Design and fabrication of multichannel Si/SiO2 autocloned photonic crystal edge filters

An Si/SiO2 multilayer with zigzag layer interfaces is fabricated on a patterned silica substrate using the autocloning method. The multilayer is designed to function as multichannel long-wave pass type edge filters with various cutoff wavelengths. A cutoff wavelength shift of the order of 190?nm in the near infrared region (1300-1500?nm) is experimentally demonstrated.     

Polarization aberrations. 1. Rotationally symmetric optical systems

The polarization in isotropic radially symmetric lens and mirror systems in the paraxial approximation is examined. Polarized aberrations are variations in the phase, amplitude, and polarization state of the electromagnetic field across the exit pupil. Some are dependent on the incident polarization state and some are not. Expressions through fourth order for phase, amplitude, linear diattenuation, and linear retardance aberrations are derived in terms of the chief and marginal ray angles of incidence and the Taylor series expansion coefficients of the Fresnel equations for reflection and transmission at uncoated and thin-film-coated interfaces. Applications to polarization ray tracing are discussed.     

Fabrication of autocloned photonic crystals using electron-beam guns with ion-assisted deposition

The autocloning technique is an attractive deposition method for the making of photonic crystals. With it various photonic crystals can be produced simply by changing the substrate periodicity and the structure of the stacking materials. We report on a method for the fabrication of autocloned photonic crystals. This method has better step-coverage, a higher deposition rate and a larger deposition area than can be achieved by the more traditional sputtering method and the periodic surface corrugation is preserved even after ion-assisted deposition (IAD) of multilayer stacks using E-beam gun evaporation. The shaping process can be freely controlled by controlling the IAD power and the ion source etching time. Ion source etching is a physical etching process which does not require any chemical reaction or dangerous reactive gas. The process parameters are described in this paper. The refractive index can be adjusted by changing the deposition rate and the substrate temperature during the deposition process. The deposition rate is about 0.7-1 nm/s for SiO₂ which is almost ten times faster than that of the sputtering method. This makes this method good for the mass production of photonic crystals.     

Analysis of a two-dimensional symmetric problem on extension of an Al-polyimide-Cu layered structure with a model crack

To increase the efficiency of designing systems intended for monitoring surface cracks in aluminum structures during their working life, we have analyzed a two-dimensional symmetric problem on uniaxial extension of an Al-polyimide-Cu layered structure with ideal adhesion between layers and a model crack in the aluminum base. The problem has been first solved for a sample with the crack modeled by a zero-thickness notch using the ANSYS engineering simulation program package. It is shown that this setting of the problem can lead to inadequate results as manifested, in particular, by significantly overstated mechanical stresses in aluminum in the region of crack emergence on the surface. In order to eliminate this difficulty, we propose to use the structure with a model defect in the form of a notch of nonzero thickness in the initial unstressed state of the structure. Recommendations for selecting the thickness of a notch used in the model structure are given.

     

Surface plasmon polariton based band-pass and stop-band filters in symmetric double ring resonators

We carried out the numerical simulations on plasmonic filters composed by a Metal–Insulator–Metal (MIM) waveguide and a resonator of double rings. Both the band-pass filter and stop-band filters are discussed. The results show that the characteristic wavelengths of the band-pass or stop-band filter have red shift when the size of the resonator increases. The filters of double-ring resonator show better sensitivity on the wavelength than the one for the single ring. The simulations are based on the two-dimensional (2D) finite-difference time-domain (FDTD) method. The introduced filters have potential applications on optical integrated circuits.     

Passband widening of transversely coupled resonator filters using the fundamental symmetric and antisymmetric modes

This paper describes a method for widening the passband of transversely coupled resonator filters (TCF) using only the fundamental symmetric and antisymmetric modes. The coupling of modes analysis in the transverse direction is applied to the TCF design to investigate the passband width. As a result, it is found that the passband width can be increased by making the surface acoustic wave (SAW) velocity difference between the interdigital transducer (IDT) region and the resonator gap region smaller. It is proposed that a grating structure be applied to the common ground bar, instead of the uniform metal, to reduce the SAW velocity difference. Using the grating-type common ground bar, filters are fabricated on ST-quartz substrate. The passband of a single filter with a center frequency of 248 MHz is widened up to 410 kHz without any increase of the insertion loss. The effect of the impedance mismatch at the junction of two cascaded devices is investigated. It is shown that the filter performance is improved by reduction of the small parasitic capacitance existing at the cascade point. Experimentally, the capacitance formed between the bus bar of the IDT and the bottom surface of the ceramic package is reduced. The insertion loss is reduced by 0.0 dB, and 3 dB passband is widened by 8 kHz for a filter with a center frequency of 248 MHz. On the basis of these two improvements, cascaded TCFs are fabricated. For a filter with a center frequency of 248 MHz, an insertion loss of 5.5 dB and a 3-dB passband width of 270 kHz are obtained     

