M E Zoorob

University of Bath, Bath, England, United Kingdom

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Publications (60)90.5 Total impact

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    ABSTRACT: The far-field profile of photonic quasi-crystal patterned and unpatterned LEDs, fabricated from commercial epitaxial substrates by electron beam lithography, has been measured prior to lapping and dicing. Emission enhancements reach a maximum of 62%, and are strongly dependent on the filling factor. Qualitative agreement is achieved between 2-D finite-difference time-domain calculations and the experimental data.
    IEEE Journal of Selected Topics in Quantum Electronics 09/2009; · 4.08 Impact Factor
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    ABSTRACT: Enhanced light extraction from photonic crystal light-emitting diodes etched into the device surface is described. Finite Difference Time Domain modeling indicates that scattering or absorption at the substrate-epilayer interface is the dominant limiting process.
    International Quantum Electronics Conference (IQEC); 01/2009
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    ABSTRACT: Mesostructured metallic substrates composed of square pyramidal pits are shown to confine localized plasmons. Plasmon frequency tuning is demonstrated using white light reflection spectroscopy with a wide range of structure dimensions from 400 to 3000 nm. Using a simple plasmon cavity model, we demonstrate how the individual pit morphology and not their periodicity controls the resonance frequencies. By measuring the surface-enhanced Raman scattering (SERS) signals from monolayers of benzenethiol on the same range of mesostructures, we extract a quantitative connection between absorption, field enhancement, and SERS signals. The match between theory and experiment enables effective design of plasmon devices tailored for particular applications, such as optimizing SERS substrates.
    Physical review. B, Condensed matter 07/2007; 76(3). · 3.77 Impact Factor
  • M. D. B. Charlton, M. E. Zoorob, T. Lee
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    ABSTRACT: In this paper we investigate improvement in performance attainable by etching Photonic Crystals and Photonic Quasi-Crystals into the top emitting surface of LEDs. We describe the physical mechanisms of extraction enhancement through ordered surface patterning and investigate benefits in terms of total extraction enhancement, beam directionality, and far field beam quality. Factors such as lattice geometry, etch depth, and epitaxy thickness are investigated. We show that a great variety of far field beam profiles of benefit in applications such as projection TV light engines and direct flat panel display illumination can be obtained simply by adjusting geometric design parameters. Our results show that PCs can provide significant improvement in extraction enhancement for applications requiring non Lambertian beam shapes when etched into standard "production line" epitaxy wafers in comparison to "state of the art" surface roughened thin-GaN LED devices. We investigate PC beam steering effects in these devices confirming that PCs do in fact re-direct light from trapped modes confined within the epi-structure to radiating modes. We also show that by tailoring the thickness of the epi-structure to complement the properties of the photonic crystal, extraction enhancement can be improved by a factor of 9 for some applications.
    Proc SPIE 03/2007;
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    ABSTRACT: We investigate improvement in performance attainable by etching Photonic Crystals and Photonic Quasicrystals (PQC) into the top emitting surface of LEDs (PQC-LEDs). We describe the physical mechanisms of extraction enhancement through ordered surface patterning and investigate benefits in terms of total extraction enhancement, beam directionality, and far field beam quality. We show that a great variety of far field beam profiles tailored for specific applications such as projection TV light engines and direct flat panel display illumination can be obtained simply by adjusting geometric design parameters. Our results show that PQC-LEDs can provide around 50% improvement in extraction enhancement and coupling efficiency for applications requiring non Lambertian beam shapes when etched into standard epitaxy wafers in comparison to "state of the art" surface roughened GaN LED devices. We also show that by tailoring the epi-structure to complement the properties of the PQC, extraction as well as directional light coupling enhancements can be improved by a factor of 9 amounting to a total coupling enhancement of around 78%.
    01/2007;
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    ABSTRACT: We describe what is to our knowledge the first nondestructive measurement of the evolution of an optical continuum as a function of distance along a nonlinear waveguide. Spectral mapping is achieved on a subwavelength scale by utilizing near-field microscopy to probe the waveguide's evanescent field. The measured continuum broadening along the waveguide agrees in general form with predictions of broadening from theoretical calculations, but differs in some important details. Subwavelength resolution measurements are made both along and across the waveguide to reveal spectral variations not seen before by other techniques.
