B. S. Ooi

King Abdullah University of Science and Technology, Djidda, Makkah, Saudi Arabia

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Publications (242)274.69 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The advances in lasers, electronic and photonic integrated circuits (EPIC), optical interconnects as well as the modulation techniques allow the present day society to embrace the convenience of broadband, high speed internet and mobile network connectivity. However, the steep increase in energy demand and bandwidth requirement calls for further innovation in ultra-compact EPIC technologies. In the optical domain, advancement in the laser technologies beyond the current quantum well (Qwell) based laser technologies are already taking place and presenting very promising results. Homogeneously grown quantum dot (Qdot) lasers and optical amplifiers, can serve in the future energy saving information and communication technologies (ICT) as the work-horse for transmitting and amplifying information through optical fiber. The encouraging results in the zero-dimensional (0D) structures emitting at 980 nm, in the form of vertical cavity surface emitting laser (VCSEL), are already operational at low threshold current density and capable of 40 Gbp s error-free transmission at 108 fJ/bit. Subsequent achievements for lasers and amplifiers operating in the O–, C–, L–, U–bands, and beyond will eventually lay the foundation for green ICT. On the hand, the inhomogeneously grown quasi 0D quantum dash (Qdash) lasers are brilliant solutions for potential broadband connectivity in server farms or access network. A single broadband Qdash laser operating in the stimulated emission mode can replace tens of discrete narrow-band lasers in dense wavelength division multiplexing (DWDM) transmission thereby further saving energy, cost and footprint. We herein reviewed the progress of both Qdots and Qdash devices, based on the InAs/InGaAlAs/InP and InAs/InGaAsP/InP material systems, from the angles of growth and device performance. In particular, we discussed the progress in lasers, semiconductor optical amplifiers (SOA), mode locked lasers, and superluminescent diodes, which are the building blocks of EPIC and ICT. Alternatively, these optical sources are potential candidates for other multi-disciplinary field applications.
    Progress in Quantum Electronics 11/2014; · 4.69 Impact Factor
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    M.Z.M. Khan, T.K. Ng, B.S. Ooi
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    ABSTRACT: We report on the high performance characteristics from superluminescent diodes (SLD) based on four-stack InAs/InGaAlAs chirped-barrier thickness quantum dash (Qdash) in a well structure. The active region exhibits a measured broad gain spectrum of ~140 nm with peak modal gain ~41 cm-1. The non-coated two section gain-absorber broad area and ridge-waveguide device configuration exhibits an output power >20 mW and >12 mW, respectively. The corresponding -3 dB bandwidths span ~82 nm and ~72 nm, with small spectral ripple <0.2 dB, related largely to the contribution from dispersive height dash ensembles of the highly inhomogeneous active region. These C-L communication band devices will find applications in various cross-disciplinary fields of optical metrology, optical coherent tomography, etc.
    IEEE Photonics Journal 08/2014; · 2.33 Impact Factor
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    ABSTRACT: A silicon-based laser, preferably electrically pumped, has long been a scientific and engineering goal. We demonstrate here, for the first time, an edge-emitting InGaN/GaN disk-in-nanowire array electrically pumped laser emitting in the green (λ=533nm) on (001)silicon substrate. The devices display excellent dc and dynamic characteristics with values of threshold current density, differential gain, T0 and small signal modulation bandwidth equal to 1.76kA/cm2, 3x10-17cm2, 232K and 5.8GHz respectively under continuous wave operation. Preliminary reliability measurements indicate a lifetime of 7000 hours. The emission wavelength can be tuned by varying the alloy composition in the quantum disks. The monolithic nanowire laser on (001)Si can therefore address wide-ranging applications such as solid state lighting, displays, plastic fiber communication, medical diagnostics and silicon photonics.
    Nano Letters 06/2014; · 12.94 Impact Factor
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    ABSTRACT: The InGaN/GaN quantum-disks-in-nanowire light-emitting diode (LED) with emission centered at ~830nm, the longest emission wavelength ever reported in the InGaN/GaN system, and spectral linewidth of 290nm, has been fabricated with p-side-down on a Cu substrate.
    CLEO: Science and Innovations; 06/2014
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    ABSTRACT: Extraordinary optical transmission (EOT) through arrays of gold nanoholes was studied with light across the visible to the near-infrared spectrum. The EOT effect was found to be improved by bridging pairs of nanoholes due to the concentration of the electromagnetic field in the slit between the holes. The geometrical shape and separation of the holes in these pairs of nanoholes affected the intensity of the transmission and the wavelength of resonance. Changing the geometrical shapes of these nanohole pairs from triangles to circles to squares leads to increased transmission intensity as well as red-shifting resonance wavelengths. The performance of bridged nanohole pairs as a plasmonic sensor was investigated. The bridged nanohole pairs were able to distinguish methanol, olive oil and microscope immersion oil for the different surface plasmon resonance in transmission spectra. Numerical simulation results were in agreement with experimental observations.
