基于光子晶体的Kretschmann结构中自准直光束的Goos-H¨anchen位移研究

利用平面波展开法和时域有限差分法,模拟研究了基于自准直条件下的高斯光束入射光子晶体Kretschmann结构时发生的同时具有正向和负向Goos-H¨anchen位移的双束反射现象.研究表明,反射光束中具有一束较小的正向位移,而另一束具有较大的负向位移,发现当Kretschmann结构支持的泄漏的表面模式被激发时才出现这一特殊现象;表面模式的场分布说明介质波导中存在着强局域稳态场,大的位移来自于表面模式与自准直体模式间的强耦合,同时探讨了表面模式与光子晶体自准直体模式之间发生耦合的条件和影响参数.本文负向位移最大达到?23.23a (a为晶格常数),对应入射光波长的4.99倍,是束腰半径的1.1615倍.     

基于古斯-汉欣位移的双通道窄带滤波器

本文利用光束在对称金属包覆波导表面反射得到的异常大的古斯-汉欣(Goos-Hänchen)位移,通过实验实现了双通道窄带滤波.当入射激光波长为859.60 nm时,两通道滤波的峰值位置分别为859.604 nm和859.688 nm,峰值半宽(FWHM)为0.036 nm,而消光比达到15.3 dB.峰值波长可通过改变入射角或小孔位置实现调谐. 关键词： 古斯-汉欣(Goos-Hä nchen)位移 光波导 双通道 滤波器     

二维光子晶体分束器和偏转器

针对二维光子晶体在光束调整和光束偏转中的应用,采用平面波展开法、二维有限时域差分法和完全匹配层吸收边界条件,从理论上研究了二维方形光子晶体结构中TM模式的自准直现象.通过分析光子晶体的能带结构和等频图,基于二维光子晶体的自准直效应和光子带隙,对光波在二维光子晶体中的传播特性进行了讨论.数值计算表明,通过在合适的方向引入不同的线缺陷,可以实现自准直光束的1×2和1×3分束以及光束偏转.最后讨论了透射光束和偏转光束的能量随线缺陷半径的变化关系.所设计的器件极大地扩展了光子晶体在高密度光学集成电路中的应用.     

非常偏振光在单轴晶体表面的全反射分析

利用透射波函数和由菲涅尔公式求解反射相位差并对其求导的方法,分析了非常偏振光在单轴晶体表面发生的全反射现象,求解出晶体光轴在入射面内时,非常偏振光从各向同性介质入射到晶体和从晶体出射到各向同性介质两种情况的隐失波穿透深度和Goos-Hnchen位移的一般表达式。通过计算机模拟给出了单轴晶体为方解石和水晶情况时的穿透深度和Goos-Hnchen位移图像。结果表明,对于不同的晶体,光轴的取向对穿透深度和Goos-Hnchen位移的影响是明显不同的,若选取合适的晶体、光轴取向和入射角,可以得到较大的隐失波穿透深度和Goos-Hnchen位移。     

光子晶体自准直光束偏振分束器

结合能带图和等频图分析,基于光子晶体自准直效应和光子带隙,设计了一种紧凑、高效的偏振分束器.时域有限差分法(FDTD)模拟表明,该设计可以在一个较大的频率范围f=0.268—0.278(c/a) 内实现TE模和TM模的高效(85%)、大角度(90°)分离.在光通讯波长λ=1.55 μm,该设计尺寸仅为9 μm×9 μm.这些特性使其在光通讯领域中具有重要的应用前景. 关键词： 光子晶体 偏振分束器 自准直     

二维空气环型光子晶体的负折射成像特性

采用平面波展开法和时域有限差分法研究了由空气环组成的二维三角晶格光子晶体平板的负折射成像特性.研究结果表明对于外半径为 0.4 a,内半径 0—0.13a的空气环型光子晶体,第二能带中归一化频率为 0.3 的电磁波可以实现有效折射率为-1的负折射成像.通过光子晶体有效折射率的计算,得到了有效折射率为-1的电磁波频率随空气环内径由0—0.2 a变化的规律,并由对应等频曲线的变化解释了结构参数对光子晶体平板成像的影响. 关键词： 光子晶体 空气环 负折射 等频曲线     

波状结构二维光子晶体的自准直特性及亚波长成像的研究

利用平面波展开方法计算了波状结构二维光子晶体(2DPC)的等频面，对等频面内矩形轮廓的等频线进行研究，提出了波状结构2DPC的自准直特性，运用时域有限差分(FDTD)方法模拟了波状结构2DPC在不同入射角情况下对所入射高斯光束的自准直作用.将波状结构2DPC的自准直特性运用到近场亚波长成像，模拟了波状结构2DPC的自准直亚波长成像效果，单光源的成像分辨率达到0.28λ，且随着光源逐渐远离近场范围而降低. 关键词： 光子晶体 自准直 等频面 亚波长成像     

