Browsing by Author "Cheng, Chih-Hsien"

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850/940-nm VCSEL for optical communication and 3D sensing
(2018-01-01)
Cheng, Chih-Hsien
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Shen, Chih-Chiang
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Kao, Hsuan-Yun
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Hsieh, Dan-Hua
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Wang, Huai-Yung
This paper is going to review the state-of-the-art of the high-speed 850/940-nm vertical cavity surface emitting laser (VCSEL), discussing the structural design, mode control and the related data transmission performance. InGaAs/AlGaAs multiple quantum well (MQW) was used to increase the differential gain and photon density in VCSEL. The multiple oxide layers and oxide-confined aperture were well designed in VCSEL to decrease the parasitic capacitance and generate single mode (SM) VCSEL. The maximal modulation bandwidth of 30 GHz was achieved with well-designed VCSEL structure. At the end of the paper, other applications of the near-infrared VCSELs are discussed.
Catalytically solid-phase self-organization of nanoporous SnS with optical depolarizability
(2016)
Cheng, Chih-Hsien
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Chi, Yu-Chieh
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Wu, Chung-Lun
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Lin, Chun-Jung
;
Tsai, Ling-Hsuan
The catalytic solid-phase synthesis of self-organized nanoporous tin sulfide (SnS) with enhanced absorption, manipulative transmittance and depolarization features is demonstrated. Using an ultralow radio-frequency (RF) sputtering power, the variation of the orientation angle between the anodized aluminum oxide (AAO) membrane and the axis of the sputtered ion beam detunes the catalytically synthesized SnS from nanorod to nanoporous morphology, along the sidewall of the AAO membrane. The ultraslow catalytic sputtering synthesis on the AAO at the RF plasma power of 20 W and the orientation angle of 0 degrees regulates the porosity and integrality of nanoporous SnS, with average pore diameter of 80-150 nm. When transferring from planar to nanoporous structure, the phase composition changes from SnS to SnS2-Sn2S3, and the optical bandgap shrinks from 1.43 to 1.16 eV, due to the preferred crystalline orientation, which also contributes to an ultralow reflectance of <1% at 200-500 nm when both the transmittance and the surface scattering remain at their maxima. The absorption coefficient is enhanced by nearly one order of magnitude with its minimum of >5 x 10(4) cm(-1) at the wavelength between 200 and 700 nm, due to the red-shifting of the absorption spectrum to at least 100 nm. The catalytically self-organized nanoporous SnS causes strong haze and beam divergence of 20 degrees-30 degrees by depolarized nonlinear scattering at the surface, which favors the solar energy conversion with reduced surface reflection and enhanced photon scattering under preserved transmittance.
CdSe/ZnS core-shell quantum dot assisted color conversion of violet laser diode for white lighting communication
(2019-12-01)
Wang, Wei-Chun
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Wang, Huai-Yung
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Chen, Tzu-Yu
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Tsai, Cheng-Ting
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Cheng, Chih-Hsien
By color-converting the violet laser diode (VLD) with a cadmium selenide and zinc sulfide (CdSe/ZnS) core-shell-quantum dot (QD) doped polydimethylsiloxane (PDMS) film, the VLD+CdSe/ZnS core-shell-QD transferred white-light with improved color rendering index (CRI) is demonstrated for high-speed indoor visible lighting communication. To facilitate hue saturation value (HSV) of the VLD +CdSe/ZnS core-shell-QD white-lighting module, dual-sized CdSe/ZnS core-shell-QDs with two luminescent wavelengths centered at 515 and 630 nm are doped into the PDMS. The CdSe/ZnS core-shell-QD doped PDMS phosphor with the optimized thickness of 2.5 mm serves as the beam divergent color-converter, which not only excites red (R) and green (G) fluorescence to detune the correlated color temperature (CCT) and CRI of the mixed red/green/violet (RGV) white-light, but also remains the residual VLD signal for data transmission. With a divergent angle of 127 degrees, such a VLD + CdSe/ZnS core-shell-QD can deliver cold white-light with a CCT of 6389 K and a CRI of 63.3 at Commission International de l'Eclairage coordinate of 0.3214, 0.2755. Most important, the residual VLD light component is relatively weak with its wavelength out of the peak optical sensitivity region of the human retina centered at 441 nm. The directly encoded VLD+CdSe/ZnS core-shell-QD white light successfully carries the 16-quadrature amplitude modulation (QAM) discrete multitone data, which supports the maximal transmission data rate of 9.6 Gbit/s with a bit error ratio (BER) of 3.59 x 10(-3).
