Dispersion Properties Of Fibers Research Articles

On characteristic behavior and flattened chromatic dispersion properties of bent photonic crystal fibers

Abstract In this paper by using modified scalar effective index method, first effective refractive index of straight and bent photonic crystal fibers are determined and then propagation parameters, such as chromatic dispersions for different structural designs of PCF, are obtained. By changing the values of affecting parameters in the bent PCF, such as different bent radius, distance between air holes Λ $\Lambda $ and air-filling factor d / Λ , $d/\Lambda ,$ the chromatic dispersion is determined in terms of propagating wavelengths. The obtained results of bent PCF are compared with the results of straight PCF. The results of the present paper might be useful in designing optical devices and sensing systems.

Synergy effect of hybrid steel-polyvinyl alcohol fibers in engineered cementitious composites: Fiber distribution and mechanical performance

The fiber distribution is a crucial factor governing the superb strain-hardening and multiple cracking behavior of engineered cementitious composites (ECC). However, the desired uniform distribution of fibers is challenging in ECC with large amounts of binders and fibers, especially for hybrid fiber system. In the present study, we employed image analysis to investigate the fiber distribution characteristics in hybrid steel-polyvinyl alcohol (PVA) fiber ECC and its influence on the mechanical performance. Special attention was paid to the impact of additional steel fiber content and its size. The results show that the dispersion coefficient of PVA fibers in hybrid fiber system was at most 50% higher than that of mono fiber system. Fiber hybridization rendered more fibers distributed in smaller angles of 0°–40°, which helped to enhance the fiber bridging capacity. The addition of steel fibers significantly improved the flexural properties of ECC, with maximized strength at steel fiber content of 1.0% and maximized deformability at 0.6% dosage. The incorporation of steel fibers greatly enhanced the crack control ability of hybrid fiber ECC. The average crack width was reduced to 36.1 μm when the volume fraction of steel fiber gone to 1.0%. Furthermore, larger sized steel fibers played a more pronounced role in improving the fiber dispersion, fiber orientation and mechanical properties than that with smaller size. Synergy effect of hybrid steel-PVA fiber on fiber distribution and mechanical properties was revealed. The findings are expected to contribute to the blending ratio design of hybrid fibers and the selection of fiber size in preparing ECC. And the obtained robust ECC can provide strong support for performance enhancement and maintenance of building engineering.

Optimization of matrix viscosity improves polypropylene fiber dispersion and properties of engineered cementitious composites

• PP fiber dispersion can be improved by tailoring ECC matrix viscosity using VMA. • At optimal state, PP-ECC attains 7 % tensile strain and 3.5 MPa tensile strength. • Adding VMA beyond optimal state lowers ECC’s tensile strength and ductility. Engineered cementitious composites (ECC) is a durable cementitious material with high tensile ductility and strain-hardening characteristics. Although considered as a cost-effective fiber for ECC, polypropylene (PP) fiber is reportedly difficult to disperse in mortar matrix due to its high aspect ratio and hydrophobicity. In this study, the matrix viscosity of a low-carbon ECC based on limestone calcined clay cement was tailored as a variable to improve PP fiber dispersion under a pre-determined mixing protocol. The effect of matrix viscosity on the composite fresh and hardened properties was investigated experimentally. Results suggested an optimal range of matrix viscosity (10.3–11.5 Pa‧s) favors the composite tensile strength and strain capacity at 28 days. At the optimal state with a 0.1 % viscosity modifying admixture (VMA)-to-binder mass ratio, PP-ECC achieved 7.0 % tensile strain capacity and 3.5 MPa ultimate tensile strength. When matrix viscosity falls outside the desired range, both ultimate tensile strength and strain capacity were diminished. By tailoring the VMA dosage, the matrix viscosity can be adjusted for desired fiber dispersion, workability, and mechanical properties. The findings of this study provide a technical reference for the practical design and application of PP-ECC.

Dispersion and nonlinearity properties of small solid-core photonic fibers with As2Se3 substrate

Characteristics of As2Se3 photonic crystal fibers (PCFs) with a solid-core and small-core diameter are numerically investigated in the long-wavelength range (from 2 to 10 μm). A full modal analysis and optical properties of designed photonic crystal fibers with lattice constant Λ and filling factor d/Λ are presented in terms of chromatic dispersion, effective refractive index, nonlinear coefficients, and confinement loss. The simulation results show that a high nonlinear coefficient of 4410.303 W–1·km–1 and a low confinement loss of 10−20 dB·km–1 can simultaneously be achieved in the proposed PCFs at a 4.5 μm wavelength. Chromatic dispersions are flat. The values of dispersion increase with increasing filling factor d/Λ and decrease with the increase in lattice constant Λ. In particular, some chromatic dispersion curves also cut the zero-dispersion line at two points. The flat dispersion feature, high nonlinearity, and small confinement loss of the proposed photonic crystal fiber structure make it suitable for supercontinuum.

