110 research outputs found
Waveguiding properties of surface states in photonic crystals
We propose and analyze novel surface-state-based waveguides in bandgap
photonic crystals. We discuss surface mode band structure, field localization
and effect of imperfections on the waveguiding properties of the surface modes.
We demonstrate that surface-state-based waveguides can be used to achieve
directional emission out of the waveguide. We also discuss the application of
the surface-state waveguides as efficient light couplers for conventional
photonic crystal waveguides.Comment: 4 pages 5 figure
Quantum localization in rough billiards
We study the level spacing statistics p(s) and eigenfunction properties in a
billiard with a rough boundary. Quantum effects lead to localization of
classical diffusion in the angular momentum space and the Shnirelman peak in
p(s) at small s. The ergodic regime with Wigner-Dyson statistics is identified
as a function of roughness. Applications for the Q-spoiling in optical
resonators are also discussed.Comment: revtex, 4 pages, 5 figure
Emergence of Quantum Ergodicity in Rough Billiards
By analytical mapping of the eigenvalue problem in rough billiards on to a
band random matrix model a new regime of Wigner ergodicity is found. There the
eigenstates are extended over the whole energy surface but have a strongly
peaked structure. The results of numerical simulations and implications for
level statistics are also discussed.Comment: revtex, 4 pages, 4 figure
Nonlinear localized waves in a periodic medium
We analyze the existence and stability of nonlinear localized waves in a
periodic medium described by the Kronig-Penney model with a nonlinear defect.
We demonstrate the existence of a novel type of stable nonlinear band-gap
localized states, and also reveal an important physical mechanism of the
oscillatory wave instabilities associated with the band-gap resonances.Comment: 4 pages, 5 figure
Chaotic Waveguide-Based Resonators for Microlasers
We propose the construction of highly directional emission microlasers using
two-dimensional high-index semiconductor waveguides as {\it open} resonators.
The prototype waveguide is formed by two collinear leads connected to a cavity
of certain shape. The proposed lasing mechanism requires that the shape of the
cavity yield mixed chaotic ray dynamics so as to have the appropiate (phase
space) resonance islands. These islands allow, via Heisenberg's uncertainty
principle, the appearance of quasi bound states (QBS) which, in turn,
propitiate the lasing mechanism. The energy values of the QBS are found through
the solution of the Helmholtz equation. We use classical ray dynamics to
predict the direction and intensity of the lasing produced by such open
resonators for typical values of the index of refraction.Comment: 5 pages, 5 figure
Metallo-dielectric diamond and zinc-blende photonic crystals
It is shown that small inclusions of a low absorbing metal can have a
dramatic effect on the photonic band structure. In the case of diamond and
zinc-blende photonic crystals, several complete photonic band gaps (CPBG's) can
open in the spectrum, between the 2nd-3rd, 5th-6th, and 8th-9th bands. Unlike
in the purely dielectric case, in the presence of small inclusions of a low
absorbing metal the largest CPBG for a moderate dielectric constant
(epsilon<=10) turns out to be the 2nd-3rd CPBG. The 2nd-3rd CPBG is the most
important CPBG, because it is the most stable against disorder. For a diamond
and zinc-blende structure of nonoverlapping dielectric and metallo-dielectric
spheres, a CPBG begins to decrease with an increasing dielectric contrast
roughly at the point where another CPBG starts to open--a kind of gap
competition. A CPBG can even shrink to zero when the dielectric contrast
increases further. Metal inclusions have the biggest effect for the dielectric
constant 2<=epsilon<=12, which is a typical dielectric constant at near
infrared and in the visible for many materials, including semiconductors and
polymers. It is shown that one can create a sizeable and robust 2nd-3rd CPBG at
near infrared and visible wavelengths even for a photonic crystal which is
composed of more than 97% low refractive index materials (n<=1.45, i.e., that
of silica glass or a polymer). These findings open the door for any
semiconductor and polymer material to be used as genuine building blocks for
the creation of photonic crystals with a CPBG and significantly increase the
possibilities for experimentalists to realize a sizeable and robust CPBG in the
near infrared and in the visible. One possibility is a construction method
using optical tweezers, which is analyzed here.Comment: 25 pp, 23 figs, RevTex, to appear in Phys Rev B. For more information
look at
http://www.amolf.nl/research/photonic_materials_theory/moroz/moroz.htm
Dynamical Tunneling in Mixed Systems
We study quantum-mechanical tunneling in mixed dynamical systems between
symmetry-related phase space tori separated by a chaotic layer. Considering
e.g. the annular billiard we decompose tunneling-related energy splittings and
shifts into sums over paths in phase space. We show that tunneling transport is
dominated by chaos-assisted paths that tunnel into and out of the chaotic layer
via the ``beach'' regions sandwiched between the regular islands and the
chaotic sea. Level splittings are shown to fluctuate on two scales as functions
of energy or an external parameter: they display a dense sequence of peaks due
to resonances with states supported by the chaotic sea, overlaid on top of slow
modulations arising from resonances with states supported by the ``beaches''.
