Superposition Of Intensities Research Articles

Synthetic photonic lantern characterization and power regulation with intensity superposition mode decomposition.

Photonic lanterns (PLs) enable to convert the spatial modes, making it possible to simply add/drop modes in multimode division multiplexing (MDM) systems. The parameters of PLs have a significant impact on the modal purity, signal quality, transmission distance, and efficiency. This paper proposes a method for the synthetic characterization and power regulation of PLs with multi-channel intensity superposition mode decomposition (MD). The observation reveals that the single channel on the charge-coupled device (CCD) comprises a combination of the fundamental and higher mode fields. However, when the multi-channel is input together, the intensity of each few-mode spot is superimposed on the CCD, and the parameters that cannot be acquired by a single channel can be obtained through the detection of multi-channel input. This offers a novel avenue for optimizing the PLs. Thus, the insertion loss (IL), modal dependent loss (MDL), mode conversion efficiency (MCE), crosstalk, and mode multiplexing power ratio difference (MMPRD) can be obtained. Furthermore, the power regulation is implemented based on the multi-channel intensity superposition MD. The difference between the two modes before power control at the output of the PL is 0.28 dB. However, after implementing power control measurements, this difference was reduced to 0.05 dB, facilitating power equalization throughout the entire communication system.

An improved analytical framework for flow prediction inside and downstream of wind farms

This study evaluates available analytical wake models for flow prediction inside and downstream of wind farms of different sizes and layouts using large-eddy simulation (LES), and introduces an enhanced analytical framework. All the tested analytical wake models, based on the superposition of individual turbine wakes, systematically overestimate the wake recovery both inside and downstream of the wind farms. The results indicate that the overestimation is linked to the assumption of linear or quasilinear wake expansion, which does not hold at large downstream distances. To address this issue, an enhanced analytical framework is proposed based on the extension of a recently developed streamwise scaling model for single wakes that eliminates the need for the linear wake expansion assumption. Since the new framework computes the wake expansion based on the near-wake length and the local turbulence intensity, different methods for their calculation and the superposition of turbulence intensity within wind farms are evaluated against the LES data. The identified best methods are incorporated into the new analytical framework. The proposed framework consistently yields more accurate power estimates and flow predictions inside and downstream of finite-size wind farms with different sizes and configurations.

Propagation of radial phase modulated vortex beams in atmospheric turbulence

In practical free-space optical (FSO) communications, mitigating turbulence effects is crucial. This paper introduces radial phase modulation as a method to protect the signal's orbital angular momentum (OAM) in turbulent FSO. The results demonstrate that selecting appropriate modulation parameters can improve communication quality, particularly in stronger turbulence. However, a drawback is that radial phase modulation also increases crosstalk near the signal mode in strong turbulence. We further investigate the effects of radial phase modulation in two OAM multiplexing cases: mode broadcasting and intensity superposition. The results demonstrate that by employing radial phase modulation, both intensity and phase divergence, as well as beam wander, can be effectively reduced. In addition, the peaks in the OAM spectra enable easy identification of the signal modes. Moreover, even with a limited aperture in the detector, both channel capacity and transmission distance can be enhanced. These findings have potential applications in practical FSO communication in atmospheric turbulence.

Investigation on the Formation of Laser Transverse Pattern Possessing Optical Lattices

Optical lattices (OLs) with diverse transverse patterns and optical vortex lattices (OVLs) with special phase singularities have played important roles in the fields of atomic cooling, particle manipulation, quantum entanglement, and optical communication. As a matter of consensus until now, the OL patterns are generated by coherently superimposing multiple transverse modes with a fixed phase difference through the transverse mode locking (TML) effect. There are phase singularities in the dark area of this kind of OL pattern, so it is also called OVL pattern. However, in our research, it is found that some high-order complex symmetric OL patterns can hardly be analyzed by TML model. Instead, the analysis method of incoherent superposition of mode intensity could be applied. The OL pattern obtained by this method can be regarded as in non-TML state. Therefore, in this article, we mainly study the distinct characteristics and properties of OL patterns in TML and non-TML states. Through intensity comparison, interferometry, and beat frequency spectrum, we can effectively distinguish OL pattern in TML and non-TML states, which is of significance to explore the formation of laser transverse pattern possessing OL.

