单纯形法在非线性光波导传播特性分析中的应用

简要介绍了优化理论中的单纯形方法,并且应用到求解介质非线性光波导的色散方程。文中计算了非线性光波导传输特性的2个实例,1）非对称3层平板波导,由线性衬底、克尔型芯区和线性包层（LNL）组成;2）对称3层平板波导,由克尔型包层、衬底及线性芯区组成（NLN）。数值结果表明,非线性光波导的色散方程很困难求解时,单纯形方法对于分析非线性光波导的传输特性简便而且有效。     

改进的非线性薄膜波导导模的无量纲表示

本文对Fontaine所采用的非线性薄膜波导导模的无量纲表示法作了改进,给出了无量纲参数表示的芯区为克尔型非线性介质,衬底和包层为线性介质的LNL型非线性平板光波导的有关计算公式,色散曲线族及场分布和功率分布随模折射率变化关系的曲线族,本法易推广应用于其它非线性平板光波导NLL、NNL及NNN等的处理过程。     

Uniform Core Field in Symmetrical Planar Waveguides and Circular Fibers with Nonlinear Claddings

It is known that no uniform electric field profile exists in a planar linear waveguide. The uniform core field can be shown to exist in symmetrical planar waveguides and circular fibers with nonlinear claddings. Theoretical analysis and numerical calculations are carried out to show that when the modal index equals to the core refractive-index, the core field becomes uniform at an appropriate optical power. Analysis for a step-index circular fiber with nonlinear cladding have also shown that the core field becomes uniform under similar conditions. The occurrence of a uniform field in a waveguide core may believe to have promising applications in waveguide, optoelectronic and photonic devices.     

Coupling of Organic Semiconductor Amplified Spontaneous Emission Into Polymeric Single-Mode Waveguides Patterned by Deep-UV Irradiation

Single-mode waveguides were fabricated by deep ultraviolet radiation in poly(methyl methacrylate) (PMMA). Using a masking process, the radiation modifies the refractive index of the PMMA forming core and cladding regions for waveguiding. Following the fabrication of the waveguides, the small molecule material aluminum tris(8-hydroxyquinoline) doped with the laser dye DCM is deposited directly onto the waveguide structures. By optical pumping (lambda=355 nm) amplified spontaneous emission was observed at the end facets of the waveguides     

Analytical stability analysis of dark and bright self-guided wavesin layered self-defocusing nonlinear media

We present an analytical stability analysis on dark (black and gray) self-guided waves and the fundamental state of the bright self-guided waves with nonzero intensity background trapped in a thin self-defocusing nonlinear film bounded by an infinite self- defocusing medium of different nonlinearity. It is found that the gray self-guided wave and the fundamental state of the bright self-guided waves with nonzero intensity background are stable to both symmetric and asymmetric perturbations, whereas the black self-guided wave is stable to symmetric perturbation but unstable to asymmetric perturbation (in contrast to the corresponding one in a uniform self-defocusing medium). For the nonlinear waveguides with the linear refractive index n_c, in the cladding smaller than that n_f the film the instability of the black self-guided waves is shown to result from the presence of the complex growth rate, while the instability for that trapped in a hollow waveguide (n_cc>n_f) may arise from the presence of either real or complex growth rate, depending on the waveguide parameters     

左手材料平面波导之间的耦合特性

从电磁场理论出发,求得芯层是右手材料,包层是左手材料的两个平面波导之间耦合系数的一般公式,引入归一化频率,归一化传播常数,作出耦合系数随归一化频率变化的曲线.进一步讨论了两个平面波导之间的距离和芯层折射率改变对该曲线的影响,从而得出含左手材料平面波导之间的耦合特性.     

Cutoff Conditions in Three-Layer Cylindrical Dielectric Waveguides

Exact cutoff expressions for hybrid and circularly symmetric modes in three-layer cylindrical dielectric waveguides are derived. It analytically established that whenever the refractive index of the enter medium (n/sup2/) is higher than either the refractive index of the core (n/sub1/) or of the inner cladding (n/sub2/), i.e., n/sub1/ >n/sub3/ >n/sub2/ or n/sub2/>n/sub3/ >n/sub1/, the dominant HE/sub11/ mode can have a nonzero cutoff frequency. Inequalities relating the permittivities to the ratio of the cladding radius to the core radius, as conditions for the nonzero cutoff of the HE/sub11/ mode, are determined. The cutoff conditions presented in this paper are also applicable to similar structures used io millimeter-wave communications.     

