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Dive into the research topics where Ho Wai Howard Lee is active.

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Featured researches published by Ho Wai Howard Lee.


Applied Physics Letters | 2008

Polarization-dependent coupling to plasmon modes on submicron gold wire in photonic crystal fiber

Ho Wai Howard Lee; Markus A. Schmidt; H. K. Tyagi; L. Prill Sempere; P. St. J. Russell

We present experimental results on coupling to surface plasmon modes on gold nanowires selectively introduced into polarization-maintaining photonic crystal fibers. Highly polarization- and wavelength-dependent transmission is observed. In one sample 24.5 mm long, the transmission on and off resonance differs by as much as 45 dB. Near-field optical images of the light emerging from such a gold-filled fiber show light guided on the wire at surface plasmon resonances. Finite element simulations are in good agreement with the experimental results. These gold-filled fibers can be potentially used as in-fiber wavelength-dependent filters and polarizers and as near-field tips for sub-wavelength-scale imaging.


Nano Letters | 2016

Gate-Tunable Conducting Oxide Metasurfaces

Yao-Wei Huang; Ho Wai Howard Lee; Ruzan Sokhoyan; Ragip Pala; Krishnan Thyagarajan; Seunghoon Han; Din Ping Tsai; Harry A. Atwater

Metasurfaces composed of planar arrays of subwavelength artificial structures show promise for extraordinary light manipulation. They have yielded novel ultrathin optical components such as flat lenses, wave plates, holographic surfaces, and orbital angular momentum manipulation and detection over a broad range of the electromagnetic spectrum. However, the optical properties of metasurfaces developed to date do not allow for versatile tunability of reflected or transmitted wave amplitude and phase after their fabrication, thus limiting their use in a wide range of applications. Here, we experimentally demonstrate a gate-tunable metasurface that enables dynamic electrical control of the phase and amplitude of the plane wave reflected from the metasurface. Tunability arises from field-effect modulation of the complex refractive index of conducting oxide layers incorporated into metasurface antenna elements which are configured in reflectarray geometry. We measure a phase shift of 180° and ∼30% change in the reflectance by applying 2.5 V gate bias. Additionally, we demonstrate modulation at frequencies exceeding 10 MHz and electrical switching of ±1 order diffracted beams by electrical control over subgroups of metasurface elements, a basic requirement for electrically tunable beam-steering phased array metasurfaces. In principle, electrically gated phase and amplitude control allows for electrical addressability of individual metasurface elements and opens the path to applications in ultrathin optical components for imaging and sensing technologies, such as reconfigurable beam steering devices, dynamic holograms, tunable ultrathin lenses, nanoprojectors, and nanoscale spatial light modulators.


Science | 2012

Excitation of orbital angular momentum resonances in helically twisted photonic crystal fiber

G. K. L. Wong; Myeong Soo Kang; Ho Wai Howard Lee; Fabio Biancalana; Claudio Conti; Thomas Weiss; P. St. J. Russell

Fiber with a Twist Optic fibers provide the backbone of communication networks. Controlling light propagation through the fiber is key to maximizing the capacity of information flow. By introducing a literal twist on the photonic crystal fiber, Wong et al. (p. 446) show that adding chirality to the cladding surrounding the core may provide another route to manipulating the transmission of light. Coupling between the twisted cladding and the core results in dips in the transmission spectrum, which are dependent on the degree of twist introduced into the fiber. Such twisted microstructure fibers may offer opportunities for coupling, filtering and manipulating light. Adding chirality to the structure of a photonic crystal fiber may provide another route to controlling light transmission. Spiral twisting offers additional opportunities for controlling the loss, dispersion, and polarization state of light in optical fibers with noncircular guiding cores. Here, we report an effect that appears in continuously twisted photonic crystal fiber. Guided by the helical lattice of hollow channels, cladding light is forced to follow a spiral path. This diverts a fraction of the axial momentum flow into the azimuthal direction, leading to the formation of discrete orbital angular momentum states at wavelengths that scale linearly with the twist rate. Core-guided light phase-matches topologically to these leaky states, causing a series of dips in the transmitted spectrum. Twisted photonic crystal fiber has potential applications in, for example, band-rejection filters and dispersion control.


Optics Express | 2011

Optofluidic refractive-index sensor in step-index fiber with parallel hollow micro-channel.

Ho Wai Howard Lee; Markus A. Schmidt; Patrick Uebel; H. K. Tyagi; Nicolas Y. Joly; M. Scharrer; P. St. J. Russell

We present a simple refractive index sensor based on a step-index fiber with a hollow micro-channel running parallel to its core. This channel becomes waveguiding when filled with a liquid of index greater than silica, causing sharp dips to appear in the transmission spectrum at wavelengths where the glass-core mode phase-matches to a mode of the liquid-core. The sensitivity of the dip-wavelengths to changes in liquid refractive index is quantified and the results used to study the dynamic flow characteristics of fluids in narrow channels. Potential applications of this fiber microstructure include measuring the optical properties of liquids, refractive index sensing, biophotonics and studies of fluid dynamics on the nanoscale.


