Tunable nanojet-induced mode achieved by coupled core–shell microcylinders with nematic liquid crystals

The tunable nanojet-induced mode achieved by coupled core–shell microcylinders with nematic liquid crystals is reported. The optical transmission properties of touching core–shell microcylinders with nematic liquid crystals are studied by using high resolution finite-difference time-domain simulation. We identify two rotation mechanisms of liquid crystal in terms of the coupling efficiency between neighboring core–shell microcylinders. The nanojet-induced guided modes depend strongly on the directors of liquid crystals. The optical transport can be continuously tuned in the core–shell microcylinder by controlling the directors of liquid crystals. The coupled core–shell microcylinders can be assembled inside hollow structures to build tunable optical waveguides for effective and low-loss guiding of photons.     

一种微小型导引头视场下偏角的标定方法

描述了一种应用于微小型光学导引头视场下偏角标定的方法，通过获得导引头绕自身回转轴线转动时拍摄的固定靶标图像计算不同旋转角度时导引头中心视线落点和摄像机坐标系原点在世界坐标系下的坐标，以拟合获得的这2组点的分布建立空间几何关系进而得出下偏角。给出了3组实验数据，分别检验该方法的标定误差、实际所需的采样点数并给出了实际工作中的应用效果。实验表明该方法可以快速标定导引头系统的下偏角，其标定绝对误差小于0.10°。     

A mathematical expression for air ESD current waveform using BP neural network

A curve-fitting method based on backpropagation (BP) neural network (NN) is proposed for fitting electrostatic discharge (ESD) current waveforms and giving the corresponding expressions in order to analyze the characteristics of ESD and calculate the ESD electromagnetic pulse radiation field. According to IEC61000-4-2, this method is used to fit the ideal contact current waveform of human-metal ESD to obtain the mathematical expression. The waveform parameters of the fitting curve meet the requirements of the IEC61000-4-2. By fitting the measured air ESD current waveform at 4 kV discharge, the mathematical expression is obtained. This paper proposes the mathematical expression for arbitrary curves and analyzes the factors affecting the effects of curve-fitting.     

Method for measuring detection distance of low power laser indicator based on CCD sensor

A new method for detecting semiconductor laser indicator (3–5 μm) detection distance based on CCD array sensor is put forward in this paper. Primarily, the detection distance equation based on human eyes is deduced, through experiment and MATLAB modelling, the function mathematical model between the two parameters, optical power and gray scale, which are received by CCD array sensor, is also established. Then we obtain the related parameters via straight-line fitting of least square method in Matlab and the theory formula of the low power semiconductor laser pointer detection distance is obtained. Finally, feasibility and accuracy of this method is verified by experiment.     

Fiber chromatic dispersion measurement based on wavelength-to-time mapping using a femtosecond pulse laser and an optical comb filter

A novel method for the measurement of chromatic dispersion of an optical fiber based on wavelength-to-time mapping using a femtosecond pulse laser (FSPL) and an optical comb filter is proposed and experimentally evaluated. In the proposed approach, the spectrum of an ultrashort optical pulse generated by an FSPL is sliced by an optical comb filter. The spectrum-sliced optical pulse is then coupled into the optical fiber under test. Thanks to the chromatic-dispersion-induced wavelength-to-time mapping in the optical fiber under test, a time-domain waveform similar to the sliced spectrum is generated at the output of the optical fiber, with different frequency components having different time delays. The time delay vs. frequency data are then recorded for the estimation of the chromatic dispersion by using least square fitting. Chromatic dispersions of two types of optical fibers with different lengths are tested. The measured dispersion values agree well with those measured by the conventional modulation phase shift (MPS) method.     

Photonic Alamouti encoder for unifying hybrid FSO/RF system

A unified hybrid free-space optical–radio-frequency (HFR) system based on photonic technology is proposed to simplify the system design and remove the restriction on the azimuth rotation for point-to-point wireless links between mobile platforms. The proposed system applies parallel channel coding techniques and photonic technology to unify the two channels. The principle of a photonic encoder for Alamouti codes is proposed and verified by simulations. A 10 Gbit/s data stream is correctly encoded with an acceptable waveform distortion. Photoelectronic integrated circuits for unified photonic codecs and transceivers could be developed based on this principle.     

