Circular fourier analysis of modes of microstructured optical fibers with complex channel cross sections

A method for calculating the properties of microstructured optical fibers (MOFs) with complex channel cross sections has been developed and applied to studying leaky modes in MOFs with elliptical channels. It is demonstrated that MOFs can exhibit significantly anisotropic damping of the modes with orthogonal polarization.     

Modeling filtration performance of elliptical fibers with random distributions

The fibrous media with elliptical cross sections may improve the filtration performance, however, current researches mainly focus on the capture mechanisms of a single elliptical fiber, and the fibrous media with randomly distributed fibers are rarely involved. In this work, a 2D numerical model was developed to predict the pressure drop and particle penetration for the fibrous filter composed of randomly distributed elliptical fibers. The results show that a big solid volume fraction of filter increases the effective collision area, and enhances the capture at a low face velocity. The particle penetrations through the fibers with the diameter of 5 μm are conspicuously weaker than those with the diameter of 10 μm, especially at big solid volume fractions and high face velocities. The blunt elliptical fibers restrain the penetration more effectively than the circle ones when the solid volume fraction is high. Though the blunt fibers lead to a large drag force, the increased pressure drop cannot improve the filtration performance at low solid volume fractions. In most cases, the slim elliptical fibers can enhance the filtration performance. A bigger aspect ratio of elliptical fibers leads to a low quality factor, showing the capture efficiency increases with the penalty of a high pressure drop.     

Topological activity in Bragg elliptical twisted fibers

We have theoretically shown that Bragg twisted elliptical fibers manifest, in certain spectral regions, the property of topological activity--the ability to change in the reflected field the topological charge of incoming optical vortices and fundamental modes by two units. This property could be used for narrowband generation of optical vortices from Gaussian beams and for changing the topological charge of incoming optical vortices.     

Shape‐Enhanced Photocatalytic Activities of Thoroughly Mesoporous ZnO Nanofibers

1D mesoporous materials have attracted extensive interest recently, owning to their fascinating properties and versatile applications. However, it remains as a grand challenge to develop a simple and efficient technique to produce oxide nanofibers with mesoporous architectures, controlled morphologies, large surface areas, and optimal performances. In this work, a facile foaming‐assisted electrospinning strategy with foaming agent of tea saponin is used to produce thoroughly mesoporous ZnO nanofibers with high purity and controlled morphology. Interestingly, mesoporous fibers with elliptical cross‐section exhibit the significantly enhanced photocatalytic activity for hydrogen production, as compared to the counterparts with circular and rectangular cross‐sections, and they also perform better than the commercial ZnO nanopowders. The unexpected shape dependence of photocatalytic activities is attributed to the different stacking modes of the mesoporous fibers, and a geometrical model is developed to account for the shape dependence. This work represents an important step toward producing thoroughly mesoporous ZnO nanofibers with tailored morphologies, and the discovery that fibers with elliptical cross‐section render the best performance provides a valuable guideline for improving the photocatalytic performance of such mesoporous nanomaterials.     

Temperature and voltage sensings by mode‐mode interference in polarization‐maintaining optical fibers

Abstract

Two optic fiber sensing systems for temperature and voltage have been developed which utilize the mode‐mode interference of the two orthogonally polarized modes, HE^x _II and HE^y _II, in two commencal polarization‐maintaining fibers (bow‐tie and elliptical core fibers). A package of controlled programs in a Macintosh computer, which can record and process all related data automatically, is established for temperature sensing. The signal drifting problem in voltage sensings has been investigated, and the elimination of signal drifting is obtained by the phase tracking with direct current technology The agreement between the sensing results for temperature and dynamic voltage and those predicted by experimental principles is satisfactory, which confirms the validity of the developed sensing systems.     

Unidirectional wavelength filtering characteristics of the two-dimensional triangular-lattice photonic crystal structures with elliptical defects

The unidirectional wavelength filtering characters of the two-dimensional triangular-lattice photonic crystal structures consisting of two waveguides and an elliptic defect are theoretically studied by the finite-difference time-domain method. Through designing the coupling regions between the elliptical defect and the adjacent waveguides, the unidirectional wavelength filtering is achieved owing to the modes’ match and mismatch between the elliptical defect and waveguides, which converts the incident fundamental even-symmetric modes to the higher order odd modes. Based on the abundant defective modes with different symmetries supported by the elliptical defect, this kind of wavelength filters can allow the unidirectional light propagation with inverse forward directions, and the bidirectional propagation through the same structure at different wavelengths.     

Shear-horizontal vibration modes of an oblate elliptical cylinder and energy trapping in contoured acoustic wave resonators

We study shear-horizontal free vibrations of an elastic cylinder with an oblate elliptical cross section and a traction-free surface. Exact vibration modes and frequencies are obtained. The results show the existence of thickness-shear and thickness-twist modes. The energy-trapping behavior of these modes is examined. Trapped modes are found wherein the vibration energy is largely confined to the central portion of the cross section and little vibration energy is found at the edges. It is also shown that face-shear modes are not allowed in such a cylinder. The results are useful for the understanding of the energy trapping phenomenon in contoured acoustic wave resonators.     

