D.L. Kwong

Publications (526)981.75 Total impact

• Article: Phase modulation in horizontal metal-insulator-silicon-insulator-metal plasmonic waveguides.

  Shiyang Zhu, G Q Lo, D L Kwong
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  ABSTRACT: An extremely compact Si phase modulator is proposed and validated, which relies on effective modulation of the real part of modal index of horizontal metal-insulator-Si-insulator-metal plasmonic waveguides by a voltage applied between the metal cover and the Si core. Proof-of-concept devices are fabricated on silicon-on-insulator substrates using standard complementary metal-oxide-semiconductor technology using copper as the metal and thermal silicon dioxide as the insulator. A modulator with a 1-μm-long phase shifter inserted in an asymmetric Si Mach-Zehnder interferometer exhibits 9-dB extinction ratio under a 6-V/10-kHz voltage swing. Numerical simulations suggest that high speed and low driving voltage could be achieved by shortening the distance between the Si core and the n⁺-contact and by using a high-κ dielectric as the insulator, respectively.
  Optics Express 04/2013; 21(7):8320-30. · 3.59 Impact Factor
• Dataset: scholar

  J. W. Peng, S. J. Lee, G. C. Albert Liang, N. Singh, S. Y. Zhu, G. Q. Lo, D. L. Kwong
• Article: Microelectromechanical Maltese-cross metamaterial with tunable terahertz anisotropy.

  W M Zhu, A Q Liu, T Bourouina, D P Tsai, J H Teng, X H Zhang, G Q Lo, D L Kwong, N I Zheludev
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  ABSTRACT: Dichroic polarizers and waveplates exploiting anisotropic materials have vast applications in displays and numerous optical components, such as filters, beamsplitters and isolators. Artificial anisotropic media were recently suggested for the realization of negative refraction, cloaking, hyperlenses, and controlling luminescence. However, extending these applications into the terahertz domain is hampered by a lack of natural anisotropic media, while artificial metamaterials offer a strong engineered anisotropic response. Here we demonstrate a terahertz metamaterial with anisotropy tunable from positive to negative values. It is based on the Maltese-cross pattern, where anisotropy is induced by breaking the four-fold symmetry of the cross by displacing one of its beams. The symmetry breaking permits the excitation of a Fano mode active for one of the polarization eigenstates controlled by actuators using microelectromechanical systems. The metamaterial offers new opportunities for the development of terahertz variable waveplates, tunable filters and polarimetry.
  Nature Communications 12/2012; 3:1274. · 7.40 Impact Factor
• Article: Effect of cladding layer and subsequent heat treatment on hydrogenated amorphous silicon waveguides.

  Shiyang Zhu, G Q Lo, Weihong Li, D L Kwong
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  ABSTRACT: Although intrinsic hydrogenated amorphous silicon (a-Si:H) wire waveguides clad with normal SiO₂ layers have low propagation loss of 2.7 ± 0.1 dB/cm for transverse electric (TE) mode in the 1550-nm range, the transparency degrades when interfaced with other dielectrics (e.g., air) and/or exposed to elevated temperatures due to degradation of surface passivation in the a-Si:H waveguides. The thermal stability of a-Si:H wire waveguides with various cladding layers is systematically investigated, showing that the a-Si:H wire waveguides are stable at annealing temperature lower than ~350°C, while they degrade quickly when annealed at a higher temperature. It indicates that the thermal stability is mainly determined by the annealing temperature rather than the annealing time, which may be attributed to quick evolution of weakly bonded hydrogen in the a-Si:H waveguides. A thin Si₃N₄ intercladding layer between SiO₂ cladding and a-Si:H waveguide core may degrade transparency due to N-H bond absorption and is of no benefit to the thermal stability, thus its overall effect on the a-Si:H waveguides is detrimental.
  Optics Express 10/2012; 20(21):23676-83. · 3.59 Impact Factor
• Article: Performance of ultracompact copper-capped silicon hybrid plasmonic waveguide-ring resonators at telecom wavelengths.