测量大口径光学元件反射率用精密扫描系统误差分析

为测量高能激光传输系统中大口径高反射率光学元件的反射率,设计了一种大口径光学元件二维扫描的精密测量系统。介绍了该系统的结构及其工作原理,分析了影响系统测量精度的因素,从理论上分析了扫描系统的系统误差对测量精度的影响,结果表明在垂直于光束传播方向上,水平偏差在0.29 mm时,测量误差在10-6量级;腔长的变化量较小时,可通过对衰荡腔腔镜的调节,实现对旋转轴偏差的补偿及对系统的精细调节。通过拟合处理光强与时间的数据得到对应的一次指数函数拟合曲线,并通过计算得到衰荡时间和反射率,经过对比分析可知,该误差分析方法能比较有效地测量腔镜的反射率,并能减小实验数据本身带来的误差。     

Mechano-chemical synthesis and optical properties of ZnS nanoparticles

In the present work, we report the synthesis and optical properties of ZnS nanoparticles produced by the mechano-chemical route. We used zinc acetate and sodium sulphide as source materials in a high energy planetary ball mill at rotation speed of 300 rpm and vial rotation speed of 600 rpm with ball to powder (BPR or charge ratio CR) 5:1 for 30 and 90 min. The milled powders were washed with methanol to remove impurity and dried at 300 °C for 1 h. The prepared nanoparticles have been characterized using X-ray diffraction (XRD), Field emission scanning electron microscope (FESEM), UV–vis–NIR spectrophotometer and Fluorescence spectroscopy. The crystallite size of the synthesized ZnS nanoparticles is found to be in the range 7–8 nm which was calculated using Debye–Scherer's formula. The value of optical band gap has been found to be in the range 3.80–4.15 eV. Room temperature photoluminescence (PL) spectrum of ZnS samples exhibit a blue emission peaked at 466 nm under UV excitation.     

Waveform shaping of 1550 nm transmission through hollow quartz fiber

In this paper, we connected two single-mode fiber ends with a micron hollow quartz fiber. The hollow fiber was used to modulate the waveform of a 1550 nm light signal, resulting in a lower noise and a narrower linewidth. Specifically, the noise range and the linewidth decreased from 14% to 3% and 0.28–0.23 nm, respectively. The light field distribution and far-field intensity distribution of the hollow fiber are studied using finite difference time domain simulation. Furthermore, we discussed the research suggestions of this configuration in detail. Collectively, these results suggest that it can be used in the fields of optical signal processing, fiber laser and optical sensor.     

Modeling absorption spectrum and saturation intensity of ZnO nano-colloid

In this work, the complex magnitude of the dielectric constant of a thin film of ZnO nano-particles has been obtained in the range of visible spectrum. Using this spectrum, the UV–visible absorptive spectrum of ZnO spherical nano-colloid is obtained using Mie theory. The absorption spectrum of ZnO nano-colloid has been related to the optical properties of the prepared thin film with a simulation model based on the Mie theory and the findings are corroborated by fitting with the experimental results. Based on this curve fitting, the volume fraction of nanoparticles in the nano-colloid is obtained and the diameter (and the Bohr radius) of the molecules contributing in a nanoparticle crystal structure has been obtained. In this paper, frequency dependence of the optical properties coefficients and also local field considerations are applied. Finally the precise magnitude of saturation intensity of ZnO nano-colloid is measured.     

基于Zernike多项式拟合三平面互检的误差分析

基于Zernike多项式拟合三平面互检法,在理论上对光轴偏离、旋转角度以及有效面积对不同面型精度平面的测量误差进行了分析,并分别进行了实验验证.研究结果表明,旋转角度误差和有效面积对测量影响不敏感,可适当降低标定旋转角度成本;而光轴偏离对测量精度影响明显,在高精度面型绝对检测中应对其进行严格校准.     

