基于半导体纳米线/锥形微光纤探针的被动式近场光学扫描成像

本文结合近场扫描结构和纳米线-微光纤耦合技术,提出了一种基于硫化镉纳米线/锥形微光纤探针结构的被动近场光学扫描成像系统.该系统采用被动式纳米探针,保留了纳米探针对样品表面反射光的强约束优势.其理论收集效率为4.65‰,相比于传统的金属镀膜近场探针收集效率提高了一个数量级,可有效地提高扫描探针对样品形貌信息的检测能力;而后通过硫化镉纳米线与微光纤之间高效的倏逝场耦合,将检测的光强信号传输到远场进行光电探测,最终实现对目标样品形貌的分析成像,其样品宽度测量误差在7.28%以内.该系统不需要外部激发光路,利用显微镜自身光源进行远场照明,被动扫描探针仅作为样品表面反射光的被动收集系统.本文基于半导体纳米线/锥形微光纤探针的被动式近场光学扫描成像方案,可有效地降低探针的制备难度和目标光场的检测难度,简化扫描成像的结构,为近场光学扫描显微系统之后的发展提供新的思路.     

基于半导体纳米线/锥形微光纤探针的被动式近场光学扫描成像

本文结合近场扫描结构和纳米线-微光纤耦合技术,提出了一种基于硫化镉纳米线/锥形微光纤探针结构的被动近场光学扫描成像系统.该系统采用被动式纳米探针,保留了纳米探针对样品表面反射光的强约束优势.其理论收集效率为4.65‰,相比于传统的金属镀膜近场探针收集效率提高了一个数量级,可有效地提高扫描探针对样品形貌信息的检测能力;而后通过硫化镉纳米线与微光纤之间高效的倏逝场耦合,将检测的光强信号传输到远场进行光电探测,最终实现对目标样品形貌的分析成像,其样品宽度测量误差在7.28%以内.该系统不需要外部激发光路,利用显微镜自身光源进行远场照明,被动扫描探针仅作为样品表面反射光的被动收集系统.本文基于半导体纳米线/锥形微光纤探针的被动式近场光学扫描成像方案,可有效地降低探针的制备难度和目标光场的检测难度,简化扫描成像的结构,为近场光学扫描显微系统之后的发展提供新的思路.     

一种石墨烯波导褶皱激发表面等离子体激元的设计

设计了褶皱石墨烯波导结构激发表面等离子体激元,通过设计周期阵列结构实现了表面等离子体激元传播损耗的补偿.理论分析了周期阵列结构的表面等离子体激元传播模型和补偿损耗的方式,结果表明褶皱衍射激发表面等离子体激元波导不仅能够激发表面等离子体激元,还能利用表面等离子体激元波矢关系实现器件参数控制,周期阵列增益全程补偿损耗的方式可以显著增加表面等离子体激元的传播距离.数值分析结果进一步表明:该结构具备了保持亚波长尺寸的强局域化优势;周期阵列增益全程补偿可以显著提高纳米腔中的电场强度,降低传输损耗;波导结构的粒子反转水平较高,自发辐射噪声的扰动较低.设计的石墨烯波导器件可以为微纳光学集成、光子传感和测量等领域提供理想的亚波长光子器件.     

领结形中空表面等离子体波导的传输特性

设计了一种领结形中空表面等离子体波导.采用频域有限差分法,对这种波导所支持的基模的能流密度分布、有效折射率、传播长度和模式面积随几何结构参数和工作波长的依赖关系进行了分析.结果表明,沿纵向的能流主要分布在两个上下突起所形成的中间区域.通过调整几何参数及工作波长,可以调节模式的有效折射率、传播长度和模式面积.在工作波长确定的条件下,有效折射率随突起半径的增大呈减小趋势,而传播长度和模式面积则随着突起半径的增大呈增大趋势,四个角上的圆弧半径对波导的传输特性有微调作用,左右扇形区域的半径对波导的传输特性有较明显 关键词： 集成光学 光波导 表面等离子体波导     