FECO fringes for investigating the effect of grafting process on the dispersion properties of polyamaide-6 fibers.

Polyamide-6 fiber was modified by grafting it with poly(methyl methacrylate) PMMA polymer. The grafting process is widely used in industry to introduce new properties and overcome some obstacles, for instance, in storing energy applications. Multiple-beam interference techniques are very precise techniques to characterize the different properties of polymeric fibers. Fringes of equal chromatic order FECO technique was used to study the effect of grafting process on the dispersion properties of polyamides fibers. A mechanical drawing device was attached to the FECO system to evaluate the mechanical deformation impact on the samples and on their dispersion properties. The dispersion properties were evaluated by measuring their refractive indices, Cauchy's constants, average excitation energy, dispersion energy, lattice energy, interband oscillator wavelength, static dielectric constant, and Abbe's dispersion number. The results show that grafting polyamide-6 with PMMA produced a new material with a different structure and different dispersion properties. Microinterferograms, graphs and tables were given for illustrations.

Dispersion properties of single-mode optical fibers in telecommunication region: poly (methyl methacrylate) (PMMA) versus silica

Abstract In this paper, the dispersion characteristics of two standard single-mode optical fibers (SMFs), fabricated with silica and poly (methyl methacrylate) (PMMA) are studied in telecommunication spectral regions. The effect of structural parameters, such as the radius of the fiber core and the relative core-cladding index difference, is numerically investigated. It is found that over whole spectral range, the PMMA-based SMF shows lower dispersion than the silica SMF. Also, the zero-dispersion wavelength (ZDW) of PMMA-based SMF is longer than that of silica fiber. The results may be of practical importance for the telecommunication applications.

Effect of series explosion effects on the fiber length, fiber dispersion and structure properties in glass fiber reinforced polyamide 66

Nowadays, glass fiber (GF) reinforced polyamide 66 (PA66) composites have attracted strong interests in commercial and engineering applications due to many advantages, such as corrosion resistance, high potential of integration, self‐lubricating, and high toughness. However, it is very difficult for traditional plastic molding equipment to concurrently obtain the increase of fiber retention length and the improvement of fiber dispersion during the PA66/GF composites manufacturing, which greatly limit the widespread application of such composites. An innovative twin eccentric rotor volume pulsating plasticizing transportation equipment (TERE) based on series explosion effects, is applied to prepare PA66/GF composites at different rotor speeds and fiber loadings. Inside the PA66/GF30 composite prepared by TERE, the fibers are evenly dispersed in polymer matrix and the average fiber length increases by 3.2 times when compared to that of twin‐screw plasticizing transportation equipment (TSE). The Charpy impact strength of PA66/GF composites prepared by TERE is nearly twice that of TSE at all fiber contents. The fatigue properties, thermal oxygen aging properties, and creep properties of the TERE composites exhibit better effects than the TSE composites, indicating that the TERE can ensure longer fiber length and better dispersion effect simultaneously.

An optimum polyvinyl alcohol fiber length for reinforced high ductility cementitious composites based on theoretical and experimental analyses

High ductility cementitious composites (HDCCs) exhibit a robust tensile ductility accompanied by multiple cracking and a small crack width. The excellent performance of HDCCs can be elaborately designed by optimizing certain microscopic parameters. Due to the easily customized and controlled characteristics of fiber length, the aim of this study was to tailor the optimum PVA fiber length via theoretical and experimental methods. Based on the micromechanical bridging theory, the effects of the fiber length on the fiber bridging stress, the complementary energy and the fracture energy were determined. Experimental analyses including compressive tests, four-point bending tests and uniaxial tensile tests, were conducted, and five different PVA fiber lengths as 6 mm, 9 mm, 12 mm, 18 mm and 24 mm were employed in this study. Besides, the fiber dispersion properties were evaluated by a backscattering technique.The theoretical results showed that the fiber bridging stress and the complementary energy increased with increasing fiber length; however, the increasing tendency slowed as the proportion of ruptured fibers increased. The fracture energy initially increased and then decreased. A theoretical optimum fiber length was determined to be 10 mm. The experimental results showed that the compressive strength was not affected by the fiber length; the composites can achieve an optimum tensile ductility and flexural performance by incorporating PVA fibers with lengths of 9 mm, for which the fiber distribution coefficient was greater than 80%. The experimental results and theoretical analyses were basically consistent. Therefore, this research can be used as an important guide for tailoring appropriate fiber lengths for HDCC designs.

