Optical properties effects upon the collection efficiency of optical fibers in different probe configurations

When optical fibers are used for delivery and collection of light, two major factors affect the measurement of collected light: 1) light transport in the medium from the source to the detection fiber and 2) light coupling to the optical fiber (which depends on the angular distribution of photons entering the fiber). This paper studies the latter factor, describing how the efficiency of the coupling depends on the optical properties of the sample. The coupling dependence on optical properties is verified by comparing experimental data to a simple diffusion model and to a Monte Carlo (MC)-corrected diffusion model. Mean square errors were 7.9% and 1.4% between experiments and the diffusion, and experiments and the MC-corrected models, respectively. The efficiency of coupling was shown to be highly dependent on the numerical aperture (NA) of the optical fiber. However, for lower scattering, such as in soft tissues, the efficiency of coupling could vary two- and threefold from that predicted by fiber NA. The collection efficiency can be used as a practical guide for choosing optical fiber-based systems for biomedical applications.     

The effect of light losses in double integrating spheres on opticalproperties estimation

The double integrating sphere setup (DIS) measures diffuse reflectance, diffuse transmittance and collimated transmittance, from which the optical properties of tissue (the absorption coefficient μ _a, the scattering coefficient μ_s and the anisotropy of scattering g) are estimated. The effect of light losses in the DIS and optical thickness on optical properties estimation by the inverse adding doubling algorithm (IAD) and uniqueness of measurement have been investigated using a Monte Carlo method. Results were obtained for optical properties in turbid tissues (0.80⩽albedo⩽0.99, 0.80⩽anisotropy⩽ 0.99, 1.5⩽optical thickness⩽7.5) sandwiched between glass slides. At optical thickness=6.0 the loss of light through the glass slides is ranging from 13%±0.5% (at albedo=0.80) to 15%±0.5% (at albedo=0.98) of the incident power. The loss of light at the exit port in the transmittance sphere is increasing up to 50% of the incident power at highly forward scattering. These losses result in a dependency on optical thickness of the optical properties estimation by the IAD algorithm. Furthermore, because of these losses, the DIS setup measurement is found to be fundamentally nonunique, when simultaneously measuring the diffuse reflectance, diffuse transmittance and collimated transmittance     

Theoretical studies of AlGaAs-GaAs multiple-quantum-well opticalcouplers defined by ion-implantation-induced intermixing

A simple and accurate model is presented for the analysis of ion-implanted AlGaAs-GaAs multiple-quantum-well (MQW) symmetric and asymmetric optical couplers. The modal propagation constants and field profiles of the guided modes of the couplers are solved numerically using a quasi-vector method based on the Galerkin's method. MQW optical couplers defined by ion-implantation-induced intermixing are shown to have similar optical properties as conventional dielectric rib optical couplers. They also provide a more flexible control over the waveguiding and coupling characteristics by changing parameters such as waveguide separation, mask width, ion implant energy, and diffusion time     

光电集成强电场测量系统及其应用研究

为研发高性能强电场测量系统,在分析高压电场测量的特殊要求后,介绍了光电电场测量系统的基本原理、最新进展及其在高压测量领域的优势。通过对光电集成电场测量系统及传感器体系结构、关键参数的分析,研制了一种光电集成强电场传感器并测量它的输入输出特性。用研制的测量系统测量棒板间隙击穿过程冲击电场与复合绝缘子工频场,证明光电集成电场测量系统在高压测量研究领域的广阔应用前景。     

100-Gb/s optical communications

Optical communications is a quickly evolving field, driven by the ever increasing need for communication bandwidth. Over the next decade, the field is expected to mature substantially as high-speed components enable more advanced modulation and digital signal processing. With the standardization of 100-Gb/s Ethernet well in progress, terabit Ethernet is just over the horizon. As data rates continue to increase above 100 Gb/s, the role of the microwave engineer will become more and more critical to the success of next-generation optical communications gear. There is a tremendous opportunity for the radio engineer to migrate his or her skills to work in the field of microwave signal integrity. This is an up-and-coming field with lots of room for innovative research. In this article, the current state of the art and the research frontiers of 100 G optical communication systems is explained, and various optical modulation approaches are illustrated. Furthermore, comparison with traditional microwave communication systems is presented as well as the increasing role of the microwave engineer in high-speed optical communication design.     