Growing GaN LEDs on amorphous SiC buffer with variable C/Si compositions
(2016-01-22)
Cheng, Chih-Hsien
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Tzou, An-Jye
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Chang, Jung-Hung
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Chi, Yu-Chieh
;
Lin, Yung-Hsiang
The epitaxy of high-power gallium nitride (GaN) light-emitting diode (LED) on amorphous silicon carbide (a-SixC1-x) buffer is demonstrated. The a-SixC1-x buffers with different nonstoichiometric C/Si composition ratios are synthesized on SiO2/Si substrate by using a low-temperature plasma enhanced chemical vapor deposition. The GaN LEDs on different SixC1-x buffers exhibit different EL and C-V characteristics because of the extended strain induced interfacial defects. The EL power decays when increasing the Si content of SixC1-x buffer. The C-rich SixC1-x favors the GaN epitaxy and enables the strain relaxation to suppress the probability of Auger recombination. When the SixC1-x buffer changes from Si-rich to C-rich condition, the EL peak wavelengh shifts from 446 nm to 450 nm. Moreover, the uniform distribution contour of EL intensity spreads between the anode and the cathode because the traping density of the interfacial defect gradually reduces. In comparison with the GaN LED grown on Sirich SixC1-x buffer, the device deposited on C-rich SixC1-x buffer shows a lower turn-on voltage, a higher output power, an external quantum efficiency, and an efficiency droop of 2.48 V, 106 mW, 42.3%, and 7%, respectively.
Long-Term Thermal Stability of Single-Mode VCSEL Under 96-Gbit/s OFDM Transmission
(2019-11-01)
Kao, Hsuan-Yun
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Tsai, Cheng-Ting
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Chi, Yu-Chieh
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Peng, Chun-Yen
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Leong, Shan-Fong
Thermal-dependent transmission performance and long-term stability of a single-transverse-mode (SM) vertical-cavity surface-emitting laser (VCSEL) with directly pre-leveled 16quadrature amplitude modulation orthogonal frequency-division multiplexing (16-QAM OFDM) data over 100 m 0M4 multi-mode-fiber (MMF) are demonstrated. Although narrowing the oxide-confined aperture to 3 mu m enables the SM VCSEL with low threshold current of 0.21 mA and high modulation bandwidth of 21.4 GHz, this technology also enlarges the insulating oxide area to accumulate the heat for raising core temperature. This induces a harsh environment as the core temperature persistently increases without dissipation even under the water-cooling control at 20 degrees C. As a result, the SM VCSEL can only guarantee a stable operation for 1.5 h under the encoding of QAM-OFDM data for transmission. After optimization, the SM VCSEL successfully supports a back-to-back transmission capacity as high as 96 Gbit/s. With the assistance of OFDM pre-leveling technique, the 96-Gbit/s QAM-OFDM data transmission is qualified over 100 m OM4 MMF with a receiving power penalty as low as 13 dB.
Nonstoichiometric SiC Bus/Ring Waveguide Based All-Optical Data Format Follower and Inverter
(2016-05)
Su, Sheng-Pin
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Wu, Chung-Lun
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Cheng, Chih-Hsien
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Huang, Bo-Ji
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Wang, Huai-Yung
Nonstoichiometric silicon carbide (SiC) bus/ring waveguide resonator based all-optical data-format follower and inverter is demonstrated to perform ultrafast dual functional wavelength and data-format conversion. The buried Si quantum dots (Si-Qps) with strong quantum confinement effect effectively result in a significant change on the nonlinear refractive index of 3.14 X 10(-1)3 cm(2)/W, which induces a red shift of 0.07 nm on the resonant wavelength comb of the nonstoichiometric SiC ring waveguide resonator. By injecting the 12 Gbit/s optical pulsed return-to-zero on-off keying (PRZ-OOK) data stream into the ring waveguide at a notched wavelength of 1551.08 nm, the induced red-shift on resonant wavelengths allows versatile all-optical data processing functions, including data wavelength conversion and data format following/inversion, on the data patterns transferred to the probe. The eye-opening diagram analysis at 12 Gbit/s reveals that the data transferred to the probe can provide a signal-to-noise ratio of 9.4 dB, and a receiving power penalty is degraded by 2.6 dB as compared to that of the pump data.
Reconstructing genome trees of prokaryotes using overlapping genes
(2010-02-24)
Cheng, Chih-Hsien
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Yang, Chung-Han
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Chiu, Hsien-Tai
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Lu, Chin Lung
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生物科技學系
Background: Overlapping genes (OGs) are defined as adjacent genes whose coding sequences overlap partially or entirely. In fact, they are ubiquitous in microbial genomes and more conserved between species than nonoverlapping genes. Based on this property, we have previously implemented a web server, named OGtree, that allows the user to reconstruct genome trees of some prokaryotes according to their pairwise OG distances. By analogy to the analyses of gene content and gene order, the OG distance between two genomes we defined was based on a measure of combining OG content (i.e., the normalized number of shared orthologous OG pairs) and OG order (i.e., the normalized OG breakpoint distance) in their whole genomes. A shortcoming of using the concept of breakpoints to define the OG distance is its inability to analyze the OG distance of multi-chromosomal genomes. In addition, the amount of overlapping coding sequences between some distantly related prokaryotic genomes may be limited so that it is hard to find enough OGs to properly evaluate their pairwise OG distances. Results: In this study, we therefore define a new OG order distance that is based on more biologically accurate rearrangements (e. g., reversals, transpositions and translocations) rather than breakpoints and that is applicable to both uni-chromosomal and multi-chromosomal genomes. In addition, we expand the term "gene" to include both its coding sequence and regulatory regions so that two adjacent genes whose coding sequences or regulatory regions overlap with each other are considered as a pair of overlapping genes. This is because overlapping of regulatory regions of distinct genes suggests that the regulation of expression for these genes should be more or less interrelated. Based on these modifications, we have reimplemented our OGtree as a new web server, named OGtree2, and have also evaluated its accuracy of genome tree reconstruction on a testing dataset consisting of 21 Proteobacteria genomes. Our experimental results have finally shown that our current OGtree2 indeed outperforms its previous version OGtree, as well as another similar server, called BPhyOG, significantly in the quality of genome tree reconstruction, because the phylogenetic tree obtained by OGtree2 is greatly congruent with the reference tree that coincides with the taxonomy accepted by biologists for these Proteobacteria. Conclusions: In this study, we have introduced a new web server OGtree2 at http://bioalgorithm.life.nctu.edu.tw/ OGtree2.0/ that can serve as a useful tool for reconstructing more precise and robust genome trees of prokaryotes according to their overlapping genes.