  Shiyang Zhu, G Q Lo, D L Kwong
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  ABSTRACT: Ultracompact Cu-capped Si hybrid plasmonic waveguide-ring resonators (WRRs) with ring radii of 1.09-2.59 μm are fabricated on silicon on insulator substrates using standard complementary metal-oxide-semiconductor technology and characterized over the telecom wavelength range of 1.52-1.62 μm. The dependence of the spectral characteristics on the key structural parameters such as the Si core width, the ring radius, the separation gap between the ring and bus waveguides, and the ring configuration is systematically studied. A WRR with 2.59-μm radius and 0.250-μm nominal gap exhibits good performances such as normalized insertion loss of ~0.1 dB, extinction ratio of ~12.8 dB, free spectral range of ~47 nm, and quality factor of ~275. The resonance wavelength is redshifted by ~4.6 nm and an extinction ratio of ~7.5 dB is achieved with temperature increasing from 27 to 82°C. The corresponding effective thermo-optical coefficient (dn(g)/dT) is estimated to be ~1.6 × 10(-4) K(-1), which is contributed by the thermo-optical effect of both the Si core and the Cu cap, as revealed by numerical simulations. Combined with the compact size and the high thermal conductivity of Cu, various effective thermo-optical devices based on these Cu-capped plasmonic WRRs could be realized for seamless integration in existing Si electronic-photonic integrated circuits.
  Optics Express 07/2012; 20(14):15232-46. · 3.59 Impact Factor
• Article: A nano-opto-mechanical pressure sensor via ring resonator.

  X Zhao, J M Tsai, H Cai, X M Ji, J Zhou, M H Bao, Y P Huang, D L Kwong, A Q Liu
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  ABSTRACT: This paper reports a nano-opto-mechanical pressure sensor based on nano-scaled ring resonator. The pressure is measured through the output spectrum shift which is induced via mechanical deformation of the ring resonator. The sensitivity as high as 1.47 pm/kPa has been experimentally achieved which agrees with numerical prediction. Due to the strong variation of sensitivity with different ring radius and thickness of the diaphragm, the pressure sensor can be used to form an array structure to detect the pressure distribution in highly accurate measurement with low-cost advantages. The nano-opto-mechanical pressure sensor has potential applications such as shear stress displacement detection, pressure wave detector and pressure mapping etc.
  Optics Express 04/2012; 20(8):8535-42. · 3.59 Impact Factor
• Article: Components for silicon plasmonic nanocircuits based on horizontal Cu-SiO₂-Si-SiO₂-Cu nanoplasmonic waveguides.

  Shiyang Zhu, G Q Lo, D L Kwong
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  ABSTRACT: We report systematic results on the development of horizontal Cu-SiO₂-Si-SiO₂-Cu nanoplasmonic waveguide components operating at 1550-nm telecom wavelengths, including straight waveguides, sharp 90° bends, power splitters, and Mach-Zehnder interferometers (MZIs). Owing to the relatively low loss for propagating (~0.3 dB/µm) and for 90° sharply bending (~0.73 dB/turn), various ultracompact power splitters and MZIs are experimentally realized on a silicon-on-insulator (SOI) platform using standard CMOS technology. The demonstrated splitters exhibit a relatively low excess loss and the MZIs exhibit good performance such as high extinction ratio of ~18 dB and low normalized insertion loss of ~1.7 dB. The experimental results of these devices agree well with those predicted from numerical simulations with suitable Cu permittivity data.
  Optics Express 03/2012; 20(6):5867-81. · 3.59 Impact Factor
• Source

  Available from: T. Bourouina

  Article: Polarization dependent state to polarization independent state change in THz metamaterials

  W. M. Zhu, A. Q. Liu, W. Zhang, J. F. Tao, T. Bourouina, J. H. Teng, X. H. Zhang, Q. Y. Wu, H. Tanoto, H. C. Guo, G. Q. Lo, D. L. Kwong
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  ABSTRACT: We experimentally demonstrated a polarization dependent state to polarization independent state change in terahertz (THz) metamaterials. This is accomplished by reconfiguring the lattice structure of metamaterials from 2-fold to 4-fold rotational symmetry by using micromachined actuators. In experiment, it measures resonance frequency shift of 25.8% and 12.1% for TE and TM polarized incidence, respectively. Furthermore, single-band to dual-band switching is also demonstrated. Compared with the previous reported tunable metamaterials, lattice reconfiguration promises not only large tuning range but also changing of polarization dependent states, which can be used in photonic devices such as sensors, optical switches, and filters.
  Applied Physics Letters 11/2011; 99(22):221102-221102-3. · 3.84 Impact Factor
• Article: Electro-absorption modulation in horizontal metal-insulator-silicon-insulator-metal nanoplasmonic slot waveguides

