Optical properties of dual-core hollow waveguides

A new type of hollow glass waveguide has been fabricated that transmits radiation from visible to infrared wavelengths with low loss. The broadband transmission is achieved with a structure consisting of two distinct core regions; a silica annulus for transmission of wavelengths from 0.3 to 2.0 μm and a hollow core for transmission from 2.0 to 12.0 μm. Losses in the silica core at 633 nm are 0.3 dB/m. Losses in the 575-μm bore hollow core at 10.6 μm are 0.6 dB/m. Bending loss is negligible for radiation transmitted in the solid silica core, whereas the hollow guide loss exhibits a 1/R dependence. The dual-core waveguide can transmit broadband radiation, is rugged and flexible, and therefore, is a good candidate for medical or sensor applications.     

Loss and modal properties of Ag/AgI hollow glass waveguides

Hollow glass waveguides, composed of Ag/AgI coatings, have been studied at 10.6 μm. The losses for different bore sizes equal the theoretical loss, which for the 700 μm bore guide was about 0.15 dB/m. The losses for the guides increase upon bending, varying linearly with increasing curvature. These hollow guides propagate a single mode when the bore size of the guide is approximately 30λ. In addition, the best single-mode transmission is obtained when the thickness of the glass wall is large. These smaller bores, thick wall hollow guides, can also be used to filter higher order modes from poor quality input laser beams.     

Measurements of absorption coefficients using noncontact fiber-optic laser calorimetry

A noncontact laser calorimetric method for low absorption-coefficient measurements of various optical materials is proposed. For temperature monitoring of the samples, silver halide fiber radiometry is utilized. The capability of this technique is demonstrated by the measurement of the absorption coefficients of fused-quartz rods at 500 nm (Ar laser radiation) and of mixed silver halide crystals and fibers at 10.6 μ;m (CO(2) laser radiation). Good agreement with ordinary laser calorimetry is obtained.     

Preparation of silicon carbide whiskers from silicon nitride

Silicon carbide whiskers have been prepared by sintering silicon nitride powder in a graphite reactor at 1800°C under a nitrogen atmosphere. The whiskers differ in morphology: tubular needles, hollow faceted fibers with a square cross section, and solid fibers with a triangular cross section. The average diameter of the needles is 0.5?5 μm, and that of the faceted fibers is up to 20 μm. The fibers range in length up to several millimeters. Such silicon carbide whiskers can be used as reinforcing agents for structural ceramics based on nonoxide materials.     

Optical properties of hydrogenated hard carbon thin films

Hydrogenated amorphous carbon (a-C:H) films were deposited onto glass, silicon and germanium substrates. The films are transparent in the IR and are extremely hard (Mohs' hardness of about 8). The a-C:H coatings were prepared in an r.f.-excited discharge sustained by various hydrocarbon gases.The thickness, density, refractive index (at 0.3 μm and 2–10 μm) and relative hydrogen content were determined. Variations in the IR refractive index and the relative hydrogen content could be correlated with the deposition conditions. With a refractive index of approximately 2 a-C:H is an ideal antireflection coating for germanium (n = 4).Laser calorimetric measurements of optical absorption at 10.6 μm give a loss as low as 3% for a coating 1.3 μm thick on germanium (λ/4 for n = 2 at 10.6 μm).     

空心微球/环氧树脂复合泡沫塑料的抗压性能与破坏机制

以环氧树脂为基体, 不同粒径空心玻璃微球为填充体, 制备了轻质高强复合泡沫塑料。通过单轴准静态压缩试验研究了空心微球的粒径大小对复合泡沫塑料的抗压性能的影响, 并采用SEM对复合泡沫塑料的微观结构进行观测。通过随机空间分布法建立了空心玻璃微球/环氧树脂复合泡沫塑料的实体模型, 并且使用有限元分析软件对复合泡沫塑料在1 kPa载荷下的应力分布进行了分析。结果表明, 在相同体积含量下, 当空心微球的粒径从30 μm增大到120 μm时, 复合泡沫塑料的抗压强度无明显变化。有限元分析的结果表明, 在复合泡沫塑料中主要承载部分为空心微球, 空心微球上的应力大于树脂基体上的应力。最大应力分布在空心微球的内壁, 结合SEM图像可推测, 空心微球在破裂之前受到充分的挤压, 并且从内壁产生裂纹。     

