硅基脊型波导器件过渡区损耗及偏振效应

在绝缘层上的硅材料上制作了四种具有不同输入输出结构的星形耦合器并进行了测试,对脊形波导与平板波导相互过渡时过渡区的损耗问题进行了研究和讨论,计算得到在所使用的材料参量下利用锥形结构可以得到1dB左右的最小损耗,这一损耗是由于脊型波导与平板波导间的模式失配造成的。以文献中的实验数据为出发点,分析了脊形波导的偏振问题,并通过对脊型波导器件层厚度、脊高、脊宽进行优化设计,得到了不同偏振模式的有效折射率差仅为10^-5量级的单模脊型波导结构,这样的偏振效应在器件设计中可以忽略。     

Imaging errors in arrayed waveguide gratings

A detailed assessment of imaging errors in arrayed waveguide gratings (AWG) is presented, focussing on possible design related imaging errors as well as on typical imaging errors mediated by the fabrication process. From a design point of view, special interest is drawn to the effect of coupling within the array of grating waveguides and to the impact of the paraxial approximation for the star couplers which is commonly used in the design of AWGs. Both become important design issues affecting the performance of AWG devices when moving to high numbers of narrowly spaced channels. For the technology related imaging errors we focus on one side on the impact of almost uncorrelated phase errors at high spatial frequencies. They can typically be attributed to fluctuations in the index profile and waveguide dimensions in the grating region. On the other side correlated long range phase errors are treated which occur in the grating region as well as within the star couplers and which are typical for stress induced index changes in silica-on-silicon waveguides. It is shown that only modelling tools which include all types of the above imaging effects can provide reliable boundary conditions for a comprehensive design of high end AWG concerning spectral shape and chromatic dispersion.     

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.     

Grating couplers for thick SOI rib waveguides

The use of grating couplers in high index contrast waveguides like silicon on insulator (SOI) offers several advantages over other coupling approaches, including better alignment tolerances and allowing for wafer-scale testing. The grating couplers were developed for nanometric SOI waveguides (Si-wires), and recently also for micrometric rib waveguides. In this paper we review our work in fiber-to-chip grating couplers for thick SOI rib waveguides, where a coupling efficiency of ?2.2?dB was demonstrated experimentally. We also discuss the use of grating couplers to improve optical throughput (étendue) of a planar waveguide Fourier-Transform (FT) spectrometer implemented in thick rib waveguides.     

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.     

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。     

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.     

采用三维波束传输法的多模干涉耦合器成像位置的数值计算

多模干涉(MMI)耦合器需要精确定位成像位置,以便器件的设计制作。针对强限制和弱限制的三维多模波导干涉耦合器,采用三维交替方向隐式有限差分光束传输法(BPM),数值计算得出多模波导长度、输入波导和输出波导位置。首先通过对对称干涉多模干涉耦合器的数值分析求得多模干涉耦合器的等效宽度Weq及最低二阶模之间的拍长Lc,然后将这些参量结合光束传输法直接用于器件设计。计算显示该方法得到的成像位置和导模传输分析法(MPA)的理论预测比较接近,但Weq和Lc却是由光束传输法计算得到的,导模传输分析法理论只能在得到Weq和Lc的前提下才能得到成像位置。该方法直接针对三维波导进行,没有采用基于等效折射率方法的从三维波导到二维波导的简化处理,并且也没有采用导模传输分析法所采用的近似,保证了计算精度,对于实际多模干涉器件的设计制作可起参考作用。     

1×7锥形混合棒塑料光纤耦合器

利用光线追迹法进行数值仿真得到了锥形混合棒塑料光纤耦合器的分光比与其长度的关系.数值仿真表明:这种耦合器的分光比随锥形光波导长度增加,在0.143(即均分处)上下呈振荡型变化.选择一均分且分光比变化平缓的区域作为制作光波导的长度,通过拉伸粗的光波导棒成锥形且达到所需的长度,并采用精密的机械连接,制作出了1×7塑料光纤耦合器.测试数据表明:这种塑料光纤耦合器具有很高的均匀性.     

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.     

