Particle sorting using a subwavelength optical fiber

Size‐based particle sorting using a subwavelength optical fiber was demonstrated with 600‐nm and 1‐μm sizes of polystyrene particles. Optical forces acting on the particles were calculated based on three‐dimensional finite‐difference time‐domain simulations at wavelengths of 808, 1047, and 1310 nm propagating in a subwavelength optical fiber with diameter of 800 nm. Calculations indicate that by launching two counterpropagating laser beams at different wavelengths into the fiber, the directions of the resultant optical scattering forces acting on the two particle sizes can be opposite along the fiber, which leads to a countertransport of the particles. To verify the theoretical prediction, experiments were performed using the 800‐nm fiber to sort the two particle sizes. The results show that with two counterpropagating beams at 808 and 1310 nm, a continuous particle sorting was achieved. Measured particle velocities were in agreement with the theoretical calculations.     

亚波长尺度下混合等离子泄漏模式激光

由于光存在衍射极限,因此传统方法不能实现亚波长尺度下的激光激射.为了打破这一衍射极限,本文设计了金属-介电层-半导体堆叠结构来实现深亚波长尺度下的激光激射,并讨论了相关结构对模式传播的影响.结构设计上,采用低介电常数金属银作为衬底、10?nm厚的LiF作为介电层、具有六边形截面的半导体纳米线ZnO作为高介电常数层,采用...     

Acoustic resonators for far-field control of sound on a subwavelength scale

We prove experimentally that broadband sounds can be controlled and focused at will on a subwavelength scale by using acoustic resonators. We demonstrate our approach in the audible range with soda cans, that is, Helmholtz resonators, and commercial computer speakers. We show that diffraction-limited sound fields convert efficiently into subdiffraction modes in the collection of cans that can be controlled coherently in order to obtain focal spots as thin as 1/25 of a wavelength in air. We establish that subwavelength acoustic pressure spots are responsible for a strong enhancement of the acoustic displacement at focus, which permits us to conclude with a visual experiment exemplifying the interest of our concept for subwavelength sensors and actuators.     

Enhanced optical transmission through a subwavelength 1D aperture

We present finite difference time domain simulations of the enhancement of the optical transmission through a single subwavelength slit in a thick metal film caused by resonances of the electromagnetic fields in and near the slit. These can be enhanced by including a periodic modulation on the in-coupling surface, and the dependence of the transmission on the grating structural parameters is analysed in detail.     

Optical manipulation of microspheres along a subwavelength optical wire

The propulsion of 3 microm polystyrene spheres along a subwavelength optical wire is demonstrated. Velocities in the range of 7-15 microm/s are observed. Simulations are carried out to evaluate the evanescent field at the waveguide-water suspension interface.     

深亚波长约束的表面等离子体纳米激光器研究

本文提出了一种新颖的基于半导体纳米线/空气间隙/金属薄膜 复合结构的表面等离子体纳米激光器, 并给出了理论研究和仿真分析. 这种结构通过金属界面的表面等离子体模式与高增益介质纳米线波导模式耦合, 从而使场增强效应得到显著提高. 同时通过数值仿真研究, 得到该混合波导结构的模式特性和增益阈值随空气槽宽度、纳米线半径的变化规律, 表明它可以实现对输出光场的深亚波长约束, 同时保持低损耗传输和高场强限制能力. 通过最优化选择, 最终得到纳米等离子体激光器的最优结构尺寸. 关键词： 表面等离子体 混合等离子体波导 纳米激光器     

Coherent quantum optical control with subwavelength resolution

We suggest a new method for quantum optical control with nanoscale resolution. Our method allows for coherent far-field manipulation of individual quantum systems with spatial selectivity that is not limited by the wavelength of radiation and can, in principle, approach a few nanometers. The selectivity is enabled by the nonlinear atomic response, under the conditions of electromagnetically induced transparency, to a control beam with intensity vanishing at a certain location. Practical performance of this technique and its potential applications to quantum information science with cold atoms, ions, and solid-state qubits are discussed.     

