Photoresponsive polymer gel microvalves controlled by local light irradiation

This paper presents independent control of multiple microvalves, which are opened by local light irradiation. The application of photoresponsive polymer gel, which was developed by our research group, to photoresponsive microvalve was systematically examined. Photoresponsive polymer gels, which were composed of poly(N-isopropylacrylamide) functionalized with spirobenzopyran chromophore (pSPNIPAAm), were fabricated by in situ photo-polymerization at the desired positions in microchannels. Blue light irradiation to the pSPNIPAAm gels induced shrinkage of the gels and caused the microvalves composed of the gels to open. Local light irradiation to the discrete microvalves enabled independent control of three photoresponsive polymer gel microvalves, which had been fabricated on a single microchip. Each microvalve was opened by 18–30 s light irradiation.     

聚合物光栅光波导器件的微复制技术

采用纳米压印微复制技术方法,研制了一种新型的聚合物柔性光栅光波导敏感器件,该器件可用于介入式医用导管的微弯挠曲监测或类似场合的微变形监测.重点阐述了聚合物柔性光栅光波导器件的微复制模具和器件微复制的工艺方法,并对制备工艺技术中的关键技术问题进行了讨论,讨论了测试光纤耦合一体化光栅波导器件的工艺方法.最后利用硅微模具和紫外固化介质材料,成功制备出了截面尺寸为4 μm×20 μm、光栅周期为0.75 μm的聚合物柔性光栅光波导器件.     

The properties of free-standing epoxy polymer multi-mode optical waveguides

The paper reports on the fabrication and characterisation of free-standing multimode optical epoxy polymer waveguides consisting of a core made of EpoCore and EpoClad polymer cladding and cover protection layers. The 50 × 50 μm² rectangular waveguides are intended for short-reach optical interconnection and optimised for an operating wavelength of 850 nm. The waveguides of the proposed shapes were fabricated by a standard photolithography process on a silicon substrate provided with a Poly(vinyl alcohol) thin layer. The free-standing structure was then achieved by peeling the deposited EpoClad/EpoCore/EpoClad structures of that substrate. The optical scattering losses of the created planar waveguides, measured by the fibre probe technique at 632.8 and 964 nm, were 0.30 dB cm⁻¹ at 632.8 nm and 0.17 dB cm⁻¹ at 964 nm. Propagation optical loss measurements for rectangular waveguides were performed by the cut-back method and the best samples had optical losses below 0.55 dB cm⁻¹ at 850 and 1310 nm.

     

Electrically controlled light scattering in FLC cells

Abstract— Three types of light‐scattering effects distinguished by physical mechanisms were studied in detail in monomeric ferroelectric liquid‐crystal (FLC) compositions at different boundary conditions and electrical pulse regimes. The total time of the scattering switching on and switching off is less than 150, 250, and 500 μsec at ±50 V for different scattering types in helix and non‐helix FLCs. They are quite fast, and FLC cells are quite transparent and were used in a stack of 30–100 light‐scattering shutters for a volumetric screen of a 3‐D display.     

Application of nanoparticles dispersed polymer to micropowder blasting mask

Improvements in micropowder blasting have been realized for rapid prototyping of channels in glass substrates. The technique presented in this study consists of laser patterning of Au nanoparticles dispersed polymer and micropowder blasting. The patterned polymer was utilized as a mask material for the subsequent mechanical removal of the glass by the micropowder blasting. Five different polymers were tested for the matrix material. Using a line and space mask pattern of 110 /spl mu/m in width, fabricated channels were created in the glass with a maximum aspect ratio of 2.1. The validity of the micropowder blasting using Au nanoparticles dispersed polymer mask was confirmed; additionally, we demonstrated that the micropowder blasting technique with elevated polymer mask temperature was able to reduce erosion of the polymer mask.     

Image improvement in a laser projection display with a spatial light modulator with a deformable polymer

Abstract— The image quality of a laser projection display based on a spatial light modulator with a deformable polymer layer (SLMDPL) has been improved. Bias diffraction has been reduced by two methods: (1) by filling the spacings between electrodes with SiO₂ followed by deposition of a slightly conductive thin film and (2) by splitting electrodes. Both methods resulted in a contrast ratio of ?1200:1, which is significantly better than 50:1 measured for an earlier type of SLMDPL. Different methods of reducing the influence of electrical‐charge movement on the image quality have also been investigated. Substantial improvement has been achieved by using an alternating mode for signal voltage pulses, by increasing the conductivity of the gel layer, and by increasing the surface conductivity of the substrate between electrodes. Cross‐talk between neighboring pixels has been suppressed without a loss in the sensitivity by using a special layout of the electrodes in the SLMDPL.     

