Effects of different acetylene/nitrogen ratios on characteristics of carbon coatings on optical fibers prepared by thermal chemical vapor deposition

The effects of C₂H₂/(C₂H₂ + N₂) ratios on the characteristics of carbon coatings on optical fibers prepared by thermal chemical vapor deposition are investigated. The C₂H₂/(C₂H₂ + N₂) ratios are set to 60, 70, 80, 90, and 100%. Additionally, the deposition temperature, working pressure, and mass flow rate are 1003 K, 133 kPa, and 40 sccm, respectively. The deposition rate, microstructure, and electrical resistivity of carbon coatings are measured. The low-temperature surface morphology of carbon-coated optical fibers is elucidated. Experimental results indicate that the deposition rate increases with increasing the C₂H₂/(C₂H₂ + N₂) ratio, and the deposition process is located at a surface controlled regime. As the deposition rate increases, the electrical resistivity of carbon coatings increases, while the ordered degree, nano-crystallite size, and sp² carbon atoms of the carbon coatings decrease. Additionally, the low-temperature surface morphology of the carbon coatings shows that if the carbon coating thickness is not smaller than 289 nm, decreasing the deposition rate is good for producing hermetic optical fiber coatings.     

Absorbing TiOx thin film enabling laser welding of polyurethane membranes and polyamide fibers

We report on the optical properties of thin titanium suboxide (TiO_x) films for applications in laser transmission welding of polymers. Non-absorbing fibers were coated with TiO_x coatings by reactive magnetron sputtering. Plasma process parameters influencing the chemical composition and morphology of the deposited thin films were investigated in order to optimize their absorption properties. Optical absorption spectroscopy showed that the oxygen content of the TiO_x coatings is the main parameter influencing the optical absorbance. Overtreatment (high power plasma input) of the fiber surface leads to high surface roughness and loss of mechanical stability of the fiber. The study shows that thin substoichiometric TiO_x films enable the welding of very thin polyurethane membranes and polyamide fibers with improved adhesion properties.     

Absorbing TiOx thin film enabling laser welding of polyurethane membranes and polyamide fibers

Abstract

We report on the optical properties of thin titanium suboxide (TiO_x) films for applications in laser transmission welding of polymers. Non-absorbing fibers were coated with TiO_x coatings by reactive magnetron sputtering. Plasma process parameters influencing the chemical composition and morphology of the deposited thin films were investigated in order to optimize their absorption properties. Optical absorption spectroscopy showed that the oxygen content of the TiO_x coatings is the main parameter influencing the optical absorbance. Overtreatment (high power plasma input) of the fiber surface leads to high surface roughness and loss of mechanical stability of the fiber. The study shows that thin substoichiometric TiO_x films enable the welding of very thin polyurethane membranes and polyamide fibers with improved adhesion properties.     

Influence of depth of intermediate layer on optical power distribution in W-type optical fibers

For different depth and width of the intermediate layer, a power flow equation is used to calculate spatial transients and steady state of power distribution in W-type optical fibers (doubly clad fibers with three layers). A numerical solution has been obtained by the explicit finite difference method. Results show how the power distribution in W-type optical fibers varies with the depth of the intermediate layer for different values of intermediate layer width and coupling strength. We have found that with increasing depth of the intermediate layer, the fiber length at which the steady-state distribution is achieved increases. Such characterization of these fibers is consistent with their manifested effectiveness in reducing modal dispersion and improving bandwidth.     

The diffusion of water in optical fibers

The diffusion of “water” (OH) into the core of optical fibers can affect the transmission properties. An increase in the water will result in an increased loss of high order modes, a reduction in numerical aperture, and increased microbending losses if there is coupling to these higher order modes. An extra 10ppm OH uniformly distributed through the core would produce 12dB/km loss at 0.95μm and about 1dB/km loss at 0.90μm.Based on the extrapolation of existing diffusion coefficient measurements and solubility data, calculations are made for the diffusion of atmospheric H₂O through the cladding into the core and also for the diffusion of OH from the cladding into the core. Diffusion can occur fairly rapidly during the high temperatures reached when depositing, collapsing, and drawing the fibers, and also slowly during extended period ambient temperature storage and use.     

Propagation characteristics of Gaussian beams through a paraxial ABCD optical system with an annular aperture

By introducing a hard aperture function into a finite sum of complex Gaussian functions, an approximate analytical expression for a Gaussian beam passing through a paraxial ABCD optical system with an annular aperture has been derived. The results could be reduced to the case of circular black screen or circular aperture. Some numerical simulations are also performed and illustrated for the propagation characteristics of a Gaussian beam through a paraxial ABCD optical system with an annular aperture, a circular black screen or a circular aperture.     

