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Now showing items 17 - 32 of 270

  • Low-Loss, Silicon Integrated, Aluminum Nitride Photonic Circuits and Their Use for Electro-Optic Signal Processing

    Xiong, Chi   Pernice, Wolfram H. P.   Tang, Hong X.  

    Photonic miniaturization requires seamless integration of linear and nonlinear optical components to achieve passive and active functions simultaneously. Among the available material systems, silicon photonics holds immense promise for optical signal processing and on-chip optical networks. However, silicon is limited to wavelengths above 1.1 mu m and does not provide the desired lowest order optical nonlinearity for active signal processing. Here we report the integration of aluminum nitride (AlN) films on silicon substrates to bring active functionalities to chip-scale photonics. Using CMOS-compatible sputtered thin films we fabricate AlN-on-insulator waveguides that exhibit low propagation loss (0.6 dB/cm). Exploiting AlN's inherent Pockels effect we demonstrate electro-optic modulation up to 4.5 Gb/s with very low energy consumption (down to 10 fJ/bit). The ultrawide transparency window of AlN devices also enables high speed modulation at visible wavelengths. Our low cost, wideband, carrier-free photonic circuits hold promise for ultralow power and high-speed signal processing at the microprocessor chip level.
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  • Femtogram Doubly Clamped Nanomechanical Resonators Embedded in a High-Q Two-Dimensional Photonic Crystal Nanocavity

    Sun, Xiankai   Zheng, Jiangjun   Poot, Menno   Wong, Chee Wei   Tang, Hong X.  

    We demonstrate a new optomechanical device system which allows highly efficient transduction of femtogram nanobeam resonators. Doubly clamped nanomechanical resonators with mass as small as 25 fg are embedded in a high-finesse two-dimensional photonic crystal nanocavity. Optical transduction of the fundamental flexural mode around 1 GHz was performed at room temperature and ambient conditions, with an observed displacement sensitivity of 0.94 fm/Hz(1/2). Comparison of measurements from symmetric and asymmetric double-beam devices reveals hybridization of the mechanical modes where the structural symmetry is shown to be the key to obtain a high mechanical quality factor. Our novel configuration opens the way for a new category of "NEMS-in-cavity" devices based on optomechanical interaction at the nanoscale.
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  • Phase-dependent interference between frequency doubled comb lines in a chi((2)) phase-matched aluminum nitride microring

    Jung, Hojoong   Guo, Xiang   Zhu, Na   Papp, Scott B.   Diddams, Scott A.   Tang, Hong X.  

    Nonlinear optical conversion with frequency combs is important for self-referencing and for generating shorter wavelength combs. Here we demonstrate efficient frequency comb doubling through the combination of second-harmonic generation (SHG) and sum-frequency generation (SFG) of an input comb with a high Q, phase-matched chi((2)) microring resonator. Phase coherence of the SHG and SFG nonlinear conversion processes is confirmed by sinusoidal phase-dependent interference between frequency doubled comb lines. (C) 2016 Optical Society of America
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  • Active microcantilevers based on piezoresistive ferromagnetic thin films RID B-4476-2009 RID B-4673-2008 RID D-1587-2009

    Bhaskaran, Harish   Li, Mo   Garcia-Sanchez, Daniel   Zhao, Peng   Takeuchi, Ichiro   Tang, Hong X.  

    We report the piezoresistivity in magnetic thin films of Fe(0.7)Ga(0.3) and their use for fabricating self-transducing microcantilevers. The actuation occurs as a consequence of both the ferromagnetic and magnetostrictive properties of Fe(0.7)Ga(0.3) thin films, while the deflection readout is achieved by exploiting the piezoresistivity of these films. This self-sensing self-actuating micromechanical system involves a very simple bilayer structure, which eliminates the need for the more complex piezoelectric stack that is commonly used in active cantilevers. Thus, it potentially opens opportunities for remotely actuated cantilever-based sensors. (c) 2011 American Institute of Physics. [doi:10.1063/1.3533390]
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  • Stokes and anti-Stokes Raman scatterings from frequency comb lines in poly-crystalline aluminum nitride microring resonators

    Jung, Hojoong   Gong, Zheng   Liu, Xianwen   Guo, Xiang   Zou, Chang-ling   Tang, Hong X.  