高斯光束在双曲材料表面反射的Imbert-Fedorov位移研究

文章以由Ag/TiO2构成的多层双曲材料的电磁特性为基础,分析了一束圆偏振高斯光束被其在Kretschmann结构中反射后光束的Imbert-Fedorov位移(IF位移)。双曲材料的特性在于其等频线为双曲线,且在不同波段下具有两种不同类型的双曲色散响应。结果表明,在双曲材料板为Ⅰ型波段时,通过棱镜入射,IF位移放大到真空入射时的4倍;而在Ⅱ型双曲波段,通过棱镜入射,IF位移受到了明显的抑制,是真空入射时的十分之一。随后,用角谱法进行了光束模拟,验证了解析计算的结果。最后,通过调节双曲材料板的厚度和金属成分的填充率实现了对一定波长下IF位移大小的调控。     

光子晶体器件进展

光子晶体对光具有独特的局域、反射、传导、分束、耦合、调制、慢光等操纵能力,使其成为微/纳光电集成的重要材料之一。介绍了光子晶体的几种重要物理特性——带隙特性、慢光特性、自准直和负折射特性,叙述了光子晶体集成器件方面所取得的最新进展,对光子晶体器件的发展动向做了展望。     

棱镜-薄膜耦合结构中光束Goos-H(a)nchen位移的增强

棱镜-薄膜耦合结构是单侧镀电介质膜的双棱镜结构中的一种,在光信号传输方面具有十分重要的作用.利用稳态相位法分析了这种结构中反射和透射光束的Goos-Hanchen位移,研究结果表明,反射和透射光束的Goos-Hanchen位移随薄膜厚度或入射角的增大除出现共振峰外,还存在反射光束的Goos-Hanchen位移共振峰为负值的新现象.在共振点处透射和反射光束的正向或负向位移量最大可达百余波长.这一结构中薄膜和入射角.对光束Goos-Hanchen位移的调制在设计新型光位移调制和光传感器件中具有潜在的应用.     

Non-specular reflection of self-collimated beams in photonic-crystal-made prism and waveguide system

We demonstrate a dual-beam-reflection phenomenon for a Gaussian beam illuminating at a Kretschmann configuration composed of a photonic-crystal-made prism and a dielectric waveguide. One reflection beam has a positive shift and the other has a negative shift. The finite-difference time-domain (FDTD) shows that the specific phenomenon takes place only when the corresponding quasi-guided mode supported in the Kretschmann configuration is excited. Field profile of the quasi-guided mode demonstrates a strong localized stationary field in the dielectric waveguide. We found that the maximum positive lateral shift (LS) is 14.27a (where a is the lattice constant), corresponding to 3.07 times of the incident wavelength, which is 0.7135 times of the beam waist and much larger than that in some previous reports.     

Dual-beam-reflection phenomenon due to leaky modes in a photonic band gap

We show a dual-beam-reflection phenomenon for a Gaussian beam illuminating a hybrid structure of a dielectric waveguide and photonic crystal (WG-PC) inside the photonic band gap by numerical simulations. One reflection beam has a giant negative lateral shift, but the other has a positive lateral shift. The finite-difference time-domain (FDTD) simulations show that this phenomenon has a time delay effect and comes from the leaky surface mode of the hybrid structure. Field profile of the leaky mode demonstrates a strong localized stationary field in the higher dielectric medium. Furthermore, the maximum lateral shift is almost two times of the waist of the incident beam.     

Transmission and directionality control of light emission from a nanoslit in metallic film flanked by periodic gratings

We investigate the transmission and directional properties of light emission from a nanoslit film flanked by periodic gratings, formed on a silver film, embedded in a high index dielectric medium. Using FDTD calculations it is demonstrated that the transmission has strong dependence on dimension of the dielectric film. The directional property of the emitted beam is controlled by tapering height of output grating elements and this effect is explained by standard theory of antenna array. We propose and examine the potential of such slit grating structure as a Plasmonic antenna in axial injection of light from single mode fiber to photonic crystal waveguide.     

Ultrawide-bandwidth gain in a coaxial dielectric Cherenkov maser

A coaxial waveguide partially filled with a dielectric as the slow-wave structure of a dielectric Cherenkov maser is investigated. The dispersion of the fundamental mode of this waveguide is very weak at phase velocities close to the velocity of light, and for this reason a very wide gain bandwidth is possible under conditions of an interaction with a relativistic electron beam. The dispersion equation for an infinitely thin tubular beam in a coaxial waveguide with a dielectric liner adjoining either the outer or inner conducting surface is derived. The gain bandwidth as a function of the parameters of the electron beam and the slow-wave system are investigated on the basis of numerical solution of the dispersion equation, and a comparison with similar dependences for the conventional configuration of a dielectric Cherenkov maser is made. The structural features of the coaxial configuration which enable novel approaches to the problems of matching the microwave signal at the entrance and exit of the system are discussed. Zh. Tekh. Fiz. 67, 66–72 (May 1997)     

