A novel video-based microsphere localization algorithm for low contrast silica particles under white light illumination

On the basis of a brief review of four common image recognition algorithms for microspheres made of polystyrene or melamine resin, we present a new microsphere localization method for low-contrast silica beads under white light illumination. We compare both the polystyrene and silica procedures with respect to accuracy and precision by means of an optical tweezers setup providing CMOS video microscopy capability. By that we demonstrate that our new silica algorithm achieves a relative position uncertainty of less than ±1 nm for micron-sized microspheres, significantly exceeding the precision of the other silica approaches studied. Second, we present an advancement of our single microsphere tracking method to scenarios where two polystyrene, melamine resin or silica microspheres are in close-to-contact proximity. While the majority of the analysis algorithms studied generate artefacts due to interference effects under these conditions, we show that our new approach yields accurate and precise results.     

Tm~(3+)掺杂Ge-Ga-S玻璃微球-石英光纤锥耦合系统的荧光回廊模特性

以熔融淬冷法自制了Tm~(3+)掺杂Ge-Ga-S硫系玻璃,并以此为基质材料,用漂浮粉料熔融法制备了直径分布为50—200μm的高品质因数(Q10~4)的有源硫系玻璃微球谐振腔.在显微镜下优选出一颗表面质量好、球形度较高、直径为72.84μm的微球,与氢氧焰扫描拉锥法制备的一根腰锥直径为1.93μm的石英光纤锥进行近场耦合.根据基质材料的吸收光谱特性,选用808 nm的半导体激光器作为抽运源.实验测得光纤锥倏逝波场激发出了掺Tm~(3+)硫系玻璃微球在1460 nm附近的荧光回廊模式,其典型共振峰间隔为4.39 nm.实验测得的荧光回廊模式与米氏散射理论计算结果符合度较高(最大误差仅为0.047%),验证了本文提出的掺Tm~(3+)硫系微球制备及耦合工艺的可行性.     

Thermo-optical tuning of whispering gallery modes in Er:Yb co-doped phosphate glass microspheres

We demonstrate an all-optical, thermally assisted technique for broad-range tuning of whispering gallery modes in microsphere resonators fabricated from an Er:Yb co-doped phosphate glass (IOG-2). The microspheres are pumped at 978 nm and the heat generated by absorption of the pump expands the cavity, thereby altering the cavity size and refractive index. We demonstrate a significant nonlinear tuning range of greater than 700 GHz of both C- and L-band cavity emissions via pumping through a tapered optical fibre. Finally, we show that large linear tuning up to ∼488 GHz is achievable if the microsphere is alternatively heated by coupling laser light into its support stem.     

Fiber-coupled microsphere laser

We demonstrate a 1.5-microm - wavelength fiber laser formed by placement of glass microsphere resonators along a fiber taper. The fiber taper serves the dual purpose of transporting optical pump power into the spheres and extracting the resulting laser emission. A highly doped erbium:ytterbium phosphate glass was used to form microsphere resonant cavities with large gain at 1.5microm . Laser threshold pump powers of 60muW and fiber-coupled output powers as high as 3 muW with single-mode operation were obtained. A bisphere laser system consisting of two microspheres attached to a single fiber taper is also demonstrated.     

Nanosilicon photonics

Silicon photonics is no longer an emerging field of research and technology but a present reality with commercial products available on the market, where low‐dimensional silicon (nanosilicon or nano‐Si) can play a fundamental role. After a brief history of the field, the optical properties of silicon reduced to nanometric dimensions are introduced. The use of nano‐Si, in the form of Si nanocrystals, in the main building blocks of silicon photonics (waveguides, modulators, sources and detectors) is reviewed and discussed. Recent advances of nano‐Si devices such as waveguides, optical resonators (linear, rings, and disks) are treated. Emphasis is placed on the visible optical gain properties of nano‐Si and to the sensitization effect on Er ions to achieve infrared light amplification. The possibility of electrical injection in light‐emitting diodes is presented as well as the recent attempts to exploit nano‐Si for solar cells. In addition, nonlinear optical effects that will enable fast all‐optical switches are described.     