Pressure pulsation investigation in an electrical submersible pump based on Morlet continuous wavelet transform

Electrical Submersible Pumps (ESP) are one of the most reliable and efficient ways to lift oil or water from the ground or deep-sea to the surface. How to reduce the pressure pulsation and increase reliability is a challenging issue in the ESP design processes. In this study, a typical three-stage ESP model was selected as the research object. Based on numerical calculations and validation tests, the flow-field distribution mechanism within the dynamic and static interference zones of multi-stage ESP was investigated. Meanwhile, the inter-stage variability of pressure pulsation characteristics within the main hydraulic components was explored by Morlet continuous wavelet transform. The results showed that the numerical predicted performance has an excellent agreement with the experimental results, which confirms the accuracy of the numerical calculations. The time-domain characteristics of pressure pulsation at each monitoring location within the ESP showed high disorder due to the inter-stage propagation and coupling of the pressure pulsations. The low-frequency signal in the pressure pulsation signal had not only a cascading superposition of intensity, but also a significant phase difference. It was found that the main form of propagation between pulsating signal levels is the low-frequency signal. This work may facilitate the reduction or control of the pressure pulsations and thus improve the operation stability of ESP.

Mode competition in broad-ridge-waveguide lasers

The lateral brightness achievable with high-power GaAs-based laser diodes having long and broad waveguides is commonly regarded to be limited by the onset of higher-order lateral modes. For the study of the lateral-mode competition two complementary simulation tools are applied, representing different classes of approximations. The first tool bases on a completely incoherent superposition of mode intensities and disregards longitudinal effects like spatial hole burning, whereas the second tool relies on a simplified carrier transport and current flow. Both tools yield agreeing power-current characteristics that fit the data measured for 5–23 µm wide ridges. Also, a similarly good qualitative conformance of the near and far fields is found. However, the threshold of individual modes, the partition of power between them at a given current, and details of the near and far fields show differences. These differences are the consequence of a high sensitivity of the mode competition to details of the models and of the device structure. Nevertheless, it can be concluded concordantly that the brightness rises with increasing ridge width irrespective of the onset of more and more lateral modes. The lateral brightness at 10 MW cm−2 power density on the front facet of the investigated laser with widest ridge (23 µm) is comparable with best values known from much wider broad-area lasers. In addition, we show that one of the simulation tools is able to predict beam steering and coherent beam coupling without introducing any phenomenological coupling coefficient or asymmetries.

A comparison of the structure of lamellar stacks in a semicrystalline polymer during melting and crystallization by means of the Intensity Superposition Method

A comparison of the structure of lamellar stacks in a semicrystalline polymer during melting and crystallization by means of the Intensity Superposition Method

Topological Properties of Epidemic Aftershock Processes

AbstractEarthquakes in seismological catalogs and acoustic emission events in lab experiments can be statistically described as point events in linear Hawkes processes, where the spatiotemporal rate is a linear superposition of background intensity and aftershock clusters triggered by preceding activity. Traditionally, statistical seismology interpreted these models as the outcome of epidemic branching processes, where one‐to‐one causal links can be established between mainshocks and aftershocks. Declustering techniques are used to infer the underlying triggering trees and relate their topological properties with epidemic branching models. Here, we review how the standard Epidemic Type Aftershock Sequence (ETAS) model extends from the Galton‐Watson branching processes and bridges two extreme cases: Poisson and scale‐free power law trees. We report the statistical laws expected in triggering trees regarding some topological properties. We find that the statistics of such topological properties depend exclusively on two parameters of the standard ETAS model: the average branching ratio nb and the ratio between exponents α and b characterizing the production of aftershocks and the distribution of magnitudes, respectively. In particular, the classification of clusters into bursts and swarms proposed by Zaliapin and Ben‐Zion (2013b, https://doi.org/10.1002/jgrb.50178) appears naturally in the aftershock sequences of the standard ETAS model depending on nb and α/b. On the other hand swarms can also appear by false causal connections between independent events in nontectonic seismogenic episodes. From these results, one can use the memory‐less Galton‐Watson as a null model for empirical triggering processes and assess the validity of the ETAS hypothesis to reproduce the statistics of natural and artificial catalogs.

