Hollow-core waveguide characterization by optically induced particle transport

We introduce a method for optical characterization of hollow-core optical waveguides. Radiation pressure exerted by the waveguide modes on dielectric microspheres is used to analyze salient properties such as propagation loss and waveguide mode profiles. These quantities were measured for quasi-single-mode and multimode propagation in on-chip liquid-filled hollow-core antiresonant reflecting optical waveguides. Excellent agreement with analytical and numerical models is found, demonstrating that optically induced particle transport provides a simple, inexpensive, and nondestructive alternative to other characterization methods.     

数值模拟二维间隙表面等离子波导传输特性

利用表面等离子激元的新颖特性,设计了二维间隙表面等离子波导.以这种结构为基础通过变形和组合形成90°直角弯曲波导、T型光功率分配器和光开光,采用时域有限差分法研究了它们的传输特性.结果表明:不同于介质光波导的弯曲损耗来自于辐射泄漏,90°直角弯曲间隙表面等离子波导的能量损耗主要来自于金属中的欧姆热损耗.在间隙达到40 nm以上后,当直行段的长度适当时,弯曲段的透射率较相同长度的直波导的透射率要大.T型光功率分配器在两输出波导的间隙宽度比达到0.6及以上时,不同于传统介质波导的分光原则,能量主要沿等效折射率较小的输出臂流出.当两输入光的相位反相时,T型光开关处于输出截止的状态,当两输入光的相位同相时,T型光开关处于输出导通的状态.所有波导间隙均小于衍射极限,实现了超衍射极限传播,可用于未来了超大规模集成光路中.     

Excitation of terahertz surface polaritons in a cylindrical waveguide by femtosecond laser pulses

Generation of terahertz surface polaritons in homogeneous round cross-section plasma waveguides upon nonlinear optical rectification of femtosecond laser pulses is analyzed theoretically. It is assumed that nonlinear polarization inducing a surface electromagnetic wave is formed at the waveguide boundary in a thin layer of the nonlinear dielectric that surrounds the waveguide. The efficiency of the femtosecond radiation conversion into surface polaritons is studied as a function of the waveguide radius and duration of the exciting laser pulse.     

Design of hybrid optical waveguide with a 90° bend structure for high density photonics integrated circuits

A hybrid optical waveguide having a 90° sharp bend structure, composed of a dielectric straight waveguide, tapered dielectric strip waveguide, and microscale metal gap waveguide, is proposed and simulated to improve the efficiency of light coupling between dielectric and plasmonic waveguides. Our simulation result is a critical step for the hybrid integration of plasmonic components with conventional dielectric components.     

Dielectric‐loaded plasmonic waveguide components: Going practical

Surface plasmon propagating modes supported by metal/dielectric interfaces in various configurations can be used for radiation guiding similarly to conventional dielectric waveguides. Plasmonic waveguides offer two attractive features: subdiffraction mode confinement and the presence of conducting elements at the mode‐field maximum. The first feature can be exploited to realize ultrahigh density of nanophotonics components, whereas the second feature enables the development of dynamic components controlling the plasmon propagation with ultralow signals, minimizing heat dissipation in switching elements. While the first feature is yet to be brought close to the domain of practical applications because of high propagation losses, the second one is already being investigated for bringing down power requirements in optical communication systems. In this review, the latest application‐oriented research on radiation modulation and routing using thermo‐optic dielectric‐loaded plasmonic waveguide components integrated with silicon‐based photonic waveguides is overviewed. Their employment under conditions of real telecommunications is addressed, highlighting challenges and perspectives.     

Raman and photon scanning tunnelling microscopy of optical waveguides

Recent results from our laboratories on the design and characterization of optical waveguides are reviewed. Modelling of the design of channel optical waveguides is discussed and two means of experimental characterization that provide spatially local information are presented. Raman microprobe spectroscopy is used to explore the role of stress induced by a thin dielectric overlayer used to form channel waveguides in GaAlAs, and thus the role of photoelastic effects on waveguide behaviour. Photon scanning tunnelling microscopy is used to investigate local surface and index variations by probing the evanescent waveguide field.     

A waveguide amplifier based on a counterdirectional coupler

The propagation of continuous-wave radiation in tunnel-coupled waveguides, one of which is characterized by a negative refraction and linear losses while the other is made of an ordinary dielectric and represents a linear amplifier, is analyzed theoretically. We found that, in the case of linear waveguides, the losses can be compensated at certain values of the pump-wave amplitude depending on values of the gain and loss coefficients in the corresponding waveguides, resulting in the amplification of radiation at the output of the waveguide with the negative refraction. The Kerr nonlinearity of the amplifying waveguide prevents the compensation of losses due to the violation of the phase-matching condition between the coupled waves in a counterdirectional coupler.     

