Cellulose‐Based Microparticles for Magnetically Controlled Optical Modulation and Sensing

Responsive materials with birefringent optical properties have been exploited for the manipulation of light in several modern electronic devices. While electrical fields are often utilized to achieve optical modulation, magnetic stimuli may offer an enticing complementary approach for controlling and manipulating light remotely. Here, the synthesis and characterization of magnetically responsive birefringent microparticles with unusual magneto‐optical properties are reported. These functional microparticles are prepared via a microfluidic emulsification process, in which water‐based droplets are generated in a flow‐focusing device and stretched into anisotropic shapes before conversion into particles via photopolymerization. Birefringence properties are achieved by aligning cellulose nanocrystals within the microparticles during droplet stretching, whereas magnetic responsiveness results from the addition of superparamagnetic nanoparticles to the initial droplet template. When suspended in a fluid, the microparticles can be controllably manipulated via an external magnetic field to result in unique magneto‐optical coupling effects. Using a remotely actuated magnetic field coupled to a polarized optical microscope, these microparticles can be employed to convert magnetic into optical signals or to estimate the viscosity of the suspending fluid through magnetically driven microrheology.     

Fabrication and Sensing Performance of Smart Composite Structures Using Optical Fibre Sensors

This paper determines the performance of Fibre Bragg Grating (FBG) sensors for strain sensing applications in carbon fibre composite materials. Carbon fibre laminates in either cross-plied or quasiisotropic stacking sequences were fabricated using T300/Hexcel 914 prepregs. The FBG optical sensors were either surface attached, or embedded within laminates. The sensor orientation was aligned either parallel or transverse to the adjacent carbon fibre layers. The composite structures with integrated FBG sensors were subjected to static tensile loading. A scanning fibre Fabry-Perot filter was used to monitor the reflected Bragg wavelengths. The optical sensor embedded between two 90° carbon fibre plies shows a high sensitivity to multi-site cracking formed in the transverse plies. The embedding in 90° plies seems to change the local stress distributions and to become a source of crack initiation. Efficient stress transfer from the host materials to the sensors is dependent upon incorporation methods, the thickness of the adhesive layers, and the location of the sensors.     

Fabrication and Sensing Performance of Smart Composite Structures Using Optical Fibre Sensors

This paper determines the performance of Fibre Bragg Grating (FBG) sensors for strain sensing applications in carbon fibre composite materials. Carbon fibre laminates in either cross-plied or quasiisotropic stacking sequences were fabricated using T300/Hexcel 914 prepregs. The FBG optical sensors were either surface attached, or embedded within laminates. The sensor orientation was aligned either parallel or transverse to the adjacent carbon fibre layers. The composite structures with integrated FBG sensors were subjected to static tensile loading. A scanning fibre Fabry-Perot filter was used to monitor the reflected Bragg wavelengths. The optical sensor embedded between two 90° carbon fibre plies shows a high sensitivity to multi-site cracking formed in the transverse plies. The embedding in 90° plies seems to change the local stress distributions and to become a source of crack initiation. Efficient stress transfer from the host materials to the sensors is dependent upon incorporation methods, the thickness of the adhesive layers, and the location of the sensors.     

Observation of Fibre Laser Instabilities Through Modulation of the Cavity Optical Length

Abstract

A Nd-doped, single-mode, double-clad fibre laser (FL) is coiled around a resonant piezoelectric ceramic ring; this induces modulation of the cavity optical length and two distinct classes of laser intensity instabilities are observed as the ring drive voltage V _P-P is increased. The first class involves a slowly varying intensity, with characteristic time scale in the microsecond range. For fixed drive-voltage frequency f _m ≈ 20 kHz, we consistently observe subharmonics f _m/2 and f _m/4 in the FL output intensity spectrum; noise in the system precludes the observation of higher subharmonic bifurcations. Small-amplitude random relaxation oscillations of the unmodulated FL are strongly amplified as V _P-P is increased and transition to a state of large-amplitude chaotic relaxation oscillations occurs for V _P-P ≈ 4 V; a value of 2·6 has been measured for the correlation dimension of the chaotic attractor. The second class of laser instability occurs simultaneously for V _P-P ? 10 V, and the FL output consists of a train of pulses about 2 ns wide at a repetition rate close to the cavity frequency f _cav ≈ 15 MHz and modulated by the slowly varying chaotic envelope described above.     

