Arbitrary Wavelength Research Articles

Group velocity manipulation using cross gain modulation in erbium-doped fibers with co-direction structure

Abstract We experimentally demonstrated tunable delays using mutrally modulated cross-gain modulation (MM XGM) in erbium-doped fiber (EDF) with a new co-direction structure. The group velocity of the signal light can be controlled by the saturating light at an arbitrary wavelength in the EDF gain bandwidth. We have observed slow light propagation with a group velocity as low as 146.4 m/s, which means a 88.8 ms delay, and an advancement of 11.2 ms after a 13 m EDF at the same time. This provides a greater enhancement on the delay or advancement compared to the previous experiment. Furthermore, we confirmed the influence on delay or advancement by varying the pump power, the input power of the saturate light. Also, we discussed the influence of recovery time, the modulation depth of the saturating light and the modulation frequency on the modulation gain. This attractive approach could be one of the suitable solutions for real applications.

A spatial wavelength analysis of color variations in painting arts based on a step-function system with arbitrary wavelength

<b>A spatial wavelength analysis of color variations in painting arts </b><b>based on a step-function system with arbitrary wavelength</b>

On all-FLR order numerical modelling of RF wave propagation and damping

Determining the fate of waves in hot magnetized plasmas in magnetic confinement fusion machines close to arbitrary cyclotron harmonics retaining finite Larmor radius effects requires solving the relevant integro-differential wave equation for waves of arbitrary wavelength. Anticipating exploitation in as realistic geometry as possible this requires massive computer resources. Work is ongoing to attempt reducing the required CPU memory and time. As Morlet wavelets are localised in x-space as well as k-space, they potentially offer a means to solve the relevant wave equation at reduced CPU requirement cost. Encouraging first results are obtained.

Padé approximation of the adiabatic electron contribution to the gyrokinetic quasi-neutrality equation in the ORB5 code

This work aims at completing the implementation of a solver for the quasineutrality equation using a Padé approximation in the global gyrokinetic code ORB5. Initially [Dominski, Ph.D. thesis, 2016], the Pade approximation was only implemented for the kinetic electron model. To enable runs with adiabatic or hybrid electron models while using a Pade approximation to the polarization response, the adiabatic response term of the quasi-neutrality equation must be consistently modified.It is shown that the Pade solver is in good agreement with the arbitrary wavelength solver of ORB5 [Dominski, Ph.D. thesis, 2016]. To perform this verification, the linear dispersion relation of an ITG-TEM transition is computed for both solvers and the linear growth rates and frequencies are compared.

Alignment and absolute wavelength calibration of imaging Bragg spectrometers.

In the present and the next generation of fusion devices, imaging Bragg spectrometers are key diagnostics to measure plasma parameters in the hot core, especially ion temperature and plasma rotation. The latter quantities are routinely obtained using the Doppler-width and -shift of the emitted spectral lines, respectively. Line shift measurements require absolute accuracies Δλ/λ of about 10 ppm, where λ-is the observed wavelength. For ITER and the present fusion devices, spectral lines of He-and H-like argon, iron, and krypton as well as Ne-like tungsten are foreseen for the measurements. For these lines, Kα lines can be found, some in higher order, which fit into the narrow energy window of the spectrometers. For arbitrary wavelength settings, Kα lines are also used to measure the miscut of the spherical crystals; afterwards the spectrometers can be set according to the geometrical imaging properties using coordinate measurement machines. For the spectrometers measuring Lyα lines of H-like ions, fluorescence targets can provide in situ localized calibration lines on the spectra. The fluorescence targets are used best in transmission and are excited by the thermal x-ray radiation of the plasma. An analytic theory of fluorescence is worked out.

