Narrow Fiber Research Articles

Interference and shadow effects in the production of light by charged particles in optical fibers

A charged particle passing through or near a narrow optical fiber induces, by polarisation, coherent light guided by the fiber. In the limit of zero crossing angle, the radiation tends towards a Cherenkov radiation with a discrete spectrum, studied by different authors. If the particle crosses a bent fiber at regularly spaced points, interference gives quasi-monochromatic lines. If the particle passes near an end of the fiber, light is produced by the capture of virtual photons through the end face. An alternative way consists in sticking a metallic ball to the fiber: the passing particle induces plasmons which are then evacuated as light in the fiber. Interferences can occur between lights from several ends or balls. Applications of these various light signals to beam diagnostics are discussed. The shadow effect, which reduces the photon yield when the particle runs parallel to a row of balls, is pointed out and an upper bound - d E / d z ≤ C ( Ze / b ) 2 for the particle energy loss is conjectured (Ze is the particle charge, b the impact parameter and C a numerical constant). This bound should also apply to other kinds of light sources, in particular to Smith–Purcell radiation.

Biodegradable polymer nanocomposites: The role of nanoclays on the thermomechanical characteristics and the electrospun fibrous structure

Polymer nanocomposites, based on poly(e-caprolactone) (PCL) and organically modified montmorillonite, were prepared by the solution intercalation technique. The thermal stability of the prepared materials was analyzed by thermogravimetric analysis. Investigation of their mechanical properties revealed that incorporation of the high aspect ratio montmorillonite sheets into the matrix significantly enhanced the polymer stiffness without sacrificing its ductility. Fibrous membranes of neat and nanocomposite PCL were fabricated by electrospinning. The effect of the applied voltage, the solution concentration and the clay content of the nanocomposite materials on the final fibrous structure was investigated. The results showed that the introduction of the inorganic filler and the increase in the applied voltage from 7.5 to 15 kV facilitated the formation of fine fibers with fewer bead defects. The presence of nanoclay resulted in narrower fiber size distributions, although the mean fiber diameter was not significantly altered. The increase in the solution concentration led to the formation of more uniform fiber structures and to a slight increase in the mean fiber diameter. Furthermore, the electrospinning process affected significantly the structure of the nanocomposite material by increasing the interlayer spacing of the inorganic mineral.

A dual wavelength distributed-feedback fiber laser

An approach to accessing air holes in a structured optical fiber with a distributed-feedback (DFB) laser based on higher order mode lasing is proposed and demonstrated. A narrow linewidth DFB fiber laser is fabricated in rare-earth-doped structured optical fiber. A higher order mode is shown to lase. Dual laser operation in both fundamental and higher order modes is also achieved. Numerical simulation of the mode profiles within the fiber using the adjustable boundary conditions-Fourier decomposition method supports the experimental results. Laser performance for each mode is characterized including imaging the emission of pump and lasing mode intensity profiles.

Microscopic, Morphometric and Ultrastructural Analysis of Anastomotic Healing in the Intestine of Normal and Diabetic Rats

The purpose of this study was to investigate if experimental alloxanic diabetes could cause qualitative changes in intestinal anastomoses of the terminal ileum and distal colon in rats, as compared to controls. 192 male Wistar rats, weighing +/-300 g were split into four experimental groups of 48 animals each, after 3 months of follow-up: a control group with ileum anastomoses (G1), a control group with colon anastomoses (G2), a diabetic group with ileum anastomoses (G3) and a diabetic group with colon anastomoses (G4). Animals were evaluated and sacrificed on days 4, 14, 21 and 30 after surgery, and fragments of the small and large intestine where the anastomoses were performed were removed. Samples from 6 animals from each sacrifice moment were submitted to ultrastructural analysis of the collagen fibers using a scanning electron microscope and samples from another 6 animals were submitted to histopathology and optical microscopy studies using picrosirius red-staining. Histopathological analysis of picrosirius red-stained anastomosis slides using an optical microscope at 40x magnification showed that the distribution of collagen fibers was disarranged and also revealed a delay in scar tissue retraction. The morphometric study revealed differences in the collagen filled area for the ileum anastomoses 14 days post surgery whereas, in the case of colon anastomoses, differences were observed at days 4 and 30 post surgery, with higher values in the diabetic animals. Ultrastructure analysis of the ileum and colon anastomoses using a scanning electron microscope revealed fewer wide collagen fibers, the presence of narrower fibers and a disarranged distribution of the collagen fibers. We conclude that diabetes caused qualitative changes in scar tissue as well as in the structural arrangement of collagen fibers, what could explain the reduced wound strength in the anastomosis of diabetic animals.