光学微腔相位调制解调系统中的纹波噪声

针对光学微腔调制解调系统中存在的纹波噪声进行了理论分析,得出了纹波噪声来源于分立光学器件接头之间形成的F-P谐振腔结构。对光纤F-P腔的特性进行了分析得到了F-P腔透射光传递函数;对F-P腔的谐振特性进行了仿真得到了不同端面反射率下的谐振特性曲线,并分析了反射率与精细度的关系以及反射率对谐振特性的影响。提出了两种抑制纹波噪声的方法,即端面反射抑制方法和相位调制抑制方法,实验结果表明,两者有效地抑制了系统中的纹波噪声,提高了谐振信号的信噪比,为解调信号的获得和光学微腔的谐振点跟踪锁定奠定了基础。     

Nonlinear Coefficients and the Effective Area of Cross-phase Modulation Coupling of LP01 Optical Fibre Modes

Abstract

The dispersion relations of two nonlinearly interacting LP₀₁ modes are derived from a perturbation procedure. A step-index optical waveguide is considered here, but it should be emphasized that other index profiles can be introduced without any increase in conceptual difficulty. The cross-phase modulation couples waves with the same polarization and different frequencies. The nonlinear contributions to the linear wavenumbers arising from the effects of both self-phase and cross-phase modulation are obtained. The method used for deriving the nonlinear dispersion coefficients is novel because it uses nonlinear changes in the wave-field distribution in the transverse direction. As a consequence, the results differ from those obtained by the usual method of determining the nonlinear wavenumber shift. A set of coupled nonlinear Schrödinger equations is considered and a new nonlinear effective area involved in the cross-phase modulation effect is defined.     

新颖的CB形态学串并复合散斑噪声滤波器

基于轮廓结构元素形态学(CB形态学)和广义多结构元素的数学形态学,构造了一种新颖的用于抑制图像中的散斑噪声的串并复合滤波器.首先采用全方位多结构元素的广义多刻度形态开最大滤波器与广义多刻度形态闭最小滤波器相并联的滤波器进行滤波,力求在滤波的同时图像几何细节损失尽可能少,然后通过级联的CB开和CB闭滤波器,再滤除剩余的斑点噪声,从而在有效抑制图像中的散斑噪声的同时更好地保持了图像的细节信息.分析和仿真表明了本文提出的滤波算法的有效性.     

车用交流发电机电磁振动噪声预测研究

为了从发电机设计之初就能精确预测其振动和噪声,进而进行优化设计,需要建立一个电磁振动噪声预测分析模型。以一台36槽6极对的爪极发电机为研究对象,利用有限元法计算作用在定子铁芯上的电磁力,再耦合到电机结构模型中计算瞬态电磁振动,最后将电机振动响应作为声学边界条件,利用时域边界元法计算出电机的辐射噪声。计算表明该发电机的电磁振动噪声频率以36谐次为主,与实验测试的噪声频谱分布相同,两者最大声压级相差2.9 d B,实现了较高精度的电磁振动噪声预测分析,对发电机NVH研究具有指导意义。     

复合材料无损检测与光纤传感器

本文讨论了复合材料测试特点,介绍了光纤传感器原理及特点,重点讲述光纤传感器在复合材料无损测试中的应用。     

碳纤维复合材料在空间光学相机中的应用研究

随着空间光学相机口径的增大,相机的质量也随之增加,要满足轻质量、高分辨的空间相机要求,碳纤维复合材料是一个很好的选择.根据空间光学相机的精度、稳定性要求,对比了空间相机中常用材料的性能,分析了碳纤维复合材料应用于空间光学相机的三大优势和两大劣势,介绍了国内外碳纤维复合材料在空间相机中的应用概况和水平,指出了碳纤维复合材料在空间光学相机中的广泛应用必然是未来空间光学相机的发展方向.     

