基于电光晶体的激光PPM偏振调制设计

调制解调技术是大气激光通信系统中的关键技术。提出一种新的光与电脉冲组合调制方式,对已经进行过PPM（脉冲位置调制）调制的激光信号再用电光晶体进行偏振调制。设计了同一信道四种偏振态（0°、30°、60°和90°方向振动的偏振光束）的PPM偏振调制方案。搭建了硬件时序电路及偏振调制系统,四束偏振光通过同一大气信道,同时被衰减,信道的衰减可以相互抵消。硬件仿真结果表明：采用光与电脉冲组合调制方式可以减少甚至消除大气信道对大气激光通信的影响,而且由于光波的偏振复用可以成倍提高大气激光通信的通信容量。     

海雾和陆雾的光散射特性研究

基于Mie理论与蒙特卡罗方法对海雾和陆雾的光散射特性进行了研究,对比分析了海雾、陆雾粒子的单次和多次散射特性。首先分析了海雾和陆雾粒子的尺寸分布,然后采用Mie理论研究了入射光波长为0. 55μm时,海雾和陆雾的散射效率因子、消光效率因子、吸收效率因子和后向散射系数随粒子尺寸参数的变化关系并进行了分析。最后采用蒙特卡罗方法计算了海雾和陆雾的光传输透过率和衰减系数与粒子质量浓度的关系。结果显示随着粒子质量浓度的增加,海雾和陆雾的吸收效率因子和后向散射系数差异都逐渐变大,并且陆雾的衰减系数更小、透射率更大。     

粒径对旋叶分离器结构敏感性的影响

在不同液滴粒径工况下,对等比例旋叶分离器的旋叶倾角和上升通道高度进行结构敏感性分析。建立基于欧拉法和Realizable K-Epsilon湍流模型的空气-液滴两相流动的数学模型,通过计算流体力学软件对冷态工况下5种不同结构的旋叶分离器流场进行数值模拟,得到了不同液滴粒径下的分离效率变化曲线和液滴质量流量径向分布曲线,同时还通过冷态试验验证数值计算模型。结果表明:当液滴粒径等于5μm或大于100μm时,旋叶分离器效率对旋叶倾角和上升通道高度结构不敏感;当液滴粒径在5～100μm时,18°旋叶的旋叶分离器分离效率大于30°旋叶,上升通道高度等于其一倍直径时旋叶分离器分离效率最优;其中当液滴粒径等于30μm时,旋叶分离器分离效率差值最大,结构敏感性最为显著。     

电场、流场耦合作用下脱除细颗粒物的实验和数值模拟

细颗粒物在电、流场耦合作用下的捕获不但是电厂尾部除尘系统的核心问题,也是空间环境内灰尘限制动力或光学元件性能的关键。以电除尘器为研究对象,通过实验和数值模拟研究了细颗粒物在电、流场耦合作用下的迁移、捕获机理。实验结果表明0.1~1μm的颗粒存在穿透窗口;在电除尘器内粉尘浓度随停留时间的变化并不成比例,而是在停留时间为1.5~2 s左右存在一个较为明显的高效脱除区域,继续增加停留时间对于0.1~3μm颗粒的脱除效率的影响并不明显。通过数值模拟研究了电除尘器内的电势与电场强度分布及其脱除效率,模拟结果表明在计算1μm以下颗粒脱除效率的过程中,对曳力考虑Cunningham滑移修正后的模拟结果与实验结果较为一致,Cunningham滑移修正对于模拟计算亚微米颗粒脱除效率十分重要。     

三光源LED光信标空间布局优化计算

在航空、海运及海上救生等各方面,光学信标是一种重要的光学指示手段。为了适应较远作用距离的要求,提出了采用高亮度、高发光效率的LED光源的光学信标。针对采用三光源光信标的空间布局进行了相关理论计算,建立光束空间数学模型,给出三光源的最佳空间布置,并计算出光信标盲区范围及盲区大小。本文的计算结果为光信标的结构设计提供必要的理论基础,其计算方法为多光源信标空间布局计算提供一定的参考。     

仿沙蚁神经处理机制的偏振光导航方法研究

单点偏振光导航方法只能检测部分天空区域的大气偏振模式,所获取的导航信息依赖于观测位置,具有一定的局限性。通过模仿沙蚁感知偏振光并解析航向信息的3个层次,即小眼阵列对偏振信息的接收、POL-神经元的信息响应以及大脑神经元的航向计算,设计了一种仿沙蚁神经处理机制的偏振光导航信号处理模型,实现了全天域大气偏振模式的E-矢量分布与航向信息之间的映射。开展了模仿沙蚁导航行为的仿真实验,结果表明,该模型验证了沙蚁感知偏振光并解析航向角的信号处理机制,为偏振光导航传感器的设计提供了新的思路。     

偏振图像帧捕获器的设计与实现

提出了一种基于CameraLink接口的偏振图像帧捕获器的结构并予以实现,偏振成像帧捕获器采用了大容量缓冲器件、多路总线切换以及DSP技术,解决了多路异步图像并行采集和高速实时偏振图像合成运算问题,能够对较大幅面的偏振图像帧进行实时捕获和合成处理.     

