Semi-Analytical Simulation of Titanium-Indiffused Lithium Niobate-Integrated Optic Directional Couplers Consisting of Curved Waveguides

Integrated optic directional couplers consisting of curved waveguides are simulated analytically by solving the Riccati equation. The coupling coefficient between the curved waveguides with a parabolically varying gap and the condition of total power transfer between the waveguides are derived. In order to compute the overall coupling coefficient and hence the power distribution along the waveguides for Ti:LiNbO₃ curved waveguide directional couplers, the coupling coefficient for straight waveguide couplers is computed for different gaps using the effective-index-based matrix method (EIMM). Finally, the power distribution in the curved waveguides along the length is computed. The method is mostly analytical except the effective-index method and is computationally simple.     

Semi-Analytical Simulation of Titanium-Indiffused Lithium Niobate–Integrated Optic Directional Couplers Consisting of Curved Waveguides

Integrated optic directional couplers consisting of curved waveguides are simulated analytically by solving the Riccati equation. The coupling coefficient between the curved waveguides with a parabolically varying gap and the condition of total power transfer between the waveguides are derived. In order to compute the overall coupling coefficient and hence the power distribution along the waveguides for Ti:LiNbO ₃ curved waveguide directional couplers, the coupling coefficient for straight waveguide couplers is computed for different gaps using the effective-index-based matrix method (EIMM). Finally, the power distribution in the curved waveguides along the length is computed. The method is mostly analytical except the effective-index method and is computationally simple.     

基于光子晶体波导定向耦合的光子晶体分/合频器

在完整二维光子晶体中引入线缺陷后,就形成了光子晶体波导。将时域有限差分法(FDTD)和平面波法作为光子晶体理论研究的工具。研究结果表明,光子晶体波导之间的耦合遵循普通介质波导耦合的一般规律,有定向耦合的功能;将两个具有不同耦合长度的光子晶体波导定向耦合器顺序集成在一起,可以组成一个三波长的光子晶体分/合频器。     

Effective index method for planar lightwave circuits containing directional couplers

A simple and intuitive effective index method for planar lightwave circuits containing directional couplers is proposed. The optimal cladding refractive index of the effective two-dimensional planar waveguide is found according to the coupling length of the directional coupler involved. Numerical examples indicate that this proposed effective index method gives accurate results while saving significant computation time in simulation and design of planar lightwave circuits containing directional couplers.     

BPM Simulation and Comparison of 1 × 2 Directional Waveguide Coupling and Y-Junction Coupling Silicon-on-Insulator Optical Couplers

For developing large area opto-electronic silicon-on-insulator (SOI) devices, the optical coupler is a basic key device. In this article, the authors design and simulate 1 2 2 directional waveguide coupling and Y-branch coupling optical couplers based on Unibond SOI rib waveguides. The beam propagation method (BPM) is used for light propagation analysis. The simulation results and comparisons of the two kinds of optical couplers are reported. The S-bend waveguide for attaching to the two kinds of SOI optical coupler is also analyzed by BPM. We find that the directional coupler has lower power loss, but the Y-junction coupler is more wavelength insensitive with the same device size and splitting angle. The fabrication tolerance analysis shows Y-junction coupler has better fabrication characteristics.     

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.     

变耦合系数非线性三波导定向耦合器特性研究

报道了对高斯型及指数型变耦合系数三波导耦合器的一些重要的全光开关特性进行的研究。利用四阶龙格一库塔方法对指数型和高斯型两类变耦合系数三波导耦合器进行了数值计算。数值计算结果表明：对于变耦合系数三波导耦合器而言,功率可在波导1与波导3之间100％转换,而波导2则不可能达到100％的功率输出。与双波导变耦合系数耦合器相比,在相同的最大耦合系数情况下三波导变耦合系数耦合器开关曲线要更陡一些．即具有更好的开关特性。与平行三波导耦合器相比,变耦合系数三波导耦合器作为光开关的最大优点在于开关曲线中不存在振荡。     

Image guide couplers with isotropic and anisotropic coupling elements

Among other waveguide elements directional couplers are required in integrated millimeterwave circuits in image guide technique. Hereby an I-guide is used which consists of a dielectric slab between two conducting plates on which the electric field is perpendicularily. Flat coupling behaviour and better isolation can be reached by use of a dielectric coupling element and absorber materials. Thereby the frequency dependence is reduced significantly. Further the coupling can be steered by an additional premagnetized ferrite slab. In this way switched couplers can be realized.     

仅有相邻波导耦合的定向耦合器的一般解法

应用切比雪夫多项式 ,求得了仅有相邻波导耦合的 (N +1)× (N +1)定向耦合器在弱耦合、无损耗和忽略正交偏振模场分量间耦合的情形下波导耦合方程的通解。列出线形排列 2× 2 ,3× 3,4× 4定向耦合器的解的表达式 ,并对环形排列 3× 3定向耦合器的解作了较详细的分析     

梯形截面硅基水平多槽纳米线定向耦合器全矢量分析

定向耦合器是构成各类光子器件的基础元件. 本文采用一种基于电场分量的全矢量有限元法, 分析由梯形截面硅基水平多槽纳米线构成的定向耦合器. 给出了准TE与准TM偶、奇模有效折射率、耦合长度及模场分布, 揭示了其模式的混合特性及模场分布特点. 分析结果表明, 准TE模与准TM模的耦合长度随波导间距的增大均呈指数增长, 其中准TE模的耦合长度对波导侧壁倾角的变化敏感, 而准TM模的耦合长度对槽厚及槽折射率的变化敏感. 恰当选择结构与材料参数, 可实现两偏振态下相同耦合长度, 定向耦合器在偏振无关条件下工作.     

