采用超连续谱激光的双光束光纤光阱实验

以超连续谱激光器作为捕获光源,首次提出并搭建了超连续谱双光束光纤光阱实验系统,实现了聚苯乙烯微球的捕获和操控。通过改变光纤端面间隔和调整捕获光功率的方式精确控制微球的位置,采用CCD图像分析方法实现了微球位置的精确测量。对微球受限布朗运动下的位置变化进行傅里叶变换,计算得到功率谱,与理论功率谱函数拟合后求出了其光阱刚度。结果表明,捕获光束的功率为28 mW时,光阱刚度达到1.3×10-6N/m,高于相同实验条件下单波长光纤光阱的刚度。与传统采用单色光作为捕获光源的光镊系统不同,超连续谱双光束光阱系统利用其宽谱优势,通过研究被捕获微粒的散射光谱信息可获取其尺寸、折射率等物理特征参数。     

金纳米棒三聚体中的等离激元诱导透明

基于金纳米棒构成的三聚体微元结构模型,详细地研究了等离激元诱导透明(plasmon induced transparency,PIT)现象产生的物理过程.研究发现,三聚体的吸收谱线随着其耦合距离以及尺寸的变化,竖直金纳米棒所对应的偶极明模在平行双长条金纳米棒对应的暗模作用下会产生分裂.依据这一结果提出了一个新的物理解释,PIT现象的产生主要来自于竖直金纳米棒中偶极振荡的模式分裂后的相干叠加.同时,考虑到两个振子之间的耦合会伴随着一定的相位关联性,进而引入了耦合相位因子修正了洛伦兹振子耦合模型,解析地研究了耦合相位因子对吸收谱的调控作用和分裂明模之间的相干叠加效应对PIT效应的影响.这为在纳米尺寸范围设计人造原子、光开关、慢光效应等方面的应用提供了理论参考.     

混合腔光力系统的双光子散射

混合腔光力系统同时包含一次和二次光力相互作用。本文研究了混合腔光力系统中的双光子散射问题。在Wigner-Weisskopf框架下,通过求解散射过程,获得了混合腔光力系统散射态的解析表达式,揭示了双光子散射的4个物理过程：1)双光子均被直接反射,不进入腔中;2)一个光子被直接反射,另一个光子入射进腔中;3)两个光子按次序先后入射进腔中,但腔中最多只有一个光子;4)两个光子均入射进腔中。通过分析双光子散射谱,发现在该散射过程中可以产生双光子频率反关联,并且发现了混合腔光力系统中的参数与双光子散射谱特性之间的联系。该研究不仅提供了一种产生关联光子对的散射方法,而且提出了一种表征光力系统参数的光谱方法。     

基于去偏振-偏振图像动态光散射的纳米棒尺度测量

二维纳米棒的布朗运动可以用平移扩散和转动扩散运动来描述.提出了一种基于去偏振-偏振图像的动态光散射(DIDLS)测量方法,通过分析纳米棒布朗运动的平移扩散和转动扩散在偏振激光入射下产生的垂直-垂直和垂直-水平偏振动态光散射信号,测量了纳米棒的尺寸和尺寸分布.研究了连续测量的偏振动态光散射信号图像间的相关系数函数,通过两次反演,计算出纳米棒的长度以及长径比,进而得到颗粒的二维尺度分布.分析了不同入射激光波长对测量结果的影响,提出自相关函数的基线值可以作为信噪比的判据.采用650,780,905 nm三种波长对直径为20 nm、长度为300 nm的纳米金棒进行了测量,得到了纳米金棒的平均尺寸和尺寸分布.     

轴向多光阱微粒捕获与实时直接观测技术

传统的光镊技术使用单个物镜同时进行光学捕获与显微成像,使得捕获与成像区域被限制在物镜焦平面附近,无法同时观察到沿光轴方向(即Z向)捕获的多个微粒.本文提出一种轴平面(XZ平面)GerchbergSaxton迭代算法来产生沿轴向分布的多光阱阵列,将轴平面成像技术与光镊结合,实现了沿轴向对二氧化硅微球的多光阱同时捕获与实时观测.通过视频分析法测量了多个二氧化硅微球在轴向光镊阵列中的布朗运动,并标定了光阱刚度.本文提出的轴向多光阱微粒捕获与实时观测技术为光学微操纵提供了一个新的观测视角和操纵方法,为生物医学、物理学等相关领域研究提供了一种新的技术手段.     

