Theoretical Design of a Pump‐Free Ultrahigh Efficiency All‐Optical Switching Based on a Defect Ring Optical Waveguide Network

A theoretical design of a defect ring optical waveguide network is proposed to construct a pump‐free ultrahigh efficiency all‐optical switch. This switch creates ultrastrong photonic localization and causes the nonlinear dielectric in the defect waveguide to intensely respond. At its ON state, this material defect without Kerr response helps to produce a pair of sharp pass bands in the transmission spectrum to form the dual channel of the all‐optical switch. When it is switched to its OFF state, the strong Kerr response induced refractive index change in the high nonlinear defect waveguide strongly alters the spectrum, leading to a collapse of the dual channels. Network equation and generalized eigenfunction method are used to numerically calculate the optical properties of the switch and obtain a threshold control energy of about 2.90 zJ, which is eight orders of magnitude lower than previously reported. The switching efficiency/transmission ratio exceeds 3× 10¹¹, which is six orders of magnitude larger than previously reported. The state transition time is nearly 108 fs, which is approximately two orders of magnitude faster than the previously reported shortest time. Furthermore, the switch size can be much smaller than 2.6 µm and will be suitable for integration.     

Beam‐shaping condenser lenses for full‐field transmission X‐ray microscopy

A new type of diffractive X‐ray optical elements is reported, which have been used as beam‐shaping condenser lenses in full‐field transmission X‐ray microscopes. These devices produce a square‐shaped flat‐top illumination on the sample matched to the field of view. The size of the illumination can easily be designed depending on the geometry and requirements of the specific experimental station. Gold and silicon beam‐shapers have been fabricated and tested in full‐field microscopes in the hard and soft X‐ray regimes, respectively.     

Polycapillary‐optics‐based micro‐XANES and micro‐EXAFS at a third‐generation bending‐magnet beamline

A focusing system based on a polycapillary half‐lens optic has been successfully tested for transmission and fluorescence µ‐X‐ray absorption spectroscopy at a third‐generation bending‐magnet beamline equipped with a non‐fixed‐exit Si(111) monochromator. The vertical positional variations of the X‐ray beam owing to the use of a non‐fixed‐exit monochromator were shown to pose only a limited problem by using the polycapillary optic. The expected height variation for an EXAFS scan around the Fe K‐edge is approximately 200 µm on the lens input side and this was reduced to ～1 µm for the focused beam. Beam sizes (FWHM) of 12–16 µm, transmission efficiencies of 25–45% and intensity gain factors, compared with the non‐focused beam, of about 2000 were obtained in the 7–14 keV energy range for an incoming beam of 0.5 × 2 mm (vertical × horizontal). As a practical application, an As K‐edge µ‐XANES study of cucumber root and hypocotyl was performed to determine the As oxidation state in the different plant parts and to identify a possible metabolic conversion by the plant.     

A Photonic Nanojet as Tunable and Polarization‐Sensitive Optical Tweezers

The ability to manipulate small objects with focused laser beams has opened a venue for investigating dynamical phenomena relevant to both fundamental and applied sciences. However, manipulating nano‐sized objects requires subwavelength field localization, provided by auxiliary nano‐ and microstructures. Particularly, dielectric microparticles can be used to confine light to an intense beam with a subwavelength waist, called a photonic nanojet (PNJ), which can provide sufficient field gradients for trapping nano‐objects. Herein, the scheme for wavelength‐tunable and nanoscale‐precise optical trapping is elaborated, and the possibility of lateral nanoparticle movement using the PNJ's side lobes is shown for the first time. In addition, the possibility of subwavelength positioning using polarization switching is shown. The estimated stability with respect to Brownian motion is higher compared to conventional optical trapping schemes.     

高数值孔径聚焦三维光链的研究

通过设计衍射光学元件对入射矢量光进行调制，在高数值孔径聚焦系统焦点附近产生沿光轴方向的三维多点光俘获结构——光链.并针对不同的入射矢量偏振、聚焦透镜的数值孔径以及衍射光学元件结构，对光链性能的影响分别进行了系统的分析，实现对该独特光俘获结构的可控性研究. 关键词： 衍射光学元件 矢量光 光镊     