Dependence of the Transverse Thermal Conductivity of Unidirectional Composites on Fiber Shape

The model for the traverse thermal conductivity of unidirectional composite materials published by Springer and Tsai, which yields good results when compared to experimental results, is generalized to include fibers having elliptical cross sections. It is shown that the thermal conductivity of the unidirectional composite normal to the filaments depends strongly on fiber shape.     

Internal waves in an elliptical channel

Abstract

Internal waves in open channels of various depths are studied, in this paper, and a wetted cross section with an elliptical bottom is considered. The frequencies of the first three sloshing modes of internal waves in two superposed fluids contained in an elliptical channel are calculated for various ratios of the depths of the two layers. Numerical solutions converge to analytical solutions based on the shallow water theory as the depth of the thin lower layer approaches zero. Also, solutions for the frequencies of the longitudinal modes of progressive internal waves in two superposed fluid layers contained in an elliptical channel are calculated for various ratios of the depths of the two layers and for two different wave numbers k.     

Propagation properties of an elliptical anisotropic metamaterial cylinder

The propagation characteristics were investigated of an open elliptical cylinder comprising a uniaxial anisotropic metamaterial. The dispersion relation for hybrid modes in this cylinder was examined theoretically. It is shown that forward and backward waves can be supported by such a metamaterial cylinder. Even and odd modes have different losses in a realistic anisotropic elliptical cylinder. The forward wave can propagate longer distances than the backward wave because of its lower loss. The light can propagate backward on the cylinder without the limit of structure size. The odd modes have higher operating wavelengths than the even modes. The extraordinary properties in this structure are identified as multilayer plasmons. The validity of the effective medium approximation of this structure is examined.     

High birefringence photonic crystal fiber with a complex unit cell of asymmetric elliptical air hole cladding

High birefringence induced by elliptical air hole photonic crystal fibers (EHPCFs) is analyzed numerically using the finite-element method. Statistical correlations between the birefringence and the various parameters are obtained. We found that the complex elliptical air hole is better than that of a circular one to obtain high birefringence in photonic crystal fibers. Our suggested structures can considerably enhance the birefringence in EHPCFs and show that the birefringence can be as high as 1.1294 x 10(-2), which is higher than the birefringence obtained from conventional step-index fiber (5 x 10(-4)), circular air holes PCF (3.7 x 10(-3)), and elliptical hollow PCF (2.35 x 10(-3)).     

一种高双折射低限制性损耗光子晶体光纤设计

本文设计了一种适用于长距离光纤通信的新型光子晶体光纤。该光纤包层内椭圆形和圆形空气孔呈交错排列,纤芯两侧为两个小椭圆空气孔。利用有限元分析方法对所设计光纤的传输特性进行分析并对其结构进行了优化,确定了最佳结构。结果表明,波长为1550 nm时,此新型光子晶体光纤在最佳结构下可提供高达3.51×10^-2的高双折射和低至1.5×10^-9 dB/m的限制性损耗。与现存的引入椭圆形空气孔的光子晶体光纤相比,本文中的光子晶体光纤的双折射系数有较大提高,限制性损耗系数降低了5个数量级。另外,本文还详细研究了光子晶体光纤的色散随光子晶体光纤结构的变化以及其布里渊增益特性,并分析了其可制造性。基于其高双折射和低限制性损耗特性,此种光纤可应用于长距离光纤通信系统。     

Theory and experimental verification of a model for high gradient magnetic separation.

A mathematical model of high gradient magnetic separation (HGMS) is presented, along with data on a characterized and sized feed material. The data are fitted to the model which uses elliptical co-ordinates to approximate the ribbon-like nature of the fibers. Magnetic force terms are developed for both paramagnetic and ferromagnetic particles in the vicinity of idealized matrix fibers which can either be magnetically saturated or unsaturated. The fluid flow is simulated by superimposing a boundary layer upon the solution for potential flow thus extending the range of validity to low Reynolds Numbers. Single particle trajectories are calculated in a piecewise linear manner by considering the force balance of magnetic, hydrodynamic, gravitational and inertial forces over each increment of the trajectory. By taking orientation of the fiber with respect to the field and flow direction into account, loading can be allowed for by assuming elliptical deposits. Experimental data were generated using high grade hematite prepared in ten separate size fractions. Correlation with the model is generally fairly good except for large particles where mechanical entrapment dominates the process. Considerable discussion of the results is included by analysing the physical concepts upon which the model is based. The validity of various assumptions pertinent to HGMS modeling is tested.     

Generation and conversion of optical vortices in long-period twisted elliptical fibers

We theoretically demonstrate that long-period twisted elliptical fibers have the ability to change in a certain wavelength range the topological charge of the incoming field by two units. We also show that such fibers can generate charge-2 optical vortices from the incoming Gaussian beams.     