Visual cryptography in single-pixel imaging.

Two novel visual cryptography (VC) schemes are proposed by combining VC with single-pixel imaging (SPI) for the first time. It is pointed out that the overlapping of visual key images in VC is similar to the superposition of pixel intensities by a single-pixel detector in SPI. In the first scheme, QR-code VC is designed by using opaque sheets instead of transparent sheets. The secret image can be recovered when identical illumination patterns are projected onto multiple visual key images and a single detector is used to record the total light intensities. In the second scheme, the secret image is shared by multiple illumination pattern sequences and it can be recovered when the visual key patterns are projected onto identical items. The application of VC can be extended to more diversified scenarios by our proposed schemes.

Analysis of loose bunches of soliton molecules in passive mode-locked fibre laser using time-stretching technology

Loose bunches of soliton molecules (SMs) in a passive mode-locked fiber laser with a WTe2 saturable absorber are observed using the photonic time-stretching (TS) technique. Due to the large temporal separations between the SMs, the TS profiles of the loose bunches appear as the intensity superposition of the spectral interference fringes of the adjacent SMs. The bandwidth limitations and the electronic system sampling rate contribute to the loss of phase information between adjacent SMs and the formation of the intensity overlap profiles. The phase difference and pulse width are estimated using a simulated annealing algorithm.

Post-Yielding Behavior of Hinge-Supported Wall with Buckling-Restrained Braces in Base

A novel structural wall with hinge support and buckling restrained braces (BRBs) set in the base (HWBB) is studied. HWBB can be applied to precast manufacturing due to its considerable ductility and the separate loading mechanism in HWBB–frame structure. In elastic stage, BRBs play a brace role to make the hinged wall resist horizontal forces like a shear wall. BRBs dissipate seismic energy through plastic and hysteresis effects after yielding and the damage is only concentrated in BRBs. The performance of an HWBB is equivalent to a shear wall structure with excellent ductility and stable energy dissipation capacity. Numerical analysis indicates that the hinged wall body in the HWBB well controls the deformation mode of the structure, avoiding the concentration of story drifts, thereby protecting the remaining parts of the structure. It is revealed that the moments of the wall body will generate significant increments after BRBs yielding, and the Seismic Intensity Superposition Method is proposed to calculate the moments. In this method, nonlinear response of an HWBB can be regarded as the sum of the responses of two elastic corresponding structures excited with two parts of the seismic intensity, respectively. Modes and moments equations of the hinged wall with uniform distribution of stiffness and mass are derived, and calculation results coincide with that of the nonlinear time history analysis (NHA). For a more general case, the white noise scan method is proposed to solve the structure’s natural characteristics and to further calculate the response. Finally, the post-yielding moment calculation method and the process based on design response spectrum are proposed. It is proved that the moments from proposed Seismic Intensity Superposition Method can envelop most of the moments from NHA, and it is a good estimate of the response of HWBB in nonlinear stage.

Quantitative assessment and suppression of defect-induced scattering in low-loss mirrors.

In this Letter, defect-induced scattering in 1064nm high-reflection coatings prepared by dual ion beam sputtering and its suppression were investigated by artificial nodules, finite-difference time-domain simulations, angular resolved scattering (ARS) measurements, and planarization technology. After establishing the geometric model of the nodules grown from ϕ 1μm SiO2 microspheres, the far-field scattering of the multiple nodules was determined by intensity superposition. For a nodule density of 100 mm-2, there is good agreement between the simulated and measured ARS. The total scattering is ∼500 ppm for the multilayer coating with artificial nodules, which is more than 10 times that for the coating without nodules. Next, an iterative deposition-etching process was used to planarize the defects, which reduced scattering by almost one order of magnitude. Moreover, detailed characterization of the planarized seeds reveals that the planarization technology is a complex process, and it still does not produce a perfect flat surface. The results showed that there is a pit over each planarized seed in the coating surface, which leads to additional scattering. The possible reasons for the presence of these pits are briefly discussed, and the directions for further research are provided at the end of this Letter.

