Characteristic analysis of a directional coupler in horizontal multiple-slotted silicon wires with slanted sidewalls

The characteristics of the directional couplers based on the horizontal multiple-slotted waveguides with slanted sidewalls are analyzed in detail by using a mode solver based on the full-vectorial finite element method with perfectly matched layers absorbing boundary conditions. The coupling length of the directional coupler as functions of the structural parameters including waveguide spacing, sidewalls angle, the thickness and refractive index of the slot regions, both in quasi-TE and quasi-TM modes, is obtained. The effective indexes and the field distributions of the even and odd modes also are presented. The numerical results show that polarization-independent directional couplers can be realized by properly choosing structural and material parameters.     

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     

对称结构光纤光栅耦合器及其应用

光纤光栅耦合器(FGC)具有光纤光栅良好的波长选择特性和光纤耦合器的多端口特点，易于实现全光纤的光波分插复用。光纤光栅耦合器主要有4种结构：基于M Z干涉仪的分离型、基于100％耦合器的非对称型、基于0耦合器的非对称型和基于100％耦合器的对称型。着重介绍对称结构光纤光栅耦合器的结构、工作原理和研究现状。提出了测试方案，并探讨了这种器件在大规模波分复用光纤传感器阵列中的应用。     

Optical modes in a nonlinear double-channel waveguide

We analytically address different types of optical modes in a coupler composed by two nonlinear optical waveguides. It is shown that the coupler not only supports symmetry-preserving modes but also symmetry-breaking modes. In addition, the properties on the existence and bifurcation of those modes are analyzed in detail.     

星形光波导耦合器的耦合特性分析

根据TE0模光波导的本征场分布、瑞利索末菲标量衍射积分公式和激励源与光波导耦合的匹配效率公式,给出光波导端面衍射和耦合的归一化发射系数和接收系数计算公式,推导出光波导端面非接触耦合的耦合效率计算公式。光波导模场分布采用高斯函数近似表达,给出简洁的计算光波导端面非接触耦合的耦合效率函数表达式。最后,基于星形光波导耦合器结构参量的特点,将累加运算采用积分运算近似表达,给出星形光波导耦合器接收光波导总的接收效率与耦合器基本参量的关系,阐明了星形光波导耦合器的耦合特性。     

Optical sensing by silicon slot-based directional couplers

A theoretical investigation of an optical liquid sensor, based on asymmetric directional coupler employing slot optical waveguides, is carried out. The sensing principle is based on the shift in the waveguide transmitted spectrum induced by analyte refractive index change. Silicon-on-insulator technology has been assumed in sensor design, and sensor modelling is carried out by using the coupled modes theory and the finite element method. The influence of geometrical parameters on the sensor characteristics has been investigated. A minimum detectable refractive index change of the order of 10^?6 can be theoretically predicted.     

All optical method of developing OR and NAND logic system based on nonlinear optical fiber couplers

Logic gates are the fundamental building blocks in any digital data processing system. Several all optical logic operations are already proposed by scientists and technologists. Here the authors proposed a new method of all optical logic operation based on nonlinear directional coupler. Effective optical switching is achieved by modifying the coupling length between the coupler waveguides by means of an optical signal.     

Linear and nonlinear coupling properties of a novel multicore circular dielectric waveguide

In this work we investigate the linear and nonlinear coupling properties of a novel multicore circular dielectric waveguide. The proposed device consists of a circular central core and many circular sectoral cores at the periphery, while the whole structure can be considered as a nonlinear multicore composite optical coupler. Hybrid guided modes in a circular sectoral dielectric waveguide are derived using circular harmonic expansion for the electromagnetic fields and the Point Matching Method (PMM) for the application of boundary conditions. Several cases are investigated varying some of the parameters of the geometry and the optical frequency in order to produce dispersion diagrams. In advance, the electric and magnetic field distributions for the fundamental guided modes are produced, while linear and nonlinear coupling coefficients as well as the sectoral waveguide mode effective area are derived.     

