阵列波导光栅解复用器光谱响应特性分析

基于单模光波导本征模场及其端面衍射场分布的高斯近似表达,推导出两个端面非接触光波导耦合的耦合系数的函数表达式,并基于此推导出阵列波导光栅解复用器的简单光谱响应效率的函数表达式。建立了分析阵列波导光栅解复用器光谱响应特性的简洁数学模型,阐明了阵列波导光栅解复用器对通道中心频率的响应度和相邻信号通道间的串扰与基本参数的关系,为设计和分析阵列波导光栅解复用器提供了理论基础。     

一种新颖的偏振不敏感的阵列波导光栅

提出了一种新颖偏振不敏感的阵列波导光栅(AWG)。器件的输入端增加了一个全光学偏振自动控制器(AOPSC),可将注入AWG的随机偏振的输入光转换为与AWG中TE0模偏振方向相同且功率损耗很小的线偏振光。AWG结构设计采用非对称的平面波导,包层与波导芯层的相对折射率差为0.7%,波导芯层的宽厚比要高,可以消除TE与TM模的简并,使波导中只能激励TE0模,而使TM0模截止。这种AWG结构完全消除了不同偏振态信号光对AWG工作性能的影响,从而使器件对偏振不敏感。设计的8×0.8nm器件整体尺寸为2cm×1cm,串扰优于-30dB,最大插入损耗为4.2dB。     

Cost-effective and high-resolution wavelength interrogation unit using an incomplete asymmetric arrayed waveguide grating

This paper presents a wavelength interrogation unit using an incomplete asymmetric arrayed waveguide grating (AWG) without output waveguides. The incomplete asymmetric AWG converts the wavelengths of the incident light into a spatial intensity distribution. The center of the spatial distribution is determined by a one-dimensional position sensitive detector (PSD). The simulation results show that wavelength shifts can be precisely interrogated by the device with a wavelength resolution of 3.5 pm. The device can be applied to the interrogation of fiber Bragg grating (FBG) temperature sensors with the temperature resolution of 0.3°C.     

用于32通道阵列波导光栅的氟化聚醚醚酮

合成了一种新型可自交联的苯乙炔封端的氟化聚醚醚酮(FPEEK-PEP)，并对其光学性质和热稳定性进行了表征。DSC和TGA结果显示FPEEK-PEP起始交联温度为360℃，交联后的FPEEK-PEP的玻璃化转变温度为190℃．在空气中5％的热失重温度为540℃，具有非常好的热稳定性。折射指数在1．455～1.53l范围内可调。旋涂时具有很好的成膜性，原子力显微照片(AFM)显示，粗糙度起伏为1．986nm。用FPEEK-PEP作为波导材料制作了32通道硅基聚合物阵列波导光栅(AWG)，测量其通道间隔近似为0．8nm．中心波长为1548nm。     

光纤与有机聚合物脊形波导的耦合损耗分析

光纤与有机聚合物脊形波导的耦合是有机聚合物波导器件封装中关键的一步,它直接影响器件的插入损耗.本文利用广角有限差分束传播法和有效折射率法对光纤与有机聚合物脊形波导的耦合损耗进行分析,得出了如下结论:1)耦合损耗随着错位、间隙、夹角的增大而增大;2)因错位而引起的耦合损耗在所有耦合损耗中占有主要位置.     

统计能量分析预测飞机壁板隔声量及舱室内声场分布

飞机舱室内噪声的预测对改进飞机性能具有重要意义，并为实际飞机设计和噪声控制措施提供理论依据。文章建立了飞机壁板隔声的统计能量分析模型，研究了外部声场激励和振动激励通过飞机壁板的隔声量，预测了飞机舱室内的声场分布。在此基础上运用面向对象及可视化技术，开发出相应的专用软件，该软件界面友好，用户可根据需要选定结构参数，材料性能，更改外部激励，并对预测结果进行可视化处理。运用该软件对舱内噪声进行预测，可以缩短飞机设计周期，减小对已有结构进行噪声控制的困难，提高经济效益。文中通过对某型飞机的舱室内噪声进行预测，验证了统计能量法预测飞机壁板隔声量的可靠性和该软件的实用性。     

