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.     

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.     

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.     

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     

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.     

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.     

Coupling coefficients evaluation of a directional coupler using gain guided and index antiguided fibers

In this paper, we have investigated the mutual and self coupling characteristics of directional couplers using two individual gain guided and index antiguided fibers, which can deliver robust single mode operation with large mode area, respectively owing to the combined adequately large gain coefficients in the core; Some interesting and distinguishing properties from conventional index guided fiber couplers are obtained that: The variations of coupling coefficients are complex-valued and spatially damping oscillated, but not exponential-like decreasing as conventional index guided couplers.     

圆波导定向耦合器在高功率微波测量中的应用

介绍了大功率容量定向耦合器的设计、标定、测试与应用情况。以X波段圆波导定向耦合器为例,在9.2~10.2 GHz的频带范围内,基于小孔耦合理论优化设计的结构,其耦合度可以稳定在(55±2)dB以内,隔离度大于80 dB。在此基础上,设计加工了X波段圆波导定向耦合器并进行了标定测试,测试与仿真结果吻合较好,高功率微波实验证实了其具有较高功率容量,能够满足实验需求。该类圆波导定向耦合器已广泛应用于实验室高功率微波源的在线测量装置中。     

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。     

Effect of wall tilt on the optical properties of integrated directional couplers

The effect of wall tilt on the performance of directional couplers has been studied. There is a significant reduction in the coupling length as the tilt decreases when nonvertical walls, which are inherent in nearly all clean-room waveguide fabrication processes, are considered. Comparison of 90 degrees and 45 degrees coupling lengths reveals a difference of nearly a factor of 2 between them. Experimental data obtained with antiresonant reflecting optical waveguide directional couplers confirm that tilt effects should be considered in any device with large core thickness.     

Gain-induced soliton switching in fiber nonlinear directional coupler

With study for switching characteristics and output coupling ratio of fiber nonlinear directional couplers (NLDC), we found that the influence elements on the switching characteristics and output coupling ratio had gain of core 1 and 2, nonlinear coefficient of those, the input power and width of input soliton. We also found numerically that switching efficiencies were improved by controlling gain of core 1, different output coupling ratio would be obtained by controlling gain of core 1 or 2. And we can change the gain by changing pump power of the optical fiber amplifiers. From this, we also made fiber coupler which output coupling ratio was changeable.     

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.     

Crosstalks of two-waveguide and three-waveguide directional couplers

Crosstalks of two-waveguide and three-waveguide directional couplers are analyzed mathematically based on the relationship between the coupled mode and the normal mode. Numerical techniques such as the finite-difference method and the beam propagation method are employed to confirm the validity of the derived expressions. The calculation results show that two-waveguide directional coupler is superior to any type of three-waveguide couplers from the practical viewpoint of the crosstalk and the coupling length.     

一种全光纤型窄带梳状滤波器的特性分析

分析了由双光纤定向耦合器组成的梳状滤波器的透射特性。根据传输矩阵,推导出了该滤波器的输出光谱与有关参数之间的关系式。分析结果表明:该滤波器具有法布里_珀罗腔多光束干涉的特点,是一种窄带宽梳状滤波器;耦合器的耦合系数与法布里_珀罗腔中的反射率类似,通过控制耦合系数可以调节滤波器的通带半宽度、消光比、隔离度、输出光强等。     

熔锥型光纤耦合器宽带特性研究

报道了在常规熔锥型单模光纤定向耦合器工艺基础上，以氢氟酸腐蚀法，将两光纤耦合区直径腐蚀成适当比例，用水平直接熔融拉锥系统，将耦合区域拉制成非对称臂组合波导，从而获得了具有宽频带特性、且尺寸较小的单模光纤定向耦合器，实验结果说明：通过控制耦合区长度，可以使耦合器耦合功率在某个特定波长附近、预定小于１００％分束比上具有相当平坦（宽带）特性；从而，通过控制组合波导的不同直径比，可望得到不同分束比宽带耦合     

双芯光子晶体光纤宽带定向耦合器研究

利用半矢量有限差分法设计了具有低折射率双芯的光子晶体光纤宽带定向耦合器,并数值计算了双芯光子晶体光纤的结构参量对耦合性能的影响.数值结果表明,通过优化选取光子晶体光纤包层结构参量和纤芯掺杂浓度,双芯光子晶体光纤耦合器可以实现宽带耦合.在1.22~1.65 μm 波长范围内其耦合长度稳定在26637 nm±235 nm范围内,耦合器设计成耦合比为50%和10%,分别实现了耦合比为（50±0.702）%和（10±0.664）%的良好特性.     

Directional coupling of optical signals by odd dark beams with mixed phase dislocations

Numerical simulations on the evolution of step-screw and edge-screw optical phase dislocations in bulk saturable self-defocusing nonlinear media are presented, with emphasis on their ability to induce steering waveguides for signal beams (pulses). Two schemes for directional coupling of such signals, both ensuring a reasonable coupling-to-cross-talk efficiency ratio, are investigated. The parameters useful for performance optimization of the couplers are discussed. Received: 19 July 2000 / Revised version: 5 February 2001 / Published online: 27 April 2001     

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.     

Image guide couplers used in millimeter wave integrated circuits

The dispersion and coupling characteristics of the coupled image guides are studied by using the odd-even mode principle and effective dielectric constant method. The practical design of the image guide directional couplers is presented. The experiments of 3-dB and 10-dB couplers in ka band show several good features which are very useful to millimeter wave integrated circuits with flat coupling, easy design and fabrication, mechanical stability and low losses.     

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.