Bend loss effects in diffused, buried waveguides

Bend loss effects can be a significant concern in the design and performance of diffused, buried waveguide devices. Since diffused, buried waveguides typically do not have analytical mode solutions, the bend mode must be expressed as an expansion of straight waveguide modes. For the case of buried ion-exchanged waveguides, the bend loss is affected by bend radius, the duration of the ion exchange and burial processes, as well as the size of the mask opening used to create the waveguides and applied field during burial. The bend loss effects for each of these variables are explored under typical fabrication conditions.     

Decrease in the incoherent near-edge X-ray scattering in narrow waveguides

The role of incoherent scattering in the attenuation of transmitted radiation has been studied using the statistical theory of X-ray beam scattering in a narrow rough collimator. Based on the obtained approximation expressions for the coefficients of waveguide mode damping, it is predicted that the level of scattering near the absorption edge must exhibit a significant decrease due to dispersion, which is also manifested by decreasing intensity of the backscattered radiation.     

Resonant scattering and mode coupling in two-dimensional textured planar waveguides

A heuristic formalism is developed for efficiently determining the specular reflectivity spectrum of two-dimensionally textured planar waveguides. The formalism is based on a Green's function approach wherein the electric fields are assumed to vary little over the thickness of the textured part of the waveguide. Its accuracy, when the thickness of the textured region is much smaller than the wavelength of relevant radiation, is verified by comparison with a much less efficient, exact finite difference solution of Maxwell's equations. In addition to its numerical efficiency, the formalism provides an intuitive explanation of Fano-like features evident in the specular reflectivity spectrum when the incident radiation is phase matched to excite leaky electromagnetic modes attached to the waveguide. By associating various Fourier components of the scattered field with bare slab modes, the dispersion, unique polarization properties, and lifetimes of these Fano-like features are explained in terms of photonic eigenmodes that reveal the renormalization of the slab modes due to interaction with the two-dimensional grating. An application of the formalism, in the analysis of polarization-insensitive notch filters, is also discussed.     

Optical loss study of MPEOU-based polyceram planar waveguides

Sol-gel-derived polyceram materials based on organically modified silicon and titanium alkoxides have been synthesized in planar waveguide forms. They exhibit optical losses as low as <0.25 dB/cm and refractive indices as high as 1.685, coupled with exceptional ease of processing. The optical properties of the films (index of refraction, loss, and dispersion) are studied as functions of processing and composition, and the influence of chemistry on volume homogeneities and surface roughness of the films is investigated.     

Transverse offset loss between two identical noncircular single-mode waveguides

We derive an approximation for the transverse offset loss based on the Laplacian mode-field half-width (MFHW) and far-field second moment for two arbitrary identical noncircular single-mode waveguides. The relation is reduced to the known result for circular-symmetric, single-mode waveguides. Numerical results for symmetrical rectangular waveguides show that the transverse offset loss calculated from the Laplacian MFHW is more accurate than that from the elliptical Gaussian MFHW for small transverse offsets. To our knowledge, this is the first calculation of the errors in the approximate transverse offset loss relations derived from the Laplacian and the elliptical Gaussian MFHW for noncircular optical waveguides.     

Greatly reduced radiation loss in planar waveguides with two-dimensional conducting interfaces

A new strategy for radiation loss reduction in curved slab waveguides is presented. The proposed strategy is based on the proper modification of the boundary conditions at the core-to-cladding interface, whereupon extremely thin conductive nanolayers with non-zero surface conductance are imposed. The obtained numerical results show a noticeable decrease in the overall loss level.     

端面不平行对岩石SHPB测试结果的影响分析

为探讨岩石试件加工端面不平行对岩石材料动力学特性测试结果的影响,采用有限元分析软件LS-DYNA对13种端面不平行度的岩石试件开展SHPB数值模拟,并分析了端面不平行对加载过程应力均匀性的影响。结果表明:随端面不平行度γ的增加,岩石试件动态应力-应变曲线逐渐向右和向下移动,且峰前加载段逐渐延长。当γ1.60%时,动态应力-应变曲线在加载初期出现一个微小的加载-卸载过程,且在升时为120μs的半正弦入射波加载阶段岩石试件达不到应力均匀状态。基于数值模拟结果,建立了端面不平行度与量纲一化的动态单轴抗压强度、平均应变率和峰值应变的定量表达式。     

Beam loss by single coulomb scattering in collider rings

The ultimate cause of beam loss in a collider ring is given by particles scattered outside the ring acceptance by single Coulomb scattering. Even though small, this effect is not negligible, above all in super-cooled low energy machines, with a vertical betatron function which takes up a minimum value, at the interaction region, comparable to the average performed around the ring.     

Minimizing the bulk-wave scattering loss in dual-mode SAW devices

The losses arising from the scattering of SAW into bulk waves in the nonsynchronous areas of SAW devices are studied numerically using the boundary element method combined with the finite element method. As a reference structure, we use a typical one-port hiccup resonator on 42 degrees Y-LiTaO3. Strong scattering into bulk wave occurs in the central gap due to an abrupt change in periodicity. To reduce the scattering, we replace the gap with electrodes having reduced pitches. We show that it is possible to significantly increase the Q-factor of the resonator while keeping the resonant frequency unchanged. Two types of structures are studied: the "distributed" gap and the "accordion" gap. To minimize the bulk-wave scattering in dual-mode SAW filters, we replace the metallized gaps in the traditional filter with distributed gaps. We find an optimal combination of pitch and metallization ratio in the gaps, reducing the insertion loss by 0.3 dB.     