Permeability and effective slip in confined flows transverse to wall slippage patterns

The pressure-driven Stokes flow through a plane channel with arbitrary wall separation having a continuous pattern of sinusoidally varying slippage of arbitrary wavelength and amplitude on one/both walls is modelled semi-analytically. The patterning direction is transverse to the flow. In the special situations of thin and thick channels, respectively, the predictions of the model are found to be consistent with lubrication theory and results from the literature pertaining to free shear flow. For the same pattern-averaged slip length, the hydraulic permeability relative to a channel with no-slip walls increases as the pattern wave-number, amplitude, and channel size are decreased. Unlike discontinuous wall patterns of stick-slip zones studied elsewhere in the literature, the effective slip length of a sinusoidally patterned wall in a confined flow continues to scale with both channel size and the pattern-averaged slip length even in the limit of thin channel size to pattern wavelength ratio. As a consequence, for sufficiently small channel sizes, the permeability of a channel with sinusoidal wall slip patterns will always exceed that of an otherwise similar channel with discontinuous patterns on corresponding walls. For a channel with one no-slip wall and one patterned wall, the permeability relative to that of an unpatterned reference channel of same pattern-averaged slip length exhibits non-monotonic behaviour with channel size, with a minimum appearing at intermediate channel sizes. Approximate closed-form estimates for finding the location and size of this minimum are provided in the limit of large and small pattern wavelengths. For example, if the pattern wavelength is much larger than the channel thickness, exact results from lubrication theory indicate that a worst case permeability penalty relative to the reference channel of ∼23% arises when the average slip of the patterned wall is ∼2.7 times the channel size. The results from the current study should be applicable to microfluidic flows through channels with hydrophobized/super-hydrophobic surfaces.

Structure-induced resonant tail-state regime absorption in polymer: fullerene bulk-heterojunction solar cells

In this work, we present resonant tail-state regime absorption enhanced organic photovoltaics. We combine periodically structured ${\mathrm{TiO}}_{2}$ bottom electrodes with P3HT-PCBM bulk-heterojunction solar cells in an inverted device configuration. The wavelength-scale patterns are transferred to the electron-selective bottom electrodes via direct laser interference patterning, a fast method compatible with roll-to-roll processing. Spectroscopic and optoelectronic device measurements suggest polarization-dependent absorption enhancement along with photocurrent generation unambiguously originating from the population of tail states. We discuss the effects underlying these absorption patterns with the help of electromagnetic simulations using the discontinuous Galerkin time domain method. For this, we focus on the total absorption spectra along with spatially resolved power loss densities. Our simulations stress the tunability of the absorption resonances towards arbitrary wavelength regions.

(Invited) Visible-Light Responsible Ammonia Synthesis from Dinitrogen Via Plasmon-Induced Charge Separation