Quantum Dots Luminescence Collection Enhancement and Nanoscopy by Dielectric Microspheres

In recent years, dielectric microspheres have been used in conjunction with optical microscopes to beat the diffraction limit and to obtain superresolution imaging. The use of microspheres on quantum dots (QDs) is investigated, for the first time, to enhance the light coupling efficiency. The enhancement of the QD luminescence collection in terms of extraction and directionality is demonstrated, as well as the enhancement of spatial resolution. In particular, it is found that a dielectric microsphere, placed on top of an epitaxial QD, increases the collected radiant energy by about a factor of 42, when a low numerical aperture objective is used. Moreover, if two or more QDs are present below the microsphere, the modification of the far field emission pattern allows selective collection of the luminescence from a single QD by simply changing the collection angle. Dielectric microspheres present a simple and efficient tool to improve the QD spectroscopy, and potentially QD-based devices.     

Resonating properties of passive spherical optical microcavities

As an optically pumped device, the lasing characteristics of a spherical microcavity laser depend on the optical pumping processes. These characteristics can be described in term of the Q factor and the optical field distribution in a microsphere. We derived analytical expressions and carried out numerical calculation for Q factor and optical field. The Q factor is found to be oscillatory functions of the radius of a microsphere and the pumping wavelength, and the pumping efficiency for a resonating microsphere is much higher than that for an anti-resonating microsphere. Using tunable lasers as pumping sources is suggested in order to achieve a higher pumping efficiency. Numerical calculation on optical field distribution in spherical microcavities shows that a well focused Gaussian beam is a suitable incident wave for cavity quantum electrodynamics experiments in which strong confinement of optical field in the center of a microsphere is requested, but higher order spherical wave should be used instead for exciting whispering-gallery-mode (WGM) microsphere lasers, for the purpose of favoring optical energy transferring to WGM in optical microspheres.     

Coupled magnetic resonator optical waveguides

Optical resonators are important devices that control the properties of light and manipulate light–matter interaction. Various optical resonators are designed and fabricated using different techniques. For example, in coupled resonator optical waveguides, light energy is transported to other resonators through near‐field coupling. In recent years, magnetic optical resonators based on LC resonance have been realized in several metallic microstructures. Such devices possess stronger local resonance and lower radiation loss compared with electric optical resonators. This study provides an overall introduction on the latest progress in coupled magnetic resonator optical waveguide (CMROW). Various waveguides composed of different magnetic resonators are presented and Lagrangian formalism is used to describe the CMROW. Moreover, several interesting properties of CMROWs, such as abnormal dispersions and slow‐light effects, are discussed and CMROW applications in nonlinear and quantum optics are shown. Future novel nanophotonic devices can be developed using CMROWs.     

基于微球透镜的任选区高分辨光学显微成像新方法研究

提出和发展了基于毛细管-微球组合探针的任选区、 高分辨显微成像新方法. 建立了微球显微成像的物理模型, 利用成像理论,推导出微球成像的放大倍率; 采用3.0, 4.4, 5.6, 7.5, 10.0 μm等不同直径的SiO₂微球, 对未经刻录的DVD光盘进行了微球显微成像实验, 可以观察到DVD光盘的微纳米结构被明显放大且对比度显著提高, 与理论计算结果相符合; 采用毛细管微探针操纵微球的方法, 实现了基于微球透镜阵列的样品微纳米结构的高分辨显微成像; 在此基础上, 进一步将毛细管微探针与微球组合, 制备出毛细管-微球组合型探针, 首次实现了基于微球透镜的样品任意区域高分辨显微成像.     

Fabrication of Nanostructured Composite Microspheres Based on the Self‐Assembly of Polymers and Functional Nanomaterials

This Review examines recent developments in the morphological control of polymer microspheres fabricated via the phase separation of polymers as well as the alignment of functional nanoparticles inside microspheres prepared by so‐called bottom‐up synthesis techniques. Several methods for adjusting the internal and surface morphologies of polymer microspheres based on the phase separation of polymer blends and block copolymers are discussed, and the effects of microsphere size on phase separated structures and theoretical simulations of morphologies are also reviewed. The alignment of functional nanoparticles in phase separated polymer microspheres and applications of nanostructured and hybrid polymer microspheres are summarized.     

基于近场光学的微球超分辨显微效应

在光学成像领域,由于受到衍射极限的限制,常规成像分辨率在200nm左右.科学的不断进步对更高分辨率有着迫切需求,如何突破这个极限来获得更高质量的高分辨率图像是热门研究领域.2011年提出了微球超显微技术:在原有的光学系统中,将直径几微米至几十微米的透明微球直接置于样品表面,就能够成倍提高传统光学显微镜的成像能力.微球超显微技术以其简单直接的特点,受到广泛关注.本文介绍了光学显微镜的研究背景以及国内外团队在微球超分辨显微技术方面的研究进展,包括通过在微球表面进行环刻同心环、中心遮挡和表面涂覆的方法来调节微球所产生的光子纳米喷射方面所开展的一系列研究,并进行了理论模拟和实验验证,进一步提升了微球的超分辨显微效应.最后,展望了今后微球超分辨显微技术的应用与发展方向.     

