M E Zoorob

University of Bath, Bath, England, United Kingdom

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Publications (62)89.39 Total impact

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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;
  • T D Lee, M E Zoorob, S J Cox, G J Parker
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    ABSTRACT: A novel method for producing photonic crystals with high orders of rotational symmetry using an inverse Fourier transform (IFT) method is presented. The IFT of an n-sided polygon is taken and the position of the peaks are computed in order to obtain a set of discrete points in real space where the scattering centres are to be located. We show, by simulating the diffraction pattern, that although these points appear disordered, they possess long range order, which also confirms that the arrangement of points has n-fold rotational symmetry. The structures thus possess an arbitrary number of rotational symmetries, whilst retaining the sharp diffraction patterns characteristic of known crystal lattices which exhibit wide band gaps. We present simulation results using the finite difference time domain method (FDTDM) for large non repeating patterns of scatterers produced by this method. We also present results where around 50 points have been generated in a square unit cell and tiled to produce a lattice. These, were simulated using both the finite element method (FEM) and the FDTDM, which agree well. Our results demonstrate that the method is capable of producing crystal structures with wide band gaps where the scattering centres are either non-repeating with no fundamental unit cell, or consist of a (large) number of points in a unit cell, which may then be tiled to form a lattice.
    Proc SPIE 04/2005;
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    ABSTRACT: In this paper we demonstrate Ultra-low loss transmission across a photonic crystal super-prism device consisting of 600 lattice periods etched into a slab waveguide at wavelengths both above and below the primary bandgap. By modifying the refractive index of the holes we have reduced overall insertion loss to 4.5 dB across the entire visible region of the spectrum, greatly enhancing transmission and extinction in higher order stop-bands. In addition we show that the remaining loss is predominantly due to impedance mismatch at the boundary between patterned/unpatterned slab waveguide regions and so is no longer proportional to the length of the photonic crystal or the number of lattice periods. This is an important step forward for the realization of functional photonic crystal time delay elements, dispersion compensators and super-prism spectrometer devices. Experimental loss measurements compare extremely well with Finite difference time domain Simulations which were used to investigate the effect of etch depth on scattering loss. We find that partial penetration into the underlying buffer region Causes massive scattering loss to substrate modes due to loss of waveguiding in the holes.
    Photonic Crystal Materials and Devices III; 04/2005
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    ABSTRACT: Continuum Generation (CG) in optical waveguides has been recently attracting widespread interest in fields requiring large spectral bandwidth such as metrology and Optical Coherence Tomography (OCT). Real time and in-vivo tissue imaging with cell resolution (Deltaz
    Proc SPIE 04/2005;
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    ABSTRACT: Ultra-high bandwidth continua generated by ultrashort fs pulses have been attracting enormous interest for applications such as general spectroscopy, Optical Coherence Tomography and metrology. Dispersion engineering is one of the key aspects of optimised continuum generation in optical waveguides. However in addition, the dispersion of the pump pulse can be continuously adapted to control bandwidth and spectral characteristics of the generated continua. In this work we report on a systematic investigation of how 2nd , and 3rd order dispersion affects the continuum generated in strongly nonlinear planar waveguides. A ~30 fs Ti:Sapphire tuned to 800 nm was used as a pump source delivering ~3 nJ pulses. The chirp of the pulses was controlled completely-arbitrarily by an acousto-optic programmable dispersive filter (Dazzler). The power launched into the structures was kept constant to compare the generated continua as the pulse dispersion is varied. High refractive index tantalum pentoxide (Ta 2O 5) waveguides grown by standard silicon processing techniques were used. The devices investigated were specially designed tapered ridges with ~5 mm2 input modal volume and zero group velocity dispersion at ~l - 3.7 mm. Self-phase modulation, which is responsible for the spectral broadening of the continua, is tracked by finely tuning the both 2nd and 3rd order dispersions. The nonlinear propagation is dramatically influenced by the simultaneous presence of these dispersive effects resulting in a change of bandwidth and spectral shape. Pulse widths of up to Dl > 100 nm for launched powers as low as 300 pJ. Spectral peak intensity can also be systematically modulated by simply scanning the 2nd and 3rd order dispersion around their relative zeros. Specific combinations of high order dispersion contribution are currently targeted as a route to control and optimise the continua bandwidths and to control dispersion lengths in specifically engineered waveguides.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
    03/2005;
