VIDEO TRANSMISSION SYSTEM IN ITV APPLICATION

The transmission characteristics of video transmission mediums,coaxial cable and optical fiber ,are discussed in the paper. The formulas for frequency bandwidthare given to evaluate the video transmission distance. For typical video transmissionsystems with BB/IM and PFM/IM using optical fiber as the channel, expressions andcalculating results for both SIN and sensitivity are given. Finally. the principle for selecting different type of transmission systems according to transmission distances of the industrial TV is presented.     

An investigation of numerical aperture of air-core photonic bandgap fiber

Air-core photonic bandgap fiber(PBF)is the perfect choice of the next-generation fiber optical gyroscope(FOG),with excellent temperature,electromagnetism and radiation adaptability.Numerical aperture is an important optical parameter of PBF for application in FOG.The PBF’s maximum theoretical numerical aperture(NAmax)is calculated and compared with the far-field numerical aperture(NAeff)through experiments.The result indicates that the relationship between NAmax and NAeff has much stronger dependence on wavelength than that of the conventional fiber,and they get close at wavelengths near the middle of the photonic bandgap with the error less than 5%.Furthermore,photonic bandgap fiber optical gyroscope(PBFOG)with no fusion splicing points is proposed,and the optimization method and results of the PBF’s structure parameters for application in PBFOG are given from the aspect of numerical aperture.     

Shaking test research on connection modes between block infill wall and frame beam

In order to achieve an optimal anti-seismic behavior,or rather stability,the out-of-plane stability of infill wall in frame has been researched with the shaking test of four sets of two-layer infill wall,in which four different connection modes of filled with inclined bricks on the top,disconnection,flexibility and semi-flexibility were adapted.The acceleration and displacement response of the specimens were analyzed under the seismic load.Also,some feasible connection modes were gained by comparing the response of infill walls.Finally,the calculation of earthquake of infill wall was held.The results showed that seismic responses of the infill walls whose connect with frame in form of flexibility and semi-flexibility modes are weaker than others obviously,and their integrality is better.Thus the conclusion could be drawn that out-of-plane stability of the specimens with connection modes of flexibility and semi-flexibility are better than those with the connection modes of filled with inclined bricks on the top and disconnection.The research results can provide evidence for establishing specifications and directing the construction and therefore help reduce the casualties and property loss caused by earthquake disasters.     

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.     

Experimental Study on Penetration and Perforation of Laminated Kevlar

The penetration behavior and perforation characteristics of Kevlar/Epoxy laminates with various thickness in quasi-static and ballistic perforation penetrated by steel projectiles with different noses are investigated. Quasi-static tests are conducted on MTS810 testing system. The results indicate that global deformation is the major mechanism of energy absorption and woven laminates exhibit larger energy dissipation than that of angleplied laminates. Therefore, the woven laminates have better quasi-static penetration resistance. Ballistic tests with velocity of 200 - 700 m/s are executed by using a powder gun with 7.62 mm barrel. Comparing ballistic experimental results with those under quasi-static condition, both the perforation performance and the failure modes are related closely to the speed of penetrator. Quite different from quasi-static tests, ballistic tests indicate that thick angle-plied laminate targets are even better than woven laminates in resisting ballistic impact. It is observed that the damage zone of the laminate is localized highly with the increasing of the impact velocity and correspondingly, the failure modes are more manifold. The shape of projectile noses affects the impact resistance of laminated Kevlar significantly in the range of velocity around the ballistic limit.     

Dynamic mechanical behaviour of ultra-high performance fiber reinforced concretes

Ultra-high performance fiber reinforced concretes （UHPFRC） were prepared by replacing 60% of cement with ultra-fine industrial waste powder. The dynamic mechanical behaviour of UHPFRC with different fiber volume fraction was researched on repeated compressive impact in four kinds of impact modes through split Hopkinson pressure bar （SHPB）. The experimental results show that the peak stress and elastic modulus decrease and the strain rate and peak strain increase gradually with the increasing of impact times. The initial material damage increases and the peak stress of the specimen decreases from the second impact with the increasing of the initial incident wave. Standard strength on repeated impact is defined to compare the ability of resistance against repeated impact among different materials. The rate of reduction of standard strength is decreased by fiber reinforcement under repeated impact. The material damage is reduced and the ability of repeated impact resistance of UHPFRC is improved with the increasing of fiber volume fraction.     