Reconstructing genome trees of prokaryotes using overlapping genes
(2010-02-24)
Cheng, Chih-Hsien
;
Yang, Chung-Han
;
Chiu, Hsien-Tai
;
Lu, Chin Lung
;
生物科技學系
Background: Overlapping genes (OGs) are defined as adjacent genes whose coding sequences overlap partially or entirely. In fact, they are ubiquitous in microbial genomes and more conserved between species than nonoverlapping genes. Based on this property, we have previously implemented a web server, named OGtree, that allows the user to reconstruct genome trees of some prokaryotes according to their pairwise OG distances. By analogy to the analyses of gene content and gene order, the OG distance between two genomes we defined was based on a measure of combining OG content (i.e., the normalized number of shared orthologous OG pairs) and OG order (i.e., the normalized OG breakpoint distance) in their whole genomes. A shortcoming of using the concept of breakpoints to define the OG distance is its inability to analyze the OG distance of multi-chromosomal genomes. In addition, the amount of overlapping coding sequences between some distantly related prokaryotic genomes may be limited so that it is hard to find enough OGs to properly evaluate their pairwise OG distances. Results: In this study, we therefore define a new OG order distance that is based on more biologically accurate rearrangements (e. g., reversals, transpositions and translocations) rather than breakpoints and that is applicable to both uni-chromosomal and multi-chromosomal genomes. In addition, we expand the term "gene" to include both its coding sequence and regulatory regions so that two adjacent genes whose coding sequences or regulatory regions overlap with each other are considered as a pair of overlapping genes. This is because overlapping of regulatory regions of distinct genes suggests that the regulation of expression for these genes should be more or less interrelated. Based on these modifications, we have reimplemented our OGtree as a new web server, named OGtree2, and have also evaluated its accuracy of genome tree reconstruction on a testing dataset consisting of 21 Proteobacteria genomes. Our experimental results have finally shown that our current OGtree2 indeed outperforms its previous version OGtree, as well as another similar server, called BPhyOG, significantly in the quality of genome tree reconstruction, because the phylogenetic tree obtained by OGtree2 is greatly congruent with the reference tree that coincides with the taxonomy accepted by biologists for these Proteobacteria. Conclusions: In this study, we have introduced a new web server OGtree2 at http://bioalgorithm.life.nctu.edu.tw/ OGtree2.0/ that can serve as a useful tool for reconstructing more precise and robust genome trees of prokaryotes according to their overlapping genes.
Strong optical nonlinearity of the nonstoichiometric silicon carbide
(2015-01-01)
Cheng, Chih-Hsien
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Wu, Chung-Lun
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Lin, Yung-Hsiang
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Yan, Wen-Long
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Shih, Min-Hsiung
Enhanced nonlinear refractive indices and absorption coefficients of nonstoichiometric SixC1-x with varying C/Si composition ratios from 0.51 to 1.83 grown by low-temperature plasma-enhanced chemical vapor deposition are demonstrated. When increasing the [CH4]/[CH4 + SiH4] fluence ratio from 70% to 92%, two Raman scattering signals at 795 and 970 cm(-1) contributed by transverse and longitudinal optical modes of Si-C bonds are simultaneously enhanced in stoichiometric and C-rich SixC1-x samples, whereas the Si-associated Raman peak at 520 cm(-1) decreases with increasing C/Si composition ratio. The C-rich SixC1-x film shows additional Raman scattering peaks at 1330 and 1580 cm(-1), which are individually contributed by the diamond-like C-C bonds and the G peak of the graphite-like C-C bonds, respectively. The nonlinear refractive index increases to 1 +/- 0.1 x 10(-11) cm(2) W-1 upon increasing the C/Si composition ratio up to 1.83, which is four orders of magnitude higher than that of bulk SiC. The increased C/Si composition ratio reduces the lattice constant and the effective mass of the SixC1-x film and enhances its nonlinear refractive index effectively. In comparison with the sp(3)-orbital C-C bond, the sp(2)-orbital C-C bond in SixC1-x films dominates the enhancement of nonlinear refractive index. By contrast, the nonlinear absorption coefficient changes sign and decreases magnitude when transferring the SixC1-x film from Si-rich to C-rich conditions. This sign reversal is primarily attributed to the conversion in the absorption mechanism from two-photon absorption to nonlinear saturable absorption. Unlike Si-Si bonds which favor two-photon absorption, the sp(2)-orbital C-C bonds with delocalized pi-electrons essentially enhance the saturable absorbance. Hence, a higher nonlinear refractive index and a higher saturable absorption coefficient can be obtained by enriching the sp(2)-orbital C-C bonds in C-rich SixC1-x films.