  Shiyang Zhu, G. Q. Lo, D. L. Kwong
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  ABSTRACT: An ultracompact, broadband, and fully complementary metal-oxide-semiconductor (CMOS) compatible Si nanoplasmonic electro-absorption modulator is proposed based on the recently developed horizontal metal-insulator-silicon-insulator-metal nanoplasmonic slot waveguide. The modulation relies on a highly accumulated electron layer at the insulator/Si interface induced by an applied voltage. Proof-of-concept devices are fabricated using standard Si CMOS technology. A 3-dB modulation around 1550 nm is measured under ∼6.5 V bias for a device with total length of only 4 μm. The design suggests that larger modulation could be achieved by using high-κ dielectrics as the insulator, thinning down the insulator thickness, and narrowing the Si core of the nanoplasmonic waveguide.
  Applied Physics Letters 10/2011; 99(15):151114-151114-3. · 3.84 Impact Factor
• Source

  Available from: Tony Low

  Article: Pseudo-potential Band Structure Calculation of InSb Ultra-thin Films and its application to assess the n-Metal-Oxide-Semiconductor Transistor Performance

  Zhen Gang Zhu, Tony Low, Ming-Fu Li, Wei Jun Fan, P. Bai, D.L. Kwong, G. Samudra
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  ABSTRACT: Band structure of InSb thin films with $<100>$ surface orientation is calculated using empirical pseudopotential method (EPM) to evaluate the performance of nanoscale devices using InSb substrate. Contrary to the predictions by simple effective mass approximation methods (EMA), our calculation reveals that $\Gamma$ valley is still the lowest lying conduction valley. Based on EPM calculations, we obtained the important electronic structure and transport parameters, such as effective mass and valley energy minimum, of InSb thin film as a function of film thickness. Our calculations reveal that the 'effective mass' of $\Gamma$ valley electrons increases with the scaling down of the film thickness. We also provide an assessment of nanoscale InSb thin film devices using Non-Equilibrium Green's Function under the effective mass framework in the ballistic regime.
  09/2011;
• Source

  Available from: utexas.edu

  Article: Theoretical investigation of silicide Schottky barrier detector integrated in horizontal metal-insulator-silicon-insulator-metal nanoplasmonic slot waveguide.

  Shiyang Zhu, G Q Lo, D L Kwong
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  ABSTRACT: An ultracompact integrated silicide Schottky barrier detector (SBD) is designed and theoretically investigated to electrically detect the surface plasmon polariton (SPP) propagating along horizontal metal-insulator-silicon-insulator-metal nanoplasmonic slot waveguides at the telecommunication wavelength of 1550 nm. An ultrathin silicide layer inserted between the silicon core and the insulator, which can be fabricated precisely using the well-developed self-aligned silicide process, absorbs the SPP power effectively if a suitable silicide is chosen. Moreover, the Schottky barrier height in the silicide-silicon-silicide configuration can be tuned substantially by the external voltage through the Schottky effect owing to the very narrow silicon core. For a TaSi(2) detector with optimized dimensions, numerical simulation predicts responsivity of ~0.07 A/W, speed of ~60 GHz, dark current of ~66 nA at room temperature, and minimum detectable power of ~-29 dBm. The design also suggests that the device's size can be reduced and the overall performances will be further improved if a silicide with smaller permittivity is used.
  Optics Express 08/2011; 19(17):15843-54. · 3.59 Impact Factor
• Article: Nanoplasmonic power splitters based on the horizontal nanoplasmonic slot waveguide

  Shiyang Zhu, G. Q. Lo, D. L. Kwong
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  ABSTRACT: Ultracompact power splitters based on the horizontal nanoplasmonic slot waveguide (Cu/SiO2/Si/SiO2/Cu, whose propagation loss is measured to be ∼0.36 dB/μm at 1550 nm for waveguide with ∼47-nm-wide Si core and ∼26-nm surrounding SiO2) are designed, simulated, and fabricated using the standard complementary metal-oxide-semiconductor technology. The 1 × 2 Y-splitters with the opening angle of 60°, 120°, and 180° are measured to have the excess losses of ∼1.4, ∼1.7, and ∼3.2 dB, compared with the theoretical values of ∼1.4, ∼1.5, and ∼1.8 dB, respectively. The 1 × 3 cross-splitter delivers normalized output powers of ∼ −7.6, ∼ −4.2, and ∼ −7.2 dB at the left, middle, and right output ports, respectively, compared with the theoretical value of ∼ −6.6 dB. Reasons of the discrepancy between the experimental and theoretical results are discussed, and approaches to further reduce the excess loss are then proposed.
  Applied Physics Letters 07/2011; 99(3):031112-031112-3. · 3.84 Impact Factor
• Source