Nano‐opto‐mechanical effects in plasmonic waveguides

In order to achieve interaction between light beams, a mediating material object is required. Nonlinear materials are commonly used for this purpose. Here a new approach to control light with light, based on a nano‐opto‐mechanical system integrated in a plasmonic waveguide is proposed. Optomechanics of a free‐floating resonant nanoparticle in a subwavelength plasmonic V‐groove waveguide is studied. It is shown that nanoparticle auto‐oscillations in the waveguide induced by a control light result in the periodic modulation of a transmitted plasmonic signal. The modulation depth of 10% per single nanoparticle of 25 nm diameter with the clock frequencies of tens of MHz and the record low energy‐per‐bit energies of 10⁻¹⁸ J is observed. The frequency of auto‐oscillations depends on the intensity of the continuous control light. The efficient modulation and deep‐subwavelength dimensions make this nano‐optomechanical system of significant interest for opto‐electronic and opto‐fluidic technologies.     

Optical anisotropy in single-walled carbon nanotubes

Optical anistropy at optical communication wavelength was observed in films of vertically aligned single-walled carbon nanotubes (SWNTs). We report the control of both the polarization state and transmission of incoming light at 1550 nm by azimuthal and axial tilting of SWNT film about its aligned axis. The experiments reveal that the polarization state of light is susceptible to the azimuthal angle of the aligned direction of a SWNT having semiconductor characteristics and the intensity of the output beam after SWNT film shows cosine function dependence on the axial tilting angle.     

Planar waveguide‐resonator: a new device for x‐ray optics

Systematic investigations of the width dependence on the x‐ray beam propagation mechanism for a narrow extended slit formed by two plane dielectric plates are presented. It is shown that the mechanism of a multiple consecutive total reflection for Cu Kα radiation dominates in a slit width range s ≥ 3 µm. At the same time the manner of Cu Kα radiation propagation for super‐narrow slits s ≤ 0.1 µm is very different from the multiple total reflection mechanism. The x‐ray beam intensity proves to be constant for all this range of magnitude. This gives grounds to expect that the super‐narrow slit area is characterized by a specific type of mechanism of x‐ray beam propagation: waveguide‐resonance. A simple model for the waveguide‐resonance propagation mechanism based on the formation of a uniform x‐ray standing wave interference field in the total space of a narrow extended slit was developed. The design of a new x‐ray optical device, namely a planar x‐ray waveguide‐resonator, is proposed based on the waveguide‐resonance mechanism. Some properties of the composite planar x‐ray waveguide‐resonator are discussed. It is shown that under specific conditions the composite waveguide can demonstrate a partial tunneling effect of the x‐ray beam. The main applications of the new technique are discussed. Copyright © 2004 John Wiley & Sons, Ltd.     

Nitride‐based hetero‐field‐effect‐transistor‐type photosensors with extremely high photosensitivity

AlGaN/GaN hetero‐field‐effect‐transistor‐type (HFET‐type) photosensors are fabricated with a p‐GaInN optical gate for the detection of visible light. These photosensors employ a two‐dimensional electron gas at the heterointerface between AlGaN and GaN as a highly conductive channel with a high electron mobility. By changing the InN molar fraction in the p‐GaInN optical gate, the wavelength range of the photosensitivity of the HFET‐type photosensors can be controlled. The photosensitivity of the AlGaN/GaN HFET‐type photosensors with a p‐GaInN optical gate greatly surpassed those of commercially available Si pin and Si avalanche photodiodes, and was comparable to those of photomultiplier tubes. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interferometry of a single nanoparticle using the Gouy phase of a focused laser beam

We provide a quantitative explanation of the mechanism of the far-field intensity modulation induced by a nanoparticle in a focused Gaussian laser beam, as was demonstrated in several recent direct detection studies. Most approaches take advantage of interference between the incident light and the scattered light from a nanoparticle to facilitate a linear dependence of the signal on the nanoparticle volume. The phase relation between the incoming field and the scattered field by the nanoparticle is elucidated by the concept of Gouy phase. This phase relation is used to analyze the far-field signal-to-noise ratio as a function of exact nanoparticle position with respect to the beam focus. The calculation suggests that a purely dispersive nanoparticle should be displaced from the Gaussian beam focus to generate a far-field intensity change.     