Optical waveguides for imaging applications: Design by an inverse scattering approach

An inverse scattering theory is used to design optical waveguides capable of transmitting spatial images without degradation. The propagation characteristics of N modes each carrying a pixel of the image are specified by a transverse rational reflection coefficient. The Gel'fand-Levitan-Marchenko inverse scattering theory is used to obtain the unique solution of the permittivity profile of the waveguide from the reflection coefficient     

Single photon scattering in a pair of coupled-resonator waveguides coupled to a quantum emitter

We theoretically investigate the single photon scattering in a pair of coupled-resonator waveguides coupled to a two-level quantum emitter. It reveals that the incident photon transporting probabilities can be controlled by adjusting the coupling strength between the two-level system and the coupled-resonator waveguide. Two optical nano-devices, quantum optical switch and beam splitter are proposed. In addition, the influence of the dissipation of the two-level system on the photon transporting properties is also analyzed.     

Single-mode GaAs/AIGaAs W waveguides with a low propagation loss

We have designed a low-loss single-mode GaAs/AIGaAs optical waveguide with a symmetric five-layer heterostructure at the 1.31-μm wavelength by use of an effective-index method. Waveguides with a W-shaped refractive-index profile have been grown by use of a metallo-organic chemical vapor deposition technique and fabricated with a chemical wet-etching method. Propagation loss has been measured by use of the Fabry-Perot resonance method and a sequential-cleaving experiment. The measured loss is as low as 0.19 dB/cm for waveguides with 2.3-μm thickness and 4.3-μm width, which is comparable to the lowest-loss semiconductor waveguides yet reported. These waveguides could be used to make low-loss modulators for guided-wave devices.     

由混响衰减反演海底散射系数

1随机反演理论(高斯-马尔可夫原理) 设随机变量d与m,n有线性关系: d=Gm+n, (1) 其中d为数据矢量,m为未知参量,n为随机噪声,G为未知参量与数据矢量之间的关系. 假设m,n为零均值,其协方差矩阵分别为:     

Low loss high mesa optical waveguides based on InGaAsP/InP heterostructures

Low loss high mesa optical waveguides were fabricated on InGaAsP/InP heterostructures by utilizing inductively-coupled-plasma reactive ion etching (ICP-RIE) and electron beam lithography technique. The fabrication process was optimized by measuring sidewall roughness of deep-etched waveguides. Atomic force microscope loaded with carbon nanotude was used to obtain three-dimensional image of the etched sidewall of waveguides. The obtained statistical information such as rms roughness and correlation length was used to theoretically calculate scattering loss of waveguides. Several waveguides with different number of sharp bends and the length were fabricated and their propagation losses were measured by modified Fabry-Perot method. The measured propagation losses were compared with theoretically calculated losses.     

Numerical analysis of bent waveguides: bending loss, transmission loss, mode coupling, and polarization coupling

A rigorous, full-vectorial and computationally efficient finite-element-based modal solution, together with junction analysis and beam propagation approaches have been used to study bending loss, transition loss, mode coupling, and polarization coupling in bent optical waveguides. The waveguide offset and their widths have been optimized to reduce the transition loss and the mode beating.     

Low loss, low refractive index fluorinated self-crosslinking polymer waveguides for optical applications

Synthesis and optical applications of low loss methacrylate-based fluorinated polymers are described. The synthesis of well defined self-crosslinking fluorinated polymers has been carried out in order to tune refractive index in the range of 1.390 < n < 1.450. After thermal crosslinking, one single lithographic step followed by reactive ion etching is necessary to monomode optical waveguide fabrication on silicon substrates. Optical losses lower than 1 dB/cm at 1300 nm and 2 dB/cm at 1550 nm were measured for highly confined modes. Efficient chip coupling to lensed optical fibers was obtained. Using waveguides with an effective index close to that of bulk silica, a significant coupling interaction between the guided modes and the whispering gallery modes of a silica microsphere was evidenced thus opening the way for new device applications.     

Two-dimensional array self-assembled quantum dot sub-diffraction waveguides with low loss and low crosstalk

We model and demonstrate the behavior of two-dimensional (2D) self-assembled quantum dot (QD) sub-diffraction waveguides. By pumping the gain-enabled semiconductor nanoparticles and introducing a signal light, energy coupling of stimulated photons from the QDs enables light transmission along the waveguide. Monte Carlo simulation with randomized inter-dot separation reveals that the optical gain necessary for unity transfer is 3.1 × 10(7)?m(-1) for a 2D (2?μm length by 500?nm width) array compared to 11.6 × 10(7)?m(-1) for a 1D (2?μm length) given 8?nm diameter quantum dots. The theoretical results are borne out in experiments on 2D arrays by measurement of negligible crosstalk component with as little as 200?nm waveguide separation and is indicative of near-field optical coupling behavior. The transmission loss for 500?nm wide structures is determined to be close to 3?dB/4?μm, whereas that for 100?nm width is 3?dB/2.3?μm. Accordingly, higher pump power and gain would be necessary on the narrower device to create similar throughput. Considering existing nanoscale propagation methods, which commonly use negative dielectric materials, our waveguide shows an improved loss characteristic with comparable or smaller dimensions. Thus, the application of QDs to nanophotonic waveguiding represents a promising path towards ultra-high density photonic integrated circuits.