An accurate and efficient method for treating aerodynamic interactions of cloud droplets

Motivated by a need to improve the representation of short-range interaction forces in hybrid direct numerical simulation of interacting cloud droplets, an efficient method for treating the aerodynamic interaction of two spherical particles settling under gravity is developed. An effort is made to ensure the accuracy of our method for any inter-particle separation by considering three separation ranges. The first is the long-range interaction where a multipole method is applied. After a decomposition into six simple configurations, explicit formulae for drag forces and torques are derived from an approximate Force–Torque–Stresslet (FTS) formulation. The FTS formulation is found to be accurate when the separation distance normalized by the average radius is larger than 5. The second range concerns the short-range interaction where the interaction force could be very large. Leading-order lubrication expansions are employed for this range and are found to be accurate when the normalized separation is less than about 0.01. Finally, for the intermediate range where no simple method is available, a third-order polynomial fitting is proposed to bridge the treatments for long-range and short-range interactions. After optimizing the precise form of polynomial fitting and matching locations, the force representation is found to be highly accurate when compared with the exact solution for Stokes flows. Using this method, collision efficiencies of cloud droplets sedimenting under gravity have been calculated. It is shown that the results of collision efficiency are in excellent agreement with results based on the exact Stokes flow solution. Collision efficiency results are also compared to previous results to further illustrate the accuracy of our calculations. The effects of particle rotation and the attractive van der Waals force on the collision efficiency are also studied. The efficient force representation developed here is more general than the usual lubrication expansion and thus can serve as a better approach to correct unresolved short-range interactions in particle-resolved simulations.     

Measuring the optical rotation based on the Fast Fourier Transform

Based on the structure of polarizer–Faraday modulator–analyzer, a method of measuring the optical rotation is proposed by using Fast Fourier Transform to analyze the output signal of optical material. The output signal detected by a photodetector comprises two AC components, which angular frequencies are ω and 2ω, respectively. So, the amplitude ratio of different frequency signals can be obtained by using the Fast Fourier Transform. According to the relationship between the amplitude ratio and optical rotation, the optical rotation of material can be detected. Furthermore, the experiment results show that the correlation coefficient between the measured optical rotation and the sugar solution concentration is found to be 0.99979.     

Ultrafast optical frequency comb synthesizer and analyzer

We propose an ultrafast optical arbitrary waveform synthesizing/analyzing technique demonstrated with 2 Tbit/s waveforms. An ultrafast waveform was generated by manipulating the amplitude and phase of a 400?GHz optical frequency comb using a newly developed colorless optical synthesizer. The 400?GHz optical frequency comb was generated from a 25?GHz optical frequency comb using a colorless arrayed waveguide grating. This waveform was then analyzed on the frequency axis using a custom heterodyne-detection technique based on the dual-heterodyne mixing method. The phase and amplitude spectra can be observed in parallel using another optical frequency comb as a reference combined with an arrayed waveguide grating. This optical system, named the ultrafast optical frequency comb synthesizer and analyzer, can synthesize and analyze an arbitrary waveform in the THz frequency region.     

Temperature-dependent photoreflectance of SnS crystals

The optical properties of single-crystal SnS were studied by photoreflectance (PR) spectroscopy. Temperature-dependent PR spectra were measured in the range 20–200 K. A room-temperature bandgap energy value of E_g=1.317 eV was estimated by fitting the temperature dependence of the bandgap energy obtained from the PR spectra. The vibrational properties of orthorhombic SnS were studied using Raman spectroscopy. Four vibrational modes were detected at 95, 163, 191, and 218 cm^–1.     

