Conduction switching of photochromic molecules

We report a theoretical study of single molecule conduction switching of photochromic dithienylethene molecules. The light-induced intramolecular transformation drives a swapping of the highest occupied molecular orbital and lowest unoccupied molecular orbital between two distinct conjugated paths. The shuffling of single and double bonds produces a significant conductance change when the molecule is sandwiched between metal electrodes. We model the switching event using quantum molecular dynamics and the conductance changes using Green's function electronic transport theory. We find large on-off conductance ratios (between 10 and over 100) depending on the side group outside the switching core.     

Gap transit-time effects in fast optoelectronic semiconductor switching devices

The output shape of an electric pulse, which traverses the gap of a fast optoelectronic semiconductor switching device, is influenced by the transit time of the pulse. This dependence as well as the use of transit-time effects for pulse shortening are studied. To this end in the present paper optical and electrical time-dependent properties of the central unit, I.e. the laser-excited semiconductor, and the external passive electric elements and sources are considered and a time-variant telegraphic equation obeying appropriate boundary conditions is established. Numerical solutions for physically important cases are calculated and discussed.     

z-Scan characterization of zwitterionic chromophores for optoelectronic switching

Single beam z-scan measurements have been made on films containing amorphous polycarbonate and the zwitterionic chromophore, PYR-3, that has a very high second order nonlinear optical (NLO) figure of merit. The third order NLO figure of merit is ≈1.6 at 1030 nm and is comparable to that found in organic compounds optimized for high n ₂ values. The two-photon absorption coefficient is 2.1×10⁻¹² m/W, which is very low and advantageous for NLO device applications. The third order NLO refractive index is −1.4×10⁻¹⁸ m²/W.     

Two-dimensional optoelectronic devices for future optical switching and information processing

Recent progress is reviewed in surface-normal optoelectronic devices primarily for use in optical switching and information processing. A type of optoelectronic integrated circuit (OEIC), the surface-normal two-dimensional array, is fabricated using these devices. This improves on first-generation OEICs by featuring large-scale integration in a small area, which results in a higher production yield. It also has structures which can easily be integrated with electronic circuits and can meet multichannel requirements. This approach supports optoelectronic progress towards optical information processing.     

Electrical switching effect in a photochromic molecule between two graphene electrodes

We propose a single-molecule electrical switches consisting of a photochromic dimethyldihydropyrene/cyclophanediene molecule sandwiched between two graphene electrodes and investigate the electronic transport by using density-functional theory and nonequilibrium Green's function methods. The “open” and “closed” isomers of the photochromic molecule are shown to have electrical switching behavior and negative differential resistance effect. Moreover, it is also found that the switching ratio between two different conductive states depends on the ambient temperature, and the device behaves as a stable electrical switch around room temperature, which is in agreement with a recent experimental study of another photochromic molecule diarylethene reported by Jia et al. (2016) [17].     

Magnetic properties of single crystals based on photochromic molecules of spiropyrans and chromium oxalates

Physics of the Solid State - The influence of UV irradiation on the effective magnetic moment and the Weiss temperature of single crystals based on photochromic molecules of spiropyrans and...     

光电负反馈下垂直腔表面发射激光器偏振开关特性研究

基于扩展的自旋反转模型, 对光电负反馈下垂直腔表面发射激光器的偏振开关特性进行了数值仿真和理论分析. 研究结果表明: 对于不同的自旋反转率, 反馈强度和延迟时间对激光器偏振开关特性产生较大影响.在慢自旋反转率下运行时, 随着反馈强度的增加, 开关点电流呈线性增加, 导致X偏振模被压缩, 这与报道的基于各向同性光反馈的情景相反, 产生这一现象的原因是由于光电负反馈提高了X偏振模的阈值; 延迟时间对开关点电流的影响随反馈强度的变化而不同.在快自旋反转率下运行时, 反馈强度对开关点电流的影响与慢自旋反转率时的情形不同, 开关点电流经历先增加后减小的过程, 开关点电流受反馈强度的影响更加敏感; 而延迟时间的影响规律和慢自旋反转率时相似. 此外, 还发现自发辐射噪声对激光器偏振开关特性有较大影响. 关键词： 垂直腔表面发射激光器 偏振开关 光电负反馈 自发辐射噪声     

Enantiospecific adsorption of chiral molecules on chiral gold clusters

Enantioselectivity in gold clusters is investigated by studying the adsorption of a chiral amino acid (cysteine) on a chiral Au55 cluster using density functional calculations. The highest adsorption energies were found when the amino and thiolate functional groups of cysteine are bonded to the lowest coordinated edges of the chiral cluster. Enantiospecific adsorption is primarily obtained from the different bond location and strength, at the cluster edge, of the carboxyl groups forming the left- and right-handed enantiomers. These results provide theoretical support to convey enantioselectivity in asymmetric nanocatalysts using chiral gold clusters.     

Utilization of photoreversible optical nonlinearities intrans-cis photochromic molecules for spatial light modulation

In this paper we examine the nonlinear optical properties of molecular systems undergoing acis-trans photoisomerization process. Such a process gives rise to dynamic photochromism on a picosecond time scale significant for designing a molecular Spatial Light Modulator (SLM).A kinetic analysis of a generalcis-trans nonlinear organic absorber is performed. The analysis is used to derive an expression for the imaginary part of the complex nonlinear molecular index of refraction. The properties of a molecular SLM based on such an absorber are discussed by examining the azo-type molecular system. These calculation predict an optimum contrast ratio and fast on-off switching for the SLM performance, achieved at low read-write laser intensities.     