Experimental evaluation of a hollow glass fiber

Very high interest in making a low-loss fiber for the infrared has been stimulated by important applications in optical communication, surgery, cutting, welding, and heat treatment. The leaky waveguide is one of the most promising types of future fiber in the infrared region where low-loss materials are not available or not suitable for making fibers (i.e., CO2 laser light lambda = 10.6 microm). In this paper a comparative model of a He-Ne laser beam and an oxide glass leaky hollow fiber for a CO2 laser light beam and a chalcogenide glass leaky hollow fiber are studied. Measurements of attenuation, dependence of output power on diameter and angle, and the angular dependence of output angle vs input angle were made. The experimental data were compared with theoretical calculations, and the critical value of the wall thickness for minimum attenuation is given.     

Gradually tapered hollow glass waveguides for the transmission of CO2 laser radiation

Hollow glass waveguides with bores tapered from 1000 to 500 microm and from 700 to 500 microm over a length of 2 m were coated with silver and silver iodide inner films. These waveguides were designed for low attenuation at the 10.6-microm CO2 laser wavelength. The straight losses, which were measured to be 0.8 and 1.6 dB/m, respectively, decreased when the guides were bent. A simple ray-trajectory model is presented to explain this unexpected behavior.     

High-purity As-S-Se and As-Se-Te glasses and optical fibers

We describe a procedure for the preparation of As-S-Se and As-Se-Te glasses with low contents of gas-forming impurities (hydrogen, oxygen, and carbon) via melting of extrapure-grade elements in an evacuated silica ampule and purification of the melt by chemical distillation. The impurity concentrations in the glasses thus prepared have been reduced to the following levels: hydrogen, <0.02; oxygen, 0.2; carbon, <0.02; silicon, <0.4 ppm by weight. Using the double-crucible method, we have fabricated glass fibers with various ratios of the core and cladding diameters (1: 25 to 9: 10), protected with a tetrafluoroethylene/1,1-difluoroethylene copolymer coating, which have an average bending strength of 0.5–1 GPa. The minimal optical losses are 150 dB/km at 6.6 μm in multimode As-Se-Te glass fibers and 60 dB/km at 4.8 μm in As-S-Se glass fibers. The effect of microinhomogeneities in the melt on the optical performance of arsenic sulfoselenide glass fibers fabricated by the double-crucible method is examined.     

Elaboration of aluminum-matrix composite materials reinforced with inorganic fibers

This article is a literature survey concerning the different methods presently known for producing fiber-reinforced aluminum-matrix composites. The elaboration problems are discussed in terms of wettability between aluminum or aluminum alloys and inorganic fibers. The fibers involved are continuous monofilaments about 100 μm diameter such as boron or silicon carbide fibers, and tows of 500–6000 endless thinner filaments 5–15 μm as graphite fibers, alumina fibers and Nicalon silicon carbide fibers. The typical mechanical properties (strength, modulus, fatigue) attained with these reinforcing fibers are also reported.     

