Modeling of Ti:LiNbO3 waveguide devices. I. Directionalcouplers

An efficient modelling method to simulate Ti-indiffused LiNbO₃ channel waveguide devices from their design and fabrication parameters is discussed. Procedures are: (1) derivation of the two-dimensional (2-D) refractive index profile; (2) transformation of the 2-D transverse refractive index profile to its one-dimensional (1-D) effective index profile; and (3) use of the 2-D beam propagation method to analyze the device performance. With slight consistent adjustments on Ti-induced refractive index changes, it is possible to calculate the performance of directional couplers in good agreement with experimental measurements. This modeling method can be used to predict performance of future devices     

Design considerations for an electrooptic directional couplermodulator

A rigorous numerical model is presented for an electrooptic directional coupler (DC) modulator. It was observed that it is possible for such a device to be optimized by the variation of a number of fabrication parameters. The applied field, the induced refractive index changes, and hence the change in the waveguide optical field due to the antisymmetric refractive index change are calculated for an elected structure. Finally, the product of switching voltage and coupling length, the power transfer efficiency, obtained using the least squares boundary residual (LSBR) method, and the optical loss due to the metal electrodes are also given     

二维非线性梯度折射率介质的热辐射特性研究

发展了二维梯度折射率介质热辐射传递的数值求解方法,研究了非线性折射率介质的表观方向发射率.研究结果表明,采用本文方法计算二维梯度折射率介质的表观方向发射率,最大相对误差小于1.6%.通过研究发现,二维非线性梯度折射率介质的热辐射能够呈现非常明显的定向辐射的特征,我们定义这种现象为类相干发射.     

Characterization of Refractive Index Distribution in Spherical Microlenses Fabricated by Deep Proton Writing

In this letter, we present the results of the refractive index measurements on deep proton writing microlenses. The measurement method used is interferometric tomography. It is a nondestructive method for the determination of the 3-D internal refractive index distributions. The influence of the different fabrication steps on the refractive index distribution is discussed.     

Test structures for characterization of electrooptic waveguidemodulators in lithium niobate

A method of determining the critical parameters of waveguide modulators, using a set of test devices fabricated on a single chip, is presented. The five parameters are the depth and lateral Ti diffusion lengths, the peak index change in the waveguides, the electrooptic coefficient, and the buffer layer dielectric constant. The finite element method is used for calculation of optical modes in waveguides with graded refractive index profiles. The integral equation method is used for calculation of the static electric field due to electrodes in a three-layer structure of air, buffer layer, and LiNbO₃. The test set includes a planar waveguide, Mach-Zehnder modulators, symmetrically perturbed directional couplers, and widened X modulators. Several test chips have been fabricated using different fabrication conditions. The parameter values determined using this method are compared with those reported by other authors     

退火质子交换LiNbO3光波导低损耗耦合分析

利用光束传播法分析了退火质子交换铌酸锂光波导模场参数随波导宽度、深度和表面折射率改变的变化情况,指出波导模场受这些参数的综合影响,并讨论了波导结构参数对光纤．波导耦合效率的影响。结果表明,要实现最佳耦合,不同模场直径的光纤对波导结构参数的要求是不同的,这可供相应波导器件的设计和制备参考。     

Switching operation in a GaInAs-InP MQW integrated-twin-guide (ITG) optical switch

Switching operation in a GaInAs-InP MQW (multiple-quantum-well) three-dimensional directional coupler switch at the wavelength of 1.57 mu m was achieved with a short-length device (L=170 mu m approximately=L/sub c/). The device structure fabrication is based on a high-mesa-shaped integrated-twin-guide structure. Switching characteristics are reported, showing that the refractive index variation in the quantum well is about +0.68% with very low absorption loss increase.<>     

钛扩散Nd：LiNbO3波导激光器的1085和815nm导模和有效折射率 …

利用变分方法对钛扩散ｃ切Ｎｄ：ＬｉＮｂＯ３波导激光器的１０８５和８１５ｎｍＴＭ导模和有效折射率进行了分析,计算机几个低阶ＴＭ模式的模场尺寸和相应的有效折５射率随波导制备参数（初始钛条宽度Ｗ,扩散温度Ｔ和初始钛条厚度Ｈ）的变化关系,讨论了波导的单模条件和截止条件,所得理论结果与以前所报导的实验数据进行了比较。     

Control of Refractive Index Distribution for High-Bandwidth Graded Index Plastic Optical Fiber