Coupling characteristics of a three channel waveguide directional coupler

We develop an accurate analysis for a three channel waveguide directional coupler which takes the effect of corner regions into account through the first order perturbation theory. The applicability of the earlier approaches namely (i) effective-index method (ii) planar waveguide approximation for such couplers has also been discussed. It is found that while the effective-index approach used by earlier authors underestimates the coupling length, the planar waveguide approximation overestimates the same.     

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.     

Theoretical and experimental research on nonradiative dielectric waveguide directional couplers

A practical design of nonradiative dielectric (NRD) waveguide directional couplers is presented. The dispersion characteristics of coupled NRD-guides and the scattering coefficients of NRD-guide directional couplers are studied as well as the transitions from metal rectangular wave-guide to NRD-guide couplers. Experiments of 3-dB and 10-dB NRD-guide couplers in ka-band show that the couplers are of good performance and promise in millimeter-wave integrated circuits.     

Single and multi-section CTL and branch-line CPW directional couplers with broadband performances for SIMMWIC

Single and multisection branch-line and coupled transmission line (CTL) directional couplers have been implemented in coplanar waveguide (CPW)-technology, showing broadband performances. The branch-line and CTL couplers had a phase balance of ±5° and a power variation of 1.5 dB in the coupling over a bandwidth of greater than 25% and 75% respectively. The experimental values for the couplers were found to agree well with simulated results. The CPW couplers provide larger bandwidth than comparable microstrip couplers. Investigation on different feeding structure for the branch-line couplers is also presented.     

Implementation of photomasks for guided wave optical components by a step-and-repeat process

The fabrication of photomasks for integrated optical (i.o.) components presents the particular difficulty of an extreme aspect ratio. It is shown that this problem can often be solved by a synthesizing procedure using a photorepeater. This method is demonstrated for two different versions of i.o. directional couplers (total length 20 mm, width of waveguides 3 μ, width of coupling gap between waveguides 3 μ). Single characteristic parts of the masks, which are composed on the reticle, are joined together by a step-and-repeat process. Residual imperfections of junctions can be neglected for diffused waveguides. Further advantages of the method (constant width of the waveguide and of the separating gap along the total length) are explained. Finally, the i.o. directional couplers produced are examined, and some of their characteristic parameters are described.     

Graphical Representation of the Supermode Theory of a Waveguide Directional Coupler

A novel graphical representation of the supermode theory of a waveguide directional coupler based on phasor analysis is described. Following this approach, dependence of the magnitudes and phases of the output fields on the splitting ratio of a directional coupler is discussed. Both the cases of phase-matched (identical) and non-phase-matched (non-identical) waveguides constituting a directional coupler are investigated. This approach directly illustrates the fact that the phase shift suffered by the coupled light relative to the throughput light is π/2, regardless of the splitting ratio for identical guides, which is not the case for couplers with non-identical waveguides. It also yields additional information about the phases of the output fields of a directional coupler. The usefulness of this approach in the context of wavelength-flattened couplers, wavelength division multiplexing couplers, and polarization effects in directional couplers is also discussed. This approach should also be helpful in the analysis of guided wave interferometric devices such as wavelength interleave filters and modulators, based on concatenated directional couplers.     

Analysis of rectangular-core waveguide structures and directional couplers by an iterated moment method

Using an iterated moment method (weighted index method), formulae are derived for the accurate calculation of the dispersion characteristics and field distributions of guided modes in strip dielectric waveguides and strip-loaded waveguides, and for the calculation of the coupling length of rectangular-core dual-channel directional couplers. The formulae are simple and the results obtained by the present analysis agree well with computer-aided exact numerical analysis. This method can be readily extended to the analysis of other dielectric waveguide structures.     

Analyze and calculation of coupling coefficient based on evanescence field for plasmonic directional coupler structure

We obtain the calculation of coupling coefficient of plasmonic directional coupler made up of two monolayer waveguides separated in the range of 200 nm for TM mode and we assume each waveguides acts as a perturbation to other waveguide but does not affect the waveguide mode. We simulation the transfer distance respect to normalized frequency in two directions, x and z, values transfer distance a limitation of a bandwidth is suitable for designing of integrated optical circuits and construction of couplers and switches.     

Circuit-oriented modelling of ring-resonators

In this work we propose a circuit-based analysis of both a ring phase shifter and a single ring filter, taking into account the effects of imperfections in the directional couplers and polarization conversion in bent waveguides. New models for the directional coupler and for the bent waveguide are proposed and used to find an analytical expression of the transfer functions of ring based devices. The numerical results obtained with the new models show that defects in directional couplers and polarization conversion in bent waveguides are responsible of spectral impairments often observed experimentally, confirming the validity of the model.     

常用微波衰减器脉冲功率容量测试

提出了一种微波衰减器脉冲功率容量的测试方法,该方法可概括为利用定向耦合器组测试比对法,测试系统主要由微波源、定向耦合器组、衰减器、检波器及示波器等器件及设备组成。选取了广泛应用于高功率微波测试系统的波导衰减器及同轴衰减器进行了功率容量测试。初步测试结果表明:在X波段,对于μs量级脉冲宽度的单脉冲,衰减材料为羟基铁的BJ-100矩形波导式衰减器的脉冲功率容量可达50 kW,厚膜电阻为衰减材料的N型接头的同轴式衰减器的功率容量可达10 kW以上。