Simulation and experimental research on polymer fiber mode selection polished coupler

Multimode dispersion is the main obstacle for high bandwidth in multimode optical fiber （MMF） communication system. Mode selection is an effective method to oppress multimode dispersion. We propose and investigate a kind of polymer optical fiber polished coupler. Beam propagation method （BPM） is employed to calculate the coupling coefficient of transmission modes in MMF coupler, and an output pattern from coupling branch is obtained. Analysis and experiment show that this coupler can select certain modes by changing polished depth, contact area, and intersection angle of two branches, which means that the device can be employed both as a mode selector and a sensor. In addition, simulation shows that five times bandwidth enhancement may be realized by selecting modes with the polymer fiber polished coupler.     

Compact multimode interference coupler with tapered waveguide geometry

In this paper, a novel MMI coupler, based on general interference, with tapered waveguide geometry has been proposed for reduction of coupling length. The coupling characteristics and power imbalance of the proposed structure are compared with conventional MMI structures by using a mathematical model based on sinusoidal modes. It is seen that the beat length for tapered MMI coupler with angle of taper ∼1.05° is reduced by ∼24% of that of conventional MMI coupler and the coupling characteristics obtained with the mathematical model, match well with those obtained by more sophisticated BPM computer aided design software. The power imbalance for tapered 3 dB MMI coupler is more sensitive to the wavelength than that for conventional 3 dB MMI coupler and variation of power imbalance with fabrication tolerance for both the MMI coupler is almost same.     

低功耗聚合物波导可调耦合器的优化设计

提出并研究了一种带隔热槽的马赫-曾德尔干涉结构聚合物波导可调耦合器。仿真分析了热光电极作用下有、无隔热槽的耦合器波导温度分布,表明设置隔热槽可以降低热光调谐所需的功耗。研究了铝电极作用下不同上包层厚度对光传输损耗的影响,确定了上包层厚度。根据隔热槽与电极之间距离对热光调谐功耗的影响,结合隔热槽对导波光模式的影响及波导制备工艺,确定了隔热槽的位置。最终设计的带隔热槽聚合物波导可调耦合器实现1～0的分束比所需功耗为2.20mW,是无隔热槽的47.4%。     

Dynamic analysis of an optical fiber coupler in telecommunications

This paper studies the vibration of an optical fiber coupler which is used in telecommunications subjected to a half sine shock. The emphasis is focused on analyzing the vibration response of the optical fibers inside the coupler and examining the influence of various coupler parameters on the vibration of the optical fibers, since their dynamic behavior is a critical factor in optical fiber communications. A simplified model of the optical fiber coupler is proposed, which consists of a beam and a string representing the substrate and the bundle of the optical fibers of the coupler, respectively. The beam and the string are bonded at four points using adhesive material, and therefore the boundary conditions for their equations of motion are coupled, which increases the complexity of the problem. For the string, two models are developed— the linear model assumes that the tension in the string is constant, while the non-linear one takes into account large transverse deflection and tension variation. With each model, both analytical study and numerical simulations for the vibration of the system under a half shock are carried out. Furthermore, numerical results are compared between the two models. Finally, parametric study leads to conclusions which are of practical importance to the design of optical fiber couplers.     

新型1×4塑料光纤功率耦合器的研制

提出了一种新型的塑料光纤功率耦合器 ,该耦合器与传统的拉锥型和混合棒塑料光纤耦合器不同。理论分析了它的损耗特性。该耦合器基于塑料光纤本身的热特性 ,分别将塑料光纤进行拉锥和热缩构成耦合器的两端 ,结构简单 ,制作容易 ,实验结果表明其性能也可满足塑料光纤短距离通信网的要求     

基于少模光纤的全光纤熔融模式选择耦合器的设计及实验研究

提出了三种基于少模光纤的全光纤熔融模式选择耦合器. 根据模式匹配原理采用单模光纤与少模光纤熔融连接方式, 运用耦合模理论及光束传播法模拟分析了模式选择耦合器的结构参数对模式选择及耦合特性的影响, 实现了单模光纤中基模到少模光纤中不同阶模式的转换, 以满足不同的应用需求. 实验上以2× 2熔融光纤耦合器为例, 采用对称和非对称熔融拉锥方式, 分别实现了从基模到LP₁₁, LP₂₁模式的转换. 实验结果表明所得到的LP₁₁, LP₂₁模式在1530–1560 nm的波长带宽范围内均有较高的模式纯净度, 且模式耦合效率高于80%, 与理论模拟结果基本一致.     