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  • Directed growth of horizontally aligned gallium nitride nanowires for nanoelectromechanical resonator Arrays RID D-1587-2009

    Henry, Tania   Kim, Kyungkon   Ren, Zaiyuan   Yerino, Christopher   Han, Jung   Tang, Hong X.  

    We report the growth of horizontally aligned arrays and networks of GaN nanowires (NWs) as resonant components in nanoelectromechanical systems (NEMS). A combination of top-down selective area growth (SAG) and bottom-up vapor-liquid-solid (VLS) synthesis enables flexible fabrication of highly ordered nanowire arrays in situ with no postgrowth dispersion. Mechanical resonance of free-standing nanowires are measured, with quality factors (Q) ranging from 400 to 1000. We obtained a Young's modulus (E) of similar to 338 GPa from an array of NWs with varying diameters and lengths. The measurement allows detection of nanowire motion with a rotating frame and reveals dual fundamental resonant modes in two orthogonal planes. A universal ratio between the resonant frequencies of these two fundamental modes, irrespective of their dimensions, is observed and attributed to an isosceles cross section of GaN NWs.
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  • Control of second-harmonic generation in doubly resonant aluminum nitride microrings to address a rubidium two-photon clock transition

    Surya, Joshua B.   Guo, Xiang   Zou, Chang-Ling   Tang, Hong X.  

    Nonlinear optical effects have been studied extensively in microresonators as more photonics applications transitions to integrated on-chip platforms. Due to low optical losses and small mode volumes, microresonators are demonstrably the state-of-the-art platform for second-harmonic generation (SHG). However, the working bandwidth of such microresonator-based devices is relatively small, presenting a challenge for applications where a specifically targeted wavelength needs to be addressed. In this Letter, we analyze the phase-matching window and resonance wavelength with respect to varying microring widths, radii, and temperatures. A chip with precise design parameters was fabricated with phase matching realized at the exact wavelength of a twophoton transition of Rb-85. This procedure can be generalized to any target pump wavelength in the telecom band with picometer precision. (C) 2018 Optical Society of America
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  • A Twentieth Century Actress: A Conversation with Yunah Hong and Peter X. Feng

    Hong, Yunah; Feng, Peter X.  

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  • Fashion buying criteria of X Generation consumers in Hong Kong

    Wai Kwan Leung, Jovey; Taylor, Gail  

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  • Fashion buying criteria of X Generation consumers in Hong Kong

    Wai Kwan Leung, Jovey   Taylor, Gail  

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  • HEMIBOEA ROSEOALBA SB ZHOU, X. HONG & F. WEN (GESNERIACEAE), A NEW SPECIES FROM GUANGDONG, CHINA

    Zhou, Shou-Biao   Hong, Xin   Wen, Fang   Xiao, Hong-Mei  

    A new species of Hemiboea, H. roseoalba, from Guangdong, China, is described and illustrated. It is similar to H. gracilis and H. angustifolia in leaf and flower shape, but can be distinguished by leaf blade with serrulate from the middle to the apex, lateral veins 7-9 on each side of midrib; peduncle 2.5-3.0 cm long, glabrous; cymes 4-6-flowered; triangular calyx base connate for c. 0.3 cm; pink corolla 4.0-4.3 cm long and margin of lobes curled or retroflexed; staminodes 3; pistil 3.7-4.0 cm long; disc 2 mm high and truncate stigma slightly swollen.
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  • Frequency-tunable high- Q superconducting resonators via wireless control of nonlinear kinetic inductance

    Xu, Mingrui   Han, Xu   Fu, Wei   Zou, Chang-Ling   Devoret, Michel H.   Tang, Hong X.  