基于银纳米链的马赫-曾德干涉仪结构的生物传感器

优化了一种基于表面等离激元银纳米链的马赫-曾德干涉式传感结构.该结构由参考臂、传感臂及纳米线波导构成.纳米线波导由银纳米线包裹一定厚度的硅来构成.引入两条银纳米链分别作为马赫-曾德干涉仪的参考臂和传感臂,并研究所设计结构的传输特性,通过降低传输损耗以提高所设计结构的精确度与灵敏度.相比于两条完全相同的银纳米线作为参考臂和传感臂的情况,在参考臂和传感臂改为银纳米链后,传输特性有明显提高,单位长度损耗明显降低.这是由于银纳米链中的单元结构之间的长程/库仑相互作用增强了结构中的电磁场,进而降低了传输损耗.将两条银纳米链的晶格常数设置为不同的情况,研究发现,在特定的银包硅纳米线的宽度与某些占空比下,含有非对称的银纳米链结构的单位传输损耗小于含有对称的银纳米链结构.由此可以知道,具有小损耗的银纳米颗粒链可以弥补大损耗的银纳米颗粒链的传输损失.利用这个特点,进一步优化设计结构,将一侧银纳米链改为纳米线.改变另一侧银纳米链的晶格常数与占空比,可以发现大多数情况下,这类结构传输特性优于含有两条银纳米链以及含有两条银纳米线的结构.本文的设计结构可以大幅减小传统的马赫-曾德干涉仪的传输损耗,且在结构的制备...     

纳米金属肋混合表面等离子体波导模式特性分析

基于传统混合表面等离子体波导,提出了一种半导体纳米线和纳米金属肋混合的表面等离子体波导.采用有限元法对其模式特性进行了数值模拟,研究了该波导的有效折射率、传播损耗、归一化模场面积等特性随波导几何尺寸的变化规律,分析了该混合波导的增益阈值.结果表明:该波导具有较低的传播损耗和较强的光场限制能力,并且混合模式的最小模面积仅为0.001 52μm2.     

银纳米棒双体结构的表面等离子体共振光学特性研究

利用时域有限差分方法,研究了银纳米棒双体结构的散射光谱及其电场分布,并对其局域表面等离子体耦合共振特性进行了分析。研究表明随着银纳米棒之间的距离变大,其表面等离子共振峰的强度逐渐变弱,横向四极模式和横向偶极模式峰位基本不变。纳米棒半径的增加和夹角的变大,都会引起峰值强度明显增强。通过场分布计算发现,纳米棒半径的增加和夹角的变大都可以在颗粒的近场区域产生"热点",这种局域电磁场显著的增强对表面增强拉曼散射、荧光探针、纳米催化等方面的应用具有参考价值。     

偏振方向及结构间耦合作用对空心方形银纳米结构表面等离子体共振的影响

空心方形纳米结构能够激发更大面积的增强电场,故其可以作为衬底用于表面增强拉曼散射.应用离散偶极子近似算法研究了空心方形银纳米结构的消光光谱及其近场电场分布与入射光偏振方向之间的关系.研究表明,空心方形银纳米结构的表面等离子体共振峰不随入射光偏振方向的改变而移动,但是其表面增强电场分布却强烈地依赖于入射光的偏振方向.另外,还讨论了空心方形银纳米结构间的耦合作用对其表面等离子体共振模式的影响.结果发现,可以通过调节结构间的距离来改变结构间的耦合作用,同时改变了表面等离子体共振峰的位置.这些结果将为理解闭合纳米 关键词： 空心方形银纳米结构 表面等离子体 偏振 电场耦合     