Colloidal subwavelength nanostructures for antireflection optical coatings

A two-dimensional (2D) subwavelength nanostructure for antireflection coating is fabricated upon a transparent substrate. Self-assembled 2D colloidal crystals are used as a nanoscale composite material with controlled thickness and low refractive index. The feature size of the structure is approximately 105 nm. The structure is used for antireflection coating, and the measured reflectivity of a glass substrate is reduced to 0.3%. Enhanced transmission through the substrate is also observed.     

Multiple paths to enhance optical transmission through a single subwavelength slit

In this Letter, we explore transmission properties of a single subwavelength slit flanked by a finite array of grooves made on a thick metallic film. We identify three main mechanisms that can enhance optical transmission: groove cavity mode excitation (controlled by the depth of the grooves), in-phase groove reemission (controlled by the period of the groove array), and slit waveguide mode (controlled by the thickness of the metal film). By tuning these geometrical parameters, enhancements of transmission of light by up to 2 orders of magnitude can be achieved when all three mechanisms coincide. Experimental verification of these findings is also shown for structured silver films fabricated by focused-ion-beam milling.     

新兴的纳米结构亚波长光学器件及其发展

介绍了新颖的纳米结构亚波长光学器件的特点,从器件的基本功能特性和工作机理两个方面详细讨论了其应用状况,并阐述了纳米制造技术对亚波长光学器件发展的重要推动作用及这一领域今后的研究热点。     

Graphene supports the propagation of subwavelength optical solitons

Nonlinear propagation of light in a graphene monolayer is studied theoretically. It is shown how the large intrinsic nonlinearity of graphene at optical frequencies enables the formation of quasi one‐dimensional self‐guided beams (spatial solitons) featuring subwavelength widths at moderate electric‐field peak intensities. A novel class of nonlinear self‐confined modes resulting from the hybridization of surface plasmon polaritons with graphene optical solitons is also demonstrated.     

Study of scattering patterns and subwavelength scale imaging based on finite-sized metamaterials

A metamaterial slab, used as a superlens in a subwavelength imaging system, is frequently assumed homogeneous. It is the bulk properties of the metamaterial which are responsible for the resolution of the transferred information in the image domain, as a result of high transverse wave-vector coupling. However, how in a discretized metamaterial, individual meta-atoms (i.e., the meta-elements composing a negative index metamaterial slab) contribute to the imaging process is still actively studied. The main aim of this paper is to investigate the consequences of using only a few meta-atoms as a negative index slab-equivalent for subwavelength scale imaging. We make a specific choice for a meta-atom and investigate its resonant scattering patterns. We report on how knowledge of these 3D scattering patterns provides a means to understand the transfer of high spatial frequencies and assist with the design an improved negative index slab.     

Effects of interplay between metal subwavelength slits on extraordinary optical transmission

In this paper we study the extraordinary optical transmission of one-dimensional multi-slits in an ideal metal film.The transmissivity is calculated as a function of various structural parameters.The transmissivity oscillates,with the period being just the light wavelength,as a function of the spacing between slits.As the number of slits increases,the transmissivity varies in one of three ways.It can increase,attenuate,or remain basically unchanged,depending on the spacing between slits.Each way is in an oscillatory manner.The slit interaction responsible for the oscillating transmission strength that depends on slit spacing is the subject of more detailed investigation.The interaction most intuitively manifests as a current distribution in the metal surface between slits.We find that this current is attenuated in an oscillating fashion from the slit corners to the center of the region between two adjacent slits,and we present a mathematical expression for its waveform.     

Strong field localization in subwavelength metal-dielectric optical waveguides

Detailed calculations of eigenmodes of waveguiding structures made of silver and glass and containing coaxial cables with a nanoscale cross section of different configurations are conducted. In particular, the study focuses on optical coaxial waveguides with the core made in the form of a thin metallic cylinder filled with a dielectric. We show that these waveguides support relatively low-loss propagation of radiation that is strongly localized in the central region, has phase velocity approaching the speed of light and predominant electric-field orientation (dipole type). Optical characteristics of such waveguides are compared with those of coaxial-type waveguides containing a continuous central filament made of metal and with a multilayer structure. Using numeric modeling, we established that the proposed type of the waveguide enables the transmission of an optical image with relatively low losses with a submicron resolution over a distance considerably longer than its cross section. A typical propagation length in the waveguides based on silver and glass with the refractive index of about 1.5 at a wavelength of 500 nm is about 1700 nm.     