Polarization‐dependent gain and state of polarization effects on linewidth of semiconductor fiber ring lasers

AbstractLinewidth measurements of a tuneable, high power, narrow linewidth semiconductor fiber ring laser are presented. The laser had a typical output power of 9.72 dBm with a corresponding 170 kHz FWHM and 311 kHz 20‐dB linewidth. We demonstrate experimentally the dependence of laser's linewidth on SOP of the lasing light and polarization‐dependent gain of semiconductor gain medium. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 31–34, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22984

Switchable triple-wavelength erbium-doped fiber laser using a single fiber Bragg grating in polarization-maintaining fiber

A stable and narrow wavelength spacing multiwavelength erbium-doped fiber laser is proposed and demonstrated. The laser can produce simultaneous dual- and triple-wavelength lasing oscillations with a narrow wavelength spacing of less than 0.1 nm via using a single fiber Bragg gratings written in polarization-maintaining (PM) fiber. By adjusting polarization controller, the wavelength spacing of dual-wavelength lasing oscillations can be tuned to as small as 0.032 nm. The maximum amplitude variation for every lasing wavelength is less than 0.5 dB. The room-temperature operation principle is based on the polarization hole burning and deeply saturated effect in an ordinary erbium-doped fiber ring laser (EDFRL). The laser has the advantages of simple all-fiber configuration, low cost, high stability and operating at room temperature.

Predation by Bdellovibrio bacteriovorus HD100 requires type IV pili.

Early electron microscopy and more recent studies in our laboratory of Bdellovibrio bacteriovorus cells indicated the presence of narrow fibers at the nonflagellar pole of this unusual predatory bacterium. Analysis of the B. bacteriovorus HD100 genome showed a complete set of genes potentially encoding type IV pili and an incomplete gene set for Flp pili; therefore, the role of type IV pili in the predatory life cycle of B. bacteriovorus HD100 was investigated. Alignment of the predicted PilA protein with known type IV pilins showed the characteristic conserved N terminus common to type IVa pilins. The pilA gene, encoding the type IV pilus fiber protein, was insertionally inactivated in multiple Bdellovibrio replicate cultures, and the effect upon the expression of other pilus genes was monitored by reverse transcriptase PCR. Interruption of pilA in replicate isolates abolished Bdellovibrio predatory capability in liquid prey cultures and on immobilized yellow fluorescent protein-labeled prey, but the mutants could be cultured prey independently. Expression patterns of pil genes involved in the formation of type IV pili were profiled across the predatory life cycle from attack phase predatory Bdellovibrio throughout the intraperiplasmic bdelloplast stages to prey lysis and in prey-independent growth. Taken together, the data show that type IV pili play a critical role in Bdellovibrio predation.

Fine structure of decametric type II radio bursts

We have performed a comparative analysis of the fine structure of two decametric type II bursts observed on July 17 and August 16, 2002, with the 1024-channel spectrograph of the UTR-2 radio telescope in the frequency range 18.5-29.5 MHz and with the IZMIRAN spectrograph in the frequency range 25-270 MHz. The August 16 burst was weak, ∼ 2-5 s.f.u., but exhibited an unusual fine structure in the form of broadband fibers (∆fe > 250-500 kHz) that drifted at a rate characteristic of type II bursts and consisted of regular narrow-band fibers (∆fe > 50-90 kHz at 24 MHz) resembling a fiber bundle. The July 17 burst was three orders of magnitude more intense (up to 4500 s.f.u. at 20 MHz) and included a similar fiber structure. The narrow fibers were irregular and shorter in duration. They differed from an ordinary fiber bundle by the absence of absorption from the low-frequency edge and by slow frequency drift (slower than that of a type II burst). Both type II bursts were also observed in interplanetary space in the WIND/WAVES RAD2 spectra, but without any direct continuation. Analysis of the corresponding coronal mass ejections (CMEs) based on SOHO/LASCO C2 data has shown that the radio source of the type II burst detected on August 16 with UTR-2 was located between the narrow CME and the shock front trailing behind that was catching up with the CME. The July 17 type II fiber burst also occurred at the time when the shock front was catching up with the CME. Under such conditions, it would be natural to assume that the emission from large fibers is related to the passage of the shock front through narrow inhomogeneities in the CME tail. Resonant transition radiation may be the main radio emission mechanism. Both events are characterized by the possible generation of whistlers between the leading CME edge and the shock front. The whistlers excited at shock fronts manifest themselves only against the background of enhanced emission from large fibers (similar to the continuum modulation in type IV bursts). The reduction in whistler group velocity inside inhomogeneities to 760 km s −1 may be responsible for the unusually low drift rate of the narrow fibers. The magnetic field inside inhomogeneities determined from fiber parameters at 24 MHz is ∼0.9 G, while the density should be increased by at least a factor of 2.