[Introduction] Ammonia has received much attention as a potential energy carrier and as a fuel for vehicles in addition to its use as a fertilizer because it is easily condensed into a liquid. Ammonia is conventionally synthesized by the Haber-Bosch process under high temperature and high pressure condition. Among the energy consumed in ammonia production, the portion consumed by hydrogen production from fossil fuels exceeds 90%. Therefore, the development of a novel synthetic process for ammonia production without hydrogen gas is needed[1]. The generation of ammonia from dinitrogen and water using sunlight is a preferred approach to synthesizing ammonia as an energy carrier. The co-catalyst is an important factor in determining the activity and selectivity of a photocatalytic reaction. We focused on the binding affinity of N and H adatoms on the surface of a co-catalyst. Density functional theory calculations on a broad range of transition-metal surfaces have predicted that the adsorption energy of N is smaller than that of H on the Zr surface, indicating that preferentially adsorbs N adatoms[2]. Here, we report the visible-light responsible ammonia synthesis from dinitrogen via plasmon-induced charge separation by using a SrTiO3photoelectrode loaded with gold nanoparticles (Au-NPs) and a Zr thin film. We observed the simultaneous stoichiometric production of ammonia and oxygen from dinitrogen and water under visible-light irradiation. [Experimental] We designed an SrTiO3 photoelectrode equipped with Au-NPs as the plasmonic nanostructure and Zr as a co-catalyst. The Au-NPs/niobium-doped strontium titanate (Nb-SrTiO3)/Zr photoelectrode was fabricated as follows. Au-NPs were fabricated on a 0.05wt% Nb-SrTiO3 single crystalline substrate using an annealing method. A Zr thin film was then deposited using the electron-beam evaporation method onto the opposite side of the Nb-SrTiO3 substrate. The average size of the Au-NP and the surface coverage ratio of the Nb-SrTiO3 substrate by Au-NPs were estimated to be 45 nm and 19.7% from a scanning electron microscope image. The X-ray photoelectron spectrum and X-ray reflection revealed that the surface of the Zr film deposited onto the SrTiO3 was oxidized by air and that the thicknesses of the zirconium oxide (ZrOx) and zirconium metal layers were 2.6 nm and 2.2 nm, respectively. The N2 fixation device comprised sealed reaction cells with two reaction chambers separated by the SrTiO3 substrate. The surface with Au-NPs was designated as the front of the photoelectrode, which was irradiated with visible light for the oxidation reaction, whereas the thin Zr film was used for NH3 formation on the rear surface. The anodic chamber was filled with a KOH aqueous solution at pH 13; the cathodic chamber was filled with water-saturated N2 gas and an HCl aqueous solution. The Au nanostructured Nb-SrTiO3substrate was irradiated in an area of φ6 mm by a xenon lamp using an arbitrary light intensity and wavelength. [Results and Discussion] We attempted plasmon-induced NH3 synthesis from N2 and water by using Au-NPs/Nb-SrTiO3/Zr/ZrOx. As a result, the amount of formation of both NH3 and O2 increased linearly with increasing irradiation time, and the formation ratio between NH3 and O2 was almost 4 to 3. This result indicates that dinitrogen reduction and water oxidation proceed stoichiometrically. NH3 formation is strongly related to the localized surface plasmon resonance (LSPR) excitation because the value of apparent quantum efficiency of NH3 formation was highly dependent on the position of the LSPR band. Additionally, NH3 formation was observed in all visible wavelength regions, indicating that the plasmon-induced NH3synthesis system can efficiently utilize the sunlight. We also investigated NH3 synthesis from isotopic N2 gas. The photoelectrochemical reaction was promoted by the use of 15,15N2 gas instead of 14,14N2. The formed NH3 was collected by distillation of the reaction liquid with KOH solution because the cathodic chamber is acidic, and the reaction product was obtained in the form of ammonium chloride. The collected NH3 was identified by gas chromatography–mass spectrometry. In the case of the sample obtained from the reaction solution after 46 h of visible light irradiation, a peak derived from 15NH3 (m/z = 18) was clearly observed at the same retention time as a standard 14NH3 aqueous solution (m/z = 17). These results provide direct evidence that N2 gas and water were converted into NH3under visible-light irradiation. [References] [1] T. Oshikiri, K. Ueno, H. Misawa, Angew. Chem. Int. Ed. 2014, 53, 9802-9805 [2] E. Skulason, T. Bligaard, S. Gudmundsdottir, F. Studt, J. Rossmeisl, F. Abild-Pedersen, T. Vegge, H. Jonsson, J. K. Norskov, Phys. Chem. Chem. Phys. 2012, 14, 1235-1245

Post-bifurcation and stability of a finitely strained hexagonal honeycomb subjected to equi-biaxial in-plane loading

The buckling and crushing mechanics of cellular honeycomb materials is an important engineering problem. Motivated by the pioneering experimental and numerical studies of Papka and Kyriakides (1994, 1999a,b), we review the literature on finitely strained honeycombs subjected to in-plane loading and identify two open questions: (i) How does the mechanical response of the honeycomb depend on the applied loading device? and (ii) What can the Bloch wave representation of all bounded perturbations contribute to our understanding of the stability of post-bifurcated equilibrium configurations? To address these issues we model the honeycomb as a two-dimensional infinite perfect periodic medium. We use analytical group theory methods (as opposed to the more common, but less robust, imperfection method) to study the honeycomb’s bifurcation behavior under three different far-field loadings that produce (initially) the same equi-biaxial contractive dilatation. Using an FEM discretization of the honeycomb walls (struts), we solve the equilibrium equations to find the principal and bifurcated equilibrium paths for each of the three loading cases. We evaluate the structure’s stability using two criteria: rank-one convexity of the homogenized continuum (long wavelength perturbations) and Bloch wave stability (bounded perturbations of arbitrary wavelength). We find that the post-bifurcation behavior is extremely sensitive to the applied loading device, in spite of a common principal solution. We confirm that the flower mode is always unstable, as previously reported. However, our (first ever) Bloch wave stability analysis of the post-bifurcated equilibrium paths shows that the flower mode is stable for all sufficiently short wavelength perturbations. This new result provides a realistic explanation for why this mode has been observed in the finite size specimen experiments of Papka and Kyriakides (1999a).