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    ABSTRACT: Ultra-high bandwidth continuum generation has been attracting enormous interest for applications in optical frequency metrology, low-coherence tomography, laser spectroscopy, dispersion measurements, sensor techniques and others. The acceptance of this new technology would greatly benefit from the availability of compact and user-friendly sources. High index planar devices provide a versatile and unique approach to continuum generation. The dispersion can be carefully engineered by choosing the material and the geometry of the waveguides. Optical integration can also be provided on the same platform. Hundreds of different waveguides having different and calibrated dispersions can be integrated in few tens of millimeters. Input and output of the 2D guides can be tailored to provide mode matching to fibers and pump lasers by means of single element bulk optics. In this paper for the first time we demonstrate a low-noise, ultra-high bandwidth continuum at 1.55 μm. A bandwidth in excess of 390 nm is obtained by launching energy as low as 50 pJ in a 12 mm short tapered planar waveguides. The pump wavelength was in the normal dispersion regime and was provided by a compact, fiber-based sub-100 femtosecond source.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
    03/2005;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Ultra-high bandwidth continuum generation has been attracting enormous interest for applications in optical frequency metrology, low-coherence tomography, laser spectroscopy, dispersion measurements, sensor techniques and others. The acceptance of this new technology would greatly benefit from the availability of compact and user-friendly sources. High index planar devices provide a versatile and unique approach to continuum generation. The dispersion can be carefully engineered by choosing the material and the geometry of the waveguides. Optical integration can also be provided on the same platform. Hundreds of different waveguides having different and calibrated dispersions can be integrated in few tens of millimeters. Input and output of the 2D guides can be tailored to provide mode matching to fibers and pump lasers by means of single element bulk optics. In this paper for the first time we demonstrate a low-noise, ultra-high bandwidth continuum at 1.55 mum. A bandwidth in excess of 390 nm is obtained by launching energy as low as 50 pJ in a 12 mm short tapered planar waveguides. The pump wavelength was in the normal dispersion regime and was provided by a compact, fiber-based sub-100 femtosecond source.
    Proc SPIE 03/2005;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Ultra-high bandwidth continua generated by ultrashort fs pulses have been attracting enormous interest for applications such as general spectroscopy, Optical Coherence Tomography and metrology. Dispersion engineering is one of the key aspects of optimised continuum generation in optical waveguides. However in addition, the dispersion of the pump pulse can be continuously adapted to control bandwidth and spectral characteristics of the generated continua. In this work we report on a systematic investigation of how 2nd,and 3rd order dispersion affects the continuum generated in strongly non linear planar waveguides. A -30 fs Ti:Sapphire tuned to 800 nm was used as a pump source delivering ~3 nJ pulses. The chirp of the pulses was controlled completely-arbitrarily by an acousto-optic programmable dispersive filter (Dazzler). The power launched into the structures was kept constant to compare the generated continua as the pulse dispersion is varied. High refractive index tantalum pentoxide waveguides grown by standard silicon processing techniques were used. The devices investigated were specially designed tapered ridges with ~5mm2 input modal volume and zero group velocity dispersion at ~1-3.7 mm. Self-phase modulation, which is responsible for the spectral broadening of the continua, is tracked by finely tuning the both 2nd and 3rd order dispersions. The nonlinear propagation is dramatically influenced by the simultaneous presence of these dispersive effects resulting in a change of bandwidth and spectral shape. Pulse widths of up to D1 > 100 nm for launched powers as low as 300 pJ. Spectral peak intensity can also be systematically modulated by simply scanning the 2nd and 3rd order dispersion around their relative zeros. Specific combinations of high order dispersion contribution are currently targeted as a route to control and optimise the continua bandwidths and to control dispersion lengths in specifically engineered waveguides.
    Proc SPIE 03/2005;
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    ABSTRACT: Photonic crystal based active devices and their monolithic integration with passive photonic circuits such as waveguides, combiner structures, and examples of surface normal coupling are discussed.
    01/2005;
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    ABSTRACT: A novel method for designing photonic crystals with high orders of rotational symmetry using an inverse Fourier transform (IFT) method is presented. The IFT of an n-sided polygon is taken and the positions of the peaks are computed in order to obtain a set of discrete points in real space where the scattering centres are to be located. We show, by simulating the diffraction pattern, that although these points appear disordered they possess long range order, which also confirms that the arrangement of points has n-fold rotational symmetry. The designed structures can possess an arbitrary number of rotational symmetries, whilst retaining the sharp diffraction patterns characteristic of known crystal lattices which exhibit wide bandgaps. We present simulation results using the finite difference time domain method (FDTDM) for large non-repeating patterns of scatterers produced by this method. We also present results where around 50 points have been generated in a square unit cell and tiled to produce a lattice. These were simulated using both the finite element method (FEM) and the FDTDM, which were shown to agree. Our results demonstrate that the method is capable of producing crystal structures with wide bandgaps where the scattering centres are either non-repeating with no fundamental unit cell, or consist of a (large) number of points in a unit cell, which may then be tiled to form a lattice
    01/2005;
  • Source
