Search

We model and study the asymmetric long-range surface-plasmon waveguides using the finite-element method. We introduce two types of asymmetric structures and discuss their modal properties compared to traditional long-range surface-plasmon waveguides. Although the propagation distance is decreased, the energy-confinement capability is improved for asymmetric long-range waveguiding structures when the geometrical parameters are properly selected. Our simulation result offers guidance for tuning properties of plasmonic waveguides and providing ways for enhancing electromagnetic energy confinement in long-range surface-plasmon waveguides. [ABSTRACT FROM AUTHOR]

Lightning discharges radiate electromagnetic waves in a wide frequency range, with maximum energy in extremely low frequency/very low frequency band. A part of the radiated extremely low frequency/very low frequency wave energy is trapped in the Earth-ionosphere waveguide and travels thousands of kilometers in different modes with lower attenuation. Amplitude, frequency and phase of these waves are used to study the less explored D-region ionosphere at lower latitudes. Extremely low frequency/very low frequency observations are recorded continuously by automatic whistler detector setup installed at low-latitude Indian station Lucknow (Geom. lat. 17.6°N; long. 154.5°E). In total, 149 cases of tweeks having modes ranging from 3 to 6 have been recorded by automatic whistler detector during December 2010 and analyzed. Result shows that the propagation distance in the Earth-ionosphere waveguide lies between 1.1 and 9.4 Mm. The electron density in the lower D-region varies between 25 and 150 cm. The upper boundary of the waveguide varies between 80 and 95 km. The reported results are in good agreement with the earlier measurements at different latitudes and longitudes. [ABSTRACT FROM AUTHOR]

A compact polarization beam splitter (PBS) for silicon-based slot waveguides is proposed, where an asymmetrical multimode waveguide (AMW), cut by a right angle at one corner, is employed to efficiently separate the TE and TM modes. With the unique modal properties of the slot waveguides, the input TE mode almost passes through the AMW and enters into the bar port, while the input TM mode forms a mirror image at the cross port due to the self-imaging effect. Tapered waveguide structures and S-bend are incorporated into the PBS for enhancing the performance. Results show that a PBS with an AMW of 2.3 μm in length is achieved, where the extinction ratios are 16.6 and 20.9 dB, respectively, for TE and TM modes, and the insertion losses are 1.37 and 0.81 dB, respectively, at the wavelength of 1.55 μm, and the bandwidths can cover the entire C-band for both polarizations. In addition, fabrication tolerances to the structural parameters are investigated and field evolution along the propagation distance through the designed PBS is also demonstrated. [ABSTRACT FROM PUBLISHER]

Copyright of Safety & Fire Technology / Bezpieczeństwo i Technika Pożarnicza is the property of Centrum Naukowo-Badawcze Ochrony Przeciwpozarowej and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A compact polarization rotator (PR) for silicon-based slot waveguides is proposed, where a metal strip of aluminum (Al) is embedded in its upper-claddings. With the features of asymmetric hybrid plasmonic waveguide induced by the metal strip, an optimal optical axis rotation angle of 45° is realized, leading to high polarization conversion efficiency (PCE). The numerical results show that a PR of 11.6 μm in length at the wavelength of 1.55 μm is achieved with the PCE and insertion loss of 97.6% and 0.86 dB for TM-to-TE conversion, respectively. In addition, fabrication tolerances to the structural parameters are investigated and field evolution along the propagation distance through the PR is demonstrated. [ABSTRACT FROM PUBLISHER]

In this paper, the two-photon-excited emission spectra of polymer optical fibers doped with the conjugated polymer Poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) have been measured pumping the fibers transversely to their symmetry axis. Measurements include evolutions of the emission spectra with excitation wavelength and with propagation distance, together with an analysis of emission photostability. Comparisons with results for one-photon-excited emission are also presented and discussed. [ABSTRACT FROM PUBLISHER]