光纤激光多普勒横向位移传感器

介绍了一种光纤式激光多普勒横向传感器，被测位移和光束方向垂直。该系统采用双通道比相测量方法，消除了低频噪声并且直接得到相对位移量，可以测量从静态到２０ｋＨｚ的振动。文中给出了理论分析和实验结果。     

2D－SROP－1型光学轮廓仪中调制误差的分析与抑制

应用ＰＺＴ作为微位移驱动机构，研制成２Ｄ－ＳＲＯＰ－１型光学轮廓测量仪，它的垂直分辨率可达１ｎｍ，可测量Ｒｎ＜０．１ｕｍ的表面。本文分析了微位移调制误差对仪器的影响，导出了测量相位偏差４ψ与调制误差△β的关系，考查了串联电容对微位移特性的影响。结果表明，在微位移调制器上串联一适当电容，使在仪器工作频率范围内响应线性度达到１．０８％，保证了仪器的测量精度。     

Plastic Optical Fibre Sensors for Environmental Monitoring: Biofouling and Strain Applications

Abstract: Two long-term environmental monitoring plastic optical fibre (POF) sensors are described, using light intensity modulation. An evanescent field biofouling sensor was developed and characterised with sensitivity ±0.007 refractive index units or 0.5% below n  = 1.4 and ±0.002 refractive index units or 0.15% above n  = 1.4. A tapered POF was developed and tested as a strain sensor, which demonstrated a significant proportion of excellent linearity and exhibited good agreement with measured strain values. The POF strain sensor appeared to be well-behaved in that it showed little data scatter and was able to monitor strains up to 1.4% without failure. These two applications clearly demonstrate the potential POF sensors have for cheap, on-line continuous environmental monitoring.     

测量表面粗糙度的新型光纤传感器

介绍了一种测量表面粗糙度的准直型光纤传感器。该传感器成功地消除了光纤测头到被测表面距离变动和环境的杂散光线对输出的影响,传感器光通量的计算方法可用于位移及其它反射型光纤传感器的特性分析和结构设计。     

光纤应用于结构自修复的研究

介绍了在智能结构中采用空心光纤感器网络成自诊断,自修复的系统,在结构中埋入形状记忆合金丝网络,对地强结构强度,改善自修复的质量均起到了良好的作用。     

残留农药的光学检测技术和去噪处理

根据残留农药受到紫外光激发能够发出荧光的机理,研究了一种用于测量残留农药浓度的荧光光纤测量系统.该系统采用脉冲氙灯作为激发光源,光纤探测并传输荧光,电荷耦合器(CCD)作为荧光检测系统的光电转换器件.由于荧光是微弱信号,系统采用微弱信号处理电路对CCD输出信号进行了处理,并且采用相关双采样技术有效地抑制了CCD输出噪声的干扰.用该系统对吡虫啉溶液进行荧光分析,实现了对吡虫啉的快速测定,在5～100μg/L范围内,荧光强度和浓度基本呈线性关系,线性相关系数为0.9959.     

Optical Microresonators for Sensing and Transduction: A Materials Perspective

Optical microresonators confine light to a particular microscale trajectory, are exquisitely sensitive to their microenvironment, and offer convenient readout of their optical properties. Taken together, this is an immensely attractive combination that makes optical microresonators highly effective as sensors and transducers. Meanwhile, advances in material science, fabrication techniques, and photonic sensing strategies endow optical microresonators with new functionalities, unique transduction mechanisms, and in some cases, unparalleled sensitivities. In this progress report, the operating principles of these sensors are reviewed, and different methods of signal transduction are evaluated. Examples are shown of how choice of materials must be suited to the analyte, and how innovations in fabrication and sensing are coupled together in a mutually reinforcing cycle. A tremendously broad range of capabilities of microresonator sensors is described, from electric and magnetic field sensing to mechanical sensing, from single‐molecule detection to imaging and spectroscopy, from operation at high vacuum to in live cells. Emerging sensing capabilities are highlighted and put into context in the field. Future directions are imagined, where the diverse capabilities laid out are combined and advances in scalability and integration are implemented, leading to the creation of a sensor unparalleled in sensitivity and information content.     

流场光学诊断的光偏振相移数字剪切散斑干涉

本文提出了应用于流场光学诊断的使用光偏振相移的数字剪切散斑干涉技术，它具有如下两个显著的优点，首先，产生干涉效应的两相干光束均是物光束。它们通过几乎相同的光学元件与几何空间。这样可以降低测量过程中对环境的防震需求，便于工程中的实际应用。其二，采用光偏振相移方法来获取了干涉图上的位相信息，与通常使用的压电陶瓷相移方法相比，不需要复杂的标定，使用更为方便。     

Random Multimode Optical Media: II. Statistical Analysis of the Fibre Diameter Variations

Abstract

We analyse the stochastic fluctuations of one of the optical fibre parameters: the core diameter. The diameter variations are treated as a process. The randomness, stationarity and ergodicity of this process are analysed. The correlation functions, spectral density functions and probability density functions are also presented.