Magnetically controlled valve for flow manipulation in polymer microfluidic devices

A simple, external in-line valve for use in microfluidic devices constructed of polydimethylsiloxane (PDMS) is described. The actuation of the valve is based on the principle that flexible polymer walls of a liquid channel can be pressed together by the aid of a permanent magnet and a small metal bar. In the presence of a small NdFeB magnet lying below the channel of interest, the metal bar is pulled downward simultaneously pushing the thin layer of PDMS down thereby closing the channel stopping any flow of fluid. The operation of the valve is dependent on the thickness of the PDMS layer, the height of the channel, the gap between the chip and the magnet and the strength of the magnet. The microfluidic channels are completely closed to fluid flows ranging from 0.1 to 1.0 μL/min commonly used in microfluidic applications.     

Dynamic parameters of electrically controlled light scattering in helix FLC cells

Abstract— The light‐scattering structures in monomeric FLCs have been considered and a mechanism for the scattering on transient domains in the helix layers has been proposed. An optical response with a bistable characteristic of light scattering and transmission was realized at a defined electrical pulse regime and boundary conditions in electro‐optical FLC cells. The total time of the scattering switching on and switching off is less than 400 μsec at ±36 V. They are quite fast, and FLC cells are quite transparent to be used in a stack of 30–100 light‐scattering shutters for a volumetric screen of a 3‐D display.     

Polarized laser light reflection by polymeric films modified with TiO2 or silver nanoparticles

The ability of a polymeric polyvinyl alcohol film modified by TiO₂ or silver nanoparticles to scatter, reflect and transmit incident polarized radiation and to form an illumination background close to diffuse scattering with the minimal power losses were studied. The article is published in the original.     

Chromatic characterization of novel multicolor reflective display with electrochemically size‐controlled silver nanoparticles

Multifunctional electrochromic materials that enable control of multiple colors, color density, and specular reflection are potential candidates for novel reflective display devices. In this research, we focus on Ag nanoparticles that exhibit various optical states based on their localized surface plasmon resonance (LSPR). Because the LSPR band depends on the size and shape of the nanoparticles, control of the morphology of Ag nanoparticles can lead to dramatic changes in color. In order to apply this color variation for display devices, we investigate here the electrochemical formation of size‐controlled Ag nanoparticles using a voltage‐step method that consists of an application of two successive different voltages (V₁ and V₂). The electrochemically deposited Ag nanoparticles appear red and blue depending on the time for V₂ voltage application. The color changes between the transparent and colored states are reversible. Then, we successfully demonstrate the first LSPR‐based multicolor electrochromic device in which reversible control of five optical states—transparent, silver mirror, red, blue, and black—is possible.     

The evolution of solitons in coupled resonator optical waveguides and photonic-crystal waveguides

We successfully used the tight binding theory to derive the extended discrete nonlinear Schrödinger equation to describe the soliton propagation and to obtain the soliton propagation criteria (SPC) in the nonlinear photonic-crystal waveguides (PCWs) and coupled resonant optical waveguides (CROWs) containing Kerr media. From these criteria, we obtain the soliton-propagating region of CROWs in different numbers of separated rods and strengths of self-phase modulation (SPM). The defined soliton-propagating regions coincide with the regions of modulation instability in the CROWs. In the PCWs, the positive Kerr coefficient medium needs to be added to support the pulse propagation in low frequency or low wave vector region of the dispersion curve; while negative Kerr effect is for high frequency case. Due to the linear combination of various cosine harmonic functions in the dispersion relations of both CROWs and PCWs, the pulse broadening which is mainly caused by the third-order dispersion at SPC is the lowest at the boundary of dispersion curves. However, due to the different magnitudes of coupling coefficients in CROWs and PCWs, the group velocity, dispersion and strength of SPM in CROWs are all smaller than those in PCWs.     