The Neck to Particle Ratio Effect on the Mechanical and Morphological Sintering Features of Porous Stainless Steel (SS) Hollow Fibers

The SS hollow fibers are prepared by extruding a mixture of SS particles and a polymeric binder in a phase inversion process followed by sintering at various temperatures (950–1100 °C), resulting in the formation of void structures with a finger‐like inner shell and a sponge‐like outer shell. The mechanical strength increases by over 1000% as the SS particle size decreases from D₅₀ = 32 to 4 μm, and by ≈150% as the sintering temperature increases from 950 to 1100 °C. The best mechanical strength reached is 820 MPa for the D₅₀ = 4 μm SS hollow fiber sintered at 1100 °C. The neck to particle (N/P) ratio proves to be a morphological measurement with good correlation with the mechanical properties of the SS hollow fibers. The mechanical strength increases by ≈44% (sintering effect) and ≈92% (particle size effect) from a N/P ratio of ≈0.8 to 0.9 for the smaller SS particle hollow fiber. At this ratio, the necks for the particles are in close contact and at the boundary of full coalescence, thus at the onset of fast mass transfer and grain formation/growth as diffusion increases significantly by six order of magnitude.

     

Infrared transmissive, hollow plastic waveguides with inner Ag-Agl coatings

Hollow polycarbonate waveguides with thin-film coatings of Ag-AgI were fabricated by liquid-phase chemistry methods. These hollow waveguides, which have bore sizes ranging from 500 to 2000 microm and lengths as long as 2 m, are transmissive from 2 to more than 20 microm. The lowest loss of 0.02 dB/m was obtained for a straight 2000 microm bore guide at 10.6 microm. This is to our knowledge the lowest loss measured for any IR fiber at CO2 laser wavelengths. The bending losses were found to increase as 1/R, where R is the radius of the bend. These waveguides were able to withstand 18 W of CO2 laser input power for bore sizes greater than 1000 microm.     

Numerical aperture of optical fibers based on high-purity As2S3 glass: Unsteady-state modal distribution

The numerical aperture of core-clad multimode optical fibers with the core made from high-purity As₂S₃ glass is measured by a far-field technique using a cw CO laser (5.3-6.3 μm). The lengths at which a steady-state modal distribution is reached are determined for optical fibers with metallic coatings, tetrafluoroethylene/difluoroethylene copolymer coatings, or immersion. Various factors affecting the numerical aperture of fibers with an unsteady-state modal distribution are examined.     

Design and characterization of coherent integrated fiber-optic imaging probes

An integrated fiber-optic probe comprising a short length of multimode fiber that is fusion spliced to a monomode optical fiber has been fabricated for imaging and nonimaging applications. The fiber probe, typically 250 μm in diameter, can deliver a focused Gaussian spot approximately 25 μm in diameter at a distance of approximately 500 μm from the tip. Two off-the-shelf graded-index multimode fibers have been used in the fabrication of imaging and nonimaging probes. These integrated probes have considerably improved the spatial resolution of backscatter lensless fiber probes being utilized in the dynamic light-scattering characterization of colloidal suspension.     

M型锶铁氧体中空纤维的制备和表征

以柠檬酸和金属盐为原料,采用有机凝胶先驱体转化法制备了M型锶铁氧体（SrFe₁₂O₁₉）中空纤维. 通过FTIR、TG/DSC、XRD、SEM和VSM等技术对所得纤维进行了表征. 结果表明,凝胶的可纺性与其化学组成和pH值有关,当柠檬酸与金属离子的摩尔比为1.5∶1.0,pH=4.2左右时,凝胶的可纺性最好. 经1100℃焙烧后,制备的M型锶铁氧体中空纤维具有较大的长径比,直径可小于1μm,中空孔径约为纤维直径的一半,组成纤维的晶粒形貌为六角片状,晶粒尺寸为236nm,在室温下的饱和磁化强度为53.5A·m²/kg,矫顽力为386.96kA/m. 纤维显示出一定的形状各向异性,当定向排列的纤维平行和垂直磁场时,矫顽力分别为391.66和358.72kA/m.     

Attenuation measurement of infrared optical fibers by use of a hollow-taper-based coupling method

An alternative method for attenuation measurement of infrared (IR) fibers is described. The method includes a simple technique for direct laser-to-fiber coupling with an uncoated glass hollow taper. The operating principle of the hollow taper is based on the grazing-incidence effect of light reflection. The hollow taper forms a smooth Gaussian-shaped profile of the output laser emission and provides the proper conditions for equilibrium-mode distribution of optical power within the test IR fibers. The experimental hollow-taper-based coupling method is used for measurement of attenuation and bending losses of various kinds of IR fiber, including solid-core (fluoride, chalcogenide, and germanium-doped) and hollow fibers.     