High-Purity As2S1.5Se1.5 Glass Optical Fibers

Core–clad optical fibers were fabricated from high-purity As₂S_1.5Se_1.5 glass, and their properties were studied. The arsenic sulfo-selenide was prepared by melting a mixture of high-purity arsenic monosulfide, arsenic, and selenium. Optical fibers with core/clad diameters of 300/400 and 200/400 m were fabricated by the double-crucible method. The minimum loss was found to be 60 ± 20 dB/km at 4.8 m and 200–300 dB/km between 4 and 6 m. The numerical aperture of the fibers was 0.28. A 1.5-m-long section of the fiber transmitted 6-W CO laser radiation. The average bending strength of the 400-m-diameter fibers was 0.8 GPa.     

Characteristics of carbon coatings on optical fibers prepared by radio-frequency plasma enhanced chemical vapor deposition with different H2/C2H2 ratios

Characteristics of carbon coatings on optical fibers prepared by radio-frequency plasma enhanced chemical vapor deposition with different H₂/C₂H₂ ratios are investigated. Five kinds of carbon coatings are prepared with H₂/C₂H₂ ratios of 2, 4, 6, 8, and 10. Experimental results show that the deposition rate and surface roughness of carbon coatings decrease as the H₂/C₂H₂ ratio increases. When the H₂/C₂H₂ ratio changes from 2 to 8, the increase of H₂/C₂H₂ ratios detrimentally yields sp³ carbon atoms and sp³-CH₃ bonds in the carbon coatings. However, when the H₂/C₂H₂ ratio exceeds 8, the hydrogen retards the growth of the graphite structure. Moreover, the redundant hydrogen radicals favor bonding with the dangling bonds in the coating surface. Therefore, when the H₂/C₂H₂ ratio increases from 8 to 10, the amounts of sp³ carbon atoms and sp³-CH₃ bonds in the carbon coatings increase. At an H₂/C₂H₂ ratio of 8, the carbon coating exhibits excellent water-repellency and thermal-loading resistance, and so this ratio is the best for producing a hermetically sealed optical fiber coating.     

HL-2A托卡马克装置CXRS光学系统设计

电荷交换复合谱(CXRS)是一项先进的测量托卡马克等离子体温度及空间分布的方法。针对我国HL-2A托卡马克装置上CXRS光谱采集系统对宽光谱范围(470?660nm)、大视场(535.34mm)、宽光束(直径110mm)、高空间分辨(14道)以及与后续导光光纤数值孔径(0.22)匹配等要求,应用ZEMAX光学设计软件优化设计了一片反射镜与四片透镜组合的光学系统,并通过将像面倾斜的方法进一步减小了像差。模拟计算表明像面最大弥散斑RMS半径为88.14?m,像方数值孔径0.217,很好地满足了使用需要。     

光纤结构参数对亚毫米沟槽装药爆速测试的影响研究

为了对亚毫米尺度SY共晶沟槽装药的爆速进行测试,采用光纤探针法设计了爆速测试系统,得到的信号稳定可靠,表明光纤探针法用于亚毫米沟槽装药的爆速测试是可行的。同时,为了研究光纤结构参数对爆速测试的影响,采用了3种不同结构参数的光纤进行试验。对爆速结果和信号参数进行数据分析可得:当光纤的数值孔径越大时,爆速测试的精度越高,信号的上升时间也越短,但对信号幅值基本没有影响;当光纤的芯径越大时,爆速测试的精度越高,信号的上升时间越短,信号的幅值也会增大。当光纤的数值孔径为0.22时,测试的精度最高,对应的爆速值为4.68 mm/μs,标准方差为0.12,平均相对误差为1.88%。     

Influence of numerical aperture on mode coupling in step-index plastic optical fibers

Using the power-flow equation, we have examined the state of mode coupling in step-index plastic optical fibers with different numerical apertures. Our results confirm that the coupling rates vary with the coupling coefficient of the fibers as the dominant parameter, especially in the early stage of coupling near the input fiber end. However, we show that the fiber's numerical aperture has a significant influence on later stages of this process. Consequently, equilibrium mode distribution and steady-state distribution are achieved at overall fiber lengths that depend on both of these factors. As one of our examples demonstrates, it is possible for the coupling length of a high-aperture fiber to be similar to that of a low-aperture fiber despite the three-times-larger coupling coefficient of the former.     

High Temperature Behavior of Si3N4 and Yb2SiO5 Coated Carbon Fibers for Silicon‐Nitride CMC

For oxide‐free ceramic matrix composites (CMC), with Si₃N₄ matrix and carbon fiber reinforcement, for extreme high temperature applications, protective coatings of the C‐fibers are investigated. Two different coatings are compared: reactive CVD‐derived pure Si₃N₄ coatings to investigate C‐fiber‐matrix reactions and powder based Yb‐silicate coatings to reveal potential reactions with the Yb‐silicate additive serving as sintering aid for Si₃N₄. The reactivity toward carbon in nitrogen atmosphere is studied in the temperature interval from 20 °C up to 1700 °C. A new ceramic phase – an Yb‐carbido‐nitiridosilicate, Yb₂Si₄CN₆–is found as product of carbothermal reduction of the Yb‐silicate. The carbothermal reduction occurs also with other RE‐silicates, RE = Yb, Er, Y, Gd, and Sm while SiC is found as reaction product on carbon fibers coated with pure Si₃N₄. The oxidation resistance of the coated fibers in air was investigated in the temperature interval up to 1000 °C, and the apparent activation energy of oxidation was analyzed based on DTA‐EGA results. The oxidation kinetic reveals a significant increase of onset point of oxidation temperature by up to 150 K for Si₃N₄ coated short carbon fibers obtained from the reactive CVD coating process. Such fibers have a high application potential for carbon‐fiber reinforced Si₃N₄‐CMC. The role of Yb₂Si₄CN₆ as reinforcement for Si₃N₄‐CMC is discussed based on bond strength comparison of carbides (SiC), nitride silicates (SiAlON), and nitrides (Si₃N₄).     

Interfacial study of magnesium-containing fluoridated hydroxyapatite coatings

Magnesium-containing fluoridated hydroxyapatite (Mg_xFHA) coatings have been developed to improve the biological performances of fluoridated hydroxyapatite (FHA) coatings. The coatings are deposited on Ti6Al4V substrates via a sol-gel process. The interface between the coating and substrate is characterized by scanning electron microscopy, glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy for coating thickness, elemental distribution and chemical states. Pull-off test is used to evaluate the adhesion strength. The results show that the interdiffusion of elements happens at the coating/substrate interface. The incorporation of Mg ions into FHA coatings enhances the pull-off adhesion strength between the coating and the substrate, but no significant difference is observed with different Mg concentrations.     

Double Wigner distribution function of a first-order optical system with a hard-edge aperture

The effect of an apertured optical system on Wigner distribution can be expressed as a superposition integral of the input Wigner distribution function and the double Wigner distribution function of the apertured optical system. By introducing a hard aperture function into a finite sum of complex Gaussian functions, the double Wigner distribution functions of a first-order optical system with a hard aperture outside and inside it are derived. As an example of application, the analytical expressions of the Wigner distribution for a Gaussian beam passing through a spatial filtering optical system with an internal hard aperture are obtained. The analytical results are also compared with the numerical integral results, and they show that the analytical results are proper and ascendant.     

Preparations of TiO2 nanocrystal coating layers with various morphologies on Mullite fibers for infrared opacifier application

TiO₂ nanorods coatings (TONC) were prepared on the surface of Mullite fibers by seed-hydrothermal method, which were designed as infrared opacifier. The influences of different tetrabutyl-titanate amount on the TONC morphologies, crystalline and optical properties were investigated. Effective specific extinction (e*) was used to characterize their masking ability. The TONC morphologies could be adjusted from nanoparticles to nanorods, which had direct influence on their optical properties. In the 3 μm-6 μm range of infrared light, e* of TONC could be improved up to 2-4 folds compared with that of Mullite fibers. Present study indicated TONC is a promising infrared opacifier.     

Effect of Fe ions on the thermal and optical properties of the ceramic coating grown in-situ on AZ31 Mg Alloy

This research investigates the effect of Fe₂(SO₄)₃ on the thermal and optical properties of the ceramic coatings formed on AZ31 Mg alloy. The different ceramic coatings were obtained by plasma electrolytic oxidation (PEO) in electrolytes that contain varied concentrations of Fe₂(SO₄)₃. The microstructure, element distribution, composition as well as the thermal and optical properties of the coatings were studied with scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray Diffraction (XRD), UV–VIS–NIR spectrophotometer and infrared reflectometer. The results show that all of the coatings prepared were mainly composed with MgO, with trace-amount of Fe₃O₄ presents and Fe seems entered into the MgO crystal structure. With the increasing of the concentration of Fe₂(SO₄)₃, the solar absorptance and infrared emittance increased initially but then remain stable. We found that at the concentrations 8 g L⁻¹, the coating has the highest solar absorptance (0.94) and infrared emittance (0.83). Our results show that coatings formed with this method could be useful as a thermal control coating in a variety of applications, such as in the spacecraft.     