Scattering-induced quantum correlation in electronic waveguides with static magnetic impurities

Entanglement generation due to low-energy scattering of the transporting electrons in an electronic waveguide by a quantum dot magnetic impurity is theoretically investigated. The transverse confining potential of the waveguide is considered as a two-dimensional harmonic potential, and the interaction of the electron with the impurity is described by a zero-range pseudopotential modulated by an Ising or a Heisenberg spin interaction. Our calculation shows that the scattering process leads to creation of a considerable amount of entanglement in the state of the reflected and transmitted electrons. The situation is extended to the scattering of the electrons by two well-separated magnetic impurities localized on the nanowire axis. It is shown that the scattering process causes the magnetic impurities embedded in the nanowire to share their quantum information; subsequently, they can be entangled by spin interaction with the injected electron. The created entanglement between the impurities is calculated and discussed. It is shown that the exact three-dimensional problem can be approximated as a one-dimensional problem under certain circumstances. The approximate results are compared to exact calculations and discussed.     

Dispersion characteristics of asymmetrical coplanar waveguides with anisotropic substrates

In this article, for asymmetrical coplanar waveguides with anisotropic substrates, the analytical dispersion formulas for effective dielectric constant ϵ_eff are first derived and then used to study the frequency-dependent characteristics ϵ_eff(f). The errors in the dispersion formulas are less than 2% when compared with the available results. In addition, based on the derived dispersion formulas and the Fourier transform, the effects of signal dispersion are studied for a Gaussian pulse propagating on an asymmetrical coplanar waveguide with anisotropic substrate. © 1996 John Wiley & Sons, Inc.     

Monte Carlo analysis of ridged waveguides with transformation media

A computational model is presented for Monte Carlo simulation of waveguides with ridges, by combining the principles of transformation electromagnetics and the finite methods (such as finite element or finite difference methods). The principle idea is to place a transformation medium around the ridge structure, so that a single and easy‐to‐generate mesh can be used for each realization of the Monte Carlo simulation. Hence, this approach leads to less computational resources. The technique is validated by means of various finite element simulations in the context of 3D waveguides of uniform cross‐section. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Characterization of composite nanoparticles using an improved light scattering program for coated spheres

The objectives of this paper are twofold. First, the paper developed an improved algorithm to perform light scattering calculations by coated spheres. The improved algorithm was implemented in FORTRAN90 as a subroutine to allow flexible application of the code. Second, the new program was applied to the characterization of composite aluminum nanoparticles. In this application, multiple elements of the Mueller scattering matrix were measured at multiple angles to infer the properties of the nanoparticles, including the size distribution function and the thickness of the coating. The new program played a key role in the fitting of the measured data, and this application demonstrated the advantages of the new program in situations that demand high efficiency and reliability.

Program summary

Program title: CMIECatalogue identifier: AEFX_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEFX_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 1065No. of bytes in distributed program, including test data, etc.: 12 933Distribution format: tar.gzProgramming language: FORTRAN90/95Computer: Any machine running standard FORTRAN90/95Operating system: Windows XP (Intel FORTRAN compiler 9.1)RAM: 1-100 MbyteClassification: 16.7, 18Nature of problem: Among various scientific and engineering applications, it is highly desirable to have an efficient, reliable, and flexible program to perform scattering calculations for coated spherical particles. Though several programs are publicly available and can perform such calculations, they are designed for more complicated scatterers (non-spherical, multilayered particles, etc.). As a result, their efficiency and reliability are usually not satisfactory when applied to coated spheres. Therefore, this paper aims at developing an improved program to provide efficient and reliable scattering calculations for coated spheres. Such virtues were demonstrated to be invaluable in applications where scattering calculations need to be performed for a great number of times over a wide range of conditions.Solution method: A new algorithm is developed to directly calculate the pre-factor of the scattering coefficients. This new technique provides reliable calculation of the pre-factor for arbitrarily large size parameters, and offers better control of the termination of the calculation. Based on this algorithm, an improved program was developed to perform light scattering calculations by coated spheres.Restrictions: Only applicable to single scattering, single layer coating, and unity permeabilityRunning time: Several seconds-several minutes     