Circularly symmetric phase filters for control of primary third-order aberrations: coma and astigmatism

A quartic phase retardation function is described that reduces the variation of the intensity of the focal point of incoherent imaging systems suffering from primary third-order aberrations limited to coma and astigmatism. Corresponding modulation transfer functions are shown to remain practically invariant for moderate amounts of coma and astigmatism.     

Polarization optimization in the interference of four umbrellalike symmetric beams for making three-dimensional periodic microstructures

A systematic and comprehensive analysis of the interference of four umbrellalike beams (lFUB) is provided based on the reciprocal space theory. The concept of pattern contrast is extended to the case of the IFUB, and it is indicated that a uniform contrast for all the interference terms can be obtained by properly choosing the beam ratio and the polarization of each beam. Different polarization combinations, including linear light and linear light, circular light and circular light, and linear light and circular light, have been discussed for the purpose of maximum uniform contrast. It is shown that the use of circular light may generally improve the uniform contrast. This study may lay a theoretical foundation for holographic fabrication of three-dimensional (3D) periodic microstructures, such as simple cubic, body-centered cubic, face-centered cubic, or trigonal lattice.     

Axially symmetric problem of torsion of an elastic body with inclusions

Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 6, pp. 88–91, November – December, 1994.     

Interaction of axially symmetric waves with an annular crack in an infinitely long hollow cylinder

In this paper an analysis of the interaction of longitudinal waves with an annular crack in an infinitely long hollow cylinder is presented. Using Fourier sine and cosine as well as Hankel integral transforms, formal complete solutions to the governing equations are given. By means of Abel integral transform, the problem is reduced to the solution of a Fredholm integral equation of the second kind which is, then, solved numerically for a range of values of the frequencies of the incident waves. The numerical values of the dynamic stress intensity factor at the rim of the crack have been calculated.     

低交叉极化高隔离的双极化天线

设计了一种应用于WLAN的具有低交叉极化和高隔离度的双极化天线.天线由3层功能层和2层介质基板间隔层叠而成.3层功能层分别为1个方形辐射贴片,2个带有发夹谐振器的馈电网络和1个刻蚀H形缝隙的接地板.发夹谐振器和辐射贴片构成一个二阶滤波天线用以展宽天线的带宽.通过在接地板上蚀刻H形缝隙降低了天线端口间的耦合电流,改善了天...     

Polarization structure of lidar signals reflected from ice crystal clouds

Polarization characteristics of signals of a monostatic lidar intended for sensing of homogeneous ice crystal clouds are calculated by the Monte Carlo method. Clouds are modeled as monodisperse ensembles of randomly oriented hexagonal ice crystals. The polarization state of multiply scattered lidar signal components is analyzed for different scattering orders depending on the crystal shapes and sizes as well as on the optical and geometrical conditions of observation. Light-scattering phase matrices (SPMs), calculated by the beam splitting method (BSM), are used as input data for solving the vector radiative transfer equation. The principles of the BSM method are briefly described, and the SPM components are given for hexagonal ice plates and columns of different sizes and linearly polarized incident radiation with the wavelength lambda = 0.55 microm.     

板状粘接结构中对称和反对称纵波与界面的相互作用

为了激发粘接结构中的导波或界面波,通常需要将声波从两半无限介质同相位或反相位地同时入射多层系统。针对此问题,基于矩阵方法,推导了界面处于理想连接的情况下,对称或反对称纵波从上下半无限空间入射时,三层板状粘接结构中纵、横波的反射与透射系数表达式。分析了入射角度、粘接层厚度以及基体材料等对声波反射(或透射)特性的影响。结果表明,对称或反对称纵波垂直入射时不发生波型转换。粘接结构中声波的反射(或透射)特性与入射角度、频率以及粘接层厚度等参数密切相关。在相同的粘接层厚度(或频率)范围内,随着声波频率(或粘接层厚度)的增加,谐振频率曲线向低频漂移。该方法可作为粘接结构中体波或导波传播特性研究的重要理论基础。     

Narrow line-width filters based on rugate structure and antireflection coating

Filters that have high transmittance over the passband region of the reflectance spectrum are designed by combining rugate structures and antireflection (AR) coatings. It is found that, under certain conditions, the refractive index of the substrate could be “converted” to the air-side refractive index of the graded-refractive-index coating. A method for the fabrication of graded-index coatings by rapidly alternating deposition of low (SiO₂) and high (Nb₂O₅) refractive index materials is introduced, and this technology was used to fabricate a rugate structure. An AR coating with a refractive index of 1.23 was grown onto the rugate structure by glancing angle deposition technology. Optical measurements of the combined structure show excellent transmittances over the wavelength regions around the reflection band and high reflectances in the stopband.     