基于时域有限差分法分析等离子波导和介质波导耦合

使用Rsoft软件中的时域有限差分模块Fullwave分析二维介质波导和等离子波导耦合特性,利用软件仿真耦合结构并自动计算出光在介质波导和等离子波导中传输的耦合效率,进而测绘耦合效率随波导尺寸和光波长的变化曲线图,发现MDM导波结构的缝隙宽度和光通信质量密切相关,在确定尺寸下,传输损耗随传输距离成指数衰减.根据分析得到的耦合效率变化规律发现介质波导和等离子波导间距最佳点都应设为15 nm,进而优化波导的几何结构参数后,可以将耦合效率提高到83%.     

Numerical investigation of characteristics of laser radiation scattered in an integrated optical waveguide with three-dimensional inhomogeneities

Specifics of theoretical analysis of wave phenomena in irregular integrated optical waveguides are investigated. The object of the investigation and the main types of irregularities (smooth, statistical, and sharp) are described. The goals of the numerical modeling are formulated. The structure of the program and the general structure of the algorithm allowing numerical investigation of guided modes’ scattering from 3D-irregularities of an integrated optical waveguide are described. The dispersion relations of the TE and TM modes of the integrated optical waveguide under investigation, as well as field patterns of the radiating TE modes of the substrate and the laser radiation scattered from the three-dimensional guiding-layer inhomogeneities of an integrated optical waveguide, are presented. The results are analyzed in detail. The methods developed can be used for numerical investigation of the characteristics of laser radiation scattered in various optical waveguides with three-dimensional irregularities.     

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.     

An assessment of coherent coupling through radiation fields in time varying slab waveguides

This paper presents an analytical methodology for analysing two-dimensional, dielectric slab waveguides where the guiding region is subject to abrupt and arbitrary temporal changes in permittivity. The methodology solves Maxwell’s equations in the frequency domain and recovers the solutions for the guided and radiation fields in the time domain using the Laplace transformation (LT). Explicit separation of the complete field solution into a set of guided modes and a radiation field continuum provides a clearer insight into the transient effects present in time-varying dielectric waveguides. In particular, the method is used to assess and quantify the impact of coherent radiation field coupling for arbitrary time variation of the waveguide permittivity.     

Investigation of the thickness of Ag, AgI films in the capillary for hollow waveguides

A metallic (Ag)–dielectric (AgI) hollow glass waveguide is a promising and flexible fiber for the delivery of high-power CO₂ laser radiation. The thickness of metallic (Ag) films and dielectric (AgI) films is a critical factor which greatly influences the attenuation of the waveguides. In this paper, metallic (Ag)–dielectric (AgI) films were successfully prepared in the capillary whose inner diameter is 0.53 mm, and firstly investigated with theoretical analysis and measured by means of AES and SEM. There is good agreement between theoretical thickness and experimental results, which confirms the validity of the theoretical analysis, which makes the estimate of the thickness of both the metallic and dielectric films possible with high accuracy prior to the preparation of hollow glass waveguides. The attenuation spectra of Ag/AgI hollow waveguides shows the loss increases with the thickness of Ag, AgI films and indicates that the Ag/AgI hollow waveguide is suitable for the transmission of IR radiation.     

基于倏逝场微小粒子驱动技术研究进展

处于倏逝场中的微小粒子会受到辐射压力的作用而朝着倏逝场的传播方向运动,基于此原理的微小粒子驱动技术可用于介质颗粒、胶体颗粒、生物细胞等微小粒子的捕获和驱动.由于倏逝场光学微操作系统不会受到物镜焦深和激光光斑尺寸的限制,因此它比自由空间系统的优越性更强,而波导形成的光学力可以应用于长距离驱动,其仅仅受限于系统的散射和吸收...     

Circular arc plasmonic waveguide couplers between two-dimensional dielectric slab waveguides and plasmonic waveguides

We investigate the properties of arc plasmonic waveguide coupler between two-dimensional dielectric slab waveguides and plasmonic waveguides with two-dimensional finite difference time domain methods. The simulation results show that transmission efficiency between high index dielectric slab waveguides with width 300 nm and silver-air-silver waveguides with width 40 nm connected by the coupler can reach to 90.4% at optical communication wavelength. And, by optimizing the shapes near the ends of the coupler, the transmission efficiency can be improved to 98.4%.     