We propose to use a 1-atom-thick structure, i.e., a single graphene sheet for the dynamic control of an Airy plasmon (AiP). The graphene layer serves not only as the guiding medium but also as the modulator for the AiP. By altering the external biased voltage, the effective mode index for surface plasmon waves can be modified. Consequently, the deflection and the propagation distance of the AiP are controlled dynamically. Due to the advantages of graphene plasmons, graphene AiPs may lead to compact and flexible AiP devices. This paper could be also beneficial to relevant applications such as tunable plasmonic optical routing and on-chip signal processing. [ABSTRACT FROM PUBLISHER]

A hybrid plasmonic parallel transmission line scheme constructed by a spatial single mode with time-domain multiline waveguide is presented in this paper. The proposed configuration enables a nanometer light localization while retaining a long propagation distance (∼74 μm) at optical communication wavelengths with no crosstalk between data channels. High extinction ratio between the nanoribs peak energies (∼20 dB) has been achieved after optimization. Furthermore, the proposed optical parallel transmission line scheme shows the advantages of enabling an optical device with a large number of parallel transmission channels, as well as a good robustness with respect to the fabrication tolerances. [ABSTRACT FROM PUBLISHER]

An advanced cone-nanolayer target with nanolayers on both inside and outside of the hollow-cone tip is proposed. Two-dimensional particle-in-cell simulations show that laser interaction with such cone-nanolayer targets can efficiently produce fast electron beams with manageable spotsize, and the beams can propagate for a relatively long distance in the vacuum beyond the cone tip. [ABSTRACT FROM PUBLISHER]

Abstract: The fracturing behavior of materials can be nondestructively monitored by the acoustic emission (AE) technique, using sensors that detect the transient elastic waves after any crack propagation event. In addition to the information relatively to the total activity and the location of the cracks, certain waveform features supply detailed information on the type of cracking. The waveform of the emitted AE signal depends on the relative motion of the crack sides and therefore, it carries information on the mode of cracks. Therefore, AE is used for classification of the active cracking mode. This enables characterization of the current fracturing condition within the material and warning before final failure. Tension-related cracks, which in most materials and loading conditions are nucleated first, emit signals with higher frequency content and shorter rising time than shear cracks. However, in most cases wave propagation from the crack to the sensor is attenuative and dispersive. This results in signal distortion which is enhanced by geometry restrictions and material or damage-induced inhomogeneity. This results in strong change of the waveform shape and the calculated AE parameters. This effect is stronger as the propagation distance increases rendering crack classification troublesome for structures where the separation distance between sensors is long. In the present study, fracture experiments were conducted in cementitious specimens in order to investigate the influence of distance on the AE parameters as measured by sensors at different distances from the source. Numerical simulations based on the finite difference method are also used to enlighten the problem and expand to different material conditions. This is one of the first studies of wave dispersion examined not from the classical ultrasonics point of view of phase velocity dependence on frequency but from the AE view, where specific waveform parameters are of interest. Experimental and numerical results show that the influence of the propagation path is crucial and should be taken into consideration for AE characterization of large structures, while it should not be neglected even in small-scale laboratory studies in order to improve crack characterization. [Copyright &y& Elsevier]

Abstract: Laser measurement and laser processing techniques have been gaining strong attention from various applications. This research aims at the development of a fluidic laser beam shaper, and in order to fulfill the objective, thermal lens effect characteristics are studied. This phenomenon has the optical property of a divergent lens since the refractive index distribution on the optical axis is formed when a liquid is irradiated. In this research, effects of the pump power and the propagation distance to the probe beam profile are investigated experimentally and theoretically, with the purpose of developing a fluidic laser beam shaper. It is indicated that, by controlling some parameters in thermal lens system such as the pump power (in the regime of linear optics) and absorption coefficient, an input Gaussian beam can be converted into a flat-top beam profile. The relationship between the distance to obtain the flat-top beam, the pump power and absorption coefficient is investigated to show the flexibility of the fluidic laser beam shaper in many fields of laser application. [Copyright &y& Elsevier]

