改性石墨烯包覆光纤的马赫-曾德尔大肠杆菌传感器

针对日益严峻的食品安全问题,特别是食源性致病菌的快速检测,本文提出一种基于表面改性石墨烯粗锥型马赫-曾德尔干涉结构的光纤大肠杆菌传感器。首先,截取一根4 cm的实心光子晶体光纤,两端分别与两根单模光纤进行粗锥熔接,形成基于马赫-曾德尔干涉原理的传感结构;接着,制备一种表面改性石墨烯敏感材料,将它涂覆在实心光子晶体光纤的表面,使传感器对大肠杆菌溶液有较高的灵敏度;最后,将上述传感器置于水槽中,以此检测大肠杆菌溶液浓度。实验结果表明,在大肠杆菌溶液浓度为50~600 cfu/mL内,随着菌液的浓度增大,传感器的干涉光谱发生了明显的蓝移,灵敏度为3.43 pm/(cfu·mL^-1),菌液浓度与波长偏移的线性度为0.95649,检测限为67.18 cfu/mL,响应时间为15 s。该传感器成本低、体积小、响应时间快,适用于低浓度大肠杆菌浓度的快速检测。     

马赫-曾德尔干涉集成化的全光纤磁场与温度传感器

为了简化光纤磁场与温度传感器的结构并提高传感器灵敏度,设计并制作了马赫-曾德尔干涉集成化的全光纤磁场与温度传感器。将单根光纤的马赫-曾德尔模间干涉结构和双臂马赫-曾德尔干涉结构结合:将总长度为1.2m的单模光纤部分制备成长度为2.7cm、锥腰直径为30.1μm的锥形微纳光纤,并得到了拉锥时间与锥腰直径的关系。将锥形微纳光纤放置尼龙槽内并包覆磁凝胶构成传感头,实现模间干涉的马赫-曾德尔磁场传感器;将磁场传感器通过两耦合比为50%∶50%的耦合器并联带有可调谐光衰减器的单模光纤形成马赫-曾德尔干涉的温度传感器。从理论上分析了光谱漂移对磁场和温度传感的特性关系,实验测得室温下磁场强度在25~50mT时,磁场传感的灵敏度为0.301 14nm/mT;在磁场强度为0,温度由25℃升高到30℃时,温度传感的灵敏度为0.518 86nm/℃。该传感器可广泛应用于电力系统放电检测、材料加工、安全监控等领域。     

双马赫-曾德尔型干涉仪定位技术研究

在干涉型分布式光学振动传感系统中,双马赫-曾德尔技术具有较高的定位精度和较低的成本,更受关注。现搭建了双马赫-曾德尔分布式光纤传感系统,并对其进行了定位实验,阐述了检测系统的组成和原理。对基于互相关算法的定位性能进行研究,测试了其单点定位和多点定位功能,指出其定位局限性。另外重点分析了影响该系统定位稳定性的因素,提出一种数据处理算法,以提高其定位稳定性。实验结果表明,经过该算法数据处理之后,系统定位稳定性和可靠性得到极大提高。     

双芯光纤马赫-曾德尔干涉仪的温度特性

对适用于温度传感的双芯光纤马赫-曾德尔干涉仪进行了研究,并通过将一根单模双芯光纤熔接在两根单模光纤之间,制得了双芯光纤马赫-曾德尔干涉仪型梳状滤波器.用干涉原理分别分析了该器件传输谱的自由空间谱宽与波长、双芯光纤的长度和两纤芯间的有效折射率差的关系,实验检测了它的温度特性.结果显示,随着温度的升高,该器件的传输谱发生红...     

基于马赫-曾德尔干涉仪的全光逻辑异或门理论研究

基于半导体光放大器(SOA)和线性光放大器(LOA)构成的马赫-曾德尔干涉仪(MZI),从速率方程出发,模拟了LOA的泵浦放大和增益箝制特性,建立了SOA-MZI和LOA-MZI结构全光异或门数值模型,通过控制探测光功率和偏置电流,实现了两路40 Gbit/s 信号的异或运算。并通过求解速率方程,对异或运算的结果进行了分析和比较;从器件结构上对2种异或门运算结果的差异给出了解释。结果表明:SOA和LOA中载流子恢复时间限制了信号处理速度;合理控制偏置电流和探测光功率可以提高信号处理能力;LOA具有增益箝制作用,对输入信号的扰动具有不敏感性;与SOA-MZI异或门相比,LOA-MZI异或门输出信号的消光比较高,功率较低;对于输出脉冲波形而言,LOA-MZI异或门性能优于SOA-MZI异或门。     