光纤通信系统中PMD值的动态测试

本文实现了一种光纤通信系统中偏振模色散(PMD)值的动态测试方法,采用1∶4偏振分束器,分成四路不同偏振光信号,然后利用起偏器和四分之一波片将信号光分别转化成四个不同的偏振态,最后利用探测器件将四路光信号光电转换为相应4个电压V1 、V2 、V3 和V4,其大小分别对应4个偏振态方向的功率大小,得到信号的偏振度(DOP),利用DOP与DGD之间的相关性,即可监测线路PMD的变化情况.采用PMD仿真器和HP8509B偏振态分析仪对PMD值的动态测试方法的正确性进行了验证,两者对比分析,得到动态测试方法最大测量误差小于2%.利用DOP作为反馈信号,将其提供给DSP和FPGA构成的控制单元部分,实现了PMD的动态自适应补偿,PMD补偿结果由信号眼图实时观测.     

月球科研站多光束激光传能系统设计

针对月表阴影区的能源保障需求,提出一种基于多光束发射的激光无线能量协同传输方法,对月面激光无线传能链路效率进行了对比分析,由于808 nm半导体激光器和与之相应的GaAs光电池具有较高的转换效率,更适合距离1 km内激光传能系统。模拟了不同光束质量激光束经光学系统扩束后,发散角调节对于调焦精度的要求,以及远场光强分布,结果表明,基于多个高光束质量激光束的传能系统具有接收端光强分布可调、传输功率可扩展等优势,为面向极区阴影区探测的无线能源保障系统的实现提供理论依据。     

光纤通信系统中PMD值的动态测试

本文实现了光纤通信系统中偏振模色散(PMD)值的动态测试方法,采用1∶4偏振分束器,分成4路不同偏振光信号,然后利用起偏器和1/4一波片将信号光分别转化成4个不同的偏振态(SOP),最后利用探测器件将4路光信号光电转换为相应4个电压V1、V2、V3和V4,其大小分别对应4个偏振态方向的功率大小,得到信号的偏振度(DOP),利用DOP与DGD之间的相关性,即可监测线路PMD的变化情况.采用PMD仿真器和HP8509B偏振态分析仪对PMD值的动态测试方法的正确性进行了验证,两者对比分析,得到动态测试方法最大测量误差小于2%.利用DOP作为反馈信号,将其提供给DSP和FPGA构成的控制单元部分,实现了PMD的动态自适应补偿,PMD补偿结果由信号眼图实时观测.     

A Novel Approach to Fiber-Optic Tweezers: Numerical Analysis of the Trapping Efficiency

We present a novel all-fiber optical tweezer (OT) for biological applications. The tweezer is based on a new approach relying on total internal reflection in an annular core fiber or into a fiber bundle. The proposed device, whose trapping efficacy has been recently demonstrated experimentally, is extremely promising, also because optical manipulation and analysis functions can be easily added to the tweezer basic structure, leading to the realization of a powerful biotool. In this paper, a detailed numerical analysis of the structure properties and of its efficiency is carried out in the Mie regime. Moreover, by defining a new parameter to evaluate the trapping efficiency, we perform a comparison between the proposed tweezer structure and a standard OT based on a strongly focused Gaussian beam.     

History of optical trapping and manipulation of small-neutralparticle, atoms, and molecules

Reviews the history of optical trapping and manipulation of small-neutral particles, from the time of its origin in 1970 up to the present. As we shall see, the unique characteristics of this technique are having a major impact on the many subfields of physics, chemistry, and biology where small particles play a role     

Charge trapping and conduction in pure and iodine-dopedbiaxially-oriented polypropylene

Study of charge trapping and conduction in pure and iodine doped biaxially oriented polypropylene (BOPP) is presented. Structural and chemical modifications induced by iodine were investigated using X-ray, optical and infrared methods. Optical spectra of doped BOPP show absorption at 290 nm from charge transfer complexes. X-ray examination revealed a decrease in crystallinity and crystallite size after doping. The effect of iodine on charge trapping was determined by thermally stimulated current technique. Deep traps (120°C peak) at crystalline-amorphous interfaces are destroyed by iodine, which provides new traps (68°C peak) with activation energy 0.9 eV. Pressure dependence of conductivity indicates ionic conduction in pure samples and electronic conduction in doped samples. Steady state currents in 0.5%wt iodine doped BOPP were measured for fields 1 to 5×10⁵ V cm^-1 and at elevated temperatures 22 to 50°C. Iodine enhances conductivity by ~700× in pure BOPP and the steady state conductivity shows a good fit of the 3-D Poole-Frenkel theory to the experiment. It is proposed that trapped electrons (arising due to donor-acceptor action) thermally released through PF lowering, predominantly contribute to the conduction     

