Perturbation analysis of clad parabolic-index waveguides

A first-order perturbation technique is used to obtain the eigenfunction correction due to the cladding in a square-law dielectric waveguide. Regions both near to and far from cut-off are considered separately. It is shown that far from cut-off the fractional power carried by the guide core increases over that in the homogeneous case but that near cut-off the power in the core is less than in a homogeneous guide. Thus the stability of the modal power with variation of wavelength is increased over that in a homogeneous guide.     

Numerical analyses of optical couplers for planar waveguides

The paper presents the results of numerical analyses of optical structures realized in the form of planar waveguides made of materials with high values of the refractive index n ??1.85. The analysed structures consist of a waveguide and input-output systems. Input-output couplers are realized in the form of prisms as well as Bragg??s grating couplers. Numerical investigations were carried out by applying the finite difference time domain (FDTD) method.     

Frequency response of metal clad planar optical waveguides

The propagation characteristics of metal clad planar optical waveguide as a function of wavelength are investigated theoretically for Al, Ag, and Au. The results obtained show that attenuation of the propagation modes in these guides is highly dependent on wavelength, which can be used to design an efficient integrated optical waveguide polarizer with high extinction ratios, or to select the wavelength for the surface plasmon based metal clad optical waveguide sensors. It is observed that Al is the only metal that still supports the surface plasmons in the UV region.     

InGaAs/InAlAs多量子阱脊形波导及定向耦合器光波特性准矢量分析

提出了一种基于级数展开的三维准矢量束传播法(SE-QV-BPM)用以分析由InGaAs/InAlAs多量子阱构成的脊形光波导及定向耦合器.结果表明，刻蚀深度相同时，TM模比TE模在水平方向限制强，且TM模的模场在波导角上出现畸变；波导间距相同时，定向耦合器TM波的耦合长度大于TE波的耦合长度，对偏振态敏感.分析获得了浅/深刻脊形光波导承载的准矢量TE/TM基模、定向耦合器承载的TE/TM偶/奇模的模场分布及其有效折射率，模拟了光场在定向耦合器中的传输演变情况.另外，SE-QV-BPM导出矩阵小，计算效率高 关键词： 级数展开 准矢量束传播法 多量子阱 InGaAs/InAlAs     

Contradirectional couplers in silicon-on-insulator rib waveguides

We demonstrate contradirectional couplers in silicon-on-insulator rib waveguides using a CMOS compatible technology, in which a periodic dielectric perturbation is introduced in the coupling region between two different-sized rib waveguides. This structure enables high fabrication tolerances for narrow-bandwidth add-drop filters, using commercially available deep-ultraviolet lithography, that do not suffer from having a free spectral range. The simulation using coupled-mode theory and mode-profile calculations shows good agreement with experiment. A narrow bandwidth of 0.35?nm and a low loss of less than 1?dB have been achieved experimentally.     

Efficient couplers for photonic crystal waveguides

We use two-dimensional simulations to study the design of tapers to provide efficient, low reflection coupling between a waveguide in a two-dimensional photonic crystal (PC) and free space. We find that, largely independent of the PC parameters, or of the length and width of the tapered region, the same type of concave, horn-shaped tapering profile is optimal for coupling from the waveguide into free space, and significantly out-performs the widely used linear taper. We also find that optimal tapers can radiate nearly Gaussian beams, and therefore they can also provide efficient coupling of Gaussian beams from free space into the PC waveguide. These properties are better exhibited by rod-type PCs with E_z polarization than by hole-type PCs with H_z polarization. This study of taper couplers exemplifies a design strategy for photonic circuits which optimizes positioning of the cylinders immediately surrounding the light path, and then builds the rest of the crystal structure around these cylinders.     

光波导等参元分析

本文提出一套用于分析任意介质光波导的等参元算法,它基于严格的E_z-H_z变分公式,采用八节点曲边四边形单元。这种类型的等参元分析法尤其适用于研究各种具有曲边边界的复杂光波导和光波导器件。作为例子,文中把这一方法用于分析阶跃型光纤,渐变型光纤、各向同性以及各向异性光纤耦合器。     

A propagating beam analysis of optical waveguide couplers

We study the mode coupling among the local normal modes of couplers formed from planar parabolic graded-index tapered optical waveguides with the propagating beam method. Our results indicate that couplers whose radiia (z) depend on axial length as \Lambda /2$$ " align="middle" border="0"> , have many desirable properties not possessed by other couplers.     