    Nanoscale 06/2014; · 6.74 Impact Factor
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    ABSTRACT: Simulating light propagation in anisotropic dynamic gain media such as semiconductors and solid-state lasers using the finite difference time-domain FDTD technique is a tedious process, as many variables need to be evaluated in the same instant of time. The algorithm has to take care of the laser dynamic gain, rate equations, anisotropy and dispersion. In this paper, to the best of our knowledge, we present the first algorithm that solves this problem. The algorithm is based on separating calculations into independent layers and hence solving each problem in a layer of calculations. The anisotropic gain medium is presented and tested using a one-dimensional set-up. The algorithm is then used for the analysis of a two-dimensional problem.
    SPIE Photonics Europe; 05/2014
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    ABSTRACT: We study the enhanced hole confinement by having a large bandgap AlGaN monolayer insertion (MLI) between the quantum well (QW) and the quantum barrier (QB). The numerical analysis examines the energy band alignment diagrams, using a self-consistent 6 $times$ 6 $k cdot p$ method and, considering carrier distribution, recombination rates (Shockley–Reed–Hall, Auger, and radiative recombination rates), under equilibrium and forward bias conditions. The active region is based on $hbox{Al}_{rm a}hbox{Ga}_{1 - {rm a}}hbox{N} hbox{(barrier)}/hbox{Al}_{ rm b}hbox{Ga}_{1 - {rm b}}hbox{N} hbox{(MLI)} /hbox{Al}_{rm c}hbox{Ga}_{1 - {rm c}}hbox{N} hbox{(well)} , / ,hbox{Al}_{rm d}hbox{Ga}_{1 - {rm d}}hbox{N} hbox{(barrier)}$, where b $>$ d $>$ a $>$ c. A large bandgap $ hbox{Al}_{rm b}hbox{Ga}_{1 - {rm b}}hbox{N}$ mono layer, inserted between the QW and QB, was found to be effective in providing stronger hole confinement. With the proposed band engineering scheme, an increase of more than 30% in spatial overlap of carrier wavefunction was obtained, with a considerable increase in carrier density and direct radiative recombination rates. The single-QW-based UV-LED was designed to emit at 280 nm, which is an effective wavelength for water disinfection.
    IEEE Photonics Journal 04/2014; 6(2):1-9. · 2.33 Impact Factor
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    ABSTRACT: We report on the properties and growth kinetics of defect-free, photoluminescence (PL) efficient mushroom-like nanowires (MNWs) in the form of ~30nm thick hexagonal-shaped InGaN-nanodisk on GaN nanowires, coexisting with the conventional rod-like InGaN-on-GaN nanowires (RNWs) on (111)-silicon-substrate. When characterized using confocal microscopy (CFM) with 458nm laser excitation, while measuring spontaneous-emission at fixed detection wavelengths, the spatial intensity map evolved from having uniform pixelated emission, to having only an emission ring, and then a round emission spot. This corresponds to the PL emission with increasing indium composition; starting from emission mainly from the RNW, and then the 540 nm emission from one MNWs ensemble, followed by the 590 nm emission from a different MNW ensemble, respectively. These hexagonal-shaped InGaN-nano-disks ensembles were obtained during molecular-beam-epitaxy (MBE) growth. On the other hand, the regular rod-like InGaN-on-GaN nanowires (RNWs) were emitting at a shorter peak wavelength of 490 nm. While the formation of InGaN rod-like nanowire is well-understood, the formation of the hexagonal-shaped InGaN-nanodisk-on-GaN-nanowire requires further investigation. It was postulated to arise from the highly sensitive growth kinetics during plasma-assisted MBE of InGaN at low temperature, i.e. when the substrate temperature was reduced from 800 °C (GaN growth) to <600 °C (InGaN growth), during which sparsely populated metal-droplet formation prevails and further accumulated more indium adatoms due to a higher cohesive bond between metallic molecules.