Decreasing the widths and thicknesses of thin metal stripes can effectively increase the propagation distance of long-range surface plasmon polaritons, but at the cost of significant reduction on the overall mode confinement, which fundamentally limits the packing density in nanophotonic integration. By utilizing the coupling between the dielectric waveguide and plasmonic modes, we propose a silicon-based 3-D hybrid long-range plasmonic waveguide that not only supports long-range propagation, but also has compact modal size. Our simulation result shows that a propagation distance of 696 μm with an ultrasmall modal area of 0.0013 μm2 can be simultaneously achieved at 1.55 μ m. [ABSTRACT FROM PUBLISHER]

Reservoir dilations occur due to variety of subsurface injection operations including waste disposal, waterflooding, steam injection, CO2 sequestration and aquifer storage recovery. These reservoir dilations propagate to the surrounding formations and extend up to the ground surface resulting in surface heaves. This paper discusses modeling of the surface heave by applying both analytical and numerical methods. Results of the study demonstrate that the lateral extent of a finite element model has a direct impact on the surface heave profile and if the lateral boundaries are too close to the line of symmetry, there will be significant errors in the finite element results. This paper proposes a rapid way of estimating a sufficient lateral extent for the finite element model by using a new chart. The chart contains a family of curves, which can be used to estimate the surface heave propagation distance under various injection depths, injection periods and soil properties. [ABSTRACT FROM AUTHOR]

We have developed a model that accurately predicts the dynamics of the signal pulses and the growth of amplified spontaneous emission noise in a dispersion-managed soliton pulse train propagating in a recirculating fiber-loop experiment. Theoretically predicted dependencies of the amplitude and phase margins for the marks and the amplitude margin for the spaces as a function of distance are in remarkable agreement with the experiments. This model allows us to determine the key physical effects that limit the propagation distance in our experiments [ABSTRACT FROM PUBLISHER]

We propose to reduce intrachannel four-wave mixing by using subchannel multiplexing for each wavelength-division-multiplexed channel. We calculate the growth in both signal distortion and noise, and we show that there is a tradeoff between propagation distance and spectral efficiency. The method performs best with strong dispersion management and Raman amplification. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a novel saliency model based on double random walks with dual restarts. Two agents (also known as walkers) respectively representing the foreground and background properties simultaneously walk on a graph to explore saliency distribution. First, we propose the propagation distance measure and use it to calculate the initial distributions of the two agents instead of using geodesic distance. Second, the two agents traverse the graph starting from their own initial distribution, and then interact with each other to correct their travel routes by the restart mechanism, which enforces the agents to return to some specific nodes with a certain probability after every movement. We define the dual restarts to take into account interaction between and weighting of two agents. Extensive evaluations demonstrate that the proposed algorithm performs favorably against other state-of-the-art methods on four benchmark datasets. • We introduce the double-random-walks framework to detect salient objects. • We define dual starts to consider the interacting and weighting of two agents. • We present propagation distance to overcome the problem of geodesic distance. • The proposed algorithm performs favorably against the existing saliency methods. [ABSTRACT FROM AUTHOR]

Optical wireless communication is an energy-efficient and cost-effective solution for high-speed and highly-secure wireless connections. In this paper, we compare, discuss, and analyze three popular optical orthogonal frequency division multiplexing (OFDM) techniques, such as DC-biased optical OFDM (DCO-OFDM), asymmetrically-clipped optical OFDM (ACO-OFDM), and unipolar OFDM (U-OFDM), for underwater optical wireless communication systems. The peak power constraint, bandwidth limit of the light source, turbulence fading underwater channel, and the channel estimation error are taken into account. To maximize the achievable data propagation distance, we propose to optimize the modulation index that controls the signal magnitude, and a bitloading algorithm is applied. This optimization process trades off the clipping distortion caused by the peak power constraint and the signal to noise ratio (SNR). The SNR and clipping effects of the three compared OFDM techniques are modeled in this paper. From the numerical results, DCO-OFDM outperforms ACO- and U-OFDM when the transmitted bit rate is high compared to the channel bandwidth. Otherwise, U-OFDM can provide a longer propagation distance or requires less transmitted power. [ABSTRACT FROM AUTHOR]