硅基底平面波导光通讯集成器件的模拟、设计及工艺

随着平面波导制作工艺的日益成熟 ,制造精度的不断提高 ,成本的持续下降 ,平面波导光集成器件尤其是 Si基底上 Si O2 平面波导集成器件在光通信系统中的应用更加重要和广泛 .Y分支分束器、MMI耦合器、阵列波导光栅 (AWG)和蚀刻衍射光栅 (EDG)等平面波导集成器件正扮演着越来越重要的作用 ,BPM等数值计算方法在这些器件的设计和模拟中也起了重要作用 .本文就此作了一些探讨 .     

Low-power and high-speed thermo-optic switch using hybrid silica/polymer waveguide structure: design,fabrication and measurement

Response speed and power consumption are improved for a Mach–Zehnder interferometer (MZI) thermo-optic (TO) switch, by using a hybrid silica/polymer waveguide structure and optimizing both the thickness of the silica under cladding and that of the PMMA-GMA upper cladding. Fabrication techniques, including chemical vapor deposition (CVD), spin-coating and wet-etching, are adopted to develop the switch sample. Under 1550?nm wavelength, the driving powers under ON and OFF states are measured to be 0 and 13?mW, respectively, indicating a switching power of 13?mW. The fiber-to-fiber insertion loss under the ON state is 15?dB, the extinction ratio between the ON state and the OFF state is 18.3?dB, and the rise time and fall time are 73.5 and 96.5?µs, respectively. Compared with the TO switches based on Si/SiO₂ or all-polymer waveguide structure, the proposed device possesses both low power consumption and fast response speed, by virtue of the large TO coefficient of the polymer core, thin upper/under claddings and the large thermal conductivity of silica.     

Numerical simulation and error analysis for thermal diffusivity measurements using laser-induced thermal grating technique

The laser-induced thermal grating technique has been used to determine the thermal diffusivity of liquids and liquid mixtures. But the dynamic behaviour of the transient thermal grating has not yet been thoroughly investigated, and the systematic errors, which result from the departures from one-dimensional heat conduction, have scarcely been studied quantitatively. In this paper. a three-dimensional numerical simulation and results of the transient thermal grating technique are presented, which enable a good understanding of the dynamic behaviour of the transient thermal grating. The results of this simulation are important for the proper design of the experimental setup to keep the systematic errors for the diffusivity measurement small. Based on the simulation method, the systematic errors were analyzed quantitatively. Here, the following effects were studied: (I) sample thickness, (2) intersection angle, (3) absorption, (4) Gaussian beam intensity distribution and focusing of heating laser beam, and (5) heating pulse duration and laser power. This error analysis makes it possible to specify the criteria for optimum measuring conditions, to correct the measured thermal-diffusivity values for systematic errors, and to estimate the accuracy of the measurements.     

Measurement of the thermal diffusivity and speed of sound of hydrothermal solutions via the laser-induced grating technique

We use the laser-induced grating technique to measure the thermal difusivity and speed of sound of hydrothermal solutions. In this noninvasive optical technique, a transient grating is produced in the hydrothermal solution by optical absorption from two crossed, time-coincident nanosecond laser pulses. The grating is probed by measuring the diffraction efficiency of a third laser beam. The grating relaxes via thermal diffusion, and the thermal diffusivity is determined by measuring the decay of the grating diffraction efficiency as a function of of the pump-probe delay time. In addition, intense pump pulses produce counterpropagating acoustic waves that appear as large undulations in the transient grating decay spectrum. The speed of sound in the sample is simply the grating fringe spacing divided by the undulation period. The cell is made from a commercial high-pressure fitting and is equipped with two diamond windows for optical access. Results are presented for dilute dye/water solutions withT=400° and pressures between 20 and 70 MPa.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

