水杯式光纤Bragg光栅沉降仪的研究

沉降仪是测量路基、桥梁、隧道、边坡等结构物沉降的重要仪器。利用上、下容器相连通结构,研制了一种水杯式光纤Bragg光栅沉降仪。当沉降发生时,在压差的作用下,膜片产生的挠度推动传压杆使等强度悬臂梁的自由端产生同样大小的挠度变化,使粘贴于等强度悬臂梁表面的光纤Bragg光栅发生拉伸,进而导致中心波长发生移位,实验通过检测波长移位可获得沉降量。分析结果显示,光纤Bragg光栅波长移位对沉降量呈现良好的线性关系,沉降仪的灵敏度可达15.4pm/cm,线性度为1.73%FS,迟滞为0.984%FS,重复性误差为3.61%FS。     

差动式光纤Bragg光栅沉降仪

研制了一种测量地表沉降变形的差动式光纤Bragg光栅沉降仪。等强度悬臂梁的底部固定于工地上的固定平台,顶端通过刃口、挂钩和连杆与沉降墩连接。在该测量中,沉降仪将沉降墩的地沉降量转换为悬臂梁的挠度。悬臂梁作用粘贴于其上下表面的光纤Bragg光栅产生应变,即传感光栅的Bragg波长产生了移位。对粘贴在悬臂梁上、下表面的传感光栅的Bragg波长进行差动运算,实现温度补偿,减小人为和气候因素的影响。在挂钩和沉降敦之间采用了螺旋结构连接,可通过调整螺旋或更换不同长度的挂钩来调节传感器的测量范围。荷载实验表明,该沉降仪的测量精度为0.004mm,低于变形测量中的科研级测量精度0.01~0.05mm。     

基于旋涡发生体的光纤Bragg光栅流量计的研究

结合光纤光栅传感检测技术与旋涡分离原理,研制了一种基于三角柱型旋涡发生体的光纤Bragg光栅流量计,在三角柱旋涡发生体中部设置导压腔,腔内设置粘贴Bragg光栅的等强度悬臂梁,流体经过发生体两侧时,交替分离旋涡,导压腔内部产生脉动流体,等强度悬臂梁产生振动且振动频率与旋涡分离频率成正比,通过检测悬臂梁振动频率测量流体流量。实验表明,该流量计的线性度为4.38%FS,仪表系数为K=3.659,光纤光栅波长移位频率对流量的响应度为1.182Hz/(m3/h)。     

基于旋涡发生体的光纤Bragg光栅流量计的研究

结合光纤光栅传感检测技术与旋涡分离原理,研制了一种基于三角柱型旋涡发生体的光纤Bragg光栅流量计,在三角柱旋涡发生体中部设置导压腔,腔内设置粘贴Bragg光栅的等强度悬臂梁,流体经过发生体两侧时,交替分离旋涡,导压腔内部产生脉动流体,等强度悬臂梁产生振动且振动频率与旋涡分离频率成正比,通过检测悬臂梁振动频率测量流体流量。实验表明,该流量计的线性度为4.38%FS,仪表系数为K=3.659,光纤光栅波长移位频率对流量的响应度为1.182Hz/(m3/h)。     

基于光纤Bragg光栅的锚索拉伸力测量研究

锚索通常工作在高应力状态,其健康状况直接关系到边坡的安全和稳定。为了实时反映锚索的受力状态,将光纤Bragg光栅粘贴在锚索钢丝表面。锚索受力发生形变,从而使粘贴在锚索表面的光纤Bragg光栅中心波长发生移位。拉伸试验表明:拉伸力灵敏度为19.9pm/kN,线性度为1.02%FS。通过对光纤Bragg光栅中心波长移位量的测量,可以实现对锚索所受拉伸力的在线监测。     

基于光纤Bragg光栅的量测锚头压力研究

锚头的受力情况对整个锚杆的安全性有着重要影响。为了实时反映锚头的受力状态,将2只光纤Bragg光栅沿45°粘贴在轮辐式结构锚头的两根对称辐条中点处表面上,形成轮辐式测力传感结构,辐条在压力作用下产生剪切变形,引起辐条表面的光纤Bragg光栅中心波长移位。通过对光纤Bragg光栅中心波长移位的测量,实现在锚头处锚杆轴向拉力的在线监测。锚头压力实验表明:光栅1的测力灵敏度为108.8pm/kN,线性度为0.042%FS;光栅2的测力灵敏度为115pm/kN,线性度为0.023%FS。     

基于FBG的鸭嘴式横担主材应变研究

横担是电力系统塔架结构中承力较多的构件,在线路覆冰、舞动等因素影响下横担主材受力过大,容易造成损坏。在研制的电力系统塔架模型鸭嘴式横担主材的上下表面,采用环氧树脂做为粘贴剂分别安装四根光纤Bragg光栅,实时监测横担应变。实验通过调整荷载改变横担主材所受应力,从而使得光纤Bragg光栅中心波长发生移位。荷载实验表明,在鸭嘴式横担端部进行加载和卸载时,位于4个测点的光纤Bragg光栅的实验灵敏度分别为:6pm/kg,2pm/kg,3pm/kg,2pm/kg;线性度分别为2.6%FS,6.1%FS,2.7%FS,4.5%FS。     