Negative index and indefinite media waveguide couplers

We study the coupling interaction between dielectric waveguides and coupling elements made from negative-refracting media. The coupling configuration consists of a length of dielectric waveguide, which terminates either directly into or near a planar layer composed of the negative-refracting medium, and is followed by a second waveguide. Radiation output from the first waveguide is refocused at the position of the second waveguide, so that the negative-refracting layer serves as a coupler between the waveguides. Because both isotropic negative-index layers and bilayers of indefinite media can recover the near-field, evanescent components of a source field distribution, the coupling between the input and output waveguides can be highly efficient – in principle providing perfect, lossless coupling. We present simulations and some initial experimental results illustrating the coupling effect, and speculate on the potential for optical fiber couplers and integrated modulators. PACS 42.79.Gn; 41.20.-q; 42.70.-a     

Enhancing Bremsstrahlung production from ultraintense laser-solid interactions with front surface structures

A new type of a coaxial multi-layer plasmonic waveguide is proposed. The mode propagation properties are analyzed at the communication working wavelength. Theoretical investigations reveal that the enhanced optical confinement can be achieved in the two low-index dielectric media layers. The mode size can be sub- or deep sub-wavelength scale. The mode propagation loss can be well compensated by replacing the high-index dielectric media with gain material to achieve longer propagation length with better mode confinement. The comparisons of the mode properties between the proposed waveguide and waveguides studied in the published literatures are also considered. These investigations potentially lay the groundwork for the further applications of nanowire type multilayer hybrid structures. This structure could also enable various applications such asnanophotonic waveguides, high-quality nanolasers, and optical trapping and biosensors.     

Photovoltaic modules with cylindrical waveguides in a system for the secondary concentration of solar radiation

The parameters of the concentrating photoelectric modules with triple-junction (InGaP/GaAs/Ge) solar cells whose focusing system contains an original secondary optical element are studied. The element consists of a plane-convex lens in optical contact with the front surface of an intermediate glass plate and a cylindrical waveguide that is located on the rear side of the glass plate above the surface of the solar element. It is demonstrated that the structure of the secondary optical element provides a wide misorientation characteristic of the concentrator and the cylindrical waveguide allows a more uniform radiation density over the surface of the solar cell. The effect of chromatic aberration in the primary and secondary optical systems on the parameters of photoelectric modules is analyzed. It is demonstrated that the presence of waveguides with a length of 3–5 mm leads to effective redistribution of radiation over the surface of the solar cell whereas shorter and longer waveguides provide the local concentration of radiation at the center of the photodetecting area.     

Coupled mode analysis of light modulation in dielectric waveguides

A detailed analysis of electrooptic light modulation in optical waveguides is presented. Several important problems of a waveguide modulator, such as the difference of waveguide axes from crystalline electrooptic ones, the distribution of transverse and longitudinal field components of light modes, and the traveling-wave property of the modulating field, are discussed. The analysis is based on the coupled mode theory, regarding the modulation as the coupling among sidebands of unperturbed waveguide modes. The coupled mode equation is derived for the modulation in optical waveguides. It can be solved if the normal modes of the waveguide are given. Actually the equation is solved for the modulation in dielectric slab waveguides and the mechanism of modulation is discussed. The results of the analysis are applied to designing two types of waveguide modulators. In an example (10.6 μm modulator with a GaAs slab waveguide) a new efficient crystal orientation is found. The calculated phase retardation with this orientation is 0.13 rad/(V·cm) with a 1 μm thick slab. Another example of a 0.633 μm modulator using a LiTaO₃ crystal as a substrate is also described.     

Engineering optical gradient force from coupled surface plasmon polariton modes in nanoscale plasmonic waveguides

We explore the dispersion properties and optical gradient forces from mutual coupling of surface plasmon polariton(SPP) modes at two interfaces of nanoscale plasmonic waveguides with hyperbolic metamaterial cladding.With Maxwell's equations and Maxwell stress tensor,we calculate and compare the dispersion relation and optical gradient force for symmetric and antisymmetric SPP modes in two kinds of nanoscale plasmonic waveguides.The numerical results show that the optical gradient force between two coupled hyperbolic metamaterial waveguides can be engineered flexibly by adjusting the waveguide structure parameters.Importantly,an alternative way to boost the optical gradient force is provided through engineering the hyperbolic metamaterial cladding of suitable orientation.These special optical properties will open the door for potential optomechanical applications,such as optical tweezers and actuators.     

New method for calculating the spectra and radiation losses of leaky waves in multilayer optical waveguides

The efficiency of a new method for calculating the spectrum and attenuation coefficient of leaky electromagnetic modes is demonstrated with multilayer planar optical waveguides the guiding properties of which are determined by antiresonant reflection from the multilayer cladding (antiresonant reflecting optical waveguides) rather than by total internal reflection from the core-cladding interface as in standard optical waveguides. The new method applies to calculation of both electromagnetic modes in dielectric waveguides and electron quantum states in multibarrier semiconductor heterostructures. The characteristics of multilayer waveguides calculated by the new method are compared with published data obtained from a complex dispersion relation by the transfer matrix method. As an example, the wavelength dependence of the radiation losses for the first TE mode of a planar optical waveguide containing 52 pairs of layers is calculated.