非线性平板波导中均匀芯区场的归一化形式

通过理论分析及典型实例计算，分析了包层及衬底均为非线性Kerr型介质、芯区为线性均匀介质的对称3层平板波导的TE0模出现均匀场分布的条件及其归一化形式。给出了自聚焦和自散焦情况下对称3层平板波导TE0模的归一化场分布曲线以及功率随归一化模折射率变化曲线。     

Cladding Layer Impedance Reduction to Improve Microwave Propagation Properties in p-i-n Waveguides

The cladding layer effect on microwave propagation properties of semiconductor p-i-n waveguides is investigated in this letter. Through the optical excitation in quantum wells of p-i-n waveguides, high-speed photocurrent is used to examine the microwave propagation. Two devices of p-i-n waveguides with different cladding layers are fabricated and measured, showing that a higher speed is found in the waveguide of wider cladding width. Verified by the microwave propagation properties, the higher speed is mainly attributed to lower microwave propagation loss due to the lower impedance in the wider cladding layer, suggesting this kind of structure can be applied to high-speed waveguide-based devices     

Magneto-Photonic Crystal Slab Waveguides With Lower-Refractive-Index-Silica Claddings

This letter proposes a new form of magneto-photonic crystal slab waveguides including nanoporous SiO₂, with an extremely low refractive index, as the cladding material. These structures allow us to achieve physical strength and to render unnecessary holes extending to cladding layers. Our letter investigates the significance of the waveguide geometry for nonreciprocal phase shifts and losses, using a three-dimensional finite-element method with periodic boundary conditions. The guided modes exhibit small losses well below the light line and high nonreciprocal phase shifts with appropriate parameters, according to the calculations in this letter     

Fabrication of Self-Organized Optical Waveguides in Photo-induced Refractive Index Variation Sol–Gel Materials With High-Index Contrast

Using photo-induced refractive index variation sol-gel materials, we fabricated a self-organized lightwave network (SOLNET), which is a concept of optical waveguides self-organized in photosensitive materials, whose refractive index increases by write beam exposure. The refractive index of the sol-gel materials increases from 1.65 to 1.85 when exposed to UV light/blue light and baking. When write beams with a wavelength of 405 nm are introduced into the sol-gel thin film under baking at 200degC, self-focusing is induced and a SOLNET is formed. In this study, we evaluated the light confinement effect and coupling efficiencies of the fabricated SOLNET. The half-width of the output beam spot decreases from 23.8 to 11.8 mum, and the coupling efficiencies increase as write beam intensity decreases from 1.0 to 0.1 mW. These results show that SOLNET widths become narrow when write beam intensity is reduced; thus, SOLNETs formed with a low write beam intensity produce a strong light confinement effect. Furthermore, during their formation, SOLNETs were found to be drawn toward reflective portions of the sol-gel thin film, such as defects or silver paste droplets, indicating that a reflective SOLNET is formed. We have shown that photo-induced refractive index variation sol-gel materials are promising materials for SOLNET fabrication. To create actual connections between nanoscale optical circuits, further work is necessary to optimize the baking temperature and write beam intensity required for nanoscale SOLNET formation.     

五层非线性平板波导TE模的特性

文章提出了分析中间层为非线性介质结构的五层平板波导TE模的解析方法,推导出了这种结构下普遍适用的色散关系式,给出了各层介质中的场分布和功率分布的解析式,并根据这一模型,就对称结构的五层非线性平板波导结构的模式特性进行了实例计算与讨论。     

硅基纳米波导的双模干涉

硅基(SOI)波导是近年集成光电子和集成波导的重要方向。对硅基纳米波导进行数值计算,讨论了空气包层和SiO2包层两种情况的双模传输特性,得到两种包层结构的双模工作区域和双模拍长与波导结构的关系。研究了SOI纳米波导中双模干涉现象以及双折射和温度对双模干涉的影响。     