Research on an Equal Wavelength Spectrum Reconstruction Method of Interference Imaging Spectrometer

Interference imaging spectrometer is one of the most important equipments of Chang'E 1 satellite, which is applied to analysis the material composition and its distribution of the surface on the moon. At present, the spectral resolution of level 2B scientific data obtained by existing methods is 325 cm(-1). If we use the description way of wavelength resolution, various spectrum is different: the first band is 7.6 nm, the last band is 29 nm, which introduces two questions: (1) the spectral resolution description way mismatch with the way of ground spectral library used for calibration and comparison; (2) The signal-to-noise ratio of the spectra in the shortwave band is low due to the signal entering narrow band is little. This paper discussed the relationship between wavelength resolution and cut-off function based on the reconstruction model of CE-1 interference imaging spectrometer. It proposed an adjustable cut-off function changing with wavelength or wavelength resolution, while selected the appropriate Sinc function as apodization to realize the reconstruction of arbitrary specified wavelength resolution in the band coverage. Then we used this method to CE-1 on orbit 0B data to get a spectral image of 29 nm wavelength resolution. Finally, by using the signal-to-noise ratio, principal component analysis and unsupervised classification method on the reconstruction results with 2 grade science data from ground application system for comparison, the results showed that: signal-to-noise ratio of the shortwave band increased about 4 times, and the average increased about 2.4 times, the classification based on the spectrum was consistent, and the quality of the data was greatly improved. So, EWSR method has the advantages that: (1) in the case of keeping spectral information steadiness, it can improve the signal-to-noise ratio of shortwave band spectrum though sacrificed part of spectral resolution; (2) it can achieve the spectral data reconstruction which can set arbitrary band position or specify any wavelength resolution within the band range.

Residual zonal flows in tokamaks and stellarators at arbitrary wavelengths

In the linear collisionless limit, a zonal potential perturbation in a toroidal plasma relaxes, in general, to a non-zero residual value. Expressions for the residual value in tokamak and stellarator geometries, and for arbitrary wavelengths, are derived. These expressions involve averages over the lowest order particle trajectories, that typically cannot be evaluated analytically. In this work, an efficient numerical method for the evaluation of such expressions is reported. It is shown that this method is faster than direct gyrokinetic simulations performed with the Gene and EUTERPE codes. Calculations of the residual value in stellarators are provided for much shorter wavelengths than previously available in the literature. Electrons must be treated kinetically in stellarators because, unlike in tokamaks, kinetic electrons modify the residual value even at long wavelengths. This effect, that had already been predicted theoretically, is confirmed by gyrokinetic simulations.

Filtering and sensing properties based on metal-dielectric-metal waveguide with slot cavities

A triple-channel plasmonic system, consisting of several slot cavities coupled with the bus and drop waveguides, has been investigated numerically and theoretically. The impacts of adjusting various parameters on transmissivity are researched in detail. The results demonstrate that one can separate arbitrary wavelength and attain high transmissivity by suitably setting parameters. The sensitivity of the structure is about 950 nm shift per refractive index unit and the figure of merit is as high as 25.5. The plasmonic filter system possesses advantage of easy fabrication and compactness, which can find more applications in highly integrated optical devices, optical communication, and high sensitivity nano sensor.