We obtain analytic expressions which enable us to assess the relative
importance of tunneling amplitudes into the chaotic sea vs. its internal
transport properties. Finally, we average over the statistics of the chaotic
region, and derive the asymptotic tail of the splitting distribution function
under rather general assumptions concerning the fluctuation properties of
chaotic states.Comment: 28 pages, Latex, 16 EPS figure
Photonic mode dispersion of a two-dimensional distributed feedback polymer laser
G. A. Turnbull, P. Andrew, William L. Barnes, and I. D. W. Samuel, Physical Review B, Vol. 67, article 165107 (2003). "Copyright © 2003 by the American Physical Society."We present an analysis of the photonic mode dispersion of a two-dimensional (2D) distributed feedback polymer laser based on the conjugated polymer poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene]. We use a combination of a simple model, together with experimental measurements of the photonic mode dispersion in transmission and emission, to explain the operating characteristics of the laser. The laser was found to oscillate at 636 nm on one edge of a photonic stop band in the photonic dispersion. A 2D coupling of modes traveling perpendicular to the orthogonal gratings was found to lead to a low divergence laser emission normal to the waveguide. At pump energies well above the oscillation threshold for this mode, a divergent, cross-shaped far-field emission was observed, resulting from a distributed feedback occurring over a wide range of wave vectors in one band of the photonic dispersion
Facile Phosphine-Free Synthesis of CdSe/ZnS Core/Shell Nanocrystals Without Precursor Injection
A new simple method for synthesis of core/shell CdSe/ZnS nanocrystals (NCs) is present. By adapting the use of cadmium stearate, oleylamine, and paraffin liquid to a non-injection synthesis and by applying a subsequent ZnS shelling procedure to CdSe NCs cores using Zinc acetate dihydrate and sulfur powder, luminescent CdSe/ZnS NCs with quantum yields of up to 36% (FWHM 42–43 nm) were obtained. A seeding-growth technique was first applied to the controlled synthesis of ZnS shell. This method has several attractive features, such as the usage of low-cost, green, and environmentally friendlier reagents and elimination of the need for air-sensitive, toxic, and expensive phosphines solvent. Furthermore, due to one-pot synthetic route for CdSe/ZnS NCs, the approach presented herein is accessible to a mass production of these NCs
Quantum dots coordinated with conjugated organic ligands: new nanomaterials with novel photophysics
CdSe quantum dots functionalized with oligo-(phenylene vinylene) (OPV) ligands (CdSe-OPV nanostructures) represent a new class of composite nanomaterials with significantly modified photophysics relative to bulk blends or isolated components. Single-molecule spectroscopy on these species have revealed novel photophysics such as enhanced energy transfer, spectral stability, and strongly modified excited state lifetimes and blinking statistics. Here, we review the role of ligands in quantum dot applications and summarize some of our recent efforts probing energy and charge transfer in hybrid CdSe-OPV composite nanostructures
- …