Fiber Optic Excitation of Silicon Microspheres in Amorphous and Crystalline Fluids

ABSTRACT

This study investigates the optical resonance spectra of free-standing monolithic single crystal silicon microspheres immersed in various amorphous fluids, such as air, water, ethylene glycol, and 4-Cyano-4’-pentylbiphenyl nematic liquid crystal. For the various amorphous fluids, morphology-dependent resonances with quality factors on the order of 10⁵ are observed at 1428 nm. The mode spacing is always on the order of 0.23 nm. The immersion in various amorphous fluids affects the spectral response of the silicon microsphere and heralds this technique for use in novel optofluidics applications. Even though the nematic liquid crystal is a highly birefringent, scattering, and high-index optical medium, morphology-dependent resonances with quality factors on the order of 10⁵ are observed at 1300 nm in the elastic scattering spectra of the silicon microsphere, realizing a liquid-crystal-on-silicon geometry. The relative refractive index and the size parameter of the silicon microsphere are the parameters that affect the resonance structure. The more 4-Cyano-4’-pentylbiphenyl interacting with the silicon microsphere, the lower the quality factor of the resonances is. The more 4-Cyano-4’-pentylbiphenyl is interacting with the silicon microsphere, the lower the mode spacing Δλ of the resonances is. The silicon microspheres wetted with nematic liquid crystal can be used for optically addressed liquid-crystal-on-silicon displays, light valve applications, or reconfigurable optical networks.     

样品表面银膜的粗糙度对钛酸钡微球成像性能的影响

研究了样品表面镀有不同表面粗糙度的银膜对钛酸钡（BaTiO₃ glass,BTG）微球成像效果的影响,发现当银膜表面的粗糙度（RMS）从3.23 nm增大到6.80 nm时,用直径为15 μm的BTG微球观察直径为250和580 nm的微球阵列,样品的成像范围增大.另外,BTG微球还可以清晰分辨原本不可分辨的直径为200 nm的微球阵列.结果表明,粗糙银膜引起的散射作用和表面等离激元波的局域场增强效应,使得更多物体的高频信息耦合进微球,提高了微球成像的分辨率和成像范围.     

2μm波段硫系玻璃微球激光器的制备和表征

工作在2μm波段附近的中红外微球激光器在生物医学传感、激光雷达、窄带光学滤波和空气污染监控等领域具有重要的应用价值.本文以自制的Tm~(3+)-Ho~(3+)共掺的Ge-Ga-Sb-S (2S2G)硫系玻璃为基质材料,采用玻璃粉末高温漂浮熔融法批量制备了高品质(典型品质因数大于10~5)硫系玻璃微球.优选一颗直径为205.82μm的微球为实验对象,利用光纤锥耦合法对其进行光学近场耦合实验.在808 nm抽运光的作用下,在1.8—2.1μm波段处可观测到明显的荧光回廊模现象.当抽运功率达到0.848 mW的阈值时,可在2080 nm附近观测到明显的激光输出.上述实验结果表明本文采用的2S2G硫系玻璃具有用于制备工作在中远红外波段的有源光学/光电子学器件的潜力.     

Investigation and Development of Quantum Dot-Encoded Microsphere Bioconjugates for DNA Detection by Flow Cytometry

The development of screening assays continues to be an active area of research in molecular diagnostics. Fluorescent microspheres conjugated to biomarkers (nucleic acids, proteins, lipids, carbohydrates) and analyzed on flow cytometer instruments offered a new approach for multiplexed detection platform in a suspension format. Quantum dots encoded into synthetic microspheres have the potentials to improve current screening bioassays and specifically suspension array technology. In this paper, commercialized quantum dot-encoded microsphere were evaluated and optimized as fluorescent probes to address some of the limitations of suspension array technologies. A comprehensive study was undertaken to adapt the bioconjugation procedure to the quantum dot-encoded microsphere structural and optical properties. Both the leaching-out of quantum dots and microspheres degradation under bioconjugation experimental conditions were minimized. A rapid, efficient and reproducible conjugation method was developed for the detection of single-stranded DNA with the commercialized quantum dot-encoded microsphere. Approximately ten thousand microspheres were conjugated to short amino-modified DNA sequences in one hour with high efficiency. The bioconjugated microspheres acting as fluorescent probes successfully detected a DNA target in suspension with high specificity. Quantum dot-encoded microsphere commercial products are limited which strongly prevents reproducible and comparative studies between laboratories. The method developed here contributes to the understanding of quantum dot-encoded microsphere reactivity, and to the optimization of adapted experimental procedure. This step is essential in the development of this new fluorescent probe technology for multiplex genotyping assay and molecular diagnostic applications.     