The exchange of hydrogen ions and of water molecules near the active site of cytochrome c

Three-pulse electron-spin-echo envelopes have been measured for frozen solution samples of horse heart ferric cytochrome c both before and after exchange against D₂0. The deuterium modulation pattern was enhanced relative to modulation patterns due to coupled ¹⁴N nuclei by dividing the envelope obtained with the nondeuterated sample into the envelope obtained with the deuterated sample. Measurements of the modulation depth were made by fitting single cycles of a decaying waveform having the free deuterium NMR period to early portions of the experimental quotient waveform. The observed modulation depth was compared with the depth calculated theoretically from X-ray crystallographic data. The good agreement obtained in this comparison demonstrates the reliability of the electron-spin-echo method as a means of studying the distance and/or distribution of exchangeable hydrogen nuclei in the vicinity of sufficiently well-characterized protein metal-ion active sites.     

L-M非线性拟合的TDLAS氧气测量研究

氧气浓度是工业生产过程中重要监测参数,采用可调谐二极管激光吸收光谱法(tunable diode laser absorption spectroscopy,TDLAS),结合波长调制技术,可以实现对现场氧气浓度的高精度在线监测,利用氧气位于760 nm处的特征吸收峰进行了氧气浓度的测量。由于激光具有很强的相干性,所以TDLAS技术的检测灵敏度受到光学干涉噪声的严重制约,特别在低浓度时,光学干涉引起的基线起伏使得提取吸收峰波形信号时出现较大误差,影响了TDLAS分析仪的监测灵敏度。针对这一情况,采用了Levenberg-Marquardt非线性拟合算法,并且利用了吸收谱线线型——洛伦兹线型的导数形式对波长调制后获得的二次谐波波形信号进行拟合,提取波形信息。另一方面Levenberg-Marquardt非线性拟合方法需要有大量的计算,为了使研制的TDLAS分析仪能够实现现场的实时监测,采用了支持浮点运算的DSP的C28系列芯片进行数据处理,实现仪器在现场实时监测的功能。实验结果表明,该算法能够有效提取二次谐波信号的吸收峰特征值、克服背景噪声影响,由算法反演得到的氧气浓度与实际浓度的线性比值为1.01,浓度测量的线性误差为1.18%。     

Growth,thermal, spectral optical and dielectric characterization of semiorganic material: Dihydroxylammonium tetrachlorostrontium(II) dihydrate

Single crystals of dihydroxylammonium tetrachlorostrontium(II) dihydrate were grown by slow evaporation solution growth method at ambient temperature. The suitability of this material for optical application was studied by UV–visible absorption and optical transmittance spectroscopic techniques. The powder X-ray diffraction (XRD) method was used to confirm the crystalline nature of the compound and it is observed that the compound crystallized in orthorhombic system. The thermal stability of the title compound was studied by thermogravimetry and differential thermal (TG–DTA) analyses. The thermal anomalies observed in the low temperature differential scanning calorimetry (DSC) study indicate the occurrence of the first order structural phase transitions in the compound. The FTIR spectrum characterizes the various chemical bonding and water molecules in the compound. The nonlinear optical property of the material was analyzed by modified Kurtz–Perry powder technique. The dielectric constant and dielectric loss of the compound decreases with increase in frequency.     

扩频原理在聚合物光纤性能测量中的应用

提出了一种将扩频通信原理用于聚合物光纤性能测量的新方法,使用伪随机序列对注入测量系统的光信号进行调制,实现输入光信号的扩展频带,输出光信号经光电转换后,用伪随机序列对信号进行解扩处理,根据扩频原理,解扩后的信号的信噪比会有较大提高.对测量系统的性能进行了仿真分析并与实验结果进行了比较,结果表明该方法可以精确地测量信噪比低于-20 dB的有用信号波形.     

类金刚石薄膜光学常数拟合模型的合理性研究

由于椭偏光谱测量结果不能直接反映所测量样品材料的结构和光学性质，所以需要利用最小二乘法来拟合分析椭偏光谱数据得到光学常数。而椭偏光谱分析依赖于构建的模型，且可能存在多模型解，因此考虑模型的合理性就显得十分必要。本文采用椭偏法测量了类金刚石薄膜(DLC)的光学常数，分析并拟合了脉冲真空电弧离子技术镀制的类金刚石薄膜的椭偏光谱．获得了光学常数，并对拟合模型的合理性和测量结果的可靠性进行了分析。