    Optics Letters 09/2006; 31(16):2459-61. · 3.39 Impact Factor
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    ABSTRACT: Near-field scanning optical microscopy provides a tool for studying the behavior of optical fields inside waveguides. In this experiment the authors measure directly the variation of group velocity between different modes of a planar slab waveguide as the modes propagate along the guide. The measurement is made using the spectral interference between pulses propagating inside the waveguide with different group velocities, collected using a near-field scanning optical microscope at different points down the guide and spectrally resolved. The results are compared to models of group velocities in simple guides.
    Applied Physics Letters 08/2006; · 3.79 Impact Factor
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    ABSTRACT: Measurement of spectral interference with a near-field scanning optical microscope is used to determine directly the variation of group velocity between modes of a planar slab waveguide as the modes propagate along the guide.
    05/2006;
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    ABSTRACT: A new class of Surface-Enhanced Raman Scattering (SERS) substrates have been engineered by exploiting both Photonic Crystal (PC) and semiconductor technologies. Gold coated inverted pyramids nanotextured substrates allow reproducibility <10% and enhancement factors > 106 over large areas. Modelling and optical characterization of the engineered structures is demonstrated. Examples of applications to amino acids and illicit drug detection are given. Concentrations as low as ppm-ppb (mg/mL to ng/mL) have been measured depending on the adsorbed analytes. Information on structure and conformation of the molecule is inferred due to the richer nature of SERS spectra.
    Proc SPIE 03/2006;
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    ABSTRACT: Comprehensive reflectivity mapping of the angular dispersion of nanostructured arrays comprising of inverted pyramidal pits is demonstrated. By comparing equivalently structured dielectric and metallic arrays, diffraction and plasmonic features are readily distinguished. While the diffraction features match expected theory, localised plasmons are also observed with severely flattened energy dispersions. Using pit arrays with identical pitch, but graded pit dimensions, energy scaling of the localized plasmon is observed. These localised plasmons are found to match a simple model which confines surface plasmons onto the pit sidewalls thus allowing an intuitive picture of the plasmons to be developed. This model agrees well with a 2D finite-difference time-domain simulation which shows the same dependence on pit dimensions. We believe these tuneable plasmons are responsible for the surface-enhancement of the Raman scattering (SERS) of an attached layer of benzenethiol molecules. Such SERS substrates have a wide range of applications both in security, chemical identification, environmental monitoring and healthcare.
    Optics Express 02/2006; 14(2):847-57. · 3.55 Impact Factor
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    ABSTRACT: Arranging periodic, or quasi-periodic, regions of differing refractive index in one, two, or three dimensions can form a unique class of mesoporous structures. These structures are generally known as photonic crystals, or photonic quasicrystals, and they are the optical analogue of semiconducting materials. Whereas a semiconductor's band structure arises from the interaction of electron or hole waves with an arrangement of ion cores, the photonic crystal band structure results from the interaction of light waves with an arrangement of regions of differing refractive index. What makes photonic crystals highly attractive to the optical engineer is that we can actually place the regions of differing refractive index in a pattern specifically tailored to produce a given optical function, such as an extremely high dispersion, for example. That is, we can define the geometrical arrangement of the dielectric foam to provide us with the form of band structure we require for our optical functionality. In this paper, the optical properties and applications of these highly engineered mesoporous dielectrics will be discussed.
    Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 02/2006; 364(1838):189-99. · 2.89 Impact Factor
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    ABSTRACT: We report time-of-flight experiments on photonic-crystal waveguide structures using optical Kerr gating of a femtosecond white-light supercontinuum. These photonic-crystal structures, based on engineered silicon-nitride slab waveguides, possess broadband low-loss guiding properties, allowing the group velocity dispersion of optical pulses to be directly tracked as a function of wavelength. This dispersion is shown to be radically disrupted by the spectral band gaps associated with the photonic-crystal periodicity. Increased time-of-flight effects, or "slowed light," are clearly observed at the edges of band gaps in agreement with two-dimensional plane-wave theoretical models of group velocity dispersion. A universal model for slow light in such photonic crystals is proposed, which shows that slow light is controlled predominantly by the detuning from, and the size of, the photonic band gaps. Slowed light observed up to time delays of approximately 1 ps, corresponds to anomalous dispersion of approximately 3.5 ps/nm per mm of the photonic crystal structure. From the decreasing intensity of time-gated slow light as a function of time delay, we estimate the characteristic losses of modes which are guided in the spectral proximity of the photonic band gaps.