Electronic structure of Fe1.08Te bulk crystals and epitaxial FeTe thin films on Bi2Te3

The electronic structure of thin films of FeTe grown on Bi2Te3 is investigated using angle-resolved photoemission spectroscopy, scanning tunneling microscopy and first principles calculations. As a comparison, data from cleaved bulk Fe1.08Te taken under the same experimental conditions is also presented. Due to the substrate and thin film symmetry, FeTe thin films grow on Bi2Te3 in three domains, rotated by 0°, 120°, and 240°. This results in a superposition of photoemission intensity from the domains, complicating the analysis. However, by combining bulk and thin film data, it is possible to partly disentangle the contributions from three domains. We find a close similarity between thin film and bulk electronic structure and an overall good agreement with first principles calculations, assuming a p-doping shift of 65 meV for the bulk and a renormalization factor of around two. By tracking the change of substrate electronic structure upon film growth, we find indications of an electron transfer from the FeTe film to the substrate. No significant change of the film’s electronic structure or doping is observed when alkali atoms are dosed onto the surface. This is ascribed to the film’s high density of states at the Fermi energy. This behavior is also supported by the ab initio calculations.

United block sequence mapping-based visible light positioning for dense small cell deployment

Visible light positioning (VLP) is an emerging candidate for indoor positioning, which can simultaneously meet the requirements for accuracy, cost, coverage area, and security. However, intercell interference caused by light intensity superposition limits the application of VLP. In this Letter, we propose a united block sequence mapping (UBSM)-based VLP that utilizes superposition to integrate the multidimensional information from dense small cells into 2D information. The experimental result shows that UBSM-based VLP can achieve an accuracy of 1.5 cm with a 0.4 m row spacing and 0.35 m column spacing of LED lights.

The Fano-like lineshape without interference in graphene symmetry-breaking structures

We demonstrate that the concepts in metal plasmonics cannot be totally used indiscriminately in graphene plasmonics. A typical Fano resonance for a metallic symmetry-breaking structure is simulated for graphene. Although a Fano-like extinction spectrum emerges, our analysis proves that the asymmetry is due to the intensity superposition of three plasmon modes instead of interference. The difference between graphene and metal plasmons comes from different contributions to the extinction, where the former is absorption instead of scattering. Furthermore, the asymmetric lineshape can be effectively tuned by changing not only the carrier mobility and Fermi energy of graphene, but also the geometry of the disk.

An intensity superposition model to fit the small angle X-ray scattering of semicrystalline polymers and its application to the monitoring of non-isothermal crystallization

Small angle X-ray scattering (SAXS) of Ethylene-1-Octene copolymer cooled from the melt at a constant rate is recorded and modeled. The theoretical SAXS curves based on the paracrystalline layer stacking model of Hermans cannot be well fitted to the experimental ones. Therefore it is assumed that lamellar stacks filling the copolymer volume may differ in their crystallinity and the curves are fitted by a model that combines intensities from all stacks under control of a crystallinity distribution function P(φ). It is shown that a symmetric Gauss function is not suitable to approximate this distribution while the best fit is obtained for an asymmetric, positively skewed split Gauss function. The model provides good agreement of the morphological parameters of stacks with the values obtained from the one-dimensional correlation function. Additional determined parameters are: average crystallinity of the copolymer φs, invariant Q as well as standard deviation and skewness coefficient of P(φ). During cooling the P(φ) distribution becomes less asymmetric but simultaneously it clearly broadens. The skewness decreases first slowly but much faster for temperatures lower than 40°C. Based on the transformations of the shape of P(φ) distribution the changes in the structure of stacks and homogeneity of copolymer are discussed and related to the crystallization conditions.

Controlled light field concentration through turbid biological membrane for phototherapy.

Laser propagation through a turbid rat dura mater membrane is shown to be controllable with a wavefront modulation technique. The scattered light field can be refocused into a target area behind the rat dura mater membrane with a 110 times intensity enhancement using a spatial light modulator. The efficient laser intensity concentration system is demonstrated to imitate the phototherapy for human brain tumors. The power density in the target area is enhanced more than 200 times compared with the input power density on the dura mater membrane, thus allowing continued irradiation concentration to the deep lesion without damage to the dura mater. Multibeam inputs along different directions, or at different positions, can be guided to focus to the same spot behind the membrane, hence providing a similar gamma knife function in optical spectral range. Moreover, both the polarization and the phase of the input field can be recovered in the target area, allowing coherent field superposition in comparison with the linear intensity superposition for the gamma knife.

