524 research outputs found
Exact counting of Euler Tours for Graphs of Bounded Treewidth
In this paper we give a simple polynomial-time algorithm to exactly count the
number of Euler Tours (ETs) of any Eulerian graph of bounded treewidth. The
problems of counting ETs are known to be #P-complete for general graphs
(Brightwell and Winkler, (Brightwell and Winkler, 2005). To date, no
polynomial-time algorithm for counting Euler tours of any class of graphs is
known except for the very special case of series-parallel graphs (which have
treewidth 2).Comment: 16 pages, draf
Directive emission of red conjugated polymer embedded within zero index metamaterials
Abstract: We numerically demonstrate an impedance-matched multilayer stacked fishnet metamaterial that has zero index with flat high transmittance from 600nm to 620nm. The effective refractive index
Optical fibre digital pulse-position-modulation assuming a Gaussian received pulse shape
The abundance in bandwidth available in the best monomode fibres may be exchanged for improved receiver sensitivity by employing digital PPM. The paper presents a performance and optimisation analysis for a digital PPM coding scheme operating over a fibre channel employing a PIN-BJT receiver and assuming a Gaussian received pulse shape. The authors present original results for a 50 Mbit/s, 1.3 μm wavelength digital PPM system and conclude that, provided the fibre bandwidth is several times that of the data rate, digital PPM can outperform commercially available PIN-BJT binary PCM system
Microwave properties of an inhomogeneous optically illuminated plasma in a microstrip gap
The optical illumination of a microstrip gap on a thick semiconductor substrate creates an inhomogeneous electron-hole plasma in the gap region. This allows the study of the propagation mechanism through the plasma region. This paper uses a multilayer plasma model to explain the origin of high losses in such structures. Measured results are shown up to 50 GHz and show good agreement with the simulated multilayer model. The model also allows the estimation of certain key parameters of the plasma, such as carrier density and diffusion length, which are difficult to measure by direct means. The detailed model validation performed here will enable the design of more complex microwave structures based on this architecture. While this paper focuses on monocrystalline silicon as the substrate, the model is easily adaptable to other semiconductor materials such as GaAs
GaN directional couplers for integrated quantum photonics
Large cross-section GaN waveguides are proposed as a suitable architecture to
achieve integrated quantum photonic circuits. Directional couplers with this
geometry have been designed with aid of the beam propagation method and
fabricated using inductively coupled plasma etching. Scanning electron
microscopy inspection shows high quality facets for end coupling and a well
defined gap between rib pairs in the coupling region. Optical characterization
at 800 nm shows single-mode operation and coupling-length-dependent splitting
ratios. Two photon interference of degenerate photon pairs has been observed in
the directional coupler by measurement of the Hong-Ou-Mandel dip with 96%
visibility.Comment: 4 pages, 5 figure
Spectral analysis of a four-port DBR micro-ring resonator for spectral sensing applications
In this paper, the spectral analysis of a fourport distributed Bragg reflector-micro ring resonator (DBR-MRR) is studied both analytically and numerically. First, the basic theory of the DBR-MRR is discussed and the effect of DBRs on the resonant mode-split is studied analytically. Then, the theory is supported with a numerical study using the finite difference time domain method. Finally, a potential application of the proposed structure is discussed: a sensor that keeps the concentration of a substance within a desired range; a concentration range controller. © 2018 IOP Publishing Ltd
Fast Tuning of Double Fano Resonance Using A Phase-Change Metamaterial Under Low Power Intensity
In this work, we numerically demonstrate an all-optical tunable Fano resonance in a fishnet metamaterial(MM) based on a metal/phase-change material(PCM)/metal multilayer. We show that the displacement of the elliptical nanoholes from their centers can split the single Fano resonance (FR) into a double FR, exhibiting higher quality factors. The tri-layer fishnet MMs with broken symmetry accomplishes a wide tuning range in the mid-infrared(M-IR) regime by switching between the amorphous and crystalline states of the PCM (Ge(2)Sb(2)Te(5)). A photothermal model is used to study the temporal variation of the temperature of the Ge(2)Sb(2)Te(5) film to show the potential for switching the phase of Ge(2)Sb(2)Te(5) by optical heating. Generation of the tunable double FR in this asymmetric structure presents clear advantages as it possesses a fast tuning time of 0.36 ns, a low pump light intensity of 9.6 μW/μm(2), and a large tunable wavelength range between 2124 nm and 3028 nm. The optically fast tuning of double FRs using phase change metamaterials(PCMMs) may have potential applications in active multiple-wavelength nanodevices in the M-IR region
Transfer of arbitrary quantum emitter states to near-field photon superpositions in nanocavities
We present a method to analyze the suitability of particular photonic cavity
designs for information exchange between arbitrary superposition states of a
quantum emitter and the near-field photonic cavity mode. As an illustrative
example, we consider whether quantum dot emitters embedded in "L3" and "H1"
photonic crystal cavities are able to transfer a spin superposition state to a
confined photonic superposition state for use in quantum information transfer.
Using an established dyadic Green's function (DGF) analysis, we describe
methods to calculate coupling to arbitrary quantum emitter positions and
orientations using the modified local density of states (LDOS) calculated using
numerical finite-difference time-domain (FDTD) simulations. We find that while
superposition states are not supported in L3 cavities, the double degeneracy of
the H1 cavities supports superposition states of the two orthogonal modes that
may be described as states on a Poincar\'{e}-like sphere. Methods are developed
to comprehensively analyze the confined superposition state generated from an
arbitrary emitter position and emitter dipole orientation.Comment: 22 pages, 9 figure
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