Low-Loss Multimode-Interference-Based Crossings for Silicon Wire Waveguides

We report multimode-interference (MMI)-based crossings in high-index-contrast silicon wire waveguides. Our experiments show an MMI crossing of ${sim}$0.4-dB insertion loss, which suggests ${sim}$0.9-dB improvement from a control plain crossing of the same size and refractive index contrast. We also experimentally observe significant crosstalk suppression in our MMI crossing. The MMI crossing transmission exhibits wavelength dependence of less than 0.2 dB within the 1520–1580-nm wavelength range.      

可弯曲的低损耗太赫兹波导研究进展

近年来,随着太赫兹(THz)时域光谱系统的发展,THz波导作为用于THz波传输的器件一直都是研究的重点,而寻找低损耗的材料和可弯曲的结构一直是研究人员的目标。介绍了THz时域光谱系统的现状,并总结了传统波导技术应用于THz领域时的一些不足之处。重点介绍了基于三种不同工作原理的新型THz波导,并对比了各自的优缺点,这三种原理分别是金属面反射、介质界面全反射以及反共振反射。最后简要介绍了可弯曲低损耗THz波导的应用现状及后续工作方向。     

弯曲波导损耗的一种分析方法

用射线分析法,分析了折射率渐变弯曲波导损耗的实质。根据有效折射率的变型形式分析了影响弯曲波导损耗的主要因素,并计算了最小弯曲半径及其相对应的损耗。     

Low-Loss and Low-Birefringence High-Contrast Silicon-Oxynitride Waveguides for Optical Communication

Silicon-oxynitride waveguides fabricated by plasma-enhanced chemical vapor deposition are very attractive for passive optical components used in optical networks. We use a combination of an high-index contrast and compact core dimensions for the realization of small bending radii. To achieve the high quality requirements with the desired waveguide design the layer deposition and the waveguide fabrication are optimized. Furthermore, we discuss the interface of the high-index optical components to standard single-mode fiber (SSMF) and coupling tolerances, which is more difficult compared to common fiber-mode-matched wave guides. We show results of fabricated Mach-Zehnder interferometer-switches, tunable ring resonators and present a solution to reduce the waveguide birefringence by adjusting the mechanical stress of the cover layer.     

Low-Loss Surface-Mode Waveguides for Terahertz Si–SiGe Quantum Cascade Lasers

A new design of low-loss terahertz waveguide for Si-SiGe quantum-cascade lasers (QCLs) is presented. Periodic surface gratings are used to define waveguides without the requirement of cleaved or etched end facets. As Si cleaves along the (111) planes and not in the vertical direction for standard Si (100) substrates, this significantly aids the fabrication of waveguides. Losses down to 2 cm^-1 with modal overlap of 0.4 can be achieved for shallow gratings with etched depths of only 0.56 mum for an active material layer thickness of 8 mum. Such low loss and high modal overlap is key to any Si-SiGe QCL being realized     

低损耗SOI单模脊形光波导的制备

表面散射损耗与菲涅耳反射损耗是SOI(Silicon-on-msulator)脊形光波导的主要损耗机理.通过降低光波导损耗的研究,在厚膜SOI材料上制备了长度为20 mm,插入损耗小于2.15 dB的单模脊形光波导.     

SOI波导弯曲损耗影响因素的分析

采用有效折射率方法EIM(effectiveindex method)和二维束传播算法(2D-BPM)对SOI(silicon-on-insulator)波导弯曲损耗的几种影响因素进行了分析.通过模拟发现弯曲损耗随弯曲半径的增大、波导宽度的增加及内外脊高比的减小而减小.同时,改进波导结构,例如在弯曲波导外侧刻槽可以减小SOI脊形波导的弯曲损耗.     

SOI波导弯曲损耗影响因素的分析

采用有效折射率方法EIM(effectiveindex method)和二维束传播算法(2D-BPM)对SOI(silicon-on-insulator)波导弯曲损耗的几种影响因素进行了分析.通过模拟发现弯曲损耗随弯曲半径的增大、波导宽度的增加及内外脊高比的减小而减小.同时,改进波导结构,例如在弯曲波导外侧刻槽可以减小SOI脊形波导的弯曲损耗.     

低损耗高带宽金属光子晶体弯波导的设计

设计了一种采用金属材料的二维光子晶体波导.针对金属的色散特性,运用时域有限差分方法对3种二维结构的90°转弯波导的TM波传播特性进行了研究.给出了在合适的填充率下,转弯效率随周期变化的曲线.最后对其中较优的一种结构作了进一步优化,使其3 dB时的带宽达到了99 nm,目标波长处的转弯效率达到了98.2％.该结构的主要参...     

SOI波导弯曲损耗影响因素的分析

采用有效折射率方法EIM(effective index method)和二维束传播算法（2D-BPM）对SOI (silicon-on-insulator）波导弯曲损耗的几种影响因素进行了分析. 通过模拟发现弯曲损耗随弯曲半径的增大、波导宽度的增加及内外脊高比的减小而减小. 同时，改进波导结构，例如在弯曲波导外侧刻槽可以减小SOI脊形波导的弯曲损耗.     

Low-Loss Slow Light Transmission in Photonic Crystal Waveguides Comprising of Liquid Crystal Infiltration

A low loss photonic crystal(PhC) waveguide having rectangular air holes in Si core is proposed having an average group index of 55 in the bandwidth of 1.2 THz.The possible propagation losses due to inefficient coupling are also investigated for proposed structure.It is found that high transmission is obtained for a broad bandwidth from the output of the finally designed heterogeneous waveguide consisting of a slow liquid crystal infiltrated PhC waveguide surrounded by fast PhC waveguides on both sides.     

A Simple Numerical Method for Studying the Propagation Characteristics of Single-Mode Graded-Index Planar Optical Waveguides

A simple numerical method based on the Runge-Kutta method is presented to compute the propagation constant, the modal field, and the cutoff wavelength corresponding to the fundamental TE/sub 0/ and TM/sub 0/ modes of a planar optical waveguide with an arbitrary refractive index profile. The method is much simpler and requires less computational effort than the earlier reported numerical methods. We have also used the technique for an estimation of the effect of the /spl nabla/epsilon term in TM modes.     

Application of Inverted Strip Dielectric Waveguides for Measurement of the Dielectric Constant of Low-Loss Materials at Millimeter-Wave Frequencies

An entirely new method for measuring dielectric properties of slab-type materials is developed by using a novel dielectric waveguide structure originally designed for millimeter-wave integrated circuits. The method entails the measurement of the stopband of the grating structure created in the dielectric waveguide. Several examples of measurement results are reported.     

Multiple-Frequency Operation of Y-Junction Circulators Using Single-Mode Approximation

The conditions for a Y-junction circulator to operate within more than one frequency band are studied. By taking into account only the dominant resonance mode at each circulation frequency, explicit expressions are obtained which define the properties of the circulator. The results are presented in diagrams and tables which enable rapid evaluation of obtainable performance for some of the most important mode combinations. The validity of the results are experimentally verified.     

In-Plane Coupling of Light From InP-Based Photonic Crystal Band-Edge Lasers Into Single-Mode Waveguides

In this paper, we analyze the coupling of light from photonic-crystal band-edge lasers into single-mode waveguides. Both active and passive devices lie in the same plane and coupling of light is achieved by using parabolic and nanotapers in InP based epitaxial structures. Two- and three-dimensional finite-difference time-domain methods are employed to analyze these devices. Coupling efficiencies higher than 80% can be obtained with parabolic couplers. We also present laser configurations that can reduce multiwavelength coupling of light into single-mode waveguides, using structures that are similar to coupled cavity Fabry-Peacuterot lasers     

Design and Fabrication of Polymer Cross Fiber for Large-Core Single-Mode Operation

In this paper, we report the fabrication of a polymer segmented cladding fiber (SCF) that contains four high-index cladding segments, which is coined the “cross fiber.” In particular, we highlight the difficulties experienced in the fabrication process. We find that severe shear stresses at the interface between segments can be created and, as a result, the preform tends to shatter resulting in the formation of air bubbles during fiber drawing. The problem becomes more serious as the number of segments increases. Because the single-mode performance of a SCF depends only weakly on the number of the high-index cladding segments, to minimize the fabrication difficulty, it is sufficient to use a SCF with four segments, namely, a cross fiber, for the realization of large-core single-mode operation.      

Scalar Variational Analysis of Single-Mode Waveguides with Rectangular Cross Section (Short Papers)

We use the variational method to analyze single-mode optical waveguides with rectangular cross section. In particular, we propose a new trial field and show that it gives much better results and involves less computational effort as compared to other trial functions.     

To the Problem of Single-Mode Operation in Smith-Purcell FEM

Realization of an effective single-mode oscillator based on the stimulated emission of radiation by relativistic electrons moving along a periodically corrugated waveguide, is theoretically shown to be possible in the regime, when the corrugation period is much larger than the operating wavelength.