  Available from: edu.sg

  Conference Proceeding: Design and experiments of a Nano-opto-mechanical switch using EIT-like effects of coupled-ring resonator

  M. Ren, Y.F. Yu, J.M. Tsai, H. Cai, W.M. Zhu, D.L. Kwong, A.Q. Liu
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  ABSTRACT: In this paper, a Nano-opto-mechanical (NOM) switch is designed, simulated and experimentally demonstrated, using the electromagnetically induced transparency (EIT)-like effects of coupled-ring resonator. The control of the switch is realized by optical force between the silicon waveguide and the dielectric substrate. As the injection pump power increases from 0 to 6 mW, the normalized power of transmission peak at 1553.3 nm decreases from 1 to 0.02, and the position of the initial transmission peak has a 7.8-GHz red shift. The proposed NOM switch can be potentially applied in all-optical network.
  Solid-State Sensors, Actuators and Microsystems Conference (TRANSDUCERS), 2011 16th International; 07/2011
• Source

  Available from: edu.sg

  Conference Proceeding: A NEMS optical switch driven by optical force

  J.F. Tao, H. Cai, A.B. Yu, Q.X. Zhang, J. Wu, K. Xu, J.T. Lin, G.Q. Lo, D.L. Kwong, A.Q. Liu
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  ABSTRACT: In this paper, an optical switch driven by the optical force is demonstrated based on Nanoelectromechanical system (NEMS) technology. The switch consists of a Mach-Zehnder interferometer (MZI) and a ring resonator. One of the MZI arms is suspended to enable optical switching by optical force induced displacement. The optical force is introduced by injecting a control light into the ring resonator. It has a switching contrast of 16 dB and a response time of 0.2 μs, which is 10³ times faster than the traditional millimeter-scaled optical switches. It has potential applications in the high speed optical-packet-switching communications and the silicon-photonic integrated circuits.
  Solid-State Sensors, Actuators and Microsystems Conference (TRANSDUCERS), 2011 16th International; 07/2011
• Source

  Available from: edu.sg

  Conference Proceeding: On-chip optical power measurement by optical force

  J.F. Tao, H. Cai, A.B. Yu, W.M. Zhu, Q.X. Zhang, J. Wu, K. Xu, J.T. Lin, G.Q. Lo, D.L. Kwong, A.Q. Liu
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  ABSTRACT: This paper reports a silicon-based micromachined optical power detector with on-chip measurement ability. The optical power is detected by an integrated electron-tunneling displacement transducer, in which optical force is employed as the bridge between optical energy and mechanical energy transition. Compared with the traditional optical power detectors, which are based on photo absorption, the proposed optical power detector has advantages of small size (0.08 mm × 0.3 mm), low thermal noise (0.03 V/°C), large measurement range (>;20 mW) and wavelength independence. Therefore, it has potential applications as high-speed detecting element in silicon-based photonic chips and lab-on-chip systems.
  Solid-State Sensors, Actuators and Microsystems Conference (TRANSDUCERS), 2011 16th International; 07/2011
• Source

  Available from: edu.sg

  Conference Proceeding: A tunable laser using double-ring resonator external cavity via free-carrier dispersion effect

  M. Ren, H. Cai, J.M. Tsai, W.M. Zhu, D.L. Kwong, A.Q. Liu
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  ABSTRACT: A tunable laser based on double-ring external resonant cavity is designed, fabricated and tested. The double-ring resonator external cavity consists of a silicon waveguide ring resonator, a p-i-n doped silicon ring resonator, and a superluminescent diode (SLED). The laser is fabricated on a SOI wafer and the wavelength is tuned by injecting electrical currents to p-i-n structures. In the experiment, it measures 45.8 nm wavelength tuning with 110 GHz channel spacing and the average output power is approximately -8 dBm. It advances in high tuning speed, large side mode suppression ratio, and low manufacture cost, such has potential applications in high speed WDM networks.
  Solid-State Sensors, Actuators and Microsystems Conference (TRANSDUCERS), 2011 16th International; 07/2011
• Source