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    ABSTRACT: In this paper we demonstrate low loss transmission both above and below the primary band-gap for a photonic crystal (PC) super-prism device consisting of 600 lattice periods. By modifying the refractive index of the holes, we reduce overall insertion loss to just 4.5 dB across the entire visible spectrum. We show that the remaining loss is predominantly due to impedance mismatch at the boundaries between patterned and unpatterned slab waveguide regions. Experimental loss measurements compare well with finite difference time domain simulations.
    Microelectronics Journal. 01/2005;
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    ABSTRACT: We demonstrate the fabrication of superprism devices in photonic crystal waveguides with excellent transmission through 600 rows of 160 nm diameter holes. Broadband spectral and angular measurements allow mapping of the chromatic refractivity. This shows the ability of such devices to super-refract by more than 1°∕nm close to the principal band gaps, 10× more than equivalent gratings, and 100× more than equivalent prisms. Simple theories based on plane-wave models give excellent agreement with these results.
    Applied Physics Letters 07/2004; · 3.52 Impact Factor
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    ABSTRACT: We describe waveguides of photoluminescent silicon-rich silicon dioxide, which have been patterned by triangular two-dimensional (2D) photonic crystals to give higher-order photonic bandgaps occurring within the luminescence band of the core material. Photonic crystal modification of the photoluminescence spectrum allows identification of angle-tuned photonic bandgaps, in close agreement with 2D plane wave expansion and finite-difference time domain simulations. We discuss the importance of these findings for the development of integrated optical circuitry based on silicon-compatible microelectronics.
    Applied Physics Letters 03/2004; · 3.52 Impact Factor
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    ABSTRACT: A Low-noise white-light continuum with bandwidths up to an octave is demonstrated by propagating nanojoule femtosecond pulses in planar waveguides operating in the normal dispersion region at wavelengths far from the zero dispersion point.
    01/2004;
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    ABSTRACT: We demonstrate that ultrabroadband ultrashort-pulse white light supercontina can be used to track the group velocity of photons in optical waveguides using a Kerr gate technique. Results on silicon nitride slab waveguides show both polarization birefringence and multimode dispersion, which vanish at critical wavelengths. When photonic crystals are embedded in the waveguides, the higher order modes are excited within the band-gap region, demonstrating the need to control their dispersion to make effective use of photonic crystal waveguide devices.
    Applied Physics Letters 11/2002; · 3.52 Impact Factor
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    ABSTRACT: The structuring of planar waveguides with 2D photonic crystals is promising for a whole new range of dense optoelectronics; integrated components. In particular coherent multiple scattering can be utilised for the extreme manipulation of both spectral and temporal dispersion. However very little work yet exists showing how light in reality propagates through such structures.. Many issues such as scattering loss, mode mixing, polarisation mixing and structure optimisation remain unresolved. These can only be addressed through the development of suitable tools which separate the different processes in the distinct spectral regions. We use ultrabroadband ultrashort-pulse time-of-flight measurements to resolve how light propagates through photonic crystal and quasicrystal waveguides.
    Quantum Electronics and Laser Science Conference, 2002. QELS '02. Technical Digest. Summaries of Papers Presented at the; 02/2002
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    ABSTRACT: We demonstrate that 2D photonic crystals can possess optical trirefringence in which there are six field orientations for which linear incident light is not perturbed on reflection or transmission. Such a property is rigorously forbidden in homogeneous nonmagnetic dielectrics which can possess only optical birefringence. We experimentally demonstrate this phenomena in silicon-based mesostructures formed from photonic crystal waveguides embedded in a Fabry-Perot cavity. Multirefringence is controlled by the presence of submicron dielectric patterning and is well explained by an exact scattering matrix theory.
    Physical Review Letters 03/2001; 86(8):1526-9. · 7.73 Impact Factor
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    ABSTRACT: Summary form only given. The optical impedance mismatch experienced by light propagating across high-low index waveguide-photonic crystal (PC) interface is one of the main issues regarding the application of photonic crystals in integrated optics. This strongly affects the mode coupling efficiency and the polarization insensitivity We have demonstrated the decrease of impedance in PCs having graded effective index interfaces obtained by modulating the air filling fraction at the input and/or output.
    Quantum Electronics and Laser Science Conference, 2001. Technical Digest. Summaries of Papers Presented at the; 02/2001
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    ABSTRACT: Summary form only given. The modification of photon energy dispersion by modulating the index of refraction on optical wavelength scales has led to artificial materials-photonic crystals (PC)-with unusual optical properties. The periodicity and amplitude of the index modulation are the key parameters to engineer energy dispersion and hence mode and polarization propagation in such devices. We fabricated PC structures in SiN planar waveguides with triangular lattices producing full PBGs in the visible spectrum for both TE and TM electromagnetic modes.
    Quantum Electronics and Laser Science Conference, 2001. Technical Digest. Summaries of Papers Presented at the; 02/2001

Publication Stats

566 Citations
89.39 Total Impact Points

Institutions

  • 2009
    • University of Bath
      • Department of Electronic and Electrical Engineering
      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