The transport and trapping of electrons in polymers

The conductivity of a polymer is determined by the availability of charge carriers and their mobility, and both terms are dominated by the trapping states in the polymer. The distribution in energy of these states may be studied by populating the states and observing the current that results from the relaxation of the trapped charges. In our experiments the states are populated by a pulse of electrons from an injection beam, and the surface potential of the polymer film is monitored by a second electron beam that passes above the charged surface; we have used this technique to study both charge trapping and the isothermal discharge process that follows a charging pulse. The general case of charge decay from an arbitrary distribution of states with retrapping can be analyzed by using a multiple trapping model, and this analysis yields the distribution of trapping states in the polymer. The analysis takes on a particularly simple form in the limit of negligible retrapping. Experimentally we have concentrated on PS-2 polystyrene and on several mono-dispersed polystyrenes. We find a change in the distribution of trapping states with molecular weight; there is also a change in trap distribution near the glass transition temperature     

Ultrafast all‐optical switching using pulse trapping by ultrashort soliton pulse in birefringent optical fiber

Ultrafast all‐optical switching by use of pulse trapping in birefringent optical fiber is demonstrated both experimentally and numerically. The wavelengths of the control soliton pulse and the trapped soliton pulse are shifted to satisfy the condition of group velocity matching. Furthermore, the energy of the trapped pulse is increased through Raman gain of the control pulse. Only a signal pulse in the pulse train with temporal separation of about 1.2 ps is successfully picked off. The repetition frequency corresponds to 0.83 THz. The spectrogram of the optical switching is directly observed using the X‐FROG technique. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(3): 38–44, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20470     

Widely wavelength-tunable ultrashort pulse generation usingpolarization maintaining optical fibers

Characteristics of widely wavelength tunable ultrashort pulse generation using several types of polarization maintaining fibers have been experimentally analyzed. Using the diameter reduced type of polarization maintaining fibers, the wavelength tunable soliton pulse is generated from 1.56 to 2.03 μm. It is confirmed that the almost transform-limited 340-fs soliton pulse is generated at a wavelength of around 2 μm using a frequency-resolved optical gating method. When low-birefringence fibers are used, it is observed that the orthogonally polarized small pulse spectrum is trapped by the soliton pulse and is also shifted toward the longer wavelength side in the process of soliton self-frequency shift. The wavelength of the orthogonally polarized pulse spectrum is 40-50 nm longer than that of the soliton pulse, and the birefringence of the fiber is compensated by the chromatic dispersion. Finally, a polarization maintaining highly nonlinear dispersion-shifted fiber is used as the sample fiber. When the fiber input power is low, the wavelength-tunable soliton and anti-Stokes pulses are generated. As the fiber input power is increased, the pulse spectra are gradually overlapped and the 1.1-2.1 μm widely broadened supercontinuum spectra are generated by only 520 pJ pulse energy     

The Dynamics of the Polarization State in Microchip Nd:YVO4 Laser System

For the properties of crystal and simple system structure, laser diode pumped microchip Nd:YVO4 laser have wide applications. The study of the dynamics of instability of Nd:YVO4 laser system is one of more important issue, recently. In this study, We construct a microchip Nd:YVO4 laser system with polarized optical feedback to observe the influence of polarization state. We select linear, ellipse, and circular as the polarization state of pumping beam and optical feedback beam. When the system is solitary pumped, we demonstrate that the Nd:YVO4 laser system is polarization-dependent fluctuations, and that the pumping efficiency of linearly polarization state is the best. As the system experience the optical feedback, the results shows that the linear polarized feedback is more sensitive in the laser system.     

Compensation for light intensity variation by superposing AC magnetic field in optical measurement of DC current

Optical voltage and current measurement generally necessitates the compensation of light intensity variation which occurs in the optical measuring system, because it is possible the light intensity variation may give rise to a measuring error. Therefore, such compensation methods as dividing the ac component by the dc component of the light intensity are usefully introduced in optical ac voltage and current measurement, but those methods are not useful exactly for the optical measurement of the quantities including dc components. This paper deals with a new useful compensation method for light intensity variation in the optical dc current measurement. Linearly polarized light passes through two kinds of Faraday sensors, in which one detects dc magnetic field caused by dc current and the other detects externally applied constant ac magnetic field. Then, the compensation of the light intensity variation is carried out by measuring the dc and ac components of the beam. The principle of the compensation method using the ac component is described in the paper. Experimental results of this method using flint glass as the Faraday effect cells are reported and it is clarified that this method can decrease the measuring error of the modulation depth for dc current and compensate light intensity variation validity.     

Trapping and Manipulation of Biological Particles Through a Plasmonic Platform

Enhanced optical radiation force can be induced through the resonant scattering field from a single plasmonic nanoparticle or a randomly distributed plasmonic nanoparticle array. In this paper, we utilized the dipole approximation for the Mie scattering field to analyze such radiation force in both far-field and near-field regime. This force can be utilized to develop noninvasive probes for trapping and manipulation of single biological particles. The trapping of single yeast cells is also demonstrated as an application of this approach.