    Physical Review E 02/2006; 73(1 Pt 2):016619. · 2.31 Impact Factor
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    ABSTRACT: We describe the first non-destructive measurements of the evolution of the optical continuum along a non-linear waveguide. By utilizing near-field microscopy, the spectral variation can be imaged along and across the waveguide with sub-wavelength resolution.
    01/2006;
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    ABSTRACT: We demonstrate how the enhancement of SERS is correlated to the matching of localized plasmons at the pump laser wavelength, by designing and measuring a variety of nanostructured gold surfaces, showing both tuning and reproducibility.
    Lasers and Electro-Optics, 2006 and 2006 Quantum Electronics and Laser Science Conference. CLEO/QELS 2006. Conference on; 01/2006
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    ABSTRACT: We demonstrate how localized plasmons on nanostructured gold surfaces can be made to have two independently tuneable resonant wavelengths using anisotropic voids. This allows double resonance conditions for scattering (such as SERS) to be obtained.
    Lasers and Electro-Optics, 2006 and 2006 Quantum Electronics and Laser Science Conference. CLEO/QELS 2006. Conference on; 01/2006
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    01/2006;
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    ABSTRACT: Reflectivity measurements of gold nanostructures graded in pitch and aperture size allow investigation of localized plasmons. A simple model confirmed by simulations explains the plasmon resonances. Such arrays are highly suitable Raman scattering substrates.
    Lasers and Electro-Optics, 2006 and 2006 Quantum Electronics and Laser Science Conference. CLEO/QELS 2006. Conference on; 01/2006
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    ABSTRACT: This paper describes a unique way of designing highly complex photonic nanostructures. hotonic Quasicrystals have far reaching applications in many areas of photonics including light extraction from LEDs and for the fabrication of "slow-light" devices or optical delay lines. However, it is not straightforward to produce the e-beam writer data file to produce an arbitrary symmetry photonic quasicrystal as a "lattice" as such does not exist. The location of the photonic crystal scattering centres are found by an inverse method. Starting with the n-fold diffraction pattern, where n is either 5-fold or in excess of 6-fold symmetry, an inverse Fourier transform is taken which will indicate the real space location of the scattering centres. This procedure greatly simplifies the fabrication of highly complex photonic quasicrystal devices and circuits.
    Nanotechnology 10/2005; · 3.84 Impact Factor
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    ABSTRACT: Planar photonic crystals comprised of metals and dielectrics show huge enhancements in the surface-enhanced Raman scattering of attached molecules. Plasmon engineering is key to these properties including reproducibility (std.dev.<9%), beamed output, resonances and orientation.
    05/2005;
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    ABSTRACT: We demonstrate the fabrication, characterization and simulation of visible wavelength superprism devices in photonic crystal waveguides. We studied the super refraction dependence on lattice symmetry orientation and for propagation angles close to the main symmetry orientation. A variety of rectangular lattices devices with various pitches and hole diameters as well as number of rows have been fabricated. We used our previously developed automated broadband spectral and angular measurement to map the chromatic refractivity. We found the refraction angles and sign to be dependent on the lattice orientation and bandgap. As the lattice was rotated away from the main symmetry direction the magnitude of the angular dispersion increased indicating enhanced super-refractive properties away from symmetry direction. We found the chromatic refraction to be up to 1°/nm close to the band edge of the principal bandgaps, 10x more than equivalent gratings, and 100x more than equivalent prisms [[xiv]]. Dispersion curve obtained from plane wave simulation allowed us to model the Bloch mode propagation directions in the periodic structure. We found these simple models to be in excellent agreement with the experimental results, allowing us to design a range of effective superprism devices.
    Proc SPIE 04/2005;

Publication Stats

560 Citations
90.50 Total Impact Points

Institutions

  • 2009
    • University of Bath
      Bath, England, United Kingdom
  • 1999–2005
    • University of Southampton
      • • Faculty of Physical and Applied Sciences
      • • Department of Electronics and Computer Science (ECS)
      Southampton, ENG, United Kingdom