基于相移光纤光栅传感器的碳纤维增强树脂复合材料基体裂纹超声探伤

复合材料内部的微小裂纹常会引起后续严重的破坏,因此需要对其进行检测。然而超声探伤复合材料基体裂纹非常困难。本文搭建了一个具有高灵敏度、大带宽的相移光纤光栅超声传感系统,利用此系统探测了在正交铺层碳纤维增强树脂复合材料板中传播的Lamb波。对Lamb波进行数据处理发现,随着三点弯曲实验产生的基体裂纹个数增加,Lamb波的幅值和频谱峰值线性减少。通过和传统压电传感器比较表明,相移光纤光栅传感器测得的Lamb波信号随复合材料基体裂纹数的增加其幅值具有更高的下降速率,表明相移光纤光栅传感器更适合于复合材料基体裂纹的超声探伤。研究表明,新开发的传感系统能够探测到中心频率为300 kHz的微弱超声信号,并能够对碳纤维增强树脂复合材料板中微小基体裂纹个数进行精确评估。      

Fabrication and shape detection of a catheter using fiber Bragg grating

Considering the spatial position and shape detection properties of the fiber Bragg grating (FBG) curve sensor used in the human body, the positioning accuracy of the FBG curve sensor plays a major role in the pre-diagnosis and treatment of diseases. We present a new type of shape-sensing catheter (diameter of 2.0 mm and length of 810 mm) that is integrated with an array of four optical fibers, where each contains five nodes, to track the shape. Firstly, the distribution of the four orthogonal fiber gratings is wound around a nitinol wire using novel packaging technology, and the spatial curve shape is rebuilt based on the positioning of discrete points in space. An experimental platform is built, and then a reconstruction algorithm for coordinate point fitting of the Frenet frame is used to perform the reconstruction experiment on millimeter paper. The results show that, compared with those in previous studies, in 2D test, the maximum relative error for the end position is reduced to 2.74%, and in 3D reconstruction experiment, the maximum shape error is 3.43%, which verifies both the applicability of the sensor and the feasibility of the proposed method. The results reported here will provide an academic foundation and the key technologies required for navigation and positioning of noninvasive and minimally invasive surgical robots, intelligent structural health detection, and search and rescue operations in debris.The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-019-00284-z.pdf     

Symmetry between the transfer properties of micro-ring resonators with gain and with loss

Gain and loss affect the performance of dispersive micro-ring resonator systems significantly. Through analysing the transfer functions of two-port ring-resonator (TPRR) circuits and coupled micro-ring resonators, the symmetry between the transfer properties of micro-ring resonators with loss and with gain is discovered. For two TPRRs whose attenuation and gain coefficients are equal to each other, or for two coupled micro-ring resonators whose counterparts have equal gain and loss respectively, their intensity transmissions are reciprocal, while the phase shifts and dispersions are the same. This symmetry demonstrates the action mechanism of loss and gain on the transmissions and dispersions of these micro-ring resonators. It is useful for analysing and designing micro-ring resonators in group velocity control and dispersion compensation applications.     

光敏性杂化SiO2波导薄膜的制备、表征及应用

利用有机/无机杂化方法制备了光敏性溶胶-凝胶（sol-gel）SiO2材料，在预生长了18μm厚的SiO2上包层的硅基片上旋涂成膜。经前烘、紫外曝光、后烘的薄膜在5μm×5μm的扫描范围内的表面粗糙度只有0．266nm，表面起伏度只有0．336nm。利用紫外光直写技术，制作出条形波导器件。SEM照片表明波导端面形状较好，侧壁陡直。对1×4多模干涉型分束器进行初步的通光测试，观察到分光效果较好的近场输出图像。     

Simplified loss analysis and comparison of full-bridge,full-range-ZVS DC-DC converters

The loss of zero-voltage-switching (ZVS) of active switches has been a serious limitation of full-bridge (FBZVS) converters. Many techniques have been proposed in the past to extend the range of ZVS operation over the wider and also the full range of operation. However, in these techniques ZVS is achieved at the expense of additional conduction loss in active switches and losses in the auxiliary components. In this paper, the analysis for the additional losses in various full-range FBZVS DC-DC converters and their comparative evaluation is reported. Closed form expressions are derived for average value of device currents and losses. The loss curves for various topologies are plotted and compared. The analytical results are found to be consistent with the experimental efficiency tests performed on 500 W, 100 kHz prototype. It is concluded that a recently proposed new topology has the least penalty of additional losses.     