Toward high-speed visible laser lighting based optical wireless communications
(2019-09-01)
Tsai, Cheng-Ting
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Cheng, Chih-Hsien
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Kuo, Hao-Chung
;
Lin, Gong-Ru
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光電工程學系
Visible wavelength light-emitting diodes (LEDs) and laser diodes (LDs) enabled optical wireless communication (OWC) is an emerging technology for realizing high-confidentiality and high-speed point-to-point (PtP), vehicle-to-vehicle, and white-lighting data access links in indoor/outdoor free-space and underwater environments. Notably, OWC facilitates users to access more transmission bandwidth and capacity with physical-layer security and electromagnetic-immunity features by utilizing unlicensed visible optical carriers bands covering from 400 to 800 THz as compared to the commonly employed radio-frequency bands. Hence, a large amount of heavy data exchanging, routing, and streaming traffics can be realized in the current wireless networks. This also reinforces the realistic fusion of optical fiber wireline, radio-frequency wireless, and visible lighting communication networks in the new big-data era. In this paper, developing progress as well as the current trend of visible LED and LD based OWC networks for PtP, white-lighting and underwater applications are overviewed in detail. The performance parameters and figures-of-merits of previously reported OWC systems are summarized for comparison and discussion. Three main scenarios including visible LED based lighting OWC, visible LD enabled PtP communication, and LD based white-light fidelity ("Li-Fi") are individually discussed and summarized with their allowable data rate, transmission distance, and lighting color temperature and rendering index for comparison. At first, the transmission performances of LED based PtP and white-lighting OWC system with the use of novel data formats, such as pulse amplitude modulation and quadrature amplitude modulation-orthogonal frequency division multiplexing, are surveyed to understand the increasing trend on transmission capacity of LED based OWC system. Owing to the limited bandwidth and data rate of LED based OWC system, the LD has gradually been regarded as a competitive alternative candidate transmitter due to their significantly broadened bandwidth and enhanced data capacity. By taking the aforementioned advantages, studies on the blue/violet LD based white-lighting OWC have recently emerged to demonstrate the substitutability of this technology. The impacts of LD based OWC technology with its state-of-the-art implementation are comprehensively discussed together with prospects for future developments. Undoubtedly, the blue/violet LDs are also a promising transmitter for underwater PtP transmission owing to its extremely low power extinction in water, which has recently emerged as the most intriguing source for undersea exploration and sensing applications.
Transferring the bendable substrateless GaN LED grown on a thin C-rich SiC buffer layer to flexible dielectric and metallic plates
(2017-01-21)
Cheng, Chih-Hsien
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Huang, Tzu-Wei
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Wu, Chung-Lun
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Chen, Mu Ku
;
Chu, Cheng Hung
By growing an epitaxial GaN LED on C-rich a-SiC buffer deposited SiO2/Si substrate, the simplified transfer to versatile flexible metallic/dielectric membranes is demonstrated. Both the high growth temperature at 1000 degrees C and the slow deposition rate played important roles in the meticulous MOCVD growth of n-GaN along the surface normal of the a-SiC at the very beginning. High substrate temperature facilitated the refinement of C-rich SiC buffer from amorphous to partially crystalline with (0004)-orientation, which effectively reduces the lattice mismatch between n-GaN and SiC at the interface so as to gradually improve the crystalline n-GaN regrowth. The substrateless GaN LED transferred to flexible copper plates showed reduced turn-on voltage of 2.6 V, enhanced output power of 370 mW, enlarged power-to-current slope of 1.24 W A(-1), increased external quantum efficiency of 45%, and reduced efficiency droop of 15% under a bias of 300 mA. The thermal conductivity of the transferred substrate affected the EL peak wavelength shift of the substrateless GaN LED on SiC buffer. Heating the GaN LED on flexible copper plate to 65 degrees C only reduced its power by 10% and red-shifted its wavelength by 1 nm under a bias at 100 mA; the Auger effect resulted in a degraded EQE of 39.1% and an enlarged EQE droop of 8.5%. Bending the surface diameter of the curvature of the copper plate to 1.2 cm decayed the output power by 12% and red-shifted the EL peak by 5 nm because of the lattice strain induced quantum confined Stark effect (QCSE). Such a bendable substrateless GaN LED transferred to flexible membrane with superior heat dissipation and bending tolerance is a desired lighting element for green photonics in this era.