Neural stimulation with optical radiation

This paper reviews the existing research on infrared neural stimulation, a means of artificially stimulating neurons that has been proposed as an alternative to electrical stimulation. Infrared neural stimulation (INS) is defined as the direct induction of an evoked potential in response to a transient targeted deposition of optical energy. The foremost advantage of using optical radiation for neural stimulation is its spatial resolution. Exogenously applied or trans‐genetically synthesized fluorophores are not used to achieve stimulation. Here, current work on INS is presented for motor nerves, sensory nerves, central nervous system, and in vitro preparations. A discussion follows addressing the mechanism of INS and its potential use in neuroprostheses. A brief review of neural depolarization involving other optical methods is also presented. Topics covered include optical stimulation concurrent with electrical stimulation, optical stimulation using exogenous fluorophores, and optical stimulation by transgenic induction of light‐gated ion channels.     

Spatial resonator solitons

Spatial solitons can exist in various kinds of nonlinear optical resonators with and without amplification. In the past years different types of these localized structures such as vortices, bright, dark solitons, and phase solitons have been experimentally shown to exist. Many links appear to exist to fields different from optics, such as fluids, phase transitions, or particle physics. These spatial resonator solitons are bistable and due to their mobility suggest schemes of information processing not possible with the fixed bistable elements forming the basic ingredient of traditional electronic processing. The recent demonstration of existence and manipulation of spatial solitons in semiconductor microresonators represents a step in the direction of such optical parallel processing applications. We review some proof of principle soliton experiments on slow systems, and describe in more detail the experiments on semiconductor resonator solitons which are aimed at applications.     

Pedestal antiresonant reflecting waveguides for robust coupling to microsphere resonators and for microphotonic circuits

Strip-line pedestal antiresonant reflecting waveguides are high-confinement, silica integrated optical waveguides in which the optical modes are completely isolated from the substrate by thin high-index layers. These waveguides are particularly well suited for whispering-gallery mode excitation in high-Q microspheres. They can also be used in microphotonic circuits, such as for microring resonators. The theory and design of these structures are highlighted. Experiments that show high coupling efficiency to microspheres are also demonstrated.     

Self‐assembled CdSe/CdS nanorod micro‐lasers fabricated from solution by capillary jet deposition

Here we show an innovative, simple and reliable method to fabricate micro‐lasers by self‐assembly of rod‐shaped nanocrystals. We use dot/rod core/shell CdSe/CdS nanorods to form optical micro‐resonators by exploiting their self‐organization into well‐defined coffee stain rings. The fabrication process merely consists of capillary jet deposition of a nanorod solution onto a glass substrate, and is scalable, economic, and highly reproducible. Upon optical pumping of the micro‐resonators we obtain laser emission in the red or in the blue‐green spectral region, demonstrating lasing both from core and shell transitions, with low pumping thresholds. Modeling by full‐wave numerical simulations according to generalized (i. e. scattering) formulation of laser theory demonstrates lasing from complex modes of the self‐assembled cavity.     

Theory of stimulated concentration scattering of light in a liquid suspension of transparent microspheres

A theory of stimulated light scattering in a nonlinear liquid suspension of transparent microspheres—an artificially created medium whose nonlinearity is caused by modulation of the concentration of microspheres by gradient forces in a field of spatially inhomogeneous laser radiation—is constructed. The threshold, angular, and spectral characteristics of the scattering are studied in the diffusion-limit approximation based on the solution of the system of wave equations in combination with the Planck-Nernst two-dimensional equation for the concentration of microspheres. The transient regime of scattering in the field of a specified step-like pump pulse is considered. A sharp angular dependence of the scattering efficiency on the microsphere radius is predicted and proposed for use in optical diagnostics of liquid suspensions of dielectric microspheres—highly efficient wideband nonlinear media.