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    ABSTRACT: A theoretical investigation of AlGaN UV-LED with band engineering of hole and electron blocking layers (HBL and EBL, respectively) was conducted with an aim to improve injection efficiency and reduce efficiency droop in the UV LEDs. The analysis is based on energy band diagrams, carrier distribution and recombination rates (Shockley-Reed-Hall, Auger, and radiative recombination rates) in the quantum well, under equilibrium and forward bias conditions. Electron blocking layer is based on AlaGa1-aN / Alb → cGa1-b → 1-cN / AldGa1-dN, where a < d < b < c. A graded layer sandwiched between large bandgap AlGaN materials was found to be effective in simultaneously blocking electrons and providing polarization field enhanced carrier injection. The graded interlayer reduces polarization induced band bending and mitigates the related drawback of impediment of holes injection. Similarly on the n-side, the Alx → yGa1-x → 1-yN / AlzGa1-zN (x < z < y) barrier acts as a hole blocking layer. The reduced carrier leakage and enhanced carrier density in the active region results in significant improvement in radiative recombination rate compared to a structure with the conventional rectangular EBL layers. The improvement in device performance comes from meticulously designing the hole and electron blocking layers to increase carrier injection efficiency. The quantum well based UV-LED was designed to emit at 280nm, which is an effective wavelength for water disinfection application.
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    ABSTRACT: In this paper, we assessed the effect of additionally broadened quantum dash (Qdash) optical transitions in the multi-stack dash-in-a-well laser structure at both, material and device level. A broad photoluminescence linewidth of ${sim}{rm 150}~{rm nm}$ demonstrates the formation of highly inhomogeneous InAs-dashes across the stacks. The transmission electron microscopy revealed small (large) average dash height from the Qdash stack with thick (thin) over grown barrier layer. The Fabry–Perot laser diodes fabricated from this chirped structure exhibits unique device physics under the short pulsewidth (SPW) and quasi-continuous wave (QCW) operation. Varying the ridge-width $(W)$ from 2 to 4 $mu{rm m}$ showed quenching of ultrabroad lasing signature in the SPW operation, and consistent even for a wide 15 $mu{rm m}$ oxide strip laser diode. A lasing spectral split with reduced intensity gap in the center is observed in the QCW operation with the gap decreasing with increasing ridge-width. Such atypical lasing operation, influenced by the waveguiding mechanism is qualitatively realized by associating to the reduced vertical coupling effect of the Qdash stacks in the operation of small ridge-width lasers compared with large ridge-width and oxide stripe lasers, and leading to varying non-uniform distribution of carriers among the inhomogeneously broadened Qdash stacks in each case. Our chirped 2$,times,$830 $mu{rm m}$ ridge laser demonstrated marked improvement in the internal quantum efficiency $({sim}{80%})$x> and ${-}{rm 3}~{rm dB}$ lasing bandwidth, ${>}{rm 50}~{rm nm}$ centered at ${sim}{1.61}~mu{rm m}$.
    IEEE Journal of Quantum Electronics 01/2014; 50(2):51-61. · 2.11 Impact Factor
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    ABSTRACT: Despite the recent progress in gallium nitride (GaN) growth technology, the excessively high threading dislocation (TD) density within the GaN crystal, caused by the reliance on heterogeneous substrates, impedes the development of high-efficiency, low-cost, GaN-based heterostructure devices. For the first time, the chemical exfoliation of completely TD-free, single-crystalline, ultrathin (tens of nanometers) GaN nanomembranes is demonstrated using UV-assisted electroless chemical etching. These nanomembranes can act as seeding layers for subsequent overgrowth of high-quality GaN. A model is proposed, based on scanning and transmission electron microscopy as well as optical measurements to explain the physical processes behind the formation of the GaN nanomembranes. These novel nanomembranes, once transferred to other substrates, present a unique and technologically attractive path towards integrating high-efficiency GaN optical components along with silicon electronics. Interestingly, due to their nanoscale thickness and macroscopic sizes, these nanomembranes may enable the production of flexible GaN-based optoelectronics.
    Advanced Functional Materials 12/2013; · 10.44 Impact Factor
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    ABSTRACT: The mechanisms of mesa-height dependent efficiency and efficiency droop of blue InGaN/GaN micro-LED is presented. Device with a large etch-depth (> 1.3 µm) shows significant strain relief with aggravated current crowding.
    Asia Communications and Photonics Conference; 11/2013
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    ABSTRACT: We report on the large photoluminescence redshift observed in GaN nanostructures fabricated using electroless etching method. The nanostructures emitted violet visible-light with increasing optical excitation power, the mechanism was attributed to the surface states effect.
    Asia Communications and Photonics Conference; 11/2013
  • Bilal Janjua, Tien K. Ng, Boon S. Ooi
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    ABSTRACT: A novel design based on an asymmetrically graded-well, Al(a→b)Ga(1-a→1-b) N / Al(c)Ga(1-c) N,where b>c>a, to enhance the optical matrix element of radiative transitions in an AlGaN based UV-LED, is theoretically studied.