Fine Structure of Solar Radio Bursts Observed at Decametric and Hectometric Waves

The analysis of WIND/WAVES RAD2 spectra with fine structure in the form of different fibers in 14 events covering 1997 - 2005 is carried out. A splitting of broad bands of the interplanetary (IP) type II bursts into narrow band fibers of different duration is observed. The instantaneous-frequency bandwidth of fibers is stable: 200 - 300 kHz for slow-drifting fibers in type II bursts, and 700 - 1000 kHz for fast-drifting fibers in type II + IV (contin- uum). Intermediate drift bursts (IDB or fiber bursts) and zebra patterns with variable fre- quency drift of stripes, typical for the metric range, were not found. Comparison of spectra with the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph (SOHO/LASCO C2) images shows a connection of the generation of the fiber structures with the passage of shock fronts through narrow jets in the wake of Coronal Mass Ejec- tions (CME). Therefore the most probable emission mechanism of fibers in IP type II bursts appears to be resonance transition radiation (RTR) of fast particles at the boundary of two media with different refractive indices. The same mechanism is also valid for striae in the type III bursts. Taking into account a high-density contrast in the CME wake and the actu- ally observed small-scale inhomogeneities, the effectiveness of the RTR mechanism in IP space must be considerably higher than in the meter or decimeter wavelengths. For the most part the fibers in the type IV continuum at frequencies of 14 - 8 MHz were seen as the direct expansion of similar fine structure (as fibers or "herringbone" structure) in the decametric range observed with the Nancay and IZMIRAN spectrographs.

502 Watt, single transverse mode, narrow linewidth, bidirectionally pumped Yb-doped fiber amplifier

High power operation of narrow linewidth optical fiber amplifiers is usually limited by the onset of stimulated Brillouin scattering. In this paper, we present results demonstrating over 500 Watts of power in a single mode beam from a fiber designed to suppress stimulated Brillouin scattering through a reduction in the overlap of the optical and acoustic fields. Simulations demonstrate the potential for this fiber to achieve greater than 1000 Watts of output power.

Isometric contraction of microvascular pericytes from mouse brain parenchyma

Pericytes were isolated and cultured from mouse cerebroparenchymal microvessels. A single pericyte clone was three-dimensionally cultured in a collagen gel by adding tensile stress, resulting in the reconstruction of narrow stringy fibers. When the contractility of these fibers was evaluated isometrically, they contracted in response to acetylcholine (ACh) 1 or noradrenaline; this was accompanied by an increase in intracellular calcium concentration ([Ca 2+] i). The fibers that were pre-contracted by ACh were completely relaxed by papaverine, which is a smooth-muscle relaxant. Moreover, the muscarinic ACh receptor-antagonist atropine depressed the [Ca 2+] i response that was induced by ACh. This study demonstrates for the first time the quantitative measurement of the contractions produced by cultured microvascular pericytes from mouse brain parenchyma.