The graded index plastic optical fiber (GI-POF) has been proposed as the transmission medium to realize high-speed information transmission. We have succeeded in fabricating a GI-POF by the coextrusion process, a method that allows continuous fabrication of GI-POF. Although it has been indicated that the refractive index distribution of GI-POF fabricated by this process is formed by Fick diffusion with diffusion coefficient dependent on dopant concentration, the method to control it remains unknown. The purpose of this paper is to establish the technology of controlling refractive index distribution in GI-POF fabricated by the coextrusion process. Therefore, we investigate the physical mechanism of the dependency of diffusion coefficient on dopant concentration. It has become clear that the dependency is affected by the decrease of glass transition temperature and the nonlinear increase of melt flow rate. Moreover, through simulation of dopant diffusion by our originally developed program, it has become evident that changing the molecular weight of the core and cladding material allowed control of fabricating a GI-POF with optimal refractive index distribution by this fabrication method.      

钛扩散Nd：LiNbO3波导激光器的1085和815 nm导模和有效折射率的变分分析

利用变分方法对钛扩散c切Nd：LiNbO3波导激光器的1085和815 nm TM导模和有效折射率进行了分析．计算了几个低阶TM模式的模场尺寸和相应的有效折射率随波导制备参数(初始钛条宽度W,扩散温度T和初始钛条厚度H)的变化关系,讨论了波导的单模条件和截止条件．所得理论结果与以前所报导的实验数据进行了比较．     

数值方法和计算参数对束传播方法精度影响的研究

本文参聚合物方向耦合器为对象,研究了二维ＢＰＭ和三维ＢＭＰ在模拟工方面的差别以及剖分点数、传播步长、初始有效折射率等计算参数对精度的。在研究过程中,利用有效折射率的方法,把三维波导转化为二维波导,分别采用三维ＢＰＭ和二维ＢＰＭ进行了模拟,并对模拟结果进行了模拟,并对模拟结果进行了比较,发现二者符合很好,表明二维ＢＭＰ具有很高的工。研究还表明初台有效折射率、传播步长的取值对模拟结果影响不明显,部分点     

基于飞秒激光制备的光纤Fabry-Perot折射率传感器

在对光纤Fabry-Perot(F-P)传感器多光束干 涉原理仿真分析的基础上,利用波长为800nm的飞秒 激光脉冲在普通单模光纤(SMF)上制备微型传感器,并对其折射率响应性能进行了实验测试 。理论分析表明,在低、高折射率区域,F-P传感器的反射谱对比度随着折射率的增加分别 呈现先降低后增加的趋势(折射率高低分界点1．457)。飞秒激光 的制备方法通过计算机控制腔长等可以进行参数可选择的微型光纤F-P传感器的制作。利用 制备的传感器对一系列不同折 射率的溶液进行了折射率响应测试实验,测试结果表明,传感器反射谱对比度对低折射率物 质(折射率小于 1.457)的灵敏度为27.65dB/RI,对高折射 率 物质(折射率大于1.457)的灵敏度为3.50dB /RI,且均具有良好的线性响应。     

Theoretical study of annealed proton-exchanged Nd:LiNbO3channel waveguide lasers with variational method

The controllable fabrication parameters, including anneal time, initial exchange time, channel width, dependences of TM₀₀ mode size, corresponding effective refractive index, effective pump area, and coupling efficiency between pump and laser modes in z-cut annealed proton-exchanged (APE) Nd:LiNbO₃ channel waveguide lasers were studied by using variational method. The effect of channel width on the surface index increment and the waveguide depth was taken into account. The features of mode size and effective refractive index were summarized, discussed, and compared with previously published experimental results. The effective pump area, which is directly proportional to threshold pump power, increases strongly, slightly, and very slightly with the increase of anneal time, channel width, and initial exchange time, respectively. However, the coupling efficiency, which is directly proportional to slope efficiency, remains constant (around 0.82) no matter what changes made to these parameters. The variation of the coupling loss between an APE channel waveguide and a fiber with these parameters for both laser (1085 nm) and pump (815 nm) wavelengths was also calculated. The calculated results indicate that the coupling loss decreases rapidly, slightly and very slightly with the increase of anneal time, channel width and initial exchange time, respectively     