Point interactions, metamaterials, and [formula omitted]-symmetry

We express the boundary conditions for TE and TM waves at the interfaces of an infinite planar slab of homogeneous metamaterial as certain point interactions and use them to compute the transfer matrix of the system. This allows us to demonstrate the omnidirectional reflectionlessness of Veselago’s slab for waves of arbitrary wavelength, reveal the translational and reflection symmetry of this slab, explore the laser threshold condition and coherent perfect absorption for active negative-index metamaterials, introduce a point interaction modeling phase-conjugation, determine the corresponding antilinear transfer matrix, and offer a simple proof of the equivalence of Veselago’s slab with a pair of parallel phase-conjugating plates. We also study the connection between certain optical setups involving metamaterials and a class of PT-symmetric quantum systems defined on wedge-shape contours in the complex plane. This provides a physical interpretation for the latter.

Alfa: an automated line fitting algorithm

I present the Automated Line Fitting Algorithm, ALFA, a new code which can fit emission line spectra of arbitrary wavelength coverage and resolution, fully automatically. In contrast to traditional emission line fitting methods which require the identification of spectral features suspected to be emission lines, ALFA instead uses a list of lines which are expected to be present to construct a synthetic spectrum. The parameters used to construct the synthetic spectrum are optimised by means of a genetic algorithm. Uncertainties are estimated using the noise structure of the residuals. An emission line spectrum containing several hundred lines can be fitted in a few seconds using a single processor of a typical contemporary desktop or laptop PC. I show that the results are in excellent agreement with those measured manually for a number of spectra. Where discrepancies exist, the manually measured fluxes are found to be less accurate than those returned by ALFA. Together with the code NEAT (Wesson et al. 2012), ALFA provides a powerful way to rapidly extract physical information from observations, an increasingly vital function in the era of highly multiplexed spectroscopy. The two codes can deliver a reliable and comprehensive analysis of very large datasets in a few hours with little or no user interaction.

A preliminary study on air-borne lightwave amplification using Weibel-type instabilities

Within man-made plasma sources, including the fusion experimental machines such as the Tokamaks, a phenomenon called the “Weibel EM instability” emerges at times. In all cases, such plasma instability constitutes a valid path for system energy loss, and thus is undesirable. Here, instead, a possibility is explored in which such instability is attempted for good use, viz, amplifying lightwaves in open space of arbitrary wavelengths and amplitudes. Obviously, this is to be compared with the traditional means via spatially-confined, wavelength-restricted erbium-doped optic fibers. The adopted approach here was to utilize artificial plasma in the controlled form of vertically oscillating (with respect to the intended incident light) electrons on a conductive grating. That is, free energy of the sloshing electrons was used to trigger Weibel type instability to act on the incident lightwave in the hope that exponential growth of the latter would occur. It turned out that the anticipated lighwave amplification in air was evidenced unambiguously by experiments with the aid of a lock-in amplifier. The desirable amplitude enhancement could have been one to two orders of magnitude, in principle, had the phasing, amplifier transparency been properly conditioned and arranged for the incident waves. However, to achieve these ambitious goals in the future, nontrivial tasks, especially phase synchronization among the plasma electrons and photons of different coherent wave packets, need to be accomplished in the first place.

Enabling arbitrary wavelength frequency combs on chip

AbstractA necessary condition for generation of bright soliton Kerr frequency combs in microresonators is to achieve anomalous group velocity dispersion (GVD) for the resonator modes. This condition is hard to implement in the visible as well as ultraviolet since the majority of optical materials are characterized with large normal GVD in these wavelength regions. We overcome this challenge by borrowing ideas from strongly dispersive coupled systems in solid state physics and optics. We show that photonic compound ring resonators can possess large anomalous GVD at any desirable wavelength, even if each individual resonator is characterized with normal GVD. Based on this concept, we design a mode‐locked frequency comb with thin‐film silicon nitride compound ring resonators in the vicinity of the rubidium D1 line (794.6 nm) and propose to use this optical comb as a flywheel for chip‐scale optical clocks. image

