基于LiNbO_3的长周期波导光栅可调谐耦合器的设计

设计了一种基于LiNbO_3