Determination of epithelial tissue scattering coefficient using confocal microscopy

Most models of light propagation through tissue assume the scattering properties of the various tissue layers are the same. The authors present evidence that the scattering coefficient of normal cervical epithelium is significantly lower than values previously reported for bulk epithelial tissue. They estimated the scattering coefficient of normal and precancerous cervical epithelium using measurements of the reflectance as a function of depth from confocal images. Reflectance measurements were taken from ex vivo cervical biopsies and fit to an exponential function based upon Beer's law attenuation. The mean scattering coefficients derived were 22 cm/sup -1/ for normal tissue and 69 cm/sup -1/ for precancerous tissue. These values are significantly lower than previously reported for bulk epithelial tissues and suggest that scattering of bulk tissue is dominated by the stroma. They also suggest that computational models to describe light propagation in epithelial tissue must incorporate different scattering coefficients for the epithelium and stroma. Further, the lower scattering of the epithelium suggests greater probing depths for fiber optic probes used by optical diagnostic devices which measure reflectance and fluorescence in epithelial tissue. The difference in scattering between normal and precancerous tissue is attributed to increased nuclear size, optical density, and chromatin texture. The scattering coefficients measured here are consistent with predictions of numerical solutions to Maxwell's equations for epithelial cell scattering.     

基于磁光硅基微环波导的磁场测量研究

根据磁光效应引起的附加介电常数张量,分析了磁光波导中导波光传播特性对光场模式和磁场配置的依赖关系。采用SiO_2/Si-Ce:YIG/SiO_2硅基磁光波导设计了一种微环谐振结构用于磁场测量,仿真计算了准TE模导波光传输时微环谐振波长移动随垂直磁化强度的变化。对于半径为23.6μm的磁光微环,优化波导宽度可使磁场测量灵敏度达到0.0054nm/(k A/m),饱和磁化时微环谐振波长移动为0.52nm。     

The optical properties of microbulb alumina ceramics at high temperature

The normal spectral emissivity of two types of high-temperature ceramics made of alumina microbulbs as a function of the wavelength and temperature was investigated experimentally for the first time. Data for samples of various thicknesses (2–8 mm) at wavelengths of 1.0–5.0 μm and temperatures of 1073–1873 K were obtained. The ceramics optical properties in the forms of an effective absorption factor and a radiation diffusion factor were calculated in the wavelength band from 3.2 to 4.6 μm using the dependence of emissivity on thickness. The effect the porosity of ceramics has on its optical properties was analyzed.     

基于医学阻抗技术的乳腺癌检测方法

乳腺癌是危害妇女健康的主要恶性肿瘤之一,准确检测癌组织具有十分重要的意义,生物电阻抗测量技术利用生物组织与器官的电特性(阻抗、导纳、介电常数),提取与人体生理、病理相关的生物医学信息,具有无创和功能丰富等特点,目前,乳腺癌检测常用的阻抗测量方法包括电阻抗频谱测量、阻抗扫描成像、电阻抗断层成像技术.电阻抗频谱测量主要研究生物组织的电阻抗随着外加电信号频率的不同而表现出的变化;阻抗扫描成像是应用癌变组织与正常组织的电导(阻)率存在的差异,从而使得均匀分布在组织的外加电流或电压场产生的畸变;电阻抗断层成像则通过配置于人体体表外周的电极阵列,外加一微小测量电流,提取信息,重构出截面电阻特性的图像.经过大量的研究,有些方法已在临床获得应用.     

Generation and spatiotemporal evolution of optical vortices in femtosecond laser pulses

Topology has become one of the key concepts allowing one to understand the intrinsic, qualitative properties of phenomena throughout various scientific fields. To date, this concept has been extended to the field of material science and technology. On the other hand, we can now utilize the spatially controlled light defined by the topology (so‐called “optical vortices”) in order to characterize the topological properties of materials. In particular, optical vortices in femtosecond pulses will be invaluable for advanced topological spectroscopy. In this work, the authors created femtosecond optical vortices using a spatial light modulator. Their spatiotemporal properties were evaluated using interferogram and correlation measurements. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(4): 39–46, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20791