Modeling of circular integrated optical microresonators by 2-D frequency domain coupled mode theory

Circular integrated optical (ring or disk) microresonators are increasingly employed as compact and versatile wavelength filters. In this paper, we investigate a 2-D frequency domain model for these devices, based on spatial coupled mode theory. The microresonators are functionally represented in terms of two couplers with appropriate connections using bent and straight waveguides. The abstract scattering matrices of the couplers and the propagation constants of the cavity bends allow to compute the spectral responses of the resonators. Capitalizing on the availability of rigorous analytical modal solutions for bent waveguides, the constituent bent-straight waveguide couplers are modeled using a spatial coupled mode formalism derived by means of a variational principle. The resulting scattering matrices show reciprocity properties as expected according to the symmetry of the coupler structures. We present results for the spectral response and field examples for microresonators with mono- and multi-modal cavities for TE and TM polarizations. Comparisons with finite difference time domain simulations show very good overall agreement.     

Impressing technology of optical Bragg’s gratings on planar optical sol-gel waveguides

The aim of the presented investigations was to develop a technique of producing Bragg’s grating couplers on planar waveguides. Waveguides are obtained by means of the sol-gel technology. The introduction of a light beam into the structure of the waveguide is in the case of planar or strip optical systems always an essential technical problem, requiring simple and reproducible solutions without extending excessively the waveguide structure. The paper presents a technology of producing grating couplers by impressing the pattern of the network while forming the planar waveguide structure applying the sol-gel method. Some remarks concerning the sol-gel technology are also presented. The results of investigations on grating couplers obtained in such a way have been discussed, too. Attention has been drawn to the possibility of using such structures in optoelectronic sensors, particularly gas sensors, including sensors of water vapour as well as toxic gases.     

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.     

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.     

Negative index and indefinite media waveguide couplers

We study the coupling interaction between dielectric waveguides and coupling elements made from negative-refracting media. The coupling configuration consists of a length of dielectric waveguide, which terminates either directly into or near a planar layer composed of the negative-refracting medium, and is followed by a second waveguide. Radiation output from the first waveguide is refocused at the position of the second waveguide, so that the negative-refracting layer serves as a coupler between the waveguides. Because both isotropic negative-index layers and bilayers of indefinite media can recover the near-field, evanescent components of a source field distribution, the coupling between the input and output waveguides can be highly efficient – in principle providing perfect, lossless coupling. We present simulations and some initial experimental results illustrating the coupling effect, and speculate on the potential for optical fiber couplers and integrated modulators. PACS 42.79.Gn; 41.20.-q; 42.70.-a     

Directly laser-written integrated photonics devices including diffractive optical elements

Femtosecond laser-written integrated devices involving Fresnel Zone Plates (FZPs) and waveguide arrays are demonstrated as built-in optical couplers. These structures were fabricated in borosilicate glass using a direct laser writing technique. The optical properties of these integrated photonic structures were investigated using CW lasers and high-resolution CCDs. For a single FZP coupled to a single waveguide, the overall coupling efficiency was 9%. A multiplexed optical coupler composed of three FZP layers was demonstrated to couple three waveguides simultaneously in a waveguide array. Structures of this type can be used as platforms for multichannel waveguide coupling elements or as microfluidic sensors that require higher light collecting efficiency.     

Design for broadband high-efficiency grating couplers

In this Letter, we propose general optimization methods to design broadband high-efficiency grating couplers for planar waveguides. We attribute the coupling bandwidth to the mismatch of effective indices between the diffracted beam and the actual grating structure around the operation wavelength for fiber to waveguide excitation. The coupling bandwidth formula is deduced. A simple parameter-separate optimization procedure is proposed for general layered grating couplers for high coupling efficiency. Using our principle, we optimized a grating coupler for a horizontal slot waveguide operating at wavelength 1.55 μm for TM polarization. The grating coupler has 1 dB bandwidth of 60 nm and coupling efficiency of 65% with incident light from single-mode optical fiber (SMF) at 8°.     

Metal-dielectric-metal plasmonic waveguide devices for manipulating light at the nanoscale Invited Paper

We review some of the recent advances in the development of subwavelength plasmonic devices for ma- nipulating light at the nanoscale, drawing examples from our own work in metal-dielectric-metal (MDM) plasmonic waveguide devices. We introduce bends, splitters, and mode converters for MDM waveguides with no additional loss. We also demonstrate that optical gain provides a mechanism for on/off switch- ing in MDM plasmonie waveguides. Highly efficient compact couplers between dielectric waveguides and MDM waveguides are also introduced.     

Numerical analyses of optical couplers for planar waveguides

The paper presents the results of numerical analyses of optical structures realized in the form of planar waveguides made of materials with high values of the refractive index n ??1.85. The analysed structures consist of a waveguide and input-output systems. Input-output couplers are realized in the form of prisms as well as Bragg??s grating couplers. Numerical investigations were carried out by applying the finite difference time domain (FDTD) method.     

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.