  Available from: edu.sg

  Conference Proceeding: Nano-opto-mechanical linear actuator utilizing gradient optical force

  H. Cai, K.J. Xu, J.M. Tsai, G.Q. Lo, D.L. Kwong, A.Q. Liu
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  ABSTRACT: This work presents an opto-mechanical linear actuator utilizing the gradient optical force between two identical parallel waveguides. The actuator size shrinks to nanoscale dimensions. Theoretical study shows that the actuator deflection is controlled over optical signals and linearly proportional to the applied optical power. Such optical actuator takes full advantages of the nanotechnology, and has many advantages over their electrostatic comb-drive counterparts, most importantly immunity to electromagnetic interference and mechanical shock, and avoiding the problem of side instability.
  Solid-State Sensors, Actuators and Microsystems Conference (TRANSDUCERS), 2011 16th International; 07/2011
• Source

  Available from: edu.sg

  Conference Proceeding: An absorptive filter using microfluidic switchable metamaterials

  B. Dong, W.M. Zhu, Y.H. Fu, J.M. Tsai, H. Cai, D.L. Kwong, E.P. Li, E. Rius, A.Q. Liu
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  ABSTRACT: In this paper, the microfluidic switchable absorptive metamaterials (MMs) filter in the gigahertz region is designed. It consists of a microfluidic network between the electrical resonator and the metal plate. The absorption frequency of the tunable MMs absorber can be tuned by pumping different liquids into the microchannel using the microfluidic technology. Based on the designed absorptive MMs, the absorptive peak can be shifted by introducing a microfluidic layer with frequency tunability up to 20% and absorption change up to 90%. By introducing the tunability in absorption frequency of MMs, it has great potential in the applications of filter and sensor / detector for biomedical applications.
  Solid-State Sensors, Actuators and Microsystems Conference (TRANSDUCERS), 2011 16th International; 07/2011
• Conference Proceeding: Application of piezoresistive stress sensor in wafer bumping and drop impact test of embedded ultra thin device

  Xiaowu Zhang, R. Rajoo, C.S. Selvanayagam, A. Kumar, V.S. Rao, N. Khan, V. Kripesh, J.H. Lau, D.-L. Kwong, V. Sundaram, R.R. Tummula
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  ABSTRACT: Though an understanding on the development of residual stresses in silicon device after chip level packaging processes has been investigated in previous studies, little is known about the development of stresses after wafer bumping process. In this paper, piezoresistive stress sensors were used to evaluate the stresses in device wafer after wafer bumping process, such as under bump metallization (UBM) fabrication, dry-film process, and solder bumping. For the stress evaluation, n-type piezoresistive stress sensors were fabricated on p-type (100) silicon wafer and then sensors were calibrated to determine piezoresistive coefficients. The calibrated sensor wafers were finally used to measure residual in-plane stresses at the surface of device wafer. Due to the growing demand of portable and handheld devices, the reliability of electronic packages with Pb-free solder under drop impact condition has become an issue of concern. This paper aims to measure the real-time stress in an ultra thin die during a drop test to ascertain whether die cracking is a possible problem when dealing with 50 μm thick dies. The advantages of these stress data are: (1) serve as a basis for process selection to meet the trends and needs of a reliable package, and for the development and improvement of existing processes; and (2) are important to enhance survivability during wafer bumping, handling and packaging.
  Electronic Components and Technology Conference (ECTC), 2011 IEEE 61st; 07/2011
• Article: Junctionless Vertical-Si-Nanowire-Channel-Based SONOS Memory With 2-Bit Storage per Cell

  Y. Sun, H.Y. Yu, N. Singh, K.C. Leong, G.Q. Lo, D.L. Kwong
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  ABSTRACT: This letter reports on a junctionless silicon/oxide/nitride/oxide/silicon memory realized on vertical-Si-nanowire gate-all-around structures with two physical storage nodes per cell. Two physical bits per cell are electrically evaluated by studying the second bit effect and the program/erase speeds, endurance, and retention. The relaxed channel length limitation due to the vertical structure provides more tolerance to overcome the scaling-related reliability issues. In addition, the absence of junctions reduces the process complexity and cost, thus making this device more manufacturable with a very low thermal budget.
  IEEE Electron Device Letters 07/2011; · 2.85 Impact Factor