非对称马赫-曾德尔干涉仪型不等带宽光学梳状滤波器

为提高光交错复用器系统带宽的有效利用率,满足系统中不同传输速率对带宽的要求,针对信道间隔为50 GHz的输入信号提出了新的非对称MZI型不等带宽光学梳状滤波器,研究了该系统的输出谱和制作方法。基于光纤传输理论分析了设计构成,给出了输出谱表达式及设计中所需要的实验参量。当滤波器的两对光纤干涉臂长度差相等,各耦合器的耦合系数选取适当时,该器件实现了奇偶信道上不等带宽输出,可分别用于10 Gb/s和40 Gb/s传输,信道间隔为0.8 nm,信道隔离度25 dB;分析还发现该器件对3个耦合器的耦合参数不敏感。实验表明:该器件不仅能实现不等带宽输出功能,在实际制作过程中还由于器件对耦合器的耦合参数要求不是十分严格而降低了器件实际制作难度,因此具有实用价值。     

基于3×3耦合器的双马赫-曾德尔干涉仪数字化相位解调

由于马赫-曾德尔（Mach-Zehnder）光纤干涉传感系统的定位精度在实际应用中受到初始相位偏移的影响,本文针对系统的光路结构,提出了一种基于3×3耦合器的被动数字化解调方法。利用3×3耦合器的2路输出信号构成椭圆曲线,在约束条件下对信号系数进行最小二乘拟合,然后采用微分交叉相乘法解调出相位信号。与传统的解调方法相比,提出的方法降低了对耦合器高对称性的要求,不需限制其它参数;约束条件下椭圆拟合的鲁棒性好,尤其是对于椭圆度较差的数据点具有很强的适应能力,适用于微弱振动信号的解调。仿真结果和现场实验数据证明该方法切实有效,运算量小,利用现场数据解调出的相位信号相关性达到0.992 0;互相关计算显示其在总长43 km的管道上的定位误差为81.2 m,有效提高了系统性能。     

检测激光晶体侧面致冷均匀性的马赫-泽德干涉法

提出了一种基于马赫-泽德干涉仪的检测法。理论分析表明,该法检测到的物光与参考光的干涉条纹即为晶体径向平面上的等温线。通过热分析软件对均匀和非均匀致冷晶体温度场的模拟表明,当检测到的干涉条纹为以晶体径向平面中心为圆心的圆环时,晶体周边接触良好,致冷均匀;当检测到的干涉条纹向某一方向扭曲时,该方向上致冷块与晶体边界接触不好。对装在铜致冷座里的3 mm×3 mm×5 mm,a切割,0.5% Nd³⁺掺杂的Nd:YVO₄晶体进行了检测,根据检测到的干涉条纹扭曲方向重新安装了致冷座,获得了以端面中心为圆心的干涉环。实验结果与理论分析相符,证明马赫-泽德干涉法可以检测晶体侧面致冷均匀性。     

长脉冲激光与硅相互作用气化过程的数值模拟

为了研究毫秒量级脉宽激光与半导体材料的相互作用机理,建立了一维有限元模型,对长脉冲激光与硅相互作用的气化现象进行了数值模拟.在计算中,利用热焓法处理了固一液相变过程,并根据热流方程考虑了气化产生的能量损失.在人射激光功率密度相同的条件下,定量地描绘了不同脉宽激光辐照材料的温度分布,前表面的温度历史,以及气化速度和气化深...     

Atomic scale deformation in silicon monocrystals induced by two-body and three-body contact sliding

This paper discusses the deformation of silicon monocrystals subjected to two-body and three-body contact sliding with the aid of the molecular dynamics analysis. It was found that amorphous phase transformation is the main deformation in silicon and the onset of such inelastic deformation can be well predicted by a stress criterion. In a two-body contact sliding, the deformation of silicon falls into no-wear, adhering, ploughing and cutting regimes, while in a three-body contact sliding it follows the regimes of no-wear, condensing, adhering and ploughing. Under certain conditions in three-body sliding, wear without any subsurface damage can also occur when the bonding strength among surface silicon atoms is weakened and material removal takes place through the mechanism of adhesion. Based on the detailed deformation analysis, a new friction law and a new concept for wearability evaluation were proposed.     

Ultraprecision surface flattening of porous silicon by diamond turning

Porous silicon is receiving increasing interest from a wide range of scientific and technological fields due to its excellent material properties. In this study, we attempted ultraprecision surface flattening of porous silicon by diamond turning and investigated the fundamental material removal mechanism. Scanning electron microscopy and laser Raman spectroscopy of the machined surface showed that the mechanisms of material deformation and phase transformation around the pores were greatly different from those of bulk single-crystal silicon. The mechanism of cutting was strongly dependent on the direction of cutting with respect to pore edge orientation. Crack propagation was dominant near specific pore edges due to the release of hydrostatic pressure that was essential for ductile machining. Wax was used as an infiltrant to coat the workpiece before machining, and it was found that the wax not only prevented chips from entering the pores, but also contributed to suppress brittle fractures around the pores. The machined surface showed a nanometric surface flatness with open pores, demonstrating the possibility of fabricating high-precision porous silicon components by diamond turning.     

