第34卷第1期 2015年3月 中南民族大学学报(自然科学版) Joumal of South-Central University for Nationalities(Nat.Sci.Edition) Vo1.34 No.1 Mar.20l5 Wideband Dual Polarizations Silicon Single Mode Slot Waveguide Hou Jin,Li Boya,Wang Linzhi, Chunyong ,Zhong Zhiyou,Chen Shaoping (Hubei Key Laboratory of Intelligent Wireless Communications,College of Electronics and Information Engineering,South—Central University for Nationalities,Wuhan 430074,China) Abstract Wideband dual polarizations single mode characteristics of silicon slot waveguide is investigated by three dimensional plane—wave expansion method and three dimensional finite difference time domain method.By tuning the width of the surrounding silicon region of the slot waveguides,320.6 nm wide bandwidth for both quasi—TE and quasi—TM modes can be obtained in all optimized structure,and electic frield enhanced in the low index slot zone for quasi—TE fundamentl amodes is also observed for the whole bandwidth.The investigation proposed in this paper would be served as a basis for designing polarization related silicon photonics devices. Keywords wideband;polarization;slot waveguide 中图分类号TN252;TN012文献标识码A文章编号1672-4321(2015)01-0079-04 硅基宽带双偏振单模狭缝波导 侯金,李博雅,王林枝,杨春勇,钟志有,陈少平 (中南民族大学电子信息工程学院,智能无线通信湖北省重点实验室,武汉430074) 摘要采用三维平面波法和三维有限时域差分法,研究了硅基单模狭缝波导的双偏振特性.通过调节狭缝波导 中硅介质的宽度,获得了宽达320.6 nm的双偏振带宽;并且发现在该带宽范围内,准TE模式的电场强度在狭缝中 均具有增强效果,并且狭缝中光因子均大于60%.该研究结果可为设计其他与偏振相关的硅光子器件提供 参考. 关键词宽带;偏振;狭缝波导 characteristics are needed[ , Although great research Silicon photonics built on a silicon—on—insulator(SOI) platform has enabled US to fabricate ultracompact optical waveguides and optical components ljRecently,a new kind of ..progresses associated with bandwidth and polarization have been achieved in devices based on conventional stip waveguide 7r J and photonic crystal waveguide[10' .silicon waveguide,silicon slot waveguide,which can confine and enhance light in a low—index slot,has attracted great attentions[ ' .due to the large polarization divergence in the slot waveguides,only few devices based on slot waveguide take the issues into consideration[ .Making use of this feature,a lot of high And ti1l now. performance optical devices have been developed,such as wideband dual polarizations slot waveguide,which serves as a basis for diversity functional polarization slot devices,is not well investigated. wavelength demuhiplexer[3],sensor[ , ,optical modulator[ , .directional coupler[ ]and muhimode interference splitter[ For most optical devices,bandwidth and/or polarization are essential performance parameters to be considered .To be powerful, To solve the problem,wideband dual polarizations single mode characteristics in silicon slot waveguide is investigated by sometimes devices having both wideband and polarization three dimensional plane.wave expansion method(PWEM) 4—12.29 收稿日期 201scuec.edu.ca 通讯作者杨春勇(1975一),男,教授,研究方向:光传感与光通信技术,E—mail:Cyyang@mail 作者简介 侯金(1981一),男,副教授,研究方向:光通信与光器件,E—mail:houjin@mail.scuec.edu.an 基金项目 国家自然科学基金资助项目(1 1 147014&1 1491240105);湖北省自然科学基金资助项目(2013CFA052) 80 中南民族大学学报(自然科学版) 第34卷 and three dimensional finite diference time domain method modes.From the fiure,belgow the SiO2 light line,the band structures obtained by the two different methods look approximately the same in almost all the part except a little discrepancy for the fundamental modes near the silica light line, which would be due to the inexactly leaky modes extraction in FDTD.Therefore,we can conclude that,for most of the time, (FDTD)[13 3 in this paper.Firstly,the results obtained by PWEM and FDTD are compared to find which methods are more efficiently for the analysis.Then,optimizing is done by PWEM to obtain a wide single mode bandwidth for both quasi-TE and quasi—TM 1 polarizations.Through adjusting the width of the surrounding silicon region of the slot waveguides,320.6 nm wide single mode bandwidth for dual polarizations is obtained in an optimized slot waveguide.Finally,normalized filed distributions and the optical confinement ̄ctors of the slot waveguides are distinguished and calculated,which demonstrate that the electirc ifeld enhanced in the low index slot zone for quasi—TE fundamental modes is stil】maintained in the whole bandwidth. , Fig.1 Cross section of the silicon slot waveguide 图1 狭缝波导的截面示意图 As shown in Fig.1,a silicon—on—insulator(SO1)wafer is used as a basis for design of the wideband dual polarizations silicon single mode slot waveguide.The refractive index of SiO2 is assumed to be 1.45.In the silicon layer,a low—refractive— index air slot is sandwiched between two high refractive-index silicon regions,in which the light intensity call be enhanced due to the large discontinuity of the electric permittivity at high