Insight into the Correlations Between Fiber Dispersion and Physical Properties of Chrome Tanned Leather

The correlations between fiber dispersion and physical properties of chrome tanned leather were investigated to provide new insights into improving leather quality and designing tanning agents and tannages. Wet blues were prepared by tanning pickled pelts with different amounts of chrome powder, and their pore structures in the range of 5.48 nm–120 ?m were measured using a mercury intrusion porosimetry (MIP). The porosity and total pore area of wet blue increased with increasing amount of chrome powder from 2% to 8%. These MIP data combined with the images observed using a field emission scanning electron microscopy and a scanning transmission electron microscopy–energy dispersive spectroscopy indicated that chrome tanning agent opened up the microfibrils, fibrils, elementary fibers and fiber bundles of wet blue. The sufficient fiber dispersion of wet blue was attributed to the fact that chrome tanning agent penetrated into the microfibrils and fixed collagen fibers from microfibril level to fiber bundle level. The wet blues were then fatliquored to prepare crust leathers. The tensile strength, tear strength, elongation at break, softness, fullness and water vapor permeability of the leathers improved with increasing chrome powder. These results implied that there is a positive correlation between fiber dispersion and physical properties of chrome tanned leather.

Tunable wavelength conversion based on optofluidic infiltrated photonic crystal fibers

In this paper, wavelength conversion based on optofluidic infiltration of photonic crystal fibers (PCFs) is investigated to achieve the suitable wavelength over wide tunable range. For this purpose, two designs of PCFs (the so-called PCF1 and PCF2) with appropriate dispersion properties are simulated, and wavelength conversion via four-wave mixing process for pump wavelengths in both normal and anomalous dispersion regimes is studied. By changing the refractive index [Formula: see text] of the optical fluid infiltrated into the PCF air-holes and then varying the fiber dispersion properties, the converted wavelength region can be tuned. The results show that for the pump wavelength in the normal dispersion regime, the PCF1 infiltrated with [Formula: see text] and PCF2 infiltrated with [Formula: see text] exhibit the maximum wavelength shift. Moreover, the wavelength shift is much higher than that obtained in the anomalous dispersion regime and it can be further increased by increasing the input pump power.

Intra-cavity measurement concept of dispersion properties with a tunable fiber-integrated laser

The dispersion properties of fibers depict a key characteristic to model the propagation of ultra-short pulses in waveguides. In the following, a new method is presented to directly measure the dispersion properties of fibers and optical components in the time domain. The analysis is based on pulse shape variations along the tuning range of a theta cavity fiber laser (TCFL) depending on the adjusted repetition rate. The automated measurement procedure, evaluating pulse symmetry, achieves a temporal sensitivity below 5 ps surpassing the resolution of the acquisition electronics. Exemplarily, two samples of Nufern PM980-XP fiber are investigated with an Yb-doped tunable TCFL retrieving the mean dispersion parameter by comparative measurements. The obtained results are compared to a reference method based on spectral interferometry. With deviations in between either approach of and , respectively, the results agree well within the measurement errors of the TCFL, verifying the presented concept. Due to the pulse formation process extending over multiple round trips, this approach achieves an enhanced sensitivity compared to competing direct temporal methods. Together with an alignment free operation, the fiber-integrated TCFL depicts a simple and robust concept showing potential in specific measurement scenarios such as in quality management.

Dispersion, Workability and Mechanical Properties of Different Steel-Microfiber-Reinforced Concretes with Low Fiber Content