Strength failure and crack coalescence behavior of sandstone containing single pre-cut fissure under coupled stress,fluid flowand changing chemical environment简

In order to study the strength failure and crack coalescence characteristics of cracked rocks, uniaxial compression experiments were conducted on cylindrical sandstone specimens, sampled from Longyou Grottoes of Zhejiang Province, China, with a single pre-cut crack soaking in different chemical solutions. Based on the results of uniaxial compressive test under different chemical solutions and velocities of flow, the effect of strength and deformation characteristics and main modes of crack coalescence for cracked rocks under chemical corrosion were analyzed. The results show that the pH value and velocity of the chemical solutions both have great influence on the sandstone sample＇s uniaxial compressive strength and deformation characteristics. Cracked sandstone samples are tension-destructed under uniaxial compression, and the crack propagation directions are consistent with the loading direction. The phenomena of crack initiation, propagation and coalescence of sandstone are well observed. Four different crack types are identified based on the crack propagation mechanism by analyzing the ultimate failure modes of sandstone containing a single pre-cut fissure. The failure process of specimen in air is similar with the specimen under chemical solutions, however, the initial time of crack occuring in specimen under chemical solutions is generally earlier than that in the natural specimen, and the crack propagation and coalescence process of specimen under chemical solutions are longer than those of the natural specimen due to softening of structure of rock caused by hydro-chemical action. Immersion velocity of flow and chemical solutions does not have influence on the ultimate modes of crack coalescence.     

Mechanical properties with high temperature and the microstructure of carbon/phenolic ablative composites

Carbon fiber reinforced phenolic based composites were prepared by laminating molding. The variation in mechanical characteristics of composites was evaluated with heating temperature and procedure. The microstructures of composites at different temperatures were observed by optical microscope and scanning electron microscope, respectively. The results showed that the main weight loss range of carbon/phenolic is from 300 to 800 ℃, before 700 ℃ the weight loss was resulted from pyrolysis and after that the weight loss was mainly by oxidation in the fiber phase; with the heat treatment temperature rising, the bonding at the interface of carbon fibers and resin matrix weakened; in the pyrolysis temperature range, the interlaminar shear strength(ILSS) of carbon/phenolic showed a rapid drop with temperature rising, and then decrease in the rate of ILSS became relatively slower; the fiber oxidation had little influence on the ILSS.     

Rheological behavior of basalt fiber reinforced asphalt mastic

The characters of basalt fiber are analyzed and compared with commonly used fibers. The rheological behaviors of the basalt fiber reinforced asphalt mastic are investigated by the dynamic shear rheological tests and the repeated creep tests. The results show that basalt fiber has excellent reinforced performances, such as high asphalt absorption ratio, low water absorption ratio, high tensile strength, high elastic modulus and high temperature stability. The rutting factor of the fiber reinforced asphalt mastic is higher than the plain asphalt mastic and the reinforced effects are more remarkable under high temperature. The rheological performances of the asphalt mastic demonstrate a good linear relationship between different temperature and loading frequency. The creep stiffness modulus of the asphalt mastic at different loading time can be expressed by power function. Improved Burgers model is used to represent the rheological behaviors of the asphalt mastic with basalt fiber and the model parameters are estimated.     

Measurement of creep of optical fiber by a low coherent white light double interferometer system

The creep properties of optical fiber used in fiber optical sensors were studied in this paper. A low co- herent white light double interferometer system was designed and calibrated and the creep deforma- tions of optical fibers under static and cyclic loadings were measured with this device. The research results showed that polymer coated optical fibers crept at the beginning when they were under static or cyclic load. As the number of the cyclic loading or the static loading times increased the creep tend...     

双折射光纤受激喇曼散射模式的实验研究

本文在实验上对三种不同结构的石英系双折射单模光纤中受激喇文散射传输模式进行了研究。给出了测试装置、SRS光谱和各级斯托克斯线模式尿片。其结果与圆芯多模梯度折射率光纤完全不同。受激喇更散射的光众尺寸基本不变、而且具有以高阶模传输特点。这些结果在国内外尚未见报道。     

不等线性衰减系数时的SRS分析理论

为了准确描述受激喇曼散射效应(SRS)对波分复用石英光纤通信系统的影响,基于石英光纤喇曼增益谱可以拟合为直线的特点,给出不等线性衰减系数时的N-波道前向稳态SRS耦合方程的形式解,并分情况对该形式解进行讨论,得出一些特解。所得结果能很好地验证关于等线性衰减系数时的已有研究,并为光纤喇曼放大器的设计及运用数值方法研究波分复用石英光纤通信系统中的SRS效应提供参考。     

