Novel manufacturing method of optical fiber coupler

Based on the coupling mode theory that the coupling ratio of fiber coupler changes periodically with center distance of two optical fibers, a novel manufacturing method of optical fiber couplers was developed with fused biconical taper experimental system. Its fabrication process is that the fiber is fused but not stretched when light begins to split, and the reduction of diameter of fiber is dependent on the theological characteristic of the fused fiberglass. The performance of the coupler was tested. The results show that the performance of the novel optical fiber coupler meets the performance expectations, and its diameter of coupling region （about 30 μm） is twice as long as that of classical fused biconical taper coupler （about 16 μm）, so the default, that is, the device is easy to fracture, is restrained and the reliability is greatly improved.     

Effect of technological parameters on optical performance of fiber coupler

To find out the influence of technological parameters on optical performance of fused optical fiber device, the fiber coupler was served as subject investigated by using the fused biconical taper machining as experimental setup. Fused fiber coupler＇s optical performances such as insertion loss, excess loss, directivity and uniformity were tested with the optical test system that was constituted of tunable laser and optical spectrum analyzer. Especially the relationship between optical performance and drawing speed was investigated. The experimental results show that the optical performance is closely related to process conditions. At fused temperature of 1 200℃, there exists a drawing speed of 150μm/s, which makes the device＇s performance optimum. Out of this speed region, the optical performance drops quickly. At drawing speed of 200μm/s, the excess loss is relatively small when the fused temperature is above 1 200 ℃. So the technological parameters have close relationship with optical performance of the coupler, and the good performance coupler can＇t get until the drawing speed and fused temperature match accurately.     

The relationship between IR characteristic peak and microstructure of the glass used as optical fiber

Based on the harmonic vibration equation, the relationship between IR characteristic peak of fiberglass and Si-O-Si bond angle was deduced, and 1 100 cm^-1 characteristic peak was specifically studied. It is found that 1 100 cm^-1 characteristic peak shifts to higher wave number when Si-O-Si bond angle increases. Taking fused biconical taper （FBT） coupler as an example, the microstructures of the fiber coupler manufactured at different draw- ing speeds were tested with micro infrared spectrum. According to the test results, it is found that the bond angle at the taper region is the largest, the one at the fused region is the second largest, and the one of bare fiber is the smal- lest. The characteristic peaks of fused-taper region shift to higher wave number when drawing speed increases.     

Experimental measurement and numerical analysis of fused taper shape for optical fiber coupler

To find out the effect of the shape of fused taper region on the optical fiber coupler, the fiber couplers were fabricated at different drawing speeds with a six-axes fiber coupler machine. The results, which were obtained fi＇om the shape of fused taper region measured with microscope, show that there is a close correlation between the cone angle and optical performance of fiber coupler. High-performance fiber coupler cannot be obtained until rheological shape is controlled accurately. The numerical analysis model, which was built based on generalized Maxwell viscoelastic theory, is resolved with ANSYS software. The calculated results accord with the experimental data. It can apply a theoretic basis for forecasting the shape of fiber coupler fabricated under the conditions of different technological parameters.     

Relationship between subsurface damage and surface roughness of ground optical materials

A theoretical model of relationship between subsurface damage and surface roughness was established to realize rapid and non-destructive measurement of subsurface damage of ground optical materials.Postulated condition of the model was that subsurface damage depth and peak-to-valley surface roughness are equal to depth of radial and lateral cracks in brittle surface induced by small-radius(radius≤200 μm)spherical indenter,respectively.And contribution of elastic stress field to the radial cracks propagation was also considered in the loading cycle.Subsurface damage depth of ground BK7 glasses was measured by magnetorheological finishing spot technique to validate theoretical ratio of subsurface damage to surface roughness.The results show that the ratio is directly proportional to load of abrasive grains and hardness of optical materials,while inversely proportional to granularity of abrasive grains and fracture toughness of optical materials.Moreover,the influence of the load and fracture toughness on the ratio is more significant than the granularity and hardness,respectively.The measured ratios of 80 grit and 120 grit fixed abrasive grinding of BK7 glasses are 5.8 and 5.4,respectively.     

Effect of metallic content on mechanical property of Ni/（10NiO-NiFe2O4 ） cermets

1 INTRODUCTIONThe use of inert or non-consumable anodes forreplacement of consumable carbon anodes in Hall-H啨roult electrolysis cells for the production of alu-minum has been a technical and commercial goalfor many decades .In the present process ,consumable carbon an-odes are used,andthe anode product is CO2. Withaninert anode ,the cell reaction will be :Al2O3=2Al +23O2(1)The basic requirements for aninert anode are :1) to exhibit a lowcorrosion rate in the high tem-perature melts an…     

Ratio of Fe-Al compound at interface of steel-backed Al-graphite semi-solid bonding plate

The ratio of Fe-Al compound at the bonding interface of solid steel plate to Al-7graphite slurry was used to characterize the interfacial structure of steel-Al-7graphite semi-solid bonding plate quantitatively. The relationship between the ratio of Fe-Al compound at interface and bonding parameters (such as preheat temperature of steel plate, solid fraction of Al-7graphite slurry and rolling speed) was established by artificial neural networks perfectly. The results show that when the bonding parameters are 516 ℃ for preheat temperature of steel plate, 32.5% for solid fraction of Al-7graphite slurry and 12 mm/s for rolling speed, the reasonable ratio of Fe-Al compound corresponding to the largest interfacial shear strength of bonding plate is obtained to be 70.1%. This reasonable ratio of Fe-Al compound is a quantitative criterion of interfacial embrittlement, namely, when the ratio of Fe-Al compound at interface is larger than 70.1%, interfacial embrittlement will occur.     

Effect and influence factors of sulfur removal in coal with fungus

The influence of coal desulfurization by fungus was experimentally studied. The results suggest that fungus can effectively remove inorganic and organic sulfur in coal, and main influences of desulfurization by fungus of pH value, temperature, coal slurry concentration and coal granularity were studied by orthodox experiment and the optimal experimental conditions are as follows: pH value 6, temperature 45 °C, coal slurry concentration 10% and coal granularity 100 μm. Under above conditions, fungus can remove up to 44.96% total sulfur and 54.87% inorganic sulfur within two days, and their desulfurization rates will increase along with time. Compared with sulfolobas, desulphurization by fungus is steady and more effective, and has advantage of high speed. Foundation item: Project(2002AA649220) supported by Hi-tech Research and Development Programe; project(1667) supported by the Postdoctoral Science Foundation of Central South University     

Life cycle detection of prestress in large prestressed reinforcement structures

To monitor the stress state of prestressed reinforcement in large reinforcement prestressed structure, two sensing structures, namely the direct spiral-winding structure and sawtooth modulated structure, were designed based on the ordinary communication optical fiber. The sensing theories were analyzed, and the experimental studies were also carried out. The quasi-distributed sensing system based on optical time domain reflective technology was established. The detection wavelength and spatial resolution were analyzed, and the estimation formula of maximal number of sensing point was also given. The results show that the system can realize the quasi-distributed test of measurand with single fiber, which helps to simplify the in-out wires. Moreover it can take on the important task of long-term and continuous monitoring of prestress, which helps to realize the life cycle detection of prestress, and play an important role in the estimating of bridge health state. Foundation item: Project (50278058) supported by the National Natural Science Foundation of China     

布拉格光栅辅助型上下话路滤波器的实验制作

采用波长为248nm的紫外光,在由标准单模光纤和自制的高掺锗光敏光纤熔融拉锥制作的2×2光纤失配耦合器上写入光纤光栅,实现了全光纤布拉格光栅(FBG)辅助失配耦合器型上下话路滤波器,并测试了器件的传输特性,器件的插入损耗和回波损耗分别为6.74dB和-18.84dB。用10Gbps的光信号进行了传输实验,分别测试了下话路前、后信号的眼图。与输入信号相比,下话路信号的信噪比从10.04dB降低到了9.27dB,信号的消光比从8.89dB降低到了4.68dB。     

Structure transition of nano-titania during calcination

1　INTRODUCTIONTitaniahasthreecrystallines :brookite ,anataseandrutile .Theirbasicstructuralunitisthesame[TiO6 ]octahedron ,buttheirlatticestructuresaredifferent .Forexample ,brookitebelongstorhombiccrystallo series ,whilerutileandanatasebelongtosquarecrystallo series .Thoughrutileandanatasearethesamecrystallo series ,theirsymmetricalelementsandunit cellparametersaredifferent[1] .Inrecentyears ,muchattentionhasbeenpaidtophasetransformationoftitaniaparticle ,especiallytothetemperatureofph…     

侧面级联耦合器对连续光纤激光器的影响

为了研究侧面级联耦合器对光纤激光器的影响,对自主研制的(1+1)×1侧面泵浦耦合器,以及某商品化的(2+1)×1耦合器进行了研究.实验中分别测试了2种耦合器的耦合效率,泵浦光传输损耗,以及信号光泄露等参数,然后用2种结构的耦合器分别搭建了光纤激光器.在耦合器为(1+1)×1结构的激光器中,注入975 nm泵浦功率444 W时,1 080 nm激光功率输出344 W,光-光转换效率77%;在耦合器为(2+1)×1结构的光纤激光器中,当975 nm泵浦功率注入444 W时,1 080 nm激光功率输出260 W,激光器的光-光转换效率59%.对比2种结构的激光器可以看出:对于目前商用的(2+1)×1耦合器来说,由于传输损耗比较大,很难实现级联结构,而实验室自主研制的侧面耦合器能够实现5个级联.     

Effect of working condition on thermal stress of NiFe2O4-based cermet inert anode in aluminum electrolysis

Based on the FEA software ANSYS,a model was developed to simulate the thermal stress distribution of inert anode.In order to reduce its thermal stress,the effect of some parameters on thermal stress distribution was investigated,including the temperature of electrolyte,the current,the anode cathode distance,the anode immersion depth,the surrounding temperature and the convection coefficient between anode and circumstance.The results show that there exists a large axial tensile stress near the tangent interface between the anode and bath,which is the major cause of anode breaking.Increasing the temperature of electrolyte or the anode immersion depth will deteriorate the stress distribution of inert anode.When the bath temperature increases from 750 to 970 ℃,the maximal value and absolute minimal value of the 1st principal stress increase by 29.7% and 29.6%,respectively.When the anode immersion depth is changed from 1 to 10 cm,the maximal value and absolute minimal value of the 1st principal stress increase by 52.1% and 65.0%,respectively.The effects of other parameters on stress distribution are not significant.     

A new monitoring method of cable tension of cable-stayed bridge—fiber bragg grating method

A new on-line monitoring method based on fiber Bragg grating (FBG) for cable tension of cable-stayed bridge was introduced. The major structure of sensing head using in the test of cable tension is elastic annular. The FBG is attached inflexibility to the exterior surface of annulus and form straight-through sensing head. Sensing head is installed between the anchor device and stow-board of funiculus holes of the cable-stayed bridge. Accompany with the change of the outside pressure, the Bragg center reflective wavelength of optical fiber grating changed correspondingly. According to this characteristic, through demodulating the Δλ, the value of the cable tension can be determined. The experiment results and the theory indicate that the test system has simple structure, good stability and linear, wide response capacity, and has no special request for tester. The measurement method for the test of cable tension is practical and effective. Foundation item: Project (50278058) supported by the National Natural Science Foundation of China     

Structure analysis of optical fiber coupler with infrared spectrometry

To obtain excellent performance optical fiber couplers, the structural difference of SiO2 in couplers with different manufacturing techniques was investigated. With 740-FT-IR infrared spectrometric analyzer, the infrared absorption spectrum of SiO2 in couplers at different drawing velocities was measured, and two characteristic peaks in the wavenumber range of 650 - 2000 cm^-1 were observed. One characteristic peak is at about 943 cm^-1 , which is attributed to Si--O Si bond asymmetric stretching vibration, the other is at about 773 cm^-1 , which is attributed to Si--O--Si bond symmetric stretching vibration. From the infrared spectrum, it is found that the intensity and wavenumber of the characteristic peaks are related to the manufacturing technique of couplers. The characteristic peak atabout 943 cm^-1 becomes steeper when increasing the drawing velocity. At the drawing velocity of 150μm/s, the distance between the two characteristic peaks is maximum, and then the optical fiber coupler has excellent performance, indicating that the performance of the optical fiber coupler has a close relationship with the wavenumber of the two characteristic peaks.     

New anodizing process for magnesium alloys

Compact anodic films with high hardness and good corrosion resistance on magnesium alloys were prepared by a new constant voltage and arc-free anodizing process. The effects of anodizing parameters such as applied voltage and electrolyte temperature on the peak current density and the thickness of films were investigated. In addition, the morphologies and corrosion resistance of films were investigated by scanning electron microscopy and potentiodynamic polarization, respectively. The results show that the higher the applied voltage, the higher the peak current density and the thicker the films. However, too high applied voltage may result in breakdown of films and intense sparking which may deteriorate the properties of the anodic films and bring about unsafety. The new anodizing process can be applied in a wide range of temperature. The new anodic films have numbers of pores with the diameter of 0.5 - 5.0 μm which do not transverse the entire film.     

Experimental study on wear failure course of gas-valve/valve-seat in engine

The wear failure course of gas-valve/valve-seat in engine was investigated with a simulating tester. The results show that the failure of the contact conical surface is mainly caused by the elastic and plastic deformation and the fatigue micro-crack and spalling. The creep-deformation and corrosion atmosphere accelerated wear failure course at the high temperature. The wear failure course of the gas-valve/valve-seat in engine follows general wear rules of mechanical elements, but the rate of wear in the sharp wear stage is faster. Foundation item: Project supported by Postdoctoral Foundation of Central South University; project (04B035) supported by the Youth Foundation of Hunan Province Education Bureau     

Effect of cobalt loading on reducibility, dispersion and crystallite size of Co／Al2O3 Fischer-Tropsch catalyst

Co/Al2O3 Fischer-Tropsch synthesis catalysts with different cobalt loadings were prepared using incipient wetness impregnation method. The effects of cobalt loading on the properties of catalysts were studied by means of X-ray diffraction (XRD), temperature programmed reduction (TPR), hydrogen temperature programmed desorption (H2-TPD) and O2 titration. Co-support compound formation can be detected in catalyst system by XRD.For the Co/Al2O3 catalysts with low cobalt loading, CoAl2O3 phase appears visibly. Two different reduction regions can be presented for Co/Al2O3 catalysts, which belong to Co3 O4 crystallites (reduction at 320 ““C) and cobalt oxidealumina interaction species (reduction at above 400℃). Increasing Co loading results in the increase of Co3 O4 crystallite size. The reduced Co/Al2O3 catalysts have two adsorption sites, and cobalt loading greatly influences the adsorption behavior. With the increase of cobalt loading, the amount of low temperature adsorption is increased, the amount of high temperature adsorption is decreased, and the percentage reduction and cobalt crystallite size are increased.     

Polyaniline-graphite composite film glucose oxidase electrode

1 INTRODUCTION Conducting polymers, such as polyaniline (PANI), polypyrrole (PPY) and polythiophene, have attracted much attention as an enzyme-immobilizing matrix for biosensors [1?3]. Conducting polymers are known to be compatible with biological molecules in neutral aqueous solutions. Due to the reversibility doping-undoping processes and the rapid electron transfer, the conducting polymers are promising in the immobilization of biomolecules and fabrication of efficient biosensors[4]…     

Positive periodic solutions of higher-dimensional nonlinear functional difference equations

In this paper, we apply a cone theoretic fixed point theorem to obtain sufficient conditions for the existence of multiple positive periodic solutions to the higher-dimensional functional difference equations of the form: