弯曲波导之间的耦合分析

采用极坐标下的光束传播法分析了两条平行变曲波导的中心间距、曲率半径等因素对模式耦合的影响,得到了耦合长度、耦合强度随中心间距、曲率半径的变化规律,并将直波导作为变曲波导的一种特殊情况进行了分析.     

Coupling methods in prospective single-mode fiber integrated optics systems: A progress report

A review of the research progress on the coupling of fibers to fibers, fibers to thin-film waveguides, and thin-film waveguides to thin-film waveguides is presented here. In general, the direct excitation method is preferred for the coupling of two fibers, with efficiency larger than 90%. The direct excitation method is also preferred for the coupling of two thin-film waveguides and thin-film waveguides to fibers where the two component waveguides have vastly different refractive indices. The coupling efficiency depends on matching the field pattern of component waveguides. The laser source to fiber launching is done mostly by direct excitation. The evanescent field coupling method is preferred for the coupling of two thin-film waveguides that have close refractive index profiles, with efficiency larger than 70%.     

Guiding of a one-dimensional optical beam with nanometer diameter

The concept of a one-dimensional optical wave and its waveguides are proposed for what is to our knowledge the first time. The proposed waveguides are principally new and named for one-dimensional optical waveguides. One-dimensional optical waveguides make it possible to guide very thin optical beams in the visible or the near-infrared region with a diameter in the nanometer range. The propagation properties are analyzed theoretically. The applications of the waveguides to optical devices in the nanometer range are discussed.     

平面光波导用于实时测试生化反应新方法的研究

在分析经典消逝波光波导生化传感器的基础上,为寻找性能更佳的传感器,探讨用更为直观的截止特性来进行生化传感。分别对三层及四层平板波导进行了研究,指出了作为基于截止特性的生化传感器三层波导结构存在的局限性。在理论上研究了可以在四层波导中使用变折射率材料来进行基于截止特性的生化传感,并给出了由空气隙、极化聚合物、高折射率薄膜、待测物组成的传感器结构示意图。用数值分析的方法绘出了此装置的灵敏度与高折射率薄膜厚度的关系曲线,并将它同经典消逝波光波导生化传感器灵敏度与薄膜厚度关系图进行了比较。结果表明,这种新型传感器理论上可以在较厚的薄膜结构中达到很高的灵敏度。     

Optical loss measurements in femtosecond laser written waveguides in glass

The optical loss is an important parameter for waveguides used in integrated optics. We measured the optical loss in waveguides written in silicate glass slides with high repetition-rate (MHz) femtosecond laser pulses. The average transmission loss of straight waveguides is about 0.3 dB/mm at a wavelength of 633 nm and 0.05 dB/mm at a wavelength of 1.55 μm. The loss is not polarization dependent and the waveguides allow a minimum bending radius of 36 mm without additional loss. The average numerical aperture of the waveguides is 0.065 at a wavelength of 633 nm and 0.045 at a wavelength of 1.55 μm. In straight waveguides more than 90% of the transmission loss is due to scattering.     

小尺寸低折射率差硅基二氧化硅阵列波导光栅

随着AWG型器件在光通信系统中的大规模应用,对低成本AWG芯片的需求越来越多。在各种降成本方案中,减小AWG芯片的尺寸是最有效的方法之一。本文介绍了一种新型小尺寸低折射率差硅基二氧化硅阵列波导光栅（AWG）的设计。在该AWG中,输入波导/输出波导与平板波导连接的部分制作成两侧为空气槽的高折射率差波导,所以在与输出平板波导连接处的相邻输出波导间距较小,这样可以在设计上缩短平板波导的长度、减少阵列波导的数量,实现较小的AWG芯片尺寸。该AWG的其它部分,如输入/输出波导与光纤耦合的部分、阵列波导光栅等均采用常规的低折射率波导工艺,所以就同时具有与常规的低折射率波导AWG相同的优点：如低耦合损耗、较好的串扰以及光学特性等。根据这个原理,设计了一种40通道100 GHz频率间隔的低折射率差硅基二氧化硅AWG,其芯片尺寸只有23.88 mm?10.5 mm,是传统相同材料制作的AWG尺寸的1/6。     

Reducing crosstalk between nanowire-based hybrid plasmonic waveguides

Hybrid plasmonic waveguides based on a surface oxidized dielectric nanowire placed on a metal surface can facilitate simultaneously deep subwavelength mode confinement and large propagation length. Directional coupling based on such waveguides are theoretically investigated. Much lower crosstalk is noticed for such hybrid plasmonic waveguides compared to conventional waveguides based on bare dielectric nanowires. Some modifications, such as vertically placing the metal surfaces or using a metallic block between the nanowires, are studied which can further reduce the crosstalk between two waveguides. The proposed low crosstalk structures based on hybrid plasmonic waveguides can provide a simple platform for plasmonic integration which can at the same time easily interface with traditional photonic circuits.     

New method for calculating the spectra and radiation losses of leaky waves in multilayer optical waveguides

The efficiency of a new method for calculating the spectrum and attenuation coefficient of leaky electromagnetic modes is demonstrated with multilayer planar optical waveguides the guiding properties of which are determined by antiresonant reflection from the multilayer cladding (antiresonant reflecting optical waveguides) rather than by total internal reflection from the core-cladding interface as in standard optical waveguides. The new method applies to calculation of both electromagnetic modes in dielectric waveguides and electron quantum states in multibarrier semiconductor heterostructures. The characteristics of multilayer waveguides calculated by the new method are compared with published data obtained from a complex dispersion relation by the transfer matrix method. As an example, the wavelength dependence of the radiation losses for the first TE mode of a planar optical waveguide containing 52 pairs of layers is calculated.     

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.     

Mode propagation in curved waveguides and scattering by inhomogeneities: application to the elastodynamics of helical structures

This paper reports on an investigation into the propagation of guided modes in curved waveguides and their scattering by inhomogeneities. In a general framework, the existence of propagation modes traveling in curved waveguides is discussed. The concept of translational invariance, intuitively used for the analysis of straight waveguides, is highlighted for curvilinear coordinate systems. Provided that the cross-section shape and medium properties do not vary along the waveguide axis, it is shown that a sufficient condition for invariance is the independence on the axial coordinate of the metric tensor. Such a condition is indeed checked by helical coordinate systems. This study then focuses on the elastodynamics of helical waveguides. Given the difficulty in achieving analytical solutions, a purely numerical approach is chosen based on the so-called semi-analytical finite element method. This method allows the computation of eigenmodes propagating in infinite waveguides. For the investigation of modal scattering by inhomogeneities, a hybrid finite element method is developed for curved waveguides. The technique consists in applying modal expansions at cross-section boundaries of the finite element model, yielding transparent boundary conditions. The final part of this paper deals with scattering results obtained in free-end helical waveguides. Two validation tests are also performed.     

A search-and-track algorithm for controlling the number of guided modes of planar optical waveguides with arbitrary refractive index profiles

A search-and-track algorithm is proposed for controlling the number of guided modes of planar optical waveguides with arbitrary refractive index profiles. The algorithm starts with an initial guess point in the parameter space that supports a specific number of guided modes. Then, it searches for, and tracks, the boundaries of this space or another space supporting different number of modes. It does so by monitoring the sign of a unified cutoff dispersion function. The algorithm is applied to both symmetric and asymmetric silicon-based parabolic-index waveguides. It shows that unlike asymmetric waveguides, the single-mode condition of symmetric waveguides is controlled by TM-, as opposed to TE-, polarization. This abnormal polarization control is strongest for high index contrast waveguides of sub-micrometer core sizes. The results are verified by full-vectorial beam propagation method.     

Determination of the attenuation of planar waveguides by means of detecting scattered light

Due to the variety of waveguides in planar structures, the measurements of attenuation are characterized by a considerable variety of applied methods, developed for given type of waveguides. The method of measuring scattered light is, therefore, of much importance in the case of waveguides with a rather high attenuation, because it is an exceptionally fast and simple method, which is doubtlessly the effect of the development of numerical detection systems. The paper presents the process of measurements basing on scattered light, combined with an analysis of its application, as well exemplary results concerning the planar structures of waveguides achieved by means of ion exchange on soda-lime glass.     

Plasmonic splitter based on the metal-insulator-metal waveguide with periodic grooves

In this paper, we have proposed a plasmonic splitter which is composed of a subwavelength slit and two different metal-insulator-metal (MIM) waveguides with periodic grooves. The slit is used to excite surface plasmon polaritons (SPPs) at certain wavelengths. By setting the SPPs resonance wavelengths of the slit as the Bragg wavelengths of MIM waveguides, the SPPs of different wavelengths are able to be confined and guided in the two different MIM waveguides. The numerical results of two-dimensional finite difference time domain (2D-FDTD) demonstrate that our proposed structure is capable of splitting light into two MIM waveguides.     

An Extension of the Effective Index Method to Analyze Leakage Losses in Rib Type Waveguides

An extension of the effective index method is proposed as a tool to investigate leakage losses in two-dimensional waveguides. The above method, referred to as the Extended Effective Index Method (EEIM), utilizes the Transfer Matrix Technique (TMT) for the calculation of the complex propagation constants. The results show that the EEIM can be applied to conventional rib leaky waveguides as well as to rib ARROW leaky waveguides. The results for rib ARROW waveguides show excellent agreement when compared to those obtained with Finite Element Method.     

BK7玻璃保护层掺钕磷酸盐玻璃波导特性

实验研究了基于KNO3稀释AgNO3混合熔盐离子交换法制备的镀有BK7玻璃保护层的N31型掺钕磷酸玻璃平面波导。采用棱镜耦合技术测试了其波导的有效折射率,应用IWBK方法拟合了其折射率分布。实验结果表明:在一定的扩散时间(5～7h)和交换温度(360～380℃)范围内,KNO3与AgNO3混合熔盐比对波导制备的影响起主导作用,引起的表面折射率的变化可达到0.025;BK7玻璃保护层对热离子交换掺钕磷酸盐玻璃表面起到了很好的保护作用,获得了良好的导模传输特性,其光传输损耗约为0.9dB/cm。     

Polymer waveguides from alicyclic methacrylate copolymer fabricated by deep-UV exposure

We have investigated the fabrication of waveguides from alicyclic methacrylate copolymer based on refractive-index modification by deep-UV exposure. By optimizing the UV-exposure process, we were able to obtain single-mode waveguides with a propagation loss of 0.8 dB/cm at 1550 nm, which is due only to material losses in this wavelength range. The loss obtained here is comparable with that of poly(methyl methacrylate) (PMMA) waveguides fabricated by deep-UV exposure. The fabricated waveguide is also single mode at 808 nm, and its propagation loss is 0.6 dB/cm. This alicyclic methacrylate copolymer is a promising material for the fabrication of polymer waveguides by use of deep-UV exposure.     

扩散平面光波导的传递函数方法

引入一种计算光波导传播特性的新方法传递函数方法。给出了公式推导,计算了扩散各向同性及扩散各向异性平面光波导的传播特性,并与其它方法所得结果进行了比较。结果表明用传递函数方法处理折射率渐变分布的光波导问题,计算相对简单,可以得到精确的数值结果。     

PDL free plasma enhanced chemical vapor deposition SiC optical waveguides and devices

Planar silicon carbide (SiC) waveguides are proposed for fabrication on a silicon substrate with an oxide isolation layer. Using post deposition annealing it is possible to achieve low polarisation-dependent loss (PDL) within optical SiC waveguides fabricated using a low temperature deposition technique. The proposed waveguides are optically characterised and successfully used in power splitters and vibration sensors. Results before and after annealing cycles for those devices are discussed. The interesting optical characteristics of SiC waveguides as well as the first passive components presented open the way for photonic sensing in harsh environment where SiC is a very promising material.     

制备多模聚硅氧烷光波导关键技术的改进

本文利用浇铸法,使用M&N胶和OE6450两种聚硅氧烷制备光波导.通过改进制备光波导的多个关键技术, 解决了波导制备过程中的气泡问题、脱模问题、芯层不固化问题、芯层和覆盖层产生化学反应等难题,提出了 比较完备和科学的聚硅氧烷波导制备工艺流程,从而使得波导的制备成品率从原来低于40%提高到高于80%, 波导的最大长度从原来的21 cm增加到22.5 cm,波导的损耗(截断法测量结果)从最初的0.3dB/cm(850 nm)降低到了 0.21dB/cm(850nm).本文在波导制备技术方面具有重要的实际意义和价值.     

Propagation of a focused light beam in a circuital system of tunnel-coupled waveguides

The propagation of a pencil beam in a circuital system of tunnel-coupled waveguides is considered. It is shown that the beam periodically focuses into a point when moving along the trajectory. A maximal number of waveguides supporting the propagation of the beam can be estimated in simple terms. The cross-sectional area of the waveguides can be subdivided into three zone with the beam pulsing only in the central one.