Chemomechanical effects in optical coating systems

The major in-service failure mechanisms of modern optical coatings for architectural glass can be mechanical (e.g. scratch damage). Many of these coatings are multilayer structures of less than 100 nm thickness and different coating architectures are possible (i.e. different layer materials, thickness and stacking order). These coatings are exposed to different types of climatic conditions. In such circumstances it has been shown that chemomechanical effects can lead to changes in the hardness as well as the fracture resistance of bulk oxides. High performance glass is coated with anti-reflection coatings (e.g. ZnO, SnO₂) and barrier layers (e.g. TiO_xN_y) which are also expected to suffer from such chemomechanical effects. In this study we have demonstrated the chemomechanical behaviour of a range of optical coatings exposed to water. Water exposure tends to reduce the hardness and increase the fracture resistance of the coating making it more vulnerable to plastic deformation during scratching. The susceptibility of different coatings to chemomechanical effects is discussed.     

Preparation of ZrO2 and ZrO2-Y2O3 coatings on silicon carbide fibers

The formation of ZrO₂ and ZrO₂-Y₂O₃ coatings from hydrous metal oxide sols on Nicalon NLM 202 silicon carbide fibers is investigated in detail. The results indicate that the microstructure of the oxide layer and the surface morphology of the coatings depend on the physicohemical properties of the sol. Kinetic studies of the oxidation of uncoated and coated fibers at different Y₂O₃ contents demonstrate that the oxidation rate of silicon carbide fibers decreases with increasing coating thickness. The effect of oxidation on the phase composition of Nicalon cloth samples coated with ZrO₂ and ZrO₂-Y₂O₃ is examined.     

Formation and evaluation of highly uniform aluminate interface coatings for sapphire fiber reinforced ceramic matrix composites (FRCMCs) using carboxylate-alumoxane nanoparticles

Sapphire fibers have been dip-coated in aqueous and CHCl₃ solutions of carboxylate-alumoxane nanoparticles and calcium-, lanthanum-, and yttrium-doped carboxylate-alumoxane nanoparticles and fired up to 1400°C to form uniform, conformal and contiguous, aluminate coatings. Optimum solvent, dip/dry, and firing sequences were determined for the formation of crack-free coatings. Both carboxylate-alumoxane and ceramic coated fibers were examined by field emission scanning electron and transmission electron microscopy, microprobe analysis and optical microscopy. Coatings produced were stable to thermal cycling in air up to a temperature of 1400°C. The ability of the carboxylate-alumoxanes to provide crack infiltration and repair was demonstrated. Sapphire fiber/alumina matrix FRCMCs have been prepared with calcium-, lanthanum-, and yttrium-aluminate interphase layers. Microscopy and fiber push-out data confirm that the calcium- and lanthanum-aluminate coatings provide a means for controlling failure properties at the fiber-matrix interface. However, FRCMCs containing YAG-coated fibers failed catastrophically before interfacial debonding and/or sliding occurred.     

Ferromagnetic resonance characterization of magnetostrictive metallic glass coatings

Amorphous ferromagnetic alloys are a promising class of materials that have been successfully used as magnetostrictive elements in fiber optic magnetic sensors. We have used ferromagnetic resonance (FMR) at about 9.5 GHz to characterize highly magnetostrictive film coatings of the amorphous ferromagnetic alloy Fe₈₁B_13.5Si_3.5C_2.R.f. sputtering was used to prepare films 0.1–0.6 μm thick on glass substrates and cladded single-mode optical fibers of diameter approximately 80 μm. Because of its inherent sensitivity, the FMR technique is shown to be an excellent non-destructive probe for investigating microscopic as well as macroscopic structural inhomogeneities that may arise from the fabrication process itself, subsequent handling or thermal aging of the coatings. An added advantage of the FMR technique is that it also allows a simultaneous measurement of such material parameters as the saturation magnetostriction coefficient, the saturation magnetization, the g factor and the uniaxial magnetic anisotropy energy. The effect of thermal annealing on some of these properties is also reported.