Steel-microfiber-reinforced concrete has been proven to be an effective type of hybrid fiber-reinforced concrete (HyFRC). The microfiber used in these concretes generally include microfilament steel (MS) fibers and synthetic fibers, such as polypropylene (PP), polyvinyl alcohol (PVA), and polyacrylonitrile (PAN) fibers. This study aims to obtain the optimal type of steel-microfiber HyFRC, with low fiber content, which can be easily used in engineering projects without special fabrication procedures, thus achieving the concept of sustainability. Four types of HyFRC that blend steel (S) fiber with MS, PP, PVA and PAN were studied. These HyFRC were compared through a systematic experimental campaign in which the fiber dispersion, mixture workability, and concrete mechanical properties were investigated. The experimental results of the fiber dispersion and mixture workability indicate the following qualitative relationship: MS > PVA ≈ PP > PAN. For the mechanical properties of the concretes, the S-MS, and S-PVA HyFRCs generate an overall higher enhancing effect than those of the S-PP and S-PAN HyFRCs and show a positive hybridization effect for most properties. The S-MS HyFRC is superior in strength, and the S-PVA HyFRC has a significantly improved toughness. Because PVA has relatively good dispersion and workability properties, and toughness is the most important and effective mechanical property in the fiber-reinforced concrete, this study recommends that the S-PVA HyFRC is the optimal type of steel-microfiber HyFRC.

Octave Spanning Coherent Supercontinuum Comb Generation Based on Er-Doped Fiber Lasers and Their Characterization

Wideband, octave spanning, coherent supercontinuum (SC) with high flatness is very useful for many applications, but it has been difficult to achieve such ideal SC. In this paper, we investigated the octave spanning, coherent SC generation based on Er-doped ultrashort pulse fiber laser system. First, we developed a high power ultrashort pulse system using a single-wall carbon nanotube fiber laser and similariton amplifier. A 1.0–2.2 μ m octave-spanning coherent supercontinuum was successfully generated. Next, by use of a stabilized fiber laser comb system as the seed pulse, an octave spanning SC comb was demonstrated. An octave spanning, highly coherent comb with high flatness was generated with normally dispersive highly nonlinear fiber. The characteristics of the generated supercontinuum comb were examined via balanced heterodyne beat measurements with stable continuous-wave laser diodes. The SC comb was confirmed to have high coherence and low amplitude noise at the observed wavelengths. Finally, the SC generation in two kinds of highly nonlinear fibers with different dispersion properties and the characteristics of the generated comb were examined. The dependence on fiber length, wavelength, and dispersion properties were discussed.

Modified Trust Region Algorithm for Dispersion Optimization of Photonic Crystal Fibers

In this paper, a modified derivative-free surrogate-based trust region optimization algorithm is proposed for optimizing the dispersion properties of photonic crystal fibers (PCFs) for the first time to the best of our knowledge. The modal analysis of the PCF is made using the full vectorial finite difference method with perfect matched layer boundary condition. The numerical results are compared with another trust region algorithm and other metaheuristic techniques to show the strength of the reported technique. Further, the modified algorithm is also used to achieve a nearly ultra-flattened zero dispersion over a wide range of wavelengths from 1.45 $\mu {\rm{m}}$ to 1.6 $\mu {\rm{m}}$ using an index guiding soft glass PCF selectively infiltrated with a nematic liquid crystal. In order to show the strength of the reported algorithm, a highly negative flat dispersion compensation PCF is also designed over wavelength range from 1.4 $\mu {\rm{m}}$ to 1.6 $\mu {\rm{m}}$ . Such a design has a negative dispersion of −155 ± 0.5 ps/Km·nm over the studied wavelength range. The trust region algorithms show a strong potential as an efficient tool for the design and optimization of different photonic devices. Further, these algorithms can be used as powerful techniques for solving the inverse problems.

Design of ZBLAN photonic crystal fiber with nearly zero ultra-flattened chromatic dispersion for supercontinuum generation

In this paper, we present and numerically investigate Supercontinuum Generation (SCG) in ZBLAN circular lattice photonic crystal fiber with nearly zero ultra-flattened chromatic dispersion. The fiber dispersion properties are controlled by selectively liquid-filled and reduced air holes. The structure parameters have been optimized by using the fully vectorial finite-difference frequency-domain (FDFD) method combined with the perfectly matched layers (PML) boundary condition. Results indicate that a nearly zero ultra-flattened chromatic dispersion is obtained over a broad band of 300nm centered around 1.55μm with high nonlinearity and low confinement loss. Furthermore, SCG at 1.55μm is demonstrated with the optimized design. By using a 3.2kW peak power 100fs input secant-hyperbolic pulse, a symmetrical and relatively flat supercontinuum spectrum spanning 700nm in the range of 1200–1900nm is successfully generated.

Influence of temperature on dispersion properties of photonic crystal fibers infiltrated with water

Temperature change of the water infiltrated PCF is an interesting and practical method for a dynamical fine tuning of dispersion in active dispersion shift compensating systems. In this paper we present a numerical study on the influence of the temperature of infiltrated water on the dispersion and modal characteristics of photonic crystal fiber. We study regular hexagonal lattice photonic crystal fibers with various geometrical parameters using finite element method.