Synthesis and in vitro bioactivity of novel mesoporous hollow bioactive glass microspheres

The remarkable tissue-repairing bioactivity and biocompatibility of bioactive glass make it suitable for a wide range of applications. Here, novel mesoporous hollow bioactive glass microspheres (MHBGMs) with a uniform diameter range of 2-5 µm were prepared by a sol-gel method. Structural characterization indicated that the shell of hollow sphere had a mesopore size range between 2 and 10 nm and a thickness about 500 nm. The in vitro bioactivity test indicated that the novel structure exhibited high in vitro bioactivity. The uniform microspherical morphology and mesoporous hollow structure of MHBGMs, together with their high bioactivity, turn them into a good candidate as an injectable and drug-loading biomaterial for in vivo tissue regeneration and drug control release.     

Computing Fibers: A Novel Fiber for Intelligent Fabrics?

This communication describes a possible path for transition from a wearable computer to a fiber computer in which digital processing power is integrated directly into textiles via circuits on individual fibers. Three different classes of computing fiber substrate (active, passive, and intermediate) are discussed and some technologies for their manufacture are reviewed. It is shown here that with two of these techniques it is possible to develop new substrates for the semiconductor industry. Using an silicon‐on‐insulator (SOI) process, polycrystalline silicon fibers with a length of 42 mm have been successfully produced at NMRC in Ireland. These fibers are 35 μm wide and 1 μm thick. Silicon carbide (SiC) and silicon dioxide (SiO₂) endless fibers (subsequently cut in to 20 cm lengths) have also been produced by extrusion. After sintering, this method yielded polycrystalline SiC fibers and pure amorphous SiO₂ glass fibers. For many future applications, fiber computing appears to be a possible key to success. The computing power offered by such fibers may be combined with additional in‐ and output functions by weaving fiber‐based sensors and piezoelectric materials into textiles.     

Abriebschutzbeschichtung von Kunststoffen durch plasmaaktivierte Hochratebedampfung. Abrasion Resistant Coatings on Plastics by Plasma Activated High Rate Deposition

Transparent plastics, e.g. PMMA or Polycarbonate, have low weight, optical clarity and processing benefits of a thermoplastic. A great disadvantage of such plastics is the lack of abrasion resistance. Therefore the plastics have to be protected for practical application. SiO₂ layers perform very well as clear abrasion resistant layers. The typical layer thickness ranges from 1 μm to 6 μm depending on the required abrasion resistance. To get an abrasion resistance comparable to float glass a layer thickness of about 6 μm for SiO₂ layers is needed. The layers are deposited by the HAD‐process (hollow cathode activated deposition). There the coating material is evaporated by an electron beam and is deposited on the substrate by adding reactive gases (e.g. O₂, N₂O or organic monomers) at the presence of an intensive plasma. A special hollow cathode, adapted to this process, is used as plasma source. The typical deposition rates are 300 nm/s to 600 nm/s for the deposition of SiO₂.     

Effect of short glass fibers on the mechanical properties of cast ZA-27 alloy composites

This paper aims to study the effects of short glass fiber reinforcement on the mechanical properties of cast ZA-27 zinc alloy composites containing glass fibers of content ranging from 0% to 5% by weight. The composites were fabricated using the ‘compocasting’ method in which the short glass fibers were introduced into the vortex created in the molten alloy through an impeller rotated at 500 rev./min. The molten mass was thoroughly stirred, poured into permanent moulds and squeeze-cast under pressure. The results of this study revealed that as glass fiber composition was increased, there were significant increases in the ultimate tensile strength (UTS), hardness and Young's modulus, accompanied by a reduction in its ductility and impact strength. An attempt is made in this article to provide explanations for these phenomena.