Fabrication of elliptical nanorings with highly tunable and multiple plasmonic resonances

Herein, a new and facile patterning method is demonstrated for the scalable fabrication of gold elliptical rings (ERs) in a controlled manner over large areas. In this method, well-ordered hexagonally arrayed polystyrene (PS) rings, fabricated by colloidal lithography, were used as masters to generate poly(dimethylsiloxane) (PDMS) stamps with circular apertures. The stamps were then stretched and utilized as molds for creating elliptical PS rings by a capillary filling process. Through subsequent reactive ion etching and chemical wet-etching, the elliptical PS rings could be readily transferred into an underlying gold film, leading to the formation of gold ERs. Since the aspect ratio (AR) of the elliptical PS rings could be controlled by varying the applied strain during the capillary filling process, gold ERs with different ARs could be fabricated in a scalable manner. The optical properties of the gold ERs were characterized by UV-vis/NIR and IR extinction measurements. The ERs exhibited only odd modes of polarization-dependent plasmonic resonances at normal incidence. The experiments and corresponding theoretical studies illustrated that all resonant modes could be tuned across a broad spectral range from the visible to the mid infrared (550-4700 nm) by simply varying the AR of the ERs. Moreover, the experimental data were confirmed by COMSOL simulations.     

Characterization of blue agave bagasse fibers of Mexico

This paper presents physical, chemical, thermal and tensile properties of Mexican cooked blue agave bagasse fibers extracted from this plant. The fibers are 10–12 cm long and 592.34 μm in diameter. The elliptical cells in the fiber are regularly arranged with varying lumen size. The cellulose and lignin contents of the fiber are 73.60% and 21.10% respectively. Fibers showed decreasing average values of ultimate tensile strength and constant values of Young’s modulus and average % strain values with increasing mean gauge length and decreasing mean diameter. Above results are discussed in the light of various factors that affect the properties. These fibers are found to be thermally stable due to their higher values of crystallinity and lignin. Main aim of this work is to characterize these partially degraded fibers with a view to find possible uses for such fibers such as compostable and biodegradable composites of corn starch/cooked blue agave residues.     

Dispersion effects in elliptical-core highly birefringent fibers

Modal birefringence and its sensitivity to temperature and hydrostatic pressure were measured versus wavelength in three elliptical-core fibers and one fiber with stress-induced birefringence. We carried out the measurements in the spectral range from 633 to 843 nm by using interferometric methods. In fibers with elliptical cores all the measured parameters showed high chromatic dependence, whereas in fibers with stress-induced birefringence this dependence was weak. We modeled the dispersion characteristics of two elliptical-core fibers by using the modified perturbation approach first proposed by Kumar. The modification consists of introducing into the expression for the normalized propagation constants an additional perturbation term that contains information about stress-induced birefringence. The results of modeling show that the temperature and pressure sensitivity of elliptical-core fiber are associated primarily with variations in stress induced by these parameters. The agreement between measured and calculated values of sensitivity in the worst case was equal to 20% for modal birefringence and temperature sensitivity and 50% for pressure sensitivity. Lower agreement between measured and calculated values of pressure sensitivity is most probably associated with uncertainties in the material constants used in modeling.     

Characterization of fiber orientation in short fiber reinforced composites with an image processing technique

An experimental method is developed to measure the three-dimensional fiber orientation in short fiber reinforced composites by utilizing an image processing technique. The second order orientation tensor can be calculated with geometrical data that were obtained from two parallel planar cross-sections. The orientation state of individual fibers is determined from the geometry of the elliptical cross-sectional shape on the polished surface. The basic concept in determining the three-dimensional fiber orientation tensor is to slice the composite sample twice in the same direction within a small distance. The tensor is determined by using a digital image processing technique and a computational code which calculates the tensor from the geometrical characteristics obtained for the elliptical fiber cross-sections. Experiments are performed to measure the three-dimensional orientation tensor of composite specimens and good results are obtained by using the method proposed in this study Electronic Publication     

Cylindrical vector beam generation in multiple elliptical core fiber with gold wire

A new method to generate cylindrical vector beam carrying helical phase is proposed based on a multiple elliptical core fiber integrated with gold wire. Both the light field distributions in near- and far-field are considered. The simulation results show that the multiple core fiber filled with gold wire in the center can only support low-loss transmission for the analogous azimuthally polarized (AP) light field with discrete rotational symmetric profile in a broadband range, because the resonant coupling between the surface plasmon modes and the fiber core-guided supermodes. The far-field patterns for different number core are demonstrated to represent an effective AP beam. It also acts as an effective broadband transmission filter for azimuthal modes.     

Suppression of spurious lateral modes in thickness-excited FBAR resonators

Thin film bulk acoustic wave resonators (FBAR) utilize thickness-excited modes in which the resonant frequency is determined by the thickness of the structure and the wave velocity of the mode used. Unfortunately, other resonant modes also may be excited in the device. Some of these correspond to low-frequency, laterally-excited modes and, although a relatively small amount of the total energy is absorbed by these modes, their harmonics may produce an undesirable response around the fundamental resonance frequency of the desired thickness mode. This work explores various ways of suppressing the spurious effects caused by lateral-excited modes by studying their dependence of the electrode geometry. The origin of the lateral-excited modes is discussed in detail, and the results from a number of different electrode geometries are compared. A new elliptical electrode shape for suppression of spurious modes is developed and demonstrated.