Information on real-structure phenomena in metastable GeTe-rich germanium antimony tellurides (GeTe)nSb2Te3 (n ≥ 3) by semi-quantitative analysis of diffuse X-ray scattering

Abstract Quenching cubic high-temperature polymorphs of (GeTe)nSb2Te3 (n ≥ 3) yields metastable phases whose average structures can be approximated by the rocksalt type with 1/(n + 3) cation vacancies per anion. Corresponding diffraction patterns are a superposition of intensities from individual twin domains with trigonal average structure but pseudo-cubic metrics. Their four orientations are mirrored in structured diffuse streaks that interconnect Bragg reflections along the [001] directions of individual disordered trigonal domains. These streaks exhibit a “comet-like” shape with a maximum located at the low-angle side of Bragg positions (“comet head”) accompanied by a diffuse “comet tail”. 2D extended cation defect ordering leads to parallel but not equidistantly spaced planar faults. Based on a stacking fault approach, the diffuse scattering was simulated with parameters that describe the overall metrics, the concentration and distribution of cation defect layers, atom displacements in their vicinity and the stacking sequence of Te atom layers around the planar defects. These parameters were varied in order to derive simple rules for the interpretation of the diffuse scattering. The distance between Bragg positions and “comet heads” increases with the frequency of planar faults. A sharp distance distribution of the planar faults leads to an intensity modulation along the “comet tail” which for low values of n approximates superstructure reflections. The displacement of atom layers towards the planar defects yields “comets” on the low-angle side of Bragg positions. A rocksalt-type average structure is only present if the planar defects correspond to missing cation layers in the “cubic” ABC stacking sequence of the Te atom layers. An increasing amount of hexagonal ABA transitions around the defect layers leads to increasing broadening and splitting of the Bragg reflections which then overlap with the diffuse scattering. Based on these rules, the diffuse scattering of (GeTe)nSb2Te3 (n = 2, 4, 5, 12) crystals was analyzed by comparing simulated and experimental reciprocal space sections as well as selected streaks extracted from synchrotron data. With decreasing n, both the average distance between faults and thus the slab thickness decrease, whereas the probability of hexagonal ABA transitions increases. The quenched metastable phases can be understood as intermediates between the stable high-temperature phases, which exhibit a rocksalt-type structure with randomly disordered cations and vacancies on the cation position, and the trigonal layered structures, which are stable at room temperature and consist of distorted rocksalt-type slabs separated by equidistant defect layers.

Speckle suppression in digital holographic imaging with random phases and different wavelengths

An effective speckle suppression method in digital holography is experimentally demonstrated with a wavelength-tunable coherent light source and a moving diffuser. Multiple off-axis digital holograms with different wavelengths and random phases are obtained. The Fresnel transformation algorithm is used to calculate the diffraction integral in the reconstruction. The speckle noise in the reconstructed images is suppressed by super- posing and averaging the intensity of multiple reconstruction images. Experiment results and the parameter evaluation show that the presented method is effective and feasible. © 2014 Society of Photo-Optical Instrumentation Here, a novel method for generating multiple holograms and suppressing speckle is presented. A wavelength-tunable coherent light source (LS) and a moving diffuser are used to generate multiple holograms with random phases (RP) and DWs. The intensity superposition and average of recon- structed images are performed to suppress the speckle noise. The DW intervals are experimentally used to generate holograms. The presented method of speckle suppression is compared with the random-phase intensity superposition and DWs in the experiment. The performance parameters are cal- culated and compared to demonstrate the effect of the speckle suppression.

Optical information encryption based on incoherent superposition with the help of the QR code

In this paper, a novel optical information encryption approach is proposed with the help of QR code. This method is based on the concept of incoherent superposition which we introduce for the first time. The information to be encrypted is first transformed into the corresponding QR code, and thereafter the QR code is further encrypted into two phase only masks analytically by use of the intensity superposition of two diffraction wave fields. The proposed method has several advantages over the previous interference-based method, such as a higher security level, a better robustness against noise attack, a more relaxed work condition, and so on. Numerical simulation results and actual smartphone collected results are shown to validate our proposal.