一种由椭圆形金属和介质纳米线组成的混合表面等离子体光波导的基模控制特性研究

本文研究了一种由三根并排放置的椭圆形金属-介质-金属纳米线构成的混合表面等离子体光波导所支持的电磁场基模的控制特性,中间是高折射率的介质纳米线,左右是两根对称放置的金属纳米线。研究结果表明,基模电磁场增强效应主要分布在三根纳米线形成的两个间隙区域,且对整个结构的几何参数有一定依赖性。因此,通过改变纳米线的几何尺寸、两根纳米线之间的间距以及介质的电磁参数,可以调整和控制这种波导所支持的基模的有效折射率、模式传输距离、归一化的模式面积和模式束缚因子等物理特性。基于这些有效的模式操控特性,这种混合型的表面等离子体光波导可以应用于高密度光子器件集成、纳米光子学和生物传感器等领域。     

高表面粗糙度银纳米线的分形研究和SERS效应

为了获得分布均匀、有序排列、可重复性高的表面增强拉曼散射基底(SERS),选取银离子导体RbAg_4I_5薄膜,结合真空热蒸镀工艺和固态离子学方法在外加电流作用下制备出高表面粗糙度的银纳米线。同时,选取罗丹明6G(R6G)溶液作为探针分子,研究高表面粗糙度银纳米线作为SERS基底时的表面增强拉曼特性。实验结果表明:制备得到的银纳米线在宏观上呈现为树枝状,在微观上呈现为有序排列,并且其纳米结构的分形维数为1.59;采用银纳米线作为SERS基底时,能够检测到R6G溶液的浓度低至10~(-17) mol/L。制备的高表面粗糙度和有序密集排列的银纳米线SERS基底在环境科学等领域具有潜在的应用前景。     

Demonstration of high extinction ratio modal interference in a two-mode fiber and its applications for all-fiber comb filter and high-temperature sensor

We show that high extinction ratio (>20 dB) modal interference in a two-mode dispersion compensating fiber can be utilized to build a compact, easy-to-fabricate tunable all-fiber optical comb filter. Wavelength tunability over the full free spectral range of the comb filter is demonstrated with an electrical power of 115mW using an on-fiber thin film micro-heater deposited directly on the fiber. In another configuration, the comb filter is used as a temperature sensor with dynamic range of >300 °C and sensitivity of <0.1 °C. The temperature sensor is capable of measuring a temperature as high as 500 °C.     

A high nonlinearity elliptical fiber for applications in Raman and Brillouin sensors

Raman and Brillouin effects have found special applications in distributed sensing for smart materials and structures. In these sensors, the fiber acts as a distributed sensor, sensing strain and temperature over a range of tens of kilometers and, at the same time, carries this information to the installation that will process them. In order to optimize the fiber to operate under the Brillouin and Raman regimes, a special elliptical fiber with small effective area has been designed, which will allow these sensors to cover longer distances and/or employ lower power lasers.     

Optical arithmetic unit using bit-WDM

A novel arithmetic unit is proposed consisting of a pipelined optical ripple carry adder that adds two words with bits multiplexed by different wavelengths on a single fiber. The addition result is returned to a fiber bus in the same format as the incoming words. The corresponding operand bit pairs are split off the fiber using wavelength division demultiplexers. Full adders compute the sum for each bit pair and the carry from the next lower significant bit pair. The full adder uses couplers and NOT, NOR and novel XOR logic gates constructed using semiconductor optical amplifiers for gain and wavelength shifting.     

Controllable optical bistability and multistability in a rare-earth-ion-doped optical fiber

We investigated the optical bistability and multistability in an Er³⁺-doped ZrF₄–BaF₂–LaF₃–AlF₃–NaF optical fiber inside an optical ring cavity. It is found that the optical bistability and multistability can be easily controlled via adjusting properly the parameters of the corresponding system. Our scheme may provide some new possibilities for technological applications in optoelectronics and optical-fiber communication.     