Optical fiber coupler array for multi-point sound field measurements

A pressure-sensitive device using an optical fiber coupler is proposed, and is integrated into an array system to measure sound field distributions. The optical coupling between two optical fibers is modulated by the applied sound field with the use of a membrane mechanically connected to the coupler. In the array system, a large number of the optical coupler sensors are connected two-dimensionally, and sound pressure at each sensor can be read out by switching the input light sources in turn. A prototype of the basic array system based on this principle was made, and its performance was demonstrated. The signal discrimination between each element was confirmed in a 2x2 array; then, using a four-element linear array, we demonstrated the steering of beam based on the phased array method.     

Asymmetrical optical fibre coupler for laser side pumping: optimization of its parameters and application in laser

The paper presents an optical fibre coupler with side coupling. The coupler is based on an active double clad fibre and a pumping fibre with an extended core. The optimization of the coupler’s parameters and the initial simulations results are presented. The coupler was used in a ring laser setup and multiwavelength operation with up to 25 wavelengths was achieved.     

Choosing the ranges for measuring the reflectivity of a prism coupler in the waveguide spectroscopy of thin films

A criterion for selecting the best ranges for measuring the reflectivity of a prism coupler, based on minimizing the error in reconstructing the parameters of thin films using the least-square method, is proposed. The effectiveness of the criterion is demonstrated by solving the inverse optical problem for a SiO_x film deposited on a silicon substrate as an example.     

一种覆盖全通信波段的新型宽带偏振无关双芯光纤定向耦合器的研究

提出了一种新型的双芯光子晶体光纤, 应用全矢量有限元方法分析了光纤各种结构参数对光纤宽带特性和偏振无关特性的影响. 在此基础上优化设计了一种50:50的双芯光子晶体光纤耦合器, 在1.225—1.675 μm波长范围内实现分光比小于1%、两偏振态之间的分光比差小于0.5%的优良特性. 由于引入了仅对偏振特性影响明显的相对独立的中心调制区, 不仅降低了光纤的优化设计难度, 而且实现了与普通单模光纤相匹配的模场特性, 能有效地降低耦合器的接续损耗与制作难度. 研究成果为研制接续损耗低、超宽工作带宽、偏振不敏感等特性的新型光定向耦合器提供了理论基础.     

单谐振腔束团长度监测器耦合结构设计与仿真

单谐振腔束团长度监测器利用谐振腔内的两个本征模式测量ps量级的电子束团长度,它的关键是如何将两个不同频率的模式互不干扰地耦合提取出来。为解决这个问题,基于低通和带通滤波器的理论,提出了同轴滤波耦合结构和膜片加载波导滤波结构,借助CST微波工作室对滤波器进行建模并仿真得到其S参数。为测试耦合器的应用效果,设计了一套带有该耦合结构的单谐振腔束团长度监测器探头,根据国家同步辐射实验室基于可调谐红外激光的能源化学研究大型实验装置FELiChEM的束流特点,在CST内对所设计的探头进行束流模拟仿真。仿真结果表明,该耦合器可以实现对特定模式的耦合,并有效降低其它模式的干扰,采用同轴滤波耦合结构和膜片加载波导滤波结构的谐振腔监测器可以实现对FELiChEM装置束团长度的高精度测量,测量误差小于2 %。     

Measurement of fiber propagation constants using a prism-fiber coupler

We report on the use of a prism-fiber coupler to determine the propagation constants for the scalar modes in an optical fiber by measuring, respectively, the incident angle, θ_i, and the position of the m-lines coupled out of the fiber by the prism coupler. The position is related to the value of the corresponding propagation constant. The degeneracy of the modes is shown on the m-line photographs. Good agreement is obtained between measured and calculated values of the propagation constants.