index— c0ntrast interfaces[ ].The refractive index 0f silic0n is assun1ed to be 3.45 and that of air is unity.The thickness of the silicon layer is denoted as H and fixed with an unchanged value of 0.8a.where is a reference unit constant.The width of the slot is denoted as nad has a fixed value of 0.2a.The value is chosen through a preliminary optimizing of the slot width based on a previously investigation,which would support electirc field enhancement in the low index slot zone of the waveguide[ .And the width for the high—index silicon region on the sides is denoted as Wn. In order to obtain wideband dual polarization performance, the dispersion curves of the slot waveguides are firstly investigated.Fig.2 shows the band structures of a typical slot waveguide with Wn 0.75a.The blue hollow square curves and the red hollow tirangle curves denote the quasi—TM bands and the quasi—TE bands respectively,which are calculated by PWEM. And the corresponding computational results obtained by FDTD ofr the two polarizations are denoted as green hollow circle curves nad pin dot curves,respectively.The black solid line denotes the light line for SiO2,above which the modes would be leaky to the silica layer.So it restricts the upward frequency for guided the two methods are matched very wel1.Considering that, calculating modes for a slot waveguide by three dimensional FDTD spends much more time than that by three dimensional PWEM.So,PWEM is more efficient and thus is chosen to investigate the dual polarizations characteristics. To widen the dual polarizations bandwidth of the silicon single mode slot waveguide,the width of the high-index silicon re,on is tialored while other parametem are remaining.We start from a very small width value of with,which corresponds to 150 nm thickness centered at 1550 nm.As shown in Fig.2,WH is tuned from 150 nm to 300 nm.When WH is increased,the dual polarizations bandwidth centered at 1550 nm wavelength of the slot waveguide will fisrtly increase accordingly. i 《 j》- And when reaches around 235 nm,the bandwidth gets to its m ̄imum.After that,further increasing of will make the dual polarizations bandwidth narrower.Thus.a suitable value of for a m ̄imum dual polarizations bandwidth should be chose玎. Wsve,vector/(2 ̄./a) Fig.2 Band stmctures of the slot waveguide obtained by the PWEM and the FDTD,respectively.The structure parameters of the slot waveguide are with Ws O.2a and =0.75a 图2狭缝波导的能带曲线图 Fig.2 shows the band structure of the slot waveguide with the optimized m ̄imum dual polarizations bandwidth.The structure parameters are with =0.2a, =0.75a and H= 0.8a,which correspond to =62.5 nm, =234.4 nm and H=250 nm for a center wavelength of 1550 nm.In Fig.2,the light green region denotes the border nomralized frequencies for quasi—TE and quasi—TM fundamental modes,respectively,which are with values of 0.24 and 0.195.Within the bandwidth 82 中南民族大学学报(自然科学版) 第34卷 v 卜 o e 卜・ D Fig.5 Optical confinement factor for the dual polarization bandwidth of the optimized slot waveguide 图5优化狭缝波导中双偏振带宽内的光因子 In conclusion,wideband dual polarizations single mode characteristics in silicon slot waveguide is theoretically investigated.In order to obtain a wide dual polarizations bandwidth,the width of the high region silicon is tailored.From our three dimensionaX PWEM calculation and three dimensional FDTD analysis.320.6 nm dual polarizations bandwidth can be obtained in an optimized slot waveguide.The electric field enhancement in the low dielectric slot zone is also verified by the ifeld distirbution analysis and the optical confinement factor computation in the slot waveguide.The investigation would be used as a basis for developing polarization related slot devices in polarization diversity system,such as polarization bending, couplers,splitters,and so on. Acknowledgments This work was partly supported by National Natural Science Foundation of China under Grant Nos. 1 1 147014 & l1491240105.the Natural Science Foundation of Hubei Province under Grant No.2013CFA052.and the Central Universities Fundamental Research Funds of South.Central University for Nationalities under Grant No.CZW】4020 References Tai Tsuchizawa,Koji Yamada,Hiroshi Fukuda,et a1. Microphotonic device based on silicon mierofabrieation technology[J].IEEE Journal of Selected Topics in Quantum Electronics,2005,1 1(1):232-240. [2] Vilson R Almeida,Qian fan Xu,Miehal Lipson,et a1. Guiding and confining light in void nanostructure[J]. Optics Letters,2004,29(11):1209—1211. [3] Feifei Hu,Huaxiang Yi,Zhiping Zhou.Wavelength demul— tiplexing structure based on arrayed plasmonic slot cavities [J].Optics Letters,36(8):1500—1502. 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