeneration was realized using ammonia-hydrogen peroxide mixture solutions to remove molecules bound on the sensor surface, such as self-assembled 11-mercapto-1undecanoic acid and bovine serum albumin. SPR was used to monitor the regeneration processes. The experimental results show that the sensing response did not significantly change after the sensor was reused more than 10 times. In situ regenerations of the sensors were achieved.
Non-interferometric phase retrieval using refractive index manipulation
(2017-04-07)
Chen, Chyong-Hua
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Hsu, Hsin-Feng
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Chen, Hou-Ren
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Hsieh, Wen-Feng
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光電工程學系
We present a novel, inexpensive and non-interferometric technique to retrieve phase images by using a liquid crystal phase shifter without including any physically moving parts. First, we derive a new equation of the intensity-phase relation with respect to the change of refractive index, which is similar to the transport of the intensity equation. The equation indicates that this technique is unneeded to consider the variation of magnifications between optical images. For proof of the concept, we use a liquid crystal mixture MLC 2144 to manufacture a phase shifter and to capture the optical images in a rapid succession by electrically tuning the applied voltage of the phase shifter. Experimental results demonstrate that this technique is capable of reconstructing high-resolution phase images and to realize the thickness profile of a microlens array quantitatively.
Optical cross-talk reduction in a quantum-dot-based full-color micro-light-emitting-diode display by a lithographic-fabricated photoresist mold
(2017-10-01)
Lin, Huang-Yu
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Sher, Chin-Wei
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Hsieh, Dan-Hua
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Chen, Xin-Yin
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Chen, Huang-Ming Philip
In this study, a full-color emission red-green-blue (RGB) quantum-dot (QD)-based micro-light-emitting-diode (micro-LED) array with the reduced optical cross-talk effect by a photoresist mold has been demonstrated. The UV micro-LED array is used as an efficient excitation source for the QDs. The aerosol jet technique provides a narrow linewidth on the micrometer scale for a precise jet of QDs on the micro-LEDs. To reduce the optical cross-talk effect, a simple lithography method and photoresist are used to fabricate the mold, which consists of a window for QD jetting and a blocking wall for cross-talk reduction. The cross-talk effect of the well-confined QDs in the window is confirmed by a fluorescence microscope, which shows clear separation between QD pixels. A distributed Bragg reflector is covered on the micro-LED array and the QDs' jetted mold to further increase the reuse of UV light. The enhanced light emission of the QDs is 5%, 32%, and 23% for blue, green, and red QDs, respectively. (C) 2017 Chinese Laser Press