Fabrication of DAST Channel Optical Waveguides

In order to use the large, electro‐optic coefficient of a nonlinear optical ionic crystal, 4‐(p‐dimethylaminostyryl)‐1‐methylpyridinium tosylate (DAST), a channel optical waveguide structure is needed. We successfully fabricated a waveguide using two methods: by a dry‐etching technique and by photo‐bleaching. Because DAST has a large optical loss, parts of the waveguide should be composed of a transparent polymer. We used photolithography and a reactive ion etching method to fabricate a serially grafted (conjunct) waveguide of DAST with a transparent polymer waveguide. The waveguide was also fabricated by photobleaching, whereby the refractive indices of the crystal’s a‐ and b‐axes were decreased by degrading the crystal. The cladding part of the DAST waveguide was photobleached by irradiating with UV light. The under‐ and over‐cladding layers of these channel waveguides were composed of a UV‐cured resin that did not dissolve the DAST crystal. The loss of the crystal waveguide for the crystal b‐direction was around 10 dB/cm, due to the scattering loss of the DAST single crystal.     

A Semianalytical Technique for Leaky-Mode Loss Calculation in Hollow Dielectric Waveguides With Arbitrary Cross Sections

We present an approximate semianalytical technique for the calculation of the loss coefficient of leaky modes in 3-D hollow dielectric waveguides having an arbitrary cross section. The hollow waveguides are assumed to have an axis of symmetry and to have a cladding with a higher refractive index than the core. An expression for the modal loss coefficient is derived using a ray-optics approach with paraxial approximation. For the special cases of specific cross sections with known solutions, our technique gives results that are identical to the available analytical solutions. The technique is then applied on practical waveguide geometries, allowing the calculation of polarization- and wavelength-dependent losses. Full numerical alternatives to the technique involve time-consuming simulations and, sometimes, difficulty in incorporating a suitable boundary condition to obtain leaky-mode solutions.     

Reflection Coefficient of E-Plane Tapered Waveguides

This paper treats the reflection of linearly and sinusoidally tapered waveguides. In the first part, reflection coefficients of linearly tapered waveguides for dominant modes are calculated. Graphs of the vswr of tapers for different impedance ratios are plotted showing that the vswr does not go to unity at multiples of a half wavelength. In the second part, reflection coefficients of sinusoidally tapered waveguides are calculated. Experimental data verify the theory for both kinds of tapers of various lengths at 4 kmc band. Linear tapers perform almost as well as exponential tapers, and better than shorter hyperbolic tapers. The reflection coefficients of sinusoidal tapers can be about half as small as that of the linear tapers, and these tapers compare favorably with the Dolph-Tchebycheff and the Willis taper of improved design.     

金属包层渐变折射率平板波导传播特性

本文采用多层线型分割近似，结合欧姆损耗微扰法，分析了金属包层渐变折射率平板波导的传播特性。按此方法计算了几类典型波导的传播常数数值，结果均与精确值相吻合，且物理概念清楚，计算方法简单。     

A Method Extending the Boundary Condition for Analyzing Guided Modes of Dielectric Waveguides of Arbitrary Cross-Sectional Shape

A method based on the extended boundary condition method is presented for analyzing guided modes of dielectric waveguides of arbitrary cross-sectional shape. Numerical integration needed in this method is only over the boundary periphery line of the waveguide. Nevertheless, it is applicable to the waveguides with any refractive index difference between core and cladding ranging from negligibly small to considerably large difference, as well as to certain types of waveguide with inhomogeneous core. Approximate formulas for the case of weakly guiding are also derivable from the general basic set of equations presented. Numerical examples are given to verify the usefulness and accuracy of this method.     

Computing the eigenmodes of lossy field-induced optical waveguides

Slab waveguides which achieve lateral confinement in the guiding region by applying a spatially selective electric field across a multiquantum well cladding region are modeled by solving the appropriate Helmholtz equation. Attention is focused on the effects of absorption in the cladding region of the waveguide, which leads to attenuation along the propagation direction. Galerkin's method is utilized to compute exact mode propagation constants and intensities of the fundamental mode. It is found that increased absorption in the cladding layer results in increased lateral extent of the guided mode. At a critical absorption strength, the guided mode becomes unconfined in the lateral direction. This transition can be rationalized in part in terms of the effective index method, which provides a simple approximate way to calculate the characteristics of waveguides with two-dimensional index profiles     

制备有机聚合物脊型光波导的新方法

详细讨论了ＤＲ１／ＰＭＭＡ聚合物波导在紫外光照射下,各个模式的有效折射率,薄膜厚度,以及紫外可见吸收谱的变化情况。并在此基础上,提出了以金属掩模,利用光漂白技术制备聚酰亚胺脊型光波导的新方法。