Development of organic light‐emitting diodes for electro‐optical integrated devices

Organic light‐emitting diodes (OLEDs) are discussed for electro‐optical integrated devices that are used for optical signal transmission. Organic optical devices including polymeric optical fibers are used for optical communication applications to realize polymeric electro‐optical integrated devices. The OLEDs were fabricated by vacuum process, i.e. the organic molecular beam deposition (OMBD) technique or a solution process on a polymeric or a glass substrate, for comparison. Optical signals faster than 100 MHz have been created by applying pulsed voltage directly to the OLED utilizing rubrene doped in 8‐hydoxyquinolinum aluminum (Alq₃), as an emissive layer. OLEDs fabricated by solution process utilizing rubrene doped in carrier‐transporting materials have also discussed. OLEDs utilizing polymeric materials by solution process are also fabricated and discussed. Moving‐picture signals are transmitted utilizing both vacuum‐ and solution‐processed OLEDs, respectively.     

Calculation of attenuation and x‐ray fluorescence intensities for non‐parallel x‐ray beams

With the nowadays widespreaded use of x‐ray optics in x‐ray fluorescence analysis, large convergence or divergence angles can occur. This experimental situation violates a basic assumption of the usual fundamental parameter quantification procedure. In order to take beam divergences in micro x‐ray fluorescence analysis into account, a way of calculating fluorescence intensities numerically by Monte Carlo integration is described. For three examples of typical micro‐XRF set‐ups the fluorescence intensities and their deviation from the parallel beam geometry are calculated. Furthermore, we propose a new approach with ‘equivalent angles’ which correct for the beam divergences in fundamental parameter methods. Copyright © 2003 John Wiley & Sons, Ltd.     

A computational study of the optical response of strongly coupled metal nanoparticle chains

We study the optical response of strongly coupled metal nanoparticle chains using rigorous multiple scattering calculations. The collective resonant frequency of silver nanosphere chains and the coupling between chains are considered. The coupling between silver nanoparticle chains are understood by the transmission and reflection calculations of 2D periodic arrays of nanospheres. The results are in agreement with recent experiments. The splitting of plasmon resonance modes for different polarizations of the incident light are explored. Our results show that the transverse mode resonant wavelength is very sensitive to the inter-chain distance. Results on the effect of disorder are also presented.     

基于拉曼组合放大的长距离光纤传输系统

本文改进了一种实现长距离自适应补偿光纤传输的方法.在利用光纤光栅形成的谐振腔产生激光对信号光进行拉曼放大的基础上,再利用双抽运光对信号光进行拉曼放大,从而获得更高的拉曼增益以实现更长距离的自适应补偿光纤传输.使实验自适应补偿传输距离达125km(为目前国际上已报道的最长自适应补偿光纤传输距离).实验测量并理论分析了该长距离光纤传输系统的开关增益、放大的自发辐射噪声、噪声指数和光功率分布的特性,实验结果与理论模型符合很好.     

Ultrafast on‐Chip Remotely‐Triggered All‐Optical Switching Based on Epsilon‐Near‐Zero Nanocomposites

On‐chip‐triggered all‐optical switching is a key component of ultrahigh‐speed and ultrawide‐band information processing chips. 1 - 4 This switching technique, the operating states of which are triggered by a remote control light, paves the way for the realization of cascaded and complicated logic processing circuits and quantum solid chips. Here, a strategy is reported to realize on‐chip remotely‐triggered, ultralow‐power, ultrafast, and nanoscale all‐optical switching with high switching efficiency in integrated photonic circuits. It is based on control‐light induced dynamic modulation of the coupling properties of two remotely‐coupled silicon photonic crystal nanocavities, and extremely large optical nonlinearity enhancement associated with epsilon‐near‐zero multi‐component nanocomposite achieved through dispersion engineering. Compared with previous reports of on‐chip direct‐triggered all‐optical switching, the threshold control intensity, 560 kW/cm², is reduced by four orders of magnitude, while maintaining ultrafast switching time of 15 ps. This not only provides a strategy to construct photonic materials with ultrafast and large third‐order nonlinearity, but also offers an on‐chip platform for the fundamental study of nonlinear optics.     