基于FBG的鸭嘴式横担主材应变研究

横担是电力系统塔架结构中承力较多的构件,在线路覆冰、舞动等因素影响下横担主材受力过大,容易造成损坏。在研制的电力系统塔架模型鸭嘴式横担主材的上下表面,采用环氧树脂做为粘贴剂分别安装四根光纤Bragg光栅,实时监测横担应变。实验通过调整荷载改变横担主材所受应力,从而使得光纤Bragg光栅中心波长发生移位。荷载实验表明,在鸭嘴式横担端部进行加载和卸载时,位于4个测点的光纤Bragg光栅的实验灵敏度分别为:6pm/kg,2pm/kg,3pm/kg,2pm/kg;线性度分别为2.6%FS,6.1%FS,2.7%FS,4.5%FS。     

光纤Bragg光栅在绕组温度测量中的应用研究

实时监测变压器绕组温度,可解决变压器在运行过程中因绕组温度过高而造成的寿命减少、设备损坏等问题。使用绝缘纸做成的层压板对光纤测温触头进行封装,将测温触头安装在变压器绕组上。当绕组温度发生改变时,测温触头中的光纤Bragg光栅中心波长将产生移位。温度响应实验表明,光纤Bragg光栅温度传感器的线性度为0.79%FS;温度灵敏度为8.91pm/℃,重复性误差1.76%FS。绕组测温实验结果表明,环境温度为15℃时,在75V电压下,90min后,绕组温度稳定在24℃～25℃之间在;100V电压下,105min后,绕组温度稳定在32℃～33℃之间。     

基于光纤Bragg光栅的行车模型主梁挠度的测量

简易桥式起重机的力学结构是一种简支梁,研制了一种行车模型,主要包括工字梁及一个可吊挂重物的滑块.光纤Bragg光栅沿工字梁的轴向均匀粘贴于行车主梁的下表面,侧点分别位于离主梁的1/4、1/2和3/4等三个位置.在测量中,通过吊挂重物对主梁产生挠度,从而导致粘贴其下表面的光纤Bragg光栅产生波长移位.载荷试验表明,在主...     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Retrieval of ultraviolet skylight radiances and O3 slant column densities from balloon-borne limb spectrometer

With a novel light-weight and absolutely calibrated ultraviolet （UV） spectrometer, UV skylight radiances and O3 slant column densities are measured by balloon-borne limb measurements in Xinjiang area, China. UV skylight radiances measured at the height of 31 km are compared with the results from Modtran in the wavelength range from 290 to 420 nm. O3 slant column densities are derived from radiance spectra in the Huggins bands （320 - 335 nm） using differential optical absorption spectroscopy method. And the parameter exhibits a good correlation with the same value simulated by radiative transfer model （Tracy）. The O3 profile simultaneously measured by an O3 sonde is used as input in Tracy calculations. The O3 sonde is launched on the same balloon.     

Design optimization of highly sensitive LSPR enhanced surface plasmon resonance biosensors with nanoholes

For breaking through the sensitivity limitation of conventional surface plasmon resonance (SPR) biosensors, novel highly sensitive SPR biosensors with Au nanoparticles and nanogratings enhancement have been proposed recently.But in practice, these structures have obvious disadvantages.In this study, a nanohole based sensitivity enhancement SPR biosensor is proposed and the influence of different structural parameters on the performance is investigated by using rigorous coupled wave analysis (RCWA).Electromagnetic field distributions around the nanohole are also given out to directly explain the performance difference for various structural parameters.The results indicate that significant sensitivity increase is associated with localized surface plasmons (LSPs) excitation mediated by nanoholes.Except to outcome the weakness of other LSP based biosensors, larger resonance angle shift, reflectance amplitude, and sharper SPR curves' width are obtained simultaneously under optimized structural parameters.     

Polymer gratings based on photopolymerization for low-order distributed feedback polymer lasers

Novel polymer distributed feedback(DFB)gratings are fabricated based on photopolymerization to reduce lasing threshold of polymer lasers.A photopolymer formulation sensitive to 355-nm ultraviolet(UV)light is proposed for the fabrication of polymer gratings and it can be used to form polymer films by spin-coating process.A very low surface-relief depth ranging from 12.5 to about 1.0 nm has been demonstrated with a refractive-index modulation of about 0.012.The experimental results indicate that such polymer gratings have promising potentials for the fabrication of low-order DFB organic semiconductor lasers.     

A novel methodology for photometric compensation of projection display on patterned screen

We propose a novel methodology based on the projector-camera (ProCam) system to address the photometric compensation issue for the projection display on the patterned screen.The patterned screen is treated as the combination of a perfect white screen and a color modulator.The perfect white screen is used to automatically and accurately characterize the ProCam system offline using the polynomial model,and the parameters of the color modulator can be efficiently recovered by employing only two gray images based on the linear reflectance model.The experimental results show that the color artifacts of the display image can be greatly improved with this methodology,which demonstrates its feasibility and validity in the photometric compensation.