    Solid-State and Organic Lighting; 11/2013
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    ABSTRACT: We report on the quantitative evidence of simultaneous amplified spontaneous emission from the AlGaInAs/InAs/InP-based quantum-well (Qwell) and quantum-dashes (Qdash) in a multistack dash-in-an-asymmetric-well superluminescent diode heterostructure. As a result, an emission bandwidth (full width at half-maximum) of >700 nm is achieved, covering entire O-E-S-C-L-U communication bands, and a maximum continuous wave output power of 1.3 mW, from this device structure. This demonstration paves a way to bridge entire telecommunication bands through proper optimization of device gain region, bringing significant advances and impact to a variety of cross-disciplinary field applications.
    Optics Letters 10/2013; 38(19):3720-3723. · 3.39 Impact Factor
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    ABSTRACT: We study the enhanced inhomogeneity across the InAs quantum-dash (Qdash) layers by incorporating a chirped AlGaInAs barrier thickness in the InAs/InP laser structure. The lasing operation is investigated via Fabry-Pérot ridge-waveguide laser characterization, which shows a peculiar behavior under quasi-continuous-wave (QCW) operation. Continuous energy transfer between different dash ensembles initiated quenching of lasing action among certain dash groups, causing a reduced intensity gap in the lasing spectra. We discuss these characteristics in terms of the quasi-zero-dimensional density of states (DOS) of dashes and the active region inhomogeneity.
    IEEE Photonics Journal 08/2013; 5(4):1501308-1501308. · 2.33 Impact Factor
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    ABSTRACT: We report on the observation of broad photoluminescence wavelength tunability from n-type gallium nitride nanoparticles (GaN NPs) fabricated using the ultraviolet metal-assisted electroless etching method. Transmission and scanning electron microscopy measurements performed on the nanoparticles revealed large size dispersion ranging from 10 to 100 nm. Nanoparticles with broad tunable emission wavelength from 362 to 440 nm have been achieved by exciting the samples using the excitation power-dependent method. We attribute this large wavelength tunability to the localized potential fluctuations present within the GaN matrix and to vacancy-related surface states. Our results show that GaN NPs fabricated using this technique are promising for tunable-color-temperature white light-emitting diode applications.
    Nanoscale Research Letters 07/2013; 8(1):342. · 2.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We demonstrate an ultra-broad lasing bandwidth (-3dB) of > 50 nm utilizing InAs/InGaAlAs/InP quantum-dash ridge-waveguide laser using chirped AlGaInAs barrier layer thickness. Our device exhibits a recorded bandwidth and significant improvement of laser characteristics
    CLEO: Science and Innovations; 06/2013
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    ABSTRACT: In this paper we report on the feasibility of light confinement in orbital geodesics on stationary, planar, and centro-symmetric refractive index mappings. Constrained to fabrication and [meta]material limitations, the refractive index, n, has been bounded to the range: 0.8 ? n(r?) ? 3.5. Mappings are obtained through the inverse problem to the light geodesics equations, considering trappings by generalized orbit conditions defined a priori. Our simulation results show that the above mentioned refractive index distributions trap light in an open orbit manifold, both perennial and temporal, in regards to initial conditions. Moreover, due to their characteristics, these mappings could be advantageous to optical computing and telecommunications, for example, providing an on-demand time delay or optical memories. Furthermore, beyond their practical applications to photonics, these mappings set forth an attractive realm to construct a panoply of celestial mechanics analogies and experiments in the laboratory.
    Optics Express 04/2013; 21(7):8298-310. · 3.53 Impact Factor
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    ABSTRACT: We report on the demonstration of 50 nm (full-width at half-maximum) broadband stimulated emission from a chirped AlGaInAs barrier thickness multi-stack InAs/InP quantum dash (Qdash) laser. The 2 μm wide uncoated Fabry-Perot (FP) ridge-waveguide laser exhibits a total power of 0.18 W, corresponding to an average spectral power density of 3.5 mW/nm, under pulsed current conditions. Intentional extended inhomogeneity across the Qdash stacks have been attributed to the enhancement of broadband emission.
    Applied Physics Letters 03/2013; 102(9). · 3.52 Impact Factor

Publication Stats

927 Citations
274.69 Total Impact Points


  • 2011–2014
    • King Abdullah University of Science and Technology
      • Division of Physical Sciences and Engineering (PSE)
      Djidda, Makkah, Saudi Arabia
  • 2004–2011
    • Lehigh University
      • Department of Electrical and Computer Engineering
      Bethlehem, Pennsylvania, United States
  • 2008
    • JDS Uniphase Corporation
      Milpitas, California, United States
  • 1997–2003
    • Nanyang Technological University
      • School of Electrical and Electronic Engineering
      Tumasik, Singapore
  • 2001
    • Nanyang Normal University
      Nan-yang-shih, Henan Sheng, China
  • 1994–1998
    • University of Glasgow
      • Division of Electronics and Electrical Engineering
      Glasgow, SCT, United Kingdom