Reduction of residual stress and deformation in electron beam welding by using multiple beam technique

The electron beam could be controlled by magnetic field for fast deflection, in which way multi-beam could be produced by deflection technique. The multi-beams run simultaneously for material processing with different heat input and positions. Therefore, it is possible to adjust the thermal effects and optimize the process. In this paper, the generation of multi-beams in electron beam welding (EBW) was investigated, and the processes of EBW with multi-beams were also investigated by both the numerical simulation methods, i.e., finite element analysis (FEA), and the experiments. The result shows that the residual stress of EBW could be minimized by using the multiple beam technique, and at the same time the welding deformation could also be reduced with the optimized parameters.     

Optimization of material removal rate and surface roughness during electric discharge machining of ultra-fine grained Al6082 using Taguchi technique

In the current work, the statistical analysis of various electric discharge machining parameters on Al6082 ultra-fine grained aluminium alloy using Taguchi method has been presented. Repetitive corrugation and straightening (RCS) method was employed to obtain ultra-fine grained aluminium alloy. The electric discharge machining studies were carried out for test variables – pulse off time, pulse on time and current (I). The specimens were machined in dielectric medium with current range of 3 A to 9 A in step of 3 A. Machining features of the samples analysed statistically by adopting the Taguchi's - design of experiments (DOE) methodology. Impact of parameters on material removal rate (MRR) and surface roughness (SR) were examined via signal-to-noise ratio (S/N ratio, expressed in decibel, dB) as well as analysis-of-variance (ANOVA). Outcomes disclose that every selected response explicitly surface roughness (SR) and material removal rate was significantly influenced by parameters. The material removal rate was found to rise with discharge current and decrease with the duration of pulse on time and the duration of pulse off time. On the other hand, the surface roughness increased with increase in peak current and decreased with pulse on time and pulse off time especially. The machining mechanisms were examined by scanning electron microscopy.     

Growth of silicon carbide nanorods from the hybrid of lignin and polysiloxane using sol-gel process and polymer blend technique

We report here the formation of silicon carbide (SiC) nanorods from organic-inorganic hybrid of the commercially available lignin and sol-gel derived nanosized silica. The SiC nanorods were identified by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The surface morphology shows the formation of continuous nanorods of diameter in the range of 50-200 nm. The X-ray diffraction (XRD) pattern show peaks at 2θ = 35.5° and 60.2° indicate the formation of β-SiC and a sharp peak at 2θ = 22.1° suggests the presence of unreacted crystalline silica (crystoballite). The characteristic vibration of SiC at 791 cm^− 1 in Fourier transform infrared spectroscopy (FTIR) was also observed.     

消声器传递损失预测的边界元数值配点混合方法

将边界元法与数值配点法结合形成混合方法用于计算任意截面形状消声器的传递损失。消声器划分为若干子结构,用边界元法计算具有非规则形状的子结构阻抗矩阵,用二维有限元法提取等截面子结构特征值及特征向量,用配点法获得阻抗矩阵;将每个子结构阻抗矩阵连接用于传递损失计算。为减少计算时间提出简化方法计算消声器传递损失。结果表明,混合法在保证计算精度前提下可节省计算时间。     

Yields, solids loss and effluents generation during blanching and cooling of asparagus spears

Blanching and cooling of asparagus spears (two sizes) were compared for overall product yield, total solids loss, effluents generation and chemical oxygen demand (COD). Blanching was done using steam followed by cold water (2°C) cooling or air (static or forced) cooling. Steam blanching of 1 cm diameter asparagus produced a total solids loss of 1.04%, an effluent of 9.50 g/100 g of fresh asparagus, a COD of 0.061 g/100 g of fresh asparagus and a yield of 99.20%. Yields for cold water cooling, static air cooling and forced air cooling were, respectively, 99.8, 94.7 and 96.0%. Since cold water cooling produced a total solids loss similar to steam blanching, the combination steam blanching (IQB)-cold water cooling appears to be convenient for obtaining an excellent yield with low total solids loss of a high price vegetable like asparagus.