New Journal of Physics | 2013

Ultrafast nonlinear dynamics of surface plasmon polaritons in gold nanowires due to the intrinsic nonlinearity of metals

Andrea Marini; Matteo Conforti; G. Della Valle; Ho Wai Howard Lee; Tr X Tran; Wonkeun Chang; Markus A. Schmidt; Stefano Longhi; P. St. J. Russell; Fabio Biancalana

Starting from first principles, we theoretically model the nonlinear temporal dynamics of gold-based plasmonic devices resulting from the heating of their metallic components. At optical frequencies, the gold susceptibility is determined by the interband transitions around the X, L points in the first Brillouin zone, and thermo-modulational effects ensue from Fermi smearing of the electronic energy distribution in the conduction band. As a consequence of light-induced heating of the conduction electrons, the optical susceptibility becomes nonlinear. In this paper we describe, for the first time to our knowledge, the effects of the thermo-modulational nonlinearity of gold on the propagation of surface plasmon polaritons guided on gold nanowires. We introduce a novel nonlinear Schr¨ odinger-like equation to describe pulse propagation in such nanowires, and we predict the appearance of an intense spectral red-shift caused by the delayed thermal response.


Optics Express | 2017

Rapid detection of drought stress in plants using femtosecond laser-induced breakdown spectroscopy

Jeremy N. Kunz; Dmitri V. Voronine; Ho Wai Howard Lee; Alexei V. Sokolov; Marlan O. Scully

Drought stress disrupts the balance of macro- and micronutrients and affects the yield of agriculturally and economically significant plants. Rapid detection of stress-induced changes of relative content of elements such as sodium (Na), potassium (K), calcium (Ca) and iron (Fe) in the field may allow farmers and crop growers to counter the effects of plant stress and to increase their crop return. Unfortunately, the analytical methods currently available are time-consuming, expensive and involve elaborate sample preparation such as acid digestion which hinders routine daily monitoring of crop health on a field scale. We report application of an alternative method for rapid detection of drought stress in plants using femtosecond laser-induced breakdown spectroscopy (LIBS). We demonstrate daily monitoring of relative content of Na, K, Ca and Fe in decorative indoor (gardenia) and cultivated outdoor (wheat) plant species under various degrees of drought stress. The observed differences in spectral and temporal responses indicate different mechanisms of drought resistance. We identify spectroscopic markers of drought stress which allow for distinguishing mild environmental and severe drought stress in wheat and may be used for remote field-scale estimation of plant stress resistance and health.


Journal of Modern Optics | 2017

Interaction of femtosecond laser pulses with plants: towards distinguishing weeds and crops using plasma temperature

Jeremy N. Kunz; Dmitri V. Voronine; Brian Ko; Ho Wai Howard Lee; Aman Rana; Muthukumar V. Bagavathiannan; Alexei V. Sokolov; Marlan O. Scully

Abstract The ability to distinguish between crops and weeds using sensors from a distance will greatly benefit the farming community through improved and efficient scouting for weeds, reduced herbicide input costs and improved profitability. In the present study, we examined the utility of femtosecond laser-induced breakdown spectroscopy (LIBS) for plant species differentiation. Greenhouse-grown plants of dallisgrass, wheat, soybean and bell pepper were evaluated using LIBS under an ambient environment. LIBS experiments were performed on the leaf samples of different plant species using a femtosecond laser system with an inexpensive lightweight detector. Temperatures of laser-induced plasma in plants depend on many parameters and were determined for each of the study species by the constituent elements interacting with femtosecond laser pulses. Using elemental calcium transitions in plant tissue samples to measure plasma temperatures, we report consistent differences among the four study species, with average values ranging from 5090 ± 168 K (soybean) to 5647 ± 223 K (dallisgrass).


european conference on optical communication | 2010

Plasmon resonances on gold nanowires directly drawn in step-index fiber

H. K. Tyagi; Ho Wai Howard Lee; Markus A. Schmidt; Patrick Uebel; Nicolas Y. Joly; M. Scharrer; P. St. J. Russell

High quality metallic wires (diameters down to 260nm) are fabricated using direct fiber drawing from a gold-filled cane. Measurements show coupling of light from the glass-core to plasmonic resonances on the wire, causing dips in the transmission at specific wavelengths.


photonics society summer topical meeting series | 2017

Plasmonic nanophotonic modulators

M. Z. Alam; Ho Wai Howard Lee; Y-W. Huang; Ragip Pala; Krishnan Thyagarajan; Ghazaleh Kafaie Shirmanesh; Ruzan Sokhoyan; Harry A. Atwater

Developing a compact, low power and high speed electro-optic modulator is crucial for overcoming the performance bottleneck of electronics. We review progress in chip based silicon compatible plasmonic modulator design, and discuss recent designs which have switching energy close to 1 fJ/bit.


conference on lasers and electro optics | 2015

Negative refraction due to discrete plasmon diffraction

Arian Kriesch; Ho Wai Howard Lee; Daniel Ploss; Stanley P. Burgos; Hannes Pfeifer; Jakob Naeger; Harry A. Atwater; Ulf Peschel

We experimentally demonstrate spectrally broad (λ0=1200-1800 nm) in-plane negative diffraction of SPPs in an array of plasmonic channel waveguides with negative mutual coupling resulting in negative refraction on the arrays interface and refocusing in an adjacent metal layer.

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Harry A. Atwater

California Institute of Technology

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Markus A. Schmidt

Leibniz Institute of Photonic Technology

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