All‐Dielectric Meta‐Reflectarray for Efficient Control of Visible Light

Wide‐bandgap material based all‐dielectric metasurfaces have been ideal platforms for the realization of arbitrary phase control in visible spectrum. While TiO₂ metasurfaces are very promising in broadband and high‐efficiency anomalous transmission, meta‐hologram, and meta‐lenses et al., the current realizations are strongly dependent on the sophisticated fabrication technique to fabricate TiO₂ nano‐pillars with aspect ratio > 10. Herein we experimentally demonstrate a much simpler approach to realize efficient phase control of visible light. By exploiting TiO₂ nano‐blocks as meta‐atoms on a ground metal plane, we find that TiO₂ metasurface with aspect ratio around 1‐1.5 is good enough to produce phase changes covering ‐π to π and high reflection efficiency simultaneously. Based on the phase control of the meta‐reflectarray, anomalous reflection with a ratio between anomalous reflection and normal reflection ～ 74/26 have been experimentally realized using a combination of typical electron‐beam lithography, electron‐beam evaporation, and a simple lift‐off process. Similarly, high performance TiO₂ metasurface in form of hologram has also been demonstrated for red (633 nm), green (520 nm), and blue (445 nm) wavelengths. We believe this research shall route a new way to cost‐effective all‐dielectric metasurfaces and advance their applications in encryption, anti‐counterfeiting, and wearable displays.     

Frequency‐sensitive switching control effect induced by two‐photon resonance in an EIT‐based layered medium

The optical response of an atomic vapor can be coherently manipulated by tunable quantum interference occurring in atomic transition processes. A periodic layered medium whose unit cells consist of a dielectric and an EIT (electromagnetically induced transparency) atomic vapor is designed for light propagation manipulation. Such an EIT‐based periodic layered medium exhibits a flexible frequency‐sensitive optical response, where a very small change in probe frequency can lead to a drastic variation of reflectance and transmittance. As the destructive quantum interference relevant to two‐photon resonance arises in EIT atoms interacting with both control and probe fields, the controllable optical processes that depend sensitively on the external control field will take place in this EIT‐based periodic layered medium. Such a frequency‐sensitive and field‐controlled optical behavior of reflection and transmission in the EIT photonic crystal can be applicable to designs of new devices such as photonic switches, photonic logic gates and photonic transistors, where one laser field can be controlled by the other one, and would have potential applications in the areas of integrated optical circuits and other related techniques (e.g., all‐optical instrumentations).     

圆柱型光纤螺线圈轨道角动量模式

传统的沿z轴光纤传输光线的轨道角动量(orbital angular momentum,OAM)光束的制备方法共同之处都是从内部结构着想,光束的主光线基本上不变,只是波面在变.但要获得携带高mh的光有一定的难度.针对上述问题,本文建立以波面不变,光束主光线变化为基础的理论框架,利用微分几何理论验证不沿z轴圆柱型光纤螺线圈传输的光线可以携带高mh OAM的理论设想.研究发现:利用流动坐标(α,β,γ)计算光线在绕圆柱体的光纤中传输时光纤截面的衍射分布图呈现涡旋特征,有高阶OAM模式.当θ=θ0时,圆柱形轨道光纤过渡到直线轨道光纤.计算光线沿直线传输时光纤截面的衍射分布图是Airy斑,即圆孔衍射斑,无高阶OAM模式.     

Tunneling‐induced transparency in a chaotic microcavity

A new form of induced transparency enabled by dynamical tunneling coupling of continuous chaos and discrete regular modes in a slightly deformed optical microcavity is demonstrated experimentally. An optical beam is focused on the cavity boundary and tuned on resonance with a high‐Q mode, which leads to destructive interference for the excitation of chaotic field and induces a transparency in the transmission. The experimental results are in excellent agreement with a model based on quantum scattering theory. This tunneling‐induced transparency is accompanied by extremely steep normal dispersion, and holds great potential in slow light and enhanced nonlinear interactions.     

Spatial optical (2+1)‐dimensional scalar‐ and vector‐solitons in saturable nonlinear media

(2+1)‐dimensional optical spatial solitons have become a major field of research in nonlinear physics throughout the last decade due to their potential in adaptive optical communication technologies. With the help of photorefractive crystals that supply the required type of nonlinearity for soliton generation, we are able to demonstrate experimentally the formation, the dynamic properties, and especially the interaction of solitary waves, which were so far only known from general soliton theory. Among the complex interaction scenarios of scalar solitons, we reveal a distinct behavior denoted as anomalous interaction, which is unique in soliton‐supporting systems. Further on, we realize highly parallel, light‐induced waveguide configurations based on photorefractive screening solitons that give rise to technical applications towards waveguide couplers and dividers as well as all‐optical information processing devices where light is controlled by light itself. Finally, we demonstrate the generation, stability and propagation dynamics of multi‐component or vector solitons, multipole transverse optical structures bearing a complex geometry. In analogy to the particle‐light dualism of scalar solitons, various types of vector solitons can ‐ in a broader sense ‐ be interpreted as molecules of light.