Sol-gel glass waveguide and grating on silicon

This paper reports on the fabrication and characterization of hybrid organic-inorganic glass sol-gel slab and channel waveguides by ultraviolet light imprinting in thin films deposited by a one-step dip-coating process. The adjustment of chemical composition of the materials provides precise selection of refractive index from 1.48 to 1.52 at the wavelength of 632.8 mn. The refractive index of the waveguides at 1.55 μm is similar to that of optical fiber, thus reducing the reflection loss between the two to less than 0.01 dB. The effect of ultraviolet light exposure and heat treatment on waveguide refractive index is studied. Fabrication parameters to produce ridge waveguides are optimized to achieve very smooth side walls. Propagation losses in these waveguides are ~0.1 dB/cm. Single mode buried waveguides, at 1.55 μm wavelength, with circular mode profile are demonstrated     

Characterization of Micro-Powders for the Fabrication of Compression Molded THz Lenses

We investigate different micro-powders that can be used as base materials for THz lenses fabricated by compression molding. For this application materials with a very weak THz absorbance and low dispersion are required. By measuring the THz absorption coefficient and refractive index of pellets pressed from the different micro-powders, we identify several materials that are well suited for the fabrication of compression molded THz lenses (CMLs). In addition, a considerable range of the refractive index is covered by the samples, which will allow for the fabrication of CMLs with different focal lengths for one and the same lens design.     

Design of large-core single-mode Yb3+-doped photonic crystal fiber

The effective index of the cladding fundamental space-filling mode in photonic crystal fiber (PCF) is simulated by the effective index method. The variation of the effective index with the structure parameters of the fiber is achieved. For the first time, the relations of the V parameter of Yb3+-doped PCF with the refractive index of core and the structure parameters of the fiber are provided. the single-mode characteristics of large-core Yb3+-doped photonic crystal fibers with 7 and 19 missing air holes in the core are analyzed. The large-core single-mode Yb3+-doped photonic crystal fibers with core diameters of 50 μm, 100 μm and 150 μm are designed. The results provide theory instruction for the design and fabrication of fiber.     

Optical properties of an Er3+-doped phosphate glass waveguide formed by single-energy H+ ion implantation

In this work, we report the fabrication of an optical waveguide by single-energy H+ ion implantation in the Er3+-doped phosphate glass. The ion implantation conditions are with energy of 0.4 MeV and a fluence of 8.0×1016 ions/cm2. The dark mode spectrum of the waveguide structure was measured by the prism coupling experiment. The refractive index change along with the penetration depth was fitted by using the reflectivity calculation method (RCM). Finally, the calculated near-field light intensity distribution shows superior waveguide properties, which demonstrates its promising potentials for compact optical integrated devices.     

Determination of two-dimensional optical waveguide indexdistribution function parameters from effective indexes

The method described is based on the least-squares method and gives the maximum-likelihood estimate of the parameters. Its practicality is demonstrated by application to waveguides with three types of refractive index distribution. First, the convergence of the method is shown by computer simulations of a waveguide with an exponential refractive index distribution. Second, a Ti-diffused LiNbO ₃ waveguide is considered as an example of a Gaussian refractive index distribution. The computed refractive index distribution agrees with computational results obtained by S. Fouchet et al. (1987). Third, a proton-exchanged LiNbO₃ waveguide is considered as an example of a step refractive index distribution. The computed depth of the waveguide agrees with the measured depth     

梳状大模场光纤结构的优化设计

通过在周期性梳状折射率结构的最外层增加一个高折射率平台的方法,对梳状折射率分布大模场光纤的波导结构进行了优化,使其在模场面积、模场分布及抗弯曲性能方面都有明显提升。模拟研究结果表明,与已有单一梳状折射率分布的光纤相比,优化后的大模场光纤的模场面积提高了700 m2以上,且在相同弯曲半径下,基模弯曲损耗由6 dB/m降低为0.1 dB/m。此外,通过对最外层高折射率平台的参数进行调制可实现不同的模场分布,包括高斯分布、平坦化分布和环状分布,满足特殊激光加工工业的应用需求。     

New design method for low-loss Y-branch waveguides

We propose a new method to design low-loss Y-branch waveguides. In conventional design methods, a specific geometry of branching structure is given first, and then structural parameters describing the details of the proposed geometry (for example, location, sizes, and refractive index of microprisms or phase-adjusting elements) are determined by ray optics or other means. In this paper, we take quite a different approach. Given a complex field distribution, one complex refractive index distribution that supports it is determined uniquely, according to the scalar Helmholtz equation. Using this relation, we first make up an ideal field distribution for dividing optical waves smoothly in the branching region. Next, we calculate the refractive index distribution corresponding to the ideal field. Finally, the imaginary part of the refractive index is set to be zero and its real part is discretized into three levels from the practical viewpoint. Numerical simulations show that the present design method offers extremely low-loss Y-branch waveguides