Collagen Fiber Orientation and Dispersion in the Upper Cervix of Non-Pregnant and Pregnant Women.

The structural integrity of the cervix in pregnancy is necessary for carrying a pregnancy until term, and the organization of human cervical tissue collagen likely plays an important role in the tissue’s structural function. Collagen fibers in the cervical extracellular matrix exhibit preferential directionality, and this collagen network ultrastructure is hypothesized to reorient and remodel during cervical softening and dilation at time of parturition. Within the cervix, the upper half is substantially loaded during pregnancy and is where the premature funneling starts to happen. To characterize the cervical collagen ultrastructure for the upper half of the human cervix, we imaged whole axial tissue slices from non-pregnant and pregnant women undergoing hysterectomy or cesarean hysterectomy respectively using optical coherence tomography (OCT) and implemented a pixel-wise fiber orientation tracking method to measure the distribution of fiber orientation. The collagen fiber orientation maps show that there are two radial zones and the preferential fiber direction is circumferential in a dominant outer radial zone. The OCT data also reveal that there are two anatomic regions with distinct fiber orientation and dispersion properties. These regions are labeled: Region 1—the posterior and anterior quadrants in the outer radial zone and Region 2—the left and right quadrants in the outer radial zone and all quadrants in the inner radial zone. When comparing samples from nulliparous vs multiparous women, no differences in these fiber properties were noted. Pregnant tissue samples exhibit an overall higher fiber dispersion and more heterogeneous fiber properties within the sample than non-pregnant tissue. Collectively, these OCT data suggest that collagen fiber dispersion and directionality may play a role in cervical remodeling during pregnancy, where distinct remodeling properties exist according to anatomical quadrant.

Metaheuristic algorithms for dispersion optimization of photonic crystal fibers

In this paper, recent metaheuristic algorithms such as central force optimization (CFO) and particle swarm optimization (PSO) have been used for efficient calculation and optimization of the dispersion properties of photonic crystal fibers (PCFs), in an easy, efficient, and simple way. The suggested approach depends on the use of full vectorial finite difference method along with the optimization techniques for PCF dispersion optimization. The design of ultra-flattened zero dispersion PCF over a wide band of wavelengths from 1.25 to 1.6 µm is carried out in order to introduce the advantages of using these algorithms in conjunction with the numerical methods. Additionally, the CFO and PSO algorithms have a strong potential to be intriguing tools for the design and optimization of different photonic devices. Further, these algorithms prove to be powerful techniques for solving the inverse problems.

Prospective effect in dispersion properties of photonic crystal fibers by selective water-filling of holes.

Based on a simple but accurate semivectorial solution of Helmholtz's equation by the finite difference method devised with a mode-field convergence technique, we have shown an interesting and significant effect showing an almost ultraflat zero group velocity dispersion in photonic crystal fiber when the holes of the first ring of the fiber are filled with water. Crosschecking our results with earlier results involving a deeply involved multipole method for the central core of photonic crystal fiber filled with water and fused silica, our observation in the case of filling the first ring holes with water reveals potential information in studies of supercontinuum generation.

Effect of long fiber thermoplastic extrusion process on fiber dispersion and mechanical properties of viscose fiber/polypropylene composites

Viscose fiber reinforced polypropylene (PP/VF) composites were manufactured using long fiber thermoplastic (LFT) extrusion techniques with two different methods namely LFT-l and LFT-2. The compatibilizer [maleated polypropylene (MAPP)] and dispersing agent [stearic acid (SA)] were added to the PP/VF in order to improve the fiber dispersion and interfacial adhesion. The PP/VF composites manufactured using LFT-2 showed better fiber dispersion with higher tensile and flexural properties compared to the composites manufactured using LFT-1 method. Similarly, the impact strength and toughness of the LET-2 composites showed an improvement of 36 and 20% than LFT-1 whereas the average fiber length of composites was decreased from 6.9 mm to 4.4 mm because of the increase in shear energy as a result of residence time. Further, the addition of SA and MAPP to LFT-2 process has significantly improved the fiber dispersion and mechanical performance. The fiber dispersion and fracture behavior of the LFT-1 and LFT-2 composites were studied using scanning electron microscopy analysis. The Fourier transformation infrared spectra were also studied to ascertain the existence of type of interfacial bonds. Copyright © 2015 John Wiley & Sons, Ltd.