Grating couplers for thick SOI rib waveguides

The use of grating couplers in high index contrast waveguides like silicon on insulator (SOI) offers several advantages over other coupling approaches, including better alignment tolerances and allowing for wafer-scale testing. The grating couplers were developed for nanometric SOI waveguides (Si-wires), and recently also for micrometric rib waveguides. In this paper we review our work in fiber-to-chip grating couplers for thick SOI rib waveguides, where a coupling efficiency of ?2.2?dB was demonstrated experimentally. We also discuss the use of grating couplers to improve optical throughput (étendue) of a planar waveguide Fourier-Transform (FT) spectrometer implemented in thick rib waveguides.     

Polarization-independent grating couplers for silicon-on-insulator nanophotonic waveguides

We propose the use of subwavelength structures in a waveguide grating to achieve polarization-independent coupling of light between an optical fiber and a silicon-on-insulator (SOI) optical waveguide. The subwavelength structure allows the mode effective indices of the TE and TM modes in the grating section to be precisely engineered. We calculate that coupling efficiency of over 64% is possible using the proposed design for polarization-independent coupling between single-mode optical fibers and SOI nanophotonic waveguides.     

Theory of optical couplers

The propagation of solitons through optical couplers is studied here in this paper. Both the twin-core couplers as well as the multiple-core couplers are considered here in this paper. The parameter dynamics of the solitons that are governed by the coupled generalized nonlinear Schrodinger's equation, due to non-Kerr law nonlinearity, has been obtained for such couplers.     

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%.     

Leaky mode analysis of circular optical waveguides

A leaky mode is a bound mode below its cut-off frequency. It attenuates in the direction of propagation and approximates the portion of the radiation field within the optical waveguide that is significant far from the source. The characteristics, including attenuation coefficients, of leaky modes on the circular fibre are compared with those of the more familiar slab waveguide. Except for the HE_1m leaky modes, leaky modes attenuate much faster on the slab than on the circular fibre. The greater the /(azimuthal field variation) the smaller the attenuatioN. Thus, theI?1 leaky modes are important even at great distances from the source. An effective cut-off frequency is proposed. Above this frequency the mode is either weakly leaky or trapped. An expression for the number of weakly leaky and trapped modes is given. The power of leaky modes due to illuminating one end of the fibre is determined. The effect of material absorption is considered.     

Numerical characterization of nanopillar photonic crystal waveguides and directional couplers

We numerically characterize a novel type of a photonic crystal waveguide, which consists of several rows of periodically arranged dielectric cylinders. In such a nanopillar photonic crystal waveguide, light confinement is due to the total internal reflection. A nanopillar waveguide is a multimode waveguide, where the number of modes is equal to the number of rows building the waveguide. The strong coupling between individual waveguides leads to the proposal of an ultrashort directional coupler based on nanopillar waveguides. We present a systematic analysis of the dispersion and transmission efficiency of nanopillar photonic crystal waveguides and directional couplers. Plane wave expansion and finite difference time domain methods were used to characterize numerically nanopillar photonic crystal structures both in two- and three-dimensional spaces.     

Review of optical fiber couplers

The present trends are toward implementation of fiber optics in data-distribution networks such as data buses, community antenna television, and local area networks. The thrust is, therefore, on high-volume and economical production of good quality optical fiber couplers. This paper reviews the various techniques for making fiber couplers. Important characteristics of various constructions and configurations together with their merits and demerits are discussed.     

Vectorial wave-matching mode analysis of integrated optical waveguides

For mode fields of integrated optical waveguides with piecewise constant and rectangular permittivity profile, Maxwell's equations reduce to the two-dimensional Helmholtz wave equation, supplemented by continuity requirements on the boundaries between different media. Two basic components of the mode field are expanded into factorizing harmonic or exponential functions, separately on each rectangular region. We determine approximations for guided modes and propagation constants by means of a minimization procedure based on a least squares expression for the mismatch in the continuity requirements. Results for the hybrid mode fields of typical sample waveguides classify this approach as competitive with and superior to alternative methods for vectorial mode analysis, although some open questions remain.     

Review of optical fiber couplers

The present trends are toward implementation of fiber optics in data-distribution networks such as data buses, community antenna television, and local area networks. The thrust is, therefore, on high-volume and economical production of good quality optical fiber couplers. This paper reviews the various techniques for making fiber couplers. Important characteristics of various constructions and configurations together with their merits and demerits are discussed.     

改进的光波导标量近似有限元分析

本文首次将波矢量的匹配条件应用于标量近似有限元法求解条形波导,从而将二维问题简化成两个一维问题.其结果除了具有标量近似有限元法的一切优点外,还为节省计算机的存储和时间提供了一条新的途径.