膜结构对金纳米线阵列表面增强拉曼散射的影响

金纳米线阵列作为表面增强拉曼散射的基底能够产生有效的增强效应,金纳米线阵列通过金线之间的电场耦合产生增强的拉曼信号.在实验中,制备出金纳米线阵列与金纳米刷,两种样品结构不同,金纳米刷的一面带有金膜.用巯基吡啶作为探针分子,金纳米刷的SERS实验显示出很好的增强效应,增强因子为106,不同位点的SERS谱具有区域不均一的特征.而相同实验条件下的金纳米线阵列的增强因子只有102.光学吸收谱表明这两种结构均发生了共振吸收增强电场,对其结构的分析表明,这两种结构具有不同的电场局域化分布,同时金纳米刷中金线上端强烈的电场耦合,这是其具有更好的增强效用的原因.同时,4-MP的表面增强拉曼谱的变化特征体现了化学增强效应的影响.     

基于低损光学相变和超透镜的可控多阱光镊

为提升光镊在三维空间中对粒子的捕获性能,本文设计和分析了新型的双阱和多阱超透镜光镊方案.首先基于低损耗相变材料Sb₂S₃设计了可控超透镜双阱光镊,并对两个半径为250 mm的SiO₂粒子所受光力进行了矢量横向分析和轴向分析.仿真实验结果表明,当Sb₂S₃在晶态下时,超透镜捕获的两个粒子的横向光阱刚度k_x分别达到了约25.7 pN/(μm·W)和37.4 pN/(μm·W),轴向光阱刚度k_z均约为10.0 pN/(μm·W);而当Sb₂S₃在非晶态下时,k_x和k_z值均降低到其对应晶态下的1/10,且此时粒子在z方向上不能被稳定捕获,从而实现了在三维空间中对粒子的可控捕获.进一步本文给出了阵列式的可控多阱光镊.通过调控相变材料Sb₂S₃的晶态和非晶态,能形成不同组合粒子的三维捕获方案.这些新型可控光镊可实现多...     

光纤探针型近场光镊光阱力特性研究

基于动量守恒原理,结合麦克斯韦应力张量和三维时域有限差分方法,建立了近场空间内激光光镊对纳米微粒的光阱力计算模型.分析了光纤探针型近场光镊的近场分布以及操作纳米微粒时各轴向光阱力的分布情况,并探讨了光纤探针尖端的捕获尺寸、捕获位置和操作稳定性.结果表明:微粒应处于光纤探针针尖的近场空间内才可实现稳定可靠的纳米操作,不同尺寸的微粒具有不同的捕获效果,且随初始位置的不同微粒的捕获位置亦不同.计算结果为激光近场光镊纳米操作装置的设计和制造提供了理论基础.     

空间散斑场捕获大量吸光性颗粒及其红外显微观测

光镊技术被广泛应用于捕获和操纵微纳米尺寸颗粒,主要包括捕获水中透明性颗粒和空气中吸光性颗粒两种类型.本文用激光束照射毛玻璃散射片,透射光经透镜会聚后在透镜的像平面附近产生了主观散斑场.该散斑场为空间分布,包含大量的亮斑和暗斑.大量由亮斑包围的暗斑如同一个个空间能量陷阱,被用来捕获大量的吸光性墨粉颗粒,被捕获颗粒的尺寸约2—8μm,密度约1—2 g/cm3.采用红外显微镜拍摄到空间散斑场捕获颗粒的红外像,红外图像显示被捕获颗粒吸光后温度升高,证实了空间散斑场捕获吸光性颗粒的机理为光泳力原理.     

功率谱密度法标定光镊的三维光阱刚度

采用四象限探测器和功率谱密度法,搭建了一套快速标定光镊三维光阱刚度的测量系统.实验中,用四象限探测器记录微粒做受限布朗运动时的位置信息,用功率谱密度法标定光阱刚度,测得了直径0.97μm SiO2小球和直径1μm PMMA小球的光阱刚度与激光功率的关系.结果表明:对于SiO2小球,当激光功率为50~120mW时,光阱刚度与激光功率成正比;对于PMMA小球,当激光功率为80~130mW时,光阱刚度与激光功率成正比.该光镊系统可用于生物、物理等微观领域研究的高准确度测力系统.     

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.