Extraction of optical constants and thickness of nanometre scale TiO2 film

TiOTiO2 薄膜 沉积物 磁电管喷射系统 X射线 发射光谱TiO₂ thin films, pointwise constrained optimization approach, constrained nonlinear programming, optical constants, parameters extractionProject supported by Shanghai Municipal Commission for Science and Technology (Grant No 03DZ14025) and National Basic Research Program of China (Grant No 2006CB300406).3/4/2005 12:00:00 AM2005-03-042005-07-28TiO2 thin films were deposited on glass substrates by sputtering in a conventional rf magnetron sputtering system. X-ray diffraction pattern and transmission spectrum were measured. The curves of refraction index and extinction coefficient distributions as well as the thickness of films calculated from transmission spectrum were obtained. The optimization problem was also solved using a method based on a constrained nonlinear programming algorithm.     

Modeling of near-field optical diffraction from a subwavelength aperture in a thin conducting film

A theoretical model, novel to our knowledge, to investigate the near-field optical diffraction from a subwavelength aperture in a thin conducting film is presented. A governing equation for the magnetic field distribution in an optical thin film based on the power flow theorem is derived for the first time. Thus all of the components of the electric and magnetic fields inside or outside the thin film with a subwavelength aperture embedded can be obtained by applying the Hankel transform accurately. Numerical computations are performed to illustrate the edge effect by an enhancement factor of 2.2 and the depolarization phenomenon of the transmission in terms of the distance from the film surface.     

Spin-controlled directional launching of surface plasmons at the subwavelength scale

In this paper, we demonstrate a spin-controlled directional launching of surface plasmons at the subwavelength scale.Based on the principle of optical spin's effect for the geometric phase of light, the nanostructures were designed. The inclination of the structures decides the spin-related geometric phase and their relative positions decide the distance-related phase. Hence, the propagation direction of the generated surface plasmon polaritons(SPPs) can be controlled by the spin of photons. Numerical simulations by the finite difference time domain(FDTD) method have verified our theoretical prediction. Our structure is fabricated on the Au film by using a focused ion beam etching technique. The total size of the surface plasmon polariton(SPP) launcher is 320 nm by 180 nm. The observation of the SPP launching by using scanning near-field optical microscopy is in agreement with our theory and simulations. This result may provide a new way of spin-controlled directional launching of SPP.     

Theory of extraordinary optical transmission through subwavelength hole arrays

We present a fully three-dimensional theoretical study of the extraordinary transmission of light through subwavelength hole arrays in optically thick metal films. Good agreement is obtained with experimental data. An analytical minimal model is also developed, which conclusively shows that the enhancement of transmission is due to tunneling through surface plasmons formed on each metal-dielectric interface. Different regimes of tunneling (resonant through a "surface plasmon molecule," or sequential through two isolated surface plasmons) are found depending on the geometrical parameters defining the system.     

Giant optical transmission of a subwavelength slit optimized using the magnetic field phase

In this Letter, we show that the energy equivalent to that incident on a 4.7 microm wide strip can be squeezed through a 50 nm wide slit in a metal film surrounded by grooves. This corresponds to a transmission efficiency of 9400%, which can be even further enhanced by increasing the number of grooves. We use the phase of the magnetic field to explain that the ideal slit-to-groove distance is just over half the plasmon wavelength. In addition, we also optimize the groove depth and width. Such optimized transmission enhancement is very important for near-field devices.     

Near-field distribution of optical transmission of periodic subwavelength holes in a metal film

Optical transmission of a two-dimensional array of subwavelength holes in a metal film has been numerically studied using a differential method. Transmission spectra have been calculated showing a significant increase of the transmission in certain spectral ranges corresponding to the excitation of the surface polariton Bloch waves on a metal surface with a periodic hole structure. Under the enhanced transmission conditions, the near-field distribution of the transmitted light reveals an intensity enhancement greater than 2 orders of magnitude in localized ( approximately 40 nm) spots resulting from the interference of the surface polaritons Bragg scattered by the holes in an array.