Picosecond optoelectronic switching in CdS0.5Se0.5

So far only few materials have been investigated for their application in fast opto-electronic switching. These materials are Si, GaAs and InP. The difficulty in obtaining a high resistivity specimen of group IV elemental semiconductors puts constraints on their high power handling capability. Most of the group III–V compounds have the possibility of showing up of Gunn effect at high fields, which has undesirable effect in high voltage switching. We have, therefore, investigated a mixed II–VI compound CdS_0.5Se_0.5 for its potential use as an opto-electronic switch.     

一种光电跟踪复合控制切入反馈控制的误差抑制方法

针对光电系统跟踪目标时由复合控制模式向反馈控制模式切换过程中出现的误差变大现象,从控制原理、仿真及实验方面进行分析,提出采用模式切换时上一时刻复合控制所使用的一阶微分数据,对切换后的反馈控制在速度环路进行常值补偿,使控制模式切换引起的误差显著减小,同时确保跟踪系统在采用该补偿后不增大反馈控制的稳态误差,并对此方法进行了仿真,最后针对某型光电跟踪仪进行航路实验,结果表明该方法行之有效。     

4×8 optoelectronic matrix switch equipment using InGaAsP/InP heterojunction switching photodiodes

A four input-port and an eight output-port optoelectronic matrix switch using InGaAsP/InP hetero-junction switching photodiodes was fabricated and its characteristics studied. The characteristics of the broadband switching equipment, as well as those of individual components, such as the switching photodiodes, InGaAsP/InP semiconductor lasers, eight-port optical dividers and receiver circuits, are discussed from the viewpoint of analogue signal switching. The signal-to-noise ratio attained is more than 40dB for a 30MHz bandwidth television signal. Differential gain and differential phase are less than 2% and 2°, respectively, isolation is higher than 80 dB. Crosstalk between adjacent channels is suppressed below-60 dB over the band between d.c. and 100 MHz by a simple metallic shield at the input and output electric circuits.     

C60分子瞬态全光开关

本文以YAG脉冲激光为控制光,He-Ne连续激光为信号光,在C_(60)甲苯溶液中首次实现瞬态全光开关.由光开关时间推断出C_(60)分子三重态的寿命.     

偶氮苯光致异构反饱和吸收的光学双稳态开关的理论研究

讨论了稳态条件下,反饱和吸收的偶氮苯分子光学双稳态的开关性能.先根据偶氮苯光致异构的理论模型,计算了影响偶氮苯反饱和吸收系数的因素,然后理论模拟其反饱和吸收的光学双稳态开关过程.模拟结果表明:基于偶氮苯分子的反饱和吸收可实现双稳态全光开关.增大偶氮苯分子的顺式基态吸收截面,减小热弛豫系数K能够降低反饱和吸收偶氮苯光学双稳态的开关能量;反式吸收截面大不利于反饱和吸收光学双稳态的形成.     

含二噻吩乙烯的非线性光学开关分子的新设计方案研究

本文提出了一种利用二噻吩乙烯来设计光致二阶非线性光学开关分子的新方案. 与传统设计方案不同之处在于,新方案中,二噻吩乙烯主要作为一个得失电子能力可以改变的基团处于化合物的端基上. 通过设计一组结构简单的模型化合物,并利用密度泛函理论计算它们的一阶超极化率β,我们实验了新方案的效果. 计算结果表明,使用适当的取代基,能使设计的分子的光异构体之间的β比值达到10倍左右,差值超过100×10-30 esu,使得这组模型化合物的二阶非线性光学开关能力不逊色于一些遵循传统设计方案的复杂金属有机化合物.     

含二噻吩乙烯的非线性光学开关分子的新设计方案研究

本文提出了一种利用二噻吩乙烯来设计光致二阶非线性光学开关分子的新方案.与传统设计方案不同之处在于,新方案中,二噻吩乙烯主要作为一个得失电子能力可以改变的基团处于化合物的端基上.通过设计一组结构简单的模型化合物,并利用密度泛函理论计算它们的一阶超极化率β,我们实验了新方案的效果.计算结果表明,使用适当的取代基,能使设计的分子的光异构体之间的β比值达到10倍左右,差值超过100×10-30esu,使得这组模型化合物的二阶非线性光学开关能力不逊色于一些遵循传统设计方案的复杂金属有机化合物.     

Reversible photomechanical switching of individual engineered molecules at a metallic surface

We have observed reversible light-induced mechanical switching for individual organic molecules bound to a metal surface. Scanning tunneling microscopy (STM) was used to image the features of individual azobenzene molecules on Au(111) before and after reversibly cycling their mechanical structure between trans and cis states using light. Azobenzene molecules were engineered to increase their surface photomechanical activity by attaching varying numbers of tert-butyl (TB) ligands ("legs") to the azobenzene phenyl rings. STM images show that increasing the number of TB legs "lifts" the azobenzene molecules from the substrate, thereby increasing molecular photomechanical activity by decreasing molecule-surface coupling.     

基于舰载光电跟踪装备的光电助降系统技术分析

在分析国外舰载机传统光学助降系统和雷达全自动盲降系统发展现状的基础上,给出基于舰载光电跟踪技术装备的光电助降系统的组成、配置、技术原理、技术指标,对光电助降系统中光电测量坐标系到甲板坐标系进行转换,对光电助降系统的测量误差和定位误差进行建模,在舰船无摇摆以及纵摇2周期20s,横摇10周期15s条件下,结合我国现有技术基础,分析摇摆姿态角误差、距离误差、跟踪测角误差对光电助降系统定位精度的影响并进行仿真实验,给出舰载机距着舰点距离大于1 km和小于1 km时光电助降系统的定位误差。