Measurement of specimen-induced aberrations of biological samples using phase stepping interferometry

Confocal or multiphoton microscopes, which deliver optical sections and three‐dimensional (3D) images of thick specimens, are widely used in biology. These techniques, however, are sensitive to aberrations that may originate from the refractive index structure of the specimen itself. The aberrations cause reduced signal intensity and the 3D resolution of the instrument is compromised. It has been suggested to correct for aberrations in confocal microscopes using adaptive optics. In order to define the design specifications for such adaptive optics systems, one has to know the amount of aberrations present for typical applications such as with biological samples. We have built a phase stepping interferometer microscope that directly measures the aberration of the wavefront. The modal content of the wavefront is extracted by employing Zernike mode decomposition. Results for typical biological specimens are presented. It was found for all samples investigated that higher order Zernike modes give only a small contribution to the overall aberration. Therefore, these higher order modes can be neglected in future adaptive optics sensing and correction schemes implemented into confocal or multiphoton microscopes, leading to more efficient designs.     

Fundamental investigation of subsurface damage in single crystalline silicon caused by diamond machining

Single crystalline silicon was plunge-cut using diamond tools at a low speed. Cross-sectional transmission electron microscopy and laser micro-Raman spectroscopy were used to examine the subsurface structure of the machined sample. The results showed that the thickness of the machining-induced amorphous layer strongly depends on the tool rake angle and depth of cut, and fluctuates synchronously with surface waviness. Dislocation activity was observed below the amorphous layers in all instances, where the dislocation density depended on the cutting conditions. The machining pressure was estimated from the micro-cutting forces, and a subsurface damage model was proposed by considering the phase transformation and dislocation behavior of silicon under high-pressure conditions.     

A novel dynamic opto‐thermo‐mechanical stress testing device 1: Design of the device

This article presents a dynamic opto‐thermo‐mechanical stress testing device to characterize fiber properties. The device has multi‐modes and consists of many functions. These modes include stretching, bending, rotating, twisting, and heating processes. Every process can be controlled by micro‐controller unit via software programs specially designed for this purpose. The micro‐controller unit can execute two different processes at the same time. Such as, dynamic stretching process under the effect of thermal treatment, dynamic stretching process and relaxation, bending process under the effect of thermal treatment, and so forth. Software programs with their flow charts are designed for the application of these processes. The advantage of this device is that it can be done statically and dynamically to characterize all types of fibers (polymer and optical). The device is designed to be attached with two‐beam polarizing interference microscope to investigate the dynamic opto‐thermo‐mechanical properties of the tested fiber under the effect of different applied stresses. Isotactic polypropylene, iPP, fiber is used for some applications of this device, as examples, in stretching, rotation, and twisting modes. Interferograms and graphs are given for illustration.     

Investigation of damage generation process by stress waves during femtosecond laser drilling of SiC

Femtosecond laser processing has garnered significant attention as a method for micromachining silicon carbide (SiC), which is expected to be used in next-generation power semiconductors. However, a significant amount of damage is generated around the processing area during the femtosecond laser processing of SiC. In this study, high-speed phenomena during the femtosecond laser drilling of SiC are observed with high temporal and spatial resolutions by combining pump-probe imaging and a high-speed camera. In addition, a stress wave propagation simulation based on experimental results is conducted. Based on the experimental and simulation results, the mechanism of damage generation by the stress wave generated during material removal is elucidated. The damage generation mechanism elucidated in this study will facilitate the development of damage suppression methods and the expansion of industrial applications of SiC.     

纳秒激光加工2.5维Cf/SiC复合材料的烧蚀孔洞特征

针对新型材料2.5维碳纤维增强陶瓷基（Cf/SiC）复合材料采用传统机械加工难以去除加工的问题,采用纳秒激光烧蚀2.5维Cf/SiC复合材料,烧蚀后采用扫描电子显微镜观察其烧蚀孔洞形貌特征,并分析其烧蚀去除机制,讨论激光加工参数对烧蚀孔径的影响。研究表明,Cf/SiC复合材料的激光烧蚀区域出现烧蚀孔洞、重凝、纤维断口、末端气胀,以及长轴与纤维方向一致的椭圆形材料性能变化区域等烧蚀现象;激光烧蚀Cf/SiC复合材料过程中存在氧化的化学变化现象;烧蚀产生的孔径随烧蚀功率的增加和烧蚀时间的延长而增大,烧蚀时间和烧蚀功率均较大时,可能存在烧蚀孔洞被重凝材料堵塞或部分堵塞的情况。计算出纳秒激光的束腰半径为223 μm,纳秒激光烧蚀Cf/SiC复合材料的烧蚀阈值为0.32 J/cm2。