Effects of fiber compression and length distribution on the flexural properties of short kenaf fiber‐reinforced biodegradable composites

AbstractThe effects of the fiber compression and the length distribution on the flexural properties of short kenaf fiber‐reinforced biodegradable composites were investigated. Two types of kenaf (KU and KT) that were different in the density and the length distribution were used as reinforcements. These fibers were mixed with a corn–starch‐based resin, and the composite specimens were fabricated by a hot press forming. The flexural modulus in the KU specimens was not different from that in the KT, despite the difference of the fiber Young's modulus (KU 14.5 GPa and KT 22.1 GPa). This was because the KU was compressed more than the KT in the composite specimen because of the lower density structure. However, in the longest fiber (10.5 mm), the flexural strength in the KT specimens was considerably higher by 67% than that in the KU. The reason was that the KT did not include the fibers below the critical length (4.2 mm) because of the narrower fiber distribution than the KU. In fact, the flexural strength in the KT specimen significantly decreased with decrease in the average fiber length, which included the fibers below the critical length. Moreover, the flexural modulus agreed well with the calculated values by Cox's model that incorporated the effect of the fiber compression. POLYM. COMPOS. 27:170–176, 2006. © 2006 Society of Plastics Engineers

Formation of Unstabilized and Yttria Stabilized ZrO2 Fibers from a Suspension of Monodispersed ZrO2

Unstabilized and yttria stabilized ZrO2 fibers were prepared from a monodispersed ZrO2 particles derived from hydrolysis of Zr(OBu)4. Unstabilized ZrO2 fibers with 71 to 151 μm of width and yttria stabilized ZrO2 fibers with 96 to 214 μm of width, were formed by drying the ethanol suspension of monodispersed ZrO2 particles with 116 nm in mean diameter. The morphology of the ZrO2 fibers were plate like and consisted of densely packed ZrO2 nano particles. The preparation conditions affected the fiber width. This was due to the lower concentration of ZrO2 particles in suspension, or the higher drying temperatures, which gave the narrower fiber width. The mean particle size of the 5 mol% Y2O3 doped ZrO2 fiber heat treatment at 1473 K was 0.14 μm and the fiber showed 11.0 GPa on the Vickers Hardness Test.

Rapid wavelength-swept spectrally encoded confocal microscopy

Spectrally encoded confocal microscopy (SECM) is a technique that allows confocal microscopy to be performed through the confines of a narrow diameter optical fiber probe. We present a novel scheme for performing SECM in which a rapid wavelength swept source is used. The system allows large field of view images to be acquired at rates up to 30 frames/second. Images of resolution targets and tissue specimens acquired ex vivo demonstrate high lateral (1.4 mum) and axial (6 mum) resolution. Imaging of human skin was performed in vivo at depths of up to 350 mum, allowing cellular and sub-cellular details to be visualized in real time.

Experimental investigation of adhesive meltblown web production using accessory air

Using a low-melting-point polymer, copolyamide, as raw material, adhesive meltblown webs were formed on the ordinary melt-blowing line by using the accessory air and the accessory air chamber. The webs thus produced exhibit narrower fiber diameter distribution and a more uniform pore structure. At the same time, four main melt-blowing parameters, the primary air pressure, the accessory air pressure, the melt throughput rate, and the die-to-collector distance, are discussed in terms of their influence on geometric mean diameter of fibers and fiber diameter distribution. POLYM. ENG. SCI., 46:1–7, 2006. © 2005 Society of Plastics Engineers

Yb3+doped double-clad fiber laser based on fiber Bragg grating

Fiber Bragg grating (FBG) was successfully fabricated in a Yb3+ doped double clad fiber with D-shaped inner-cladding by using phase mask method. Based on the FBG, a stable narrow line width double clad fiber laser was successfully demonstrated which resolved the output instability caused by mode-competition in common double-clad fiber lasers. The maximum output power is 570?mW at the wavelength 1058.2nm with 0.196nm line-band. Based on rate equations, the relationship between output power and pump power, the reflectivity of the FBG and the optimized length of the fiber were analyzed, which were in good agreement with the experimental results.

Development of gelatinous (reaction) fibers in stems of Gnetum gnemon (Gnetales)