1-to-N beam splitter based on photonic crystal branched waveguide structure

A novel beam splitter is proposed based on a two-dimensional (2D) photonic crystal (PC) branched waveguide structure. The beam splitter structure comprises branched waveguide channels and extra dielectric columns. These branched waveguide channels are used to obtain secondary sources and the introduced extra dielectric columns are used to control the phase difference of the secondary point sources. The field distributions of the beam are investigated using the finite-difference time-domain (FDTD). It is found that the number of beams is sensitive to the distance of the waveguide channels ports and extra dielectric columns. By adjusting the positions of the waveguide channels and the parameters of the extra dielectric columns, 1-to-N beam splitters can be realized. These simple, easily fabricated and controllable structures have important potential applications in integrated optical circuits.     

填充率渐变型波状结构二维光子晶体

填充率渐变引起的能带结构和等频面结构的变化是填充率渐变型波状结构二维(2D)光子晶体(PC)产生光路转弯现象的根本原因,由于TM模和TE模在能带结构上存在差异,光路转弯现象就具有明显的偏振选择特性,能够实现归一化频率a/λ为0.29~0.33的偏振分束。利用时域有限差分(FDTD)法模拟了TM模的U型转弯波导,发现出射光位置对入射波长和入射角的变化很敏感,位移变化量分别达到0.38μm/10 nm和0.29μm/(°)。利用TM模的U型转弯波导构建了新型的平行平面谐振腔,并指出由填充率渐变型波状结构二维光子晶体和一维多层薄膜构成的混合结构在光分束和抑制光束发散方面的作用及其在平行平面谐振腔中的潜在应用。     

An Experimental Study on Cyclotron–Cherenkov Radiation

We searched numerically dielectric-loaded cylindrical waveguide configurations with an injected electron beam in which the growth rate of the cyclotron-Cherenkov instability surpassed that of the Cherenkov instability, and found such a configuration. This configuration consists of a metallic core and an outer metallic cylinder with a dielectric liner on the inner surface. In order to investigate experimentally radiation due to the cyclotron-Cherenkov instability, we designed and assembled an experimental device using the computational results. We studied beam propagation in the dielectric-loaded coaxial waveguide and microwave radiation due to the cyclotron-Cherenkov instability and the Cherenkov instability.     

Coaxial configuration of the dielectric Cherenkov maser

The linearized Lorentz force, continuity equation, and Maxwell's equations are used to calculate the system dispersion relation for a coaxial configuration of the dielectric Cherenkov maser. The system consists of two coaxial conductors lined with dielectric and an annular relativistic electron beam, which propagates between the two liners. The dispersion relation for the beam and dielectric-lined coaxial waveguide structure and the no-beam system that describes the dependence of the generated frequency on the coaxial waveguide parameters are presented. Using the linearized dispersion relation, the growth rate for the beam-TM_0n waveguide mode instability is calculated in the strong-coupling tenuous beam limit     

Generation of millimeter wave Gaussian beams and their propagation in a dielectric waveguide

Linearly polarized fundamental mode Gaussian beams were generated and coupled to a hollow circular oversized dielectric waveguide by placing the waist of the beam at the guide entrance. The transmission properties of the waveguide were characterized as a function of frequency for a variety of coupling conditions. These conditions included changes in the input beam waist radius, angle of incidence, and displacement perpendicular and parallel to the guide axis. It has been found that: 1.) power transmission is maximized when the waist of the input beam is centered at the guide input, injected normally, and has a radius of 0.43 times the waveguide radius, 2.) power transmission decreases rapidly with increasing angle of incidence and the rate of that loss increases with frequency, 3.) the waveguide preserves the linear polarization of the input beam, 4.) power transmission in the fundamental waveguide mode is not greatly affected by moderate displacements in the input beam position, and 5.) upon exit from the waveguide the launched EH₁₁ mode propagates as a fundamental mode Gaussian beam in the quasi-far field. The results compare favorably to the transmission theory of Belland and Crenn and approximately to the near and far field mode pattern theory of Degnan.     

Splitting the surface wave in metal/dielectric nanostructures

We investigate a modified surface wave splitter with a double-layer structure, which consists of symmetrical metallic grating and an asymmetrical dielectric, using the finite-difference time-domain (FDTD) simulation method. The metal/dielectric interface structure at this two-side aperture can support bound waves of different wavelengths, thus guiding waves in opposite directions. The covered dielectric films play an important role in the enhancement and confinement of the diffraction wave by the waveguide modes. The simulation result shows that the optical intensities of the guided surface wave at wavelengths of 760-nm and 1000-nm are about 100 times and 4～5 times those of the weaker side, respectively, which means that the surface wave is split by the proposed device.