偏振控制光强调制型SPRi传感器的高灵敏检测研究

在偏振控制光强调制型SPRi传感器中,使用真实液体消光的方法实验调节困难,测量灵敏度低,线性度差.为此,提出无需真实液体消光,并将消光折射率左移的方法.首先,对在测量起点(即纯水)消光的传统方法进行光学参数的最优值仿真及其加工和调节误差仿真,结果表明,误差会引起SPRi曲线最低点在折射率轴上的左右偏移,从而影响传感器性能.接着,将消光折射率左移至1.325处,并仿真其光学参数的最优值.实验表明,与前者相比,1.325消光方法中存在的误差不会使测量曲线出现非单调的情况,此时的测量灵敏度高,线性度好,折射率分辨率达到1.85×10-6 RIU,对应NaCl溶液的检出限为35 mg/L.上述方法提高了误差存在时SPRi传感器的适用性,可以实现微量水溶液样品的高灵敏及高通量检测.     

Lattice constant effects of photonic crystals on the extraction of guided mode of GaN based light emitting diodes

We have fabricated a series of square-lattice hole photonic crystal (2PhC) arrays simultaneously at the un-current injection region on a special sample of GaN based light emitting diode (LED) by using focus ion beam milling (FIBM). The lattice constants of the 2PhC arrays vary from 230 to 1500 nm,while the 2PhC arrays have a constant area of about 9 μm×18 μm and a fixed depth of 150±10 nm which approaches but does not penetrate the active layer. Microscopic electroluminescence images and spectral measuremen...     

Combinatorial optimization with use of guided evolutionarysimulated annealing

Feasible approaches to the task of solving NP-complete problems usually entails the incorporation of heuristic procedures so as to increase the efficiency of the methods used. We propose a new technique, which incorporates the idea of simulated annealing into the practice of simulated evolution, in place of arbitrary heuristics. The proposed technique is called guided evolutionary simulated annealing (GESA). We report on the use of GESA approach primarily for combinatorial optimization. In addition, we report the case of function optimization, treating the task as a search problem. The traveling salesman problem is taken as a benchmark problem in the first case. Simulation results are reported. The results show that the GESA approach can discover a very good near optimum solution after examining an extremely small fraction of possible solutions. A very complicated function with many local minima is used in the second case. The results in both cases indicate that the GESA technique is a practicable method which yields consistent and good near optimal solutions, superior to simulated evolution.     

基于M型标准块的视觉引导机器人系统手眼标定方法研究

针对线结构光传感器引导的机器人系统的手眼标定问题,提出了一种以M型标准块为标定物的方法。该M型标定物的两条平行的脊线作为约束,基于两条平行脊线的约束建立包含手眼关系、机器人运动学以及两条直线位姿参数误差的模型。首先基于定点约束求解手眼关系初值并以此为基础解算出直线位姿参数的初值,然后通过最小二乘法解算误差参数并补偿到模型中,不断迭代直至计算的误差参数小于阈值,最终得到最终的机器人手眼关系及运动学误差参数。为了验证标定方法的有效性,以某精加工平面为被测物,利用线结构光机器人系统对平面进行测量,得到平面点云;拟合最小二乘平面,计算点到平面距离的均方根值作为评价依据。分别对所述M型标准块和标准球两种方法进行了实验对比,结果表明,相较于标准球方法,所述M型标准块方法得到的均方根误差由0.152 mm减少到0.080 mm,均方根误差的标准差由0.043 mm减少到0.005 mm,其标定结果的精度及稳定性得到显著提高。     

Simulation and fabrication of a fast fringe‐field switching liquid crystal with enhanced surface anchoring enabled by controlled polymer topology

We demonstrate a fringe‐field switching nematic liquid crystal with electro‐optical behavior modulated by both bulk and surface polymer stabilization. The polymer is formed by ultraviolet irradiation‐induced phase separation of various amounts of a reactive monomer in the planar‐aligned nematic liquid crystal. Simulation is carried out to verify the effect of anchoring energy. Experimental evidence validates the effect of monomer concentration on transmittance–voltage and response times curves of fringe‐field switching cells. The polymer‐stabilized alignment with a higher polymer concentration escalates the interaction between the liquid crystal and the polymer structure and increases the surface anchoring energy. The polymer stabilization also improves the dynamic response times of liquid crystal. The enabling polymer‐stabilized alignment technique has excellent electro‐optical properties such as a very good dark state, high optical contrast, and fast rise and decay times that may lead to development of a wide range of applications.