适合制作高性能带阻滤波器的新型C形环级联DMS结构

对韩国学者最新提出的缺陷微带结构(DMS)进行了深入的研究;利用HFSS10.0仿真软件和上海大学安捷伦8722ES网络分析仪对其进行了仿真和实际测量,分析了在导带上刻蚀左手单元互补开口谐振环(CSRR)的不足.在此基础上,提出了更简单的C形环状DMS结构,并对此新结构进行了电路理论的等效.将此新型结构和光子晶体理论结...     

Polarization sensing with visual detection

We describe a new approach to fluorescence sensing which relies on visual determination the polarization. The sensing device consists of a fluorescent probe, which changes intensity in responses to the analyte, and an oriented fluorescent film, which is not affected by the analyte. An emission filter is selected to observe the emission from both the film and the sensing fluorophore. Changes in the probe intensity result in changes in the polarization of the combined emission from the sensor and reference. The degree of polarization can be detected visually using a dual polarizer with adjacent sections oriented orthogonally to each other. The emission passing through the dual polarizer is viewed with a second analyzing polarizer. This analyzer is rotated manually to yield equal intensities from both sides of the dual polarizer. This approach was used to measure the concentration of RhB in intralipid and to measure pH using 6-carboxyfluorescein. The analyzer angle is typically accurate to 1 degree, providing pH values accurate to +/- 0.1 pH unit at the midpoint of the titration curve. We also describe a method of visual polarization sensing that does not require an oriented film and that can use the same fluorophore for the sample and reference. These approaches to visual sensing are generic and can be applied to a wide variety of analytes for which fluorescent probes are available. Importantly, the devices are simple, with the only electronic component being the light source.     

一种具有自取向极化效应的有机光折变体系

在用真空热压-饱和蒸汽扩散法制备的PVK-PBA/DR1/TNF有机聚合物体系中,观察到了无外电场作用下的较强的光折变效应.通过对样品的双波耦合、四波混频实验中,改变电场强度、电场方向或不加外电场而只改变光强,观察到的衍射效率的变化情况以及测量样品在单纯光照诱导下的光学非线性系数等一系列实验,可以认为光照时在该有机聚合物体系中由DR1分子两端的推、吸电子基团与光生分离的正负电荷相互作用而引发了"自极化",从而产生周期性空间电场,最终产生自增强光折变效应.另外进行了图象存储实验,获得了理想的结果.本研究对发展零外场聚合物光折变体系有重要的参考意义.     

SAW filters based on parallel-connected coupled resonator filters with offset frequencies

The concept of coupled resonators is applied to synthesize surface acoustic wave filters. Employing two parallel-connected filter tracks, with a frequency shift imposed between them, a wide passband with low insertion loss together with well-controlled rejections is achieved. The operation of the two-track device is based on the mutual interaction of the individual transfer functions for the pair of tracks. Each track serves to contribute a part of the passband, enabling a wide band. Outside of the passband, the signals passing through the two channels may cancel each other, thus facilitating efficient control over the rejections. However, obtaining rejection stopbands at just the predetermined frequencies requires precise values for the materials parameters and a reliable fabrication process. Prototype devices fabricated with this approach are demonstrated both on quartz and, for the first time, on 42 degrees-LiTaO3. Results for two-track devices having either two or three transducers per track and operating either single-ended or with a balanced output are presented. The devices are designed employing the coupling-of-modes model and transmission-matrix approach, and the separate tracks are optimized simultaneously and independently. The center frequencies are 868 MHz and 1960 MHz. On quartz, a minimum insertion loss of 4 dB and a passband width of 0.23% are achieved at 868 MHz. On 42 degrees-LiTaO3, the corresponding figures of merit are 1.3 dB for minimum insertion loss and 4.1% bandwidth at 1960 MHz. The filters on 42 degrees-LiTaO3 also have remarkably flat passbands.