Experimental measurement and analysis of the optical trapping force acting on a yeast cell with a lensed optical fiber probe

Based on an optical trapping system with a single-lensed fiber probe inserted at an angle, the sub-picoNewton trapping force acting on a yeast cell as a function of the displacement is measured experimentally by the static and dynamic methods, respectively, whose measurement processes are presented in detail. The measured maximum trapping efficiency is 0.07 in our experiment, which is an order of magnitude lower than that of the optical tweezers. The characteristics of the trapping force in the various horizontal directions are discussed. Finally, the analysis of the measurement error shows the factors and their magnitude which cause error, and offers a way to reduce the error in future.     

Temperature dependence of low loss polymeric AWG

We investigate on the variation of loss and temperature dependence of a polymeric arrayed waveguide grating (AWG) depending on its substrate, by fabricating 16-channel polymeric AWGs with various substrate conditions. Insertion loss for a polymeric AWG on a silicon substrate is measured as low as 3.1 dB. The temperature-dependent wavelength shift for a polymeric AWG detached from the substrate is maintained within 0.1 nm from 20 to 80 °C. But we observe a degradation of insertion loss and a little instability in wavelength characteristics both for the detached polymeric AWG and for a polymeric AWG on a polymer substrate. We investigate on those optical properties of the polymeric AWGs based on measured thermal expansion properties of the polymers.     

Method of state code matrixes in the realization of optical switching using Perfect Shuffle

Based on the Left Perfect Shuffle (LPS) optical communication network constructed by cascade multi-stage LPS interconnection, using Looping algorithm, any arbitrary sequence of the input signals can be realized. However, instead of obtaining the simultaneous state codes of the same level node switches through mathematical analytical expressions directly, only routing tags of each channel can be obtained through mathematical analytical expressions so as to draw out topological chart of the network to obtain the state codes implied in the chart. Thus, the states of the switches cannot be directly programmed and controlled by computer in practical application. In this paper, based on the Looping algorithm, a method of stage code matrixes is presented to resolve this problem. By using the method, the simultaneous state codes of the same level’s four node switches can be directly obtained, which is convenient for the computer to provide controlled signals needed to finish the permutation for each node switch. The method of stage code matrixes provides further theoretical basis for the realization of optical switching by integration of Perfect Shuffle and high-speed optical switches.     

Dichroic property of the H2O-groups in α-quartz, LiNbO3 and LiTaO3 in the infrared range

The absorptive peaks of the H₂O-groups were observed in the infrared absorption spectra in the vicinity of 3480 cm⁻¹ in LiNbO₃ and LiTaO₃, and 3580 cm⁻¹ in α-quartz. The absorptions of these lines were found to depend on the vibration direction of the polarized incident light, showing the dichroic property in these crystals. The absorption of the ordinary ray waves is much larger than that for the E-ray waves in the crystals. This observation indicates that the direction of the bond vibrations for the H₂O-groups is perpendicular to the optic axis of crystals. The dichroic property of the H₂O-groups may serve as the tracer to study the local electric field in piezoelectric crystals.     

All optical latches using quantum-dot semiconductor optical amplifier

The design and performance of two optical latches, the Set-Reset (SR) latch and D-Flip-Flop has been studied. These latches are the building blocks of large optical processors. The latches are built using two optical logic operations NAND and NOT. Both NAND and NOT operations are realized by using Mach-Zhender interferometer (MZI) utilizing semiconductor optical amplifier with quantum dot active region (QD-SOA). Nonlinear dynamics including carrier heating and spectral hole-burning in the QD-SOA are taken into account together with the rate equations in order to realize the all-optical logic operations. Results show that this scheme can realize the functions of Set-Reset latch and D-Flip-Flop at high speeds (∼250 Gb/s). The dependence of the output quality (Q factor) on QD-SOA parameters is also discussed.     

Dispersion-Managed Solitons in Multiple-Core Nonlinear Fiber Arrays

The variational principle is employed to obtain the evolution of the parameters of Gaussian and super-Gaussian chirped solitons that propagates through multiple-core nonlinear optical fiber arrays. This is governed by the dispersion-managed nonlinear Schrodinger's equation with strong dispersion management in the presence of linear coupling between the adjacent cores. The results are valid for any configuration of the cores.