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  • Hemiboea roseoalba S.B. Zhou, X. Hong & F. Wen (Gesneriaceae), a new species from Guangdong, China

    Zhou Shou-Biao   Hong Xin   Wen Fang   Xiao Hong-Mei  

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  • Hong Kong\"s Reunion with China: The Global Dimensionsby Gerard A. Postiglione; James T. H. Tang

    Review by: Ian Scott  

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  • Differences between weekday and weekend levels of ozone, NO 2, NO x, and respirable suspended particulates in Hong Kong.

    Li Bin   Liu Bin  

    Differences in ozone (O 3), nitrogen oxides (NO x), and respirable suspended particulate (RSP) weekday and weekend concentrations in Hong Kong were investigated. Data were collected hourly by the Hong Kong Environmental Protection Department from January 1999 to October 2007 at 14 sites: 9 urban, 4 newly developed, and 1 rural station. Weekend O 3 concentrations were 14% and 22% higher for the afternoon peak O 3 time and 8-h O 3 average concentrations, respectively, at six urban stations, whereas NO 2 and NO x concentrations were 19% and 25% lower, respectively, during the afternoon O 3 peak time on weekends. No significant differences in peak afternoon O 3 concentrations were found at the newly developed or rural stations. Weekend RSP concentrations were lower at most urban stations. Urban RSP concentrations were lower on weekends than weekdays, by 14% for the morning rush hour and 8% for the daily average RSP. O 3 formation sensitivity to volatile organic compounds and lower weekend NO x emissions could explain the O 3 weekend effect in urban Hong Kong. Lower weekend RSP concentrations are predominantly the result of fewer anthropogenic emissions, primarily due to decreased traffic flow.
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  • Effect of cloud-to-ground lightning and meteorological conditions on surface NOx and O3 in Hong Kong

    Leilei Fei   L.Y. Chan   Xinhui Bi   Hai Guo   Yonglin Liu   Qinhao Lin   Xinming Wang   Ping'an Peng   Guoying Sheng  

    Abstract Cloud-to-ground (CG) lightning, meteorological conditions and corresponding surface nitrogen oxides (NO x ) and ozone (O 3 ) variations in relation to thunderstorm and lightning activities over Hong Kong at Kwai Chung (urban), Tung Chung (new town) and Tap Mun (background) during active lightning seasons from 2009 to 2013 were studied by analyzing respective air quality monitoring station data along with CG lightning and meteorological data. We observed NO x enhancement and significant O 3 decline on lightning days. Influences of land use types, lightning activities and meteorological conditions on surface NO x and O 3 were examined. NO x and O 3 concentrations shifted towards higher and lower levels, respectively, during lightning days especially in the dominant wind directions. Principal component analysis/absolute principal component scores (PCA/APCS) method and stepwise multiple linear regression (MLR) analysis were employed to examine the influence of thunderstorm related lightning and meteorological parameters on surface NO x and O 3 . Wind speed was supposed to be the most important meteorological parameter affecting the concentration of NO x , and lightning activities were observed to make a positive contribution to NO x . Negative contribution of hot, cloudy and wet weather and positive contribution of wind speed were found to affect the concentration of O 3 . Lightning parameters were also found to make a small positive contribution to O 3 concentration at Tap Mun and Tung Chung, but the net effect of lightning activities and corresponding meteorological conditions was the decrease of O 3 on lightning days. Reasonably good agreement between the predicted and observed NO x and O 3 values indicates that PCA/APCS-MLR is a valuable method to study the thunderstorm induced NO x and O 3 variations. Highlights • Surface NO x enhancement and O 3 decline were observed on lightning days in Hong Kong. • Effects of land use types, lightning and meteorological conditions were examined. • PCA/APCS-MLR was applied to the study of thunderstorm induced NO x and O 3 variations.
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