Falling liquid films with blowing and suction

Flow of a thin viscous film down a flat inclined plane becomes unstable to long-wave interfacial fluctuations when the Reynolds number based on the mean film thickness becomes larger than a critical value (this value decreases as the angle of inclination to the horizontal increases, and in particular becomes zero when the plate is vertical). Control of these interfacial instabilities is relevant to a wide range of industrial applications including coating processes and heat or mass transfer systems. This study considers the effect of blowing and suction through the substrate in order to construct from first principles physically realistic models that can be used for detailed passive and active control studies of direct relevance to possible experiments. Two different long-wave, thin-film equations are derived to describe this system; these include the imposed blowing/suction as well as inertia, surface tension, gravity and viscosity. The case of spatially periodic blowing and suction is considered in detail and the bifurcation structure of forced steady states is explored numerically to predict that steady states cease to exist for sufficiently large suction speeds since the film locally thins to zero thickness, giving way to dry patches on the substrate. The linear stability of the resulting non-uniform steady states is investigated for perturbations of arbitrary wavelength, and any instabilities are followed into the fully nonlinear regime using time-dependent computations. The case of small amplitude blowing/suction is studied analytically both for steady states and their stability. Finally, the transition between travelling waves and non-uniform steady states is explored as the amplitude of blowing and suction is increased.

Automatic Resonance Alignment of High-Order Microring Filters

Automatic resonance alignment tuning is performed in high-order series coupled microring filters using a feedback system. By inputting only a reference wavelength, a filter is tuned such that passband ripples are dramatically reduced compared to the initial detuned state and the passband becomes centered at the reference. The method is tested on 5th order microring filters fabricated in a standard silicon photonics foundry process. Repeatable tuning is demonstrated for filters on multiple dies from the wafer and for arbitrary reference wavelengths within the free spectral range of the microrings.

On separate universes

The separate universe conjecture states that in General Relativity a density perturbation behaves locally (i.e. on scales much smaller than the wavelength of the mode) as a separate universe with different background density and curvature. We prove this conjecture for a spherical compensated tophat density perturbation of arbitrary amplitude and radius in ΛCDM. We then use Conformal Fermi Coordinates to generalize this result to scalar perturbations of arbitrary configuration and scale in a general cosmology with a mixture of fluids, but to linear order in perturbations. In this case, the separate universe conjecture holds for the isotropic part of the perturbations. The anisotropic part on the other hand is exactly captured by a tidal field in the Newtonian form. We show that the separate universe picture is restricted to scales larger than the sound horizons of all fluid components. We then derive an expression for the locally measured matter bispectrum induced by a long-wavelength mode of arbitrary wavelength, a new result which in standard perturbation theory is equivalent to a relativistic second-order calculation. We show that nonlinear gravitational dynamics does not generate observable contributions that scale like local-type non-Gaussianity flocNL, and hence does not contribute to a scale-dependent galaxy bias Δ b ∝ k−2 on large scales; rather, the locally measurable long-short mode coupling assumes a form essentially identical to subhorizon perturbation theory results, once the long-mode density perturbation is replaced by the synchronous-comoving gauge density perturbation. Apparent flocNL-type contributions arise through projection effects on photon propagation, which depend on the specific large-scale structure tracer and observable considered, and are in principle distinguishable from the local mode coupling induced by gravity. We conclude that any observation of flocNL beyond these projection effects signals a departure from standard single-clock inflation.

Near-Optimal Algorithm for Group Scheduling in OBS Networks

Group scheduling is an operation whereby control packets arriving in a time slot schedule their bursts simultaneously. Normally, those bursts that are of the same wavelength are scheduled on the same channel. In cases where the support of full wavelength converters is available, such scheduling can be performed on multiple channels for those bursts that are of an arbitrary wavelength. This paper presents a new algorithm for group scheduling on multiple channels. In our approach, to reach a near-optimal schedule, a maximum-weight clique needs to be determined; thus, we propose an additional algorithm for this purpose. Analysis and simulation results indicate that an optimal schedule is almost attainable, while the complexity of computation and that of implementation are reduced.