In extraxylary tissues of the stem Gnetum gnemon produces gelatinous fibers that can also function as reaction or tension fibers. These gelatinous fibers occur in all axes in the outer cortex and in displaced axes progressively in the middle and inner cortex and finally in the secondary phloem. Early cell differentiation in the cortex produces initials of laticifers that are unique in gymnosperms. Subsequently narrow fibers differentiate from cells that undergo both extensive passive elongation, as a result of internodal elongation, together with their active apical intrusive growth. Outer fibers always complete secondary wall development and become an important mechanical component of stems. Differentiation of fiber initials continues in the middle and inner cortex, but secondary wall formation can only be determined by a gravimorphic stimulus that produces eccentric development of fibers. Further eccentric development of fibers then continues in the outer secondary phloem from dedifferentiated phloem parenchyma cells that initially undergo extensive intrusive growth. All such cells have characteristic features of tension fibers of angiosperms. They exhibit a pronounced purely cellulosic innermost layer of the secondary wall (Sg layer). In addition, fiber initials are coenocytic, including up to eight nuclei that become distributed uniformly throughout the length of the cell. Mature macerated fibers are markedly brittle, making accurate length measurements difficult. Although cytologically uniform, these fibers thus originate from two kinds of initial (primary and secondary). They also differ in their response to a gravimorphic stimulus determined by their times of inception and their eccentric location. These cells show a suite of positional and gravimorphic responses that illustrate the complexity of plant cell differentiation.

A feedback-injected Fabry–Perot laser diode filtering technique for side-mode suppression and linewidth reduction of erbium-doped fiber lasers

By adding a fiber-pigtailed Fabry–Perot laser diode (FPLD) into a close-loop erbium-doped fiber amplifier (EDFA) ring cavity, and feedback-injecting the FPLD biased at just below threshold and the EDFA each other via directional couplers, we demonstrate a low-cost band-pass filtering technique for constructing narrow linewidth erbium-doped fiber laser (EDFL) with ultrahigh side-mode suppression ratio (SMSR). Under an output coupling ratio of 90%, the mutually injection-locked EDFL–FPLD link exhibits a maximum output power and SMSR of up to 98.6 mW and 49.6 dB at wavelength 1561.37 nm, respectively. Wavelength tuning of up to 6 nm can be achieved by tuning the temperature and fine adjusting the below threshold driven current of FPLD. The minimum spectral linewidth at 3dB-decay of as small as 0.017 nm measuring by commercial optical spectrum analyzer with limited resolution bandwidth of 0.01 nm are observed. The stabilities in power, SMSR, peak wavelength of ±0.01 mW, ±0.5 dB, and ±0.025 nm, respectively, are also determined.

Attenuating PP/PET bicomponent melt blown microfibers

AbstractThis research investigated the attenuation of polypropylene (PP)/poly(ethylene terephthalate) (PET) bicomponent (bico) filaments during the melt blowing (MB) process. It was found that both mono‐ and bi‐component filaments attenuated from several hundred micrometers to a few micrometers in the first 5 centimeters from the die. However, fiber diameter distributions were found to be broad in these regions. The filaments were attenuated much slower but exhibited narrower diameter distributions as they moved further from the die. The diameters of bico MB filaments were between those of 100% PP and 100% PET filaments. The PET component in a bico filament controls the final fiber diameter. During melt blowing, filaments were aligned orderly with the airflow direction in a short distance near the die. Filament entanglements started at about 2.5 cm from the die and became more and more randomly oriented as the distance‐from‐the‐die (DFD) increased. The fiber diameter distribution of bico filaments was broader than that of 100% PP filaments. A higher airflow rate led to a narrower fiber size distribution for bico filaments.

Modeling and optimizing submerged hollow fiber membrane modules

AbstractThe filtration behavior of submerged hollow fiber membranes with constant permeate flow operational mode was modeled on two different conditions: the maximum initial flux along the fiber is smaller than the critical flux (Jimax < Jcr); the maximum initial flux along the fiber is greater than the critical flux, but the averaged imposed flux is smaller than the critical flux (Jimax > Jcr but Jmi < Jcr). When the maximum initial flux along the fiber is lower than the critical flux, no particle deposition occurs and the flux distribution can be characterized by a dimensionless parameter ξ = 4LRR. On the other hand, for Jmi < Jcr and Jimax > Jcr, a steady state can be achieved after some initial deposition. The theoretical model shows that the filtration resistance caused by the initial deposition can be affected by Jmi/Jcr and fiber characteristics (L, Ri and Rm) and becomes significant for narrow and long fibers with a high Jmi/Jcr. The models were also used to determine the optimal fiber length and radius for the submerged hollow fiber module. The simulation suggests that the optimal fiber lumen radius for fiber lengths of 0.5–3 m is 0.2–0.35 mm. These results should be relevant to the design of submerged hollow fiber modules.