光纤-氮系统SRS谱的实验与理论分析

本文详细分析了光纤－氮系统的受激刺曼光谱，给出了测试SRS光谱的实验装置、光谱及模式照片，在理论上分析了阈值条件和谱线宽度与泵浦光功率之间的关系。实验和理论计算基本符合，同时在试验中还观测到微弱的氮分子和石英分子之间的耦合模式。     

基于光纤技术的井筒围岩稳定实时监测系统

针对井筒围岩变形监测受采动影响的问题,提出了采用光纤传感技术监测井筒围岩变形的方法.研究了光纤传感器的不同埋入方式、粘结材料以及施工工艺对结构变形监测的影响,结合金川Ⅱ矿区14行风井加固工程,设计并布设了光纤光栅传感监测系统.现场监测结果表明,基于BOTDR的分布式光纤传感技术具有实时性、远程和自动监测围岩变形的优点,可以直观地得到井筒在不同位置的围岩变形分布特征,为井筒围岩变形提供了准确的测试数据.     

单模保偏光纤中受激喇曼散射

本文详细地研究了双折射光纤的受激喇曼散射.我们已经观测到9级斯托克斯受激喇曼谱.讨论并测试了阈值和喇曼频移与泵浦光偏振方向间的关系,测试了当泵浦光偏振方向与光纤椭圆核的长轴或短轴平行时的传输损耗.并根据测得的阈值在理论上计算了各级斯托克斯线的喇曼增益系数.     

有限元法分析非对称光纤耦合器波导

用有限元法分析了非对称光纤耦合器波导的场特性.利用自适应法划分有限元三角形格子,计算出在不同结构下最低阶的4个模式的传播常数.数值结果表明,组成耦合器的光纤半径比对偶模和奇模的传播常数都有明显的影响.与奇模不同的是,偶模传播常数对两光纤熔融程度不敏感.     

输出平稳光功率的SRS多路波长转换研究

为了提高光通信系统的传输效率和降低网络阻塞率,利用光纤中受激拉曼散射(Stimulated Raman scattering,SRS)效应,对全光多路波长转换器提出一种改进。通过SRS效应的耦合波方程解析解,设计实现一路转四路的全光多路波长转换器,再结合拉曼光纤放大器(Raman Fiber Amplifier,RFA)增益平坦化方法,在多路波长转换器的基础上级联一段补偿光纤,前增益后补偿,实现输出信号光功率的平稳。仿真结果表明此方法可行。     

同时测量折射率和温度的光纤传感器

为了实现折射率（RI）和温度的同时测量, 提出了一种双长周期光纤光栅(LPG)结构的光纤传感器. 该传感器由两段LPG组成, 两段LPG所激发的包层模阶数不同, 且两段LPG的包层直径也不同. 理论分析了该传感器实现折射率和温度同时测量的原理, 两段LPG对折射率具有较大差异的灵敏度, 而温度灵敏度也略有不同, 利用灵敏度矩阵可以同时得到折射率和温度的变化. 实验中, 采用两个不同的周期使得两个LPG分别激发不同阶的包层模, 利用化学腐蚀方法使激发高阶模的LPG包层直径减小, 利用不同折射率的液体作为样本进行实验测量. 实验结果表明, 该传感器能实现折射率和温度的同时测量, 并具有高灵敏度和好的线性度.     

单模光纤受激喇曼散射瞬态过程分析

本文从非线性耦合波理论的观点分析了单模光纤中受激喇曼散射瞬态过程,给出了解答的解析表达式。由此得到稳态过程的解答,并分析了该稳态过程。该稳态分析所得结论与 Yariv 等从光子转换理论所得稳态结论相一致,并对 Smith 的小信号解答作了进一步完善。     

A Dnal-Mode Bow Tie Optical Fiber Sensor for Measurement of Axial Strain

An optical fiber strain sensor utilizing the mode-mode interference of LP_(01)~x,andLR_(11)~x,modes in bow tie optical fibers is described.The heterodyne interference caused byfrequency modulation of laser diode(LD) with ramp injection current is used torealize the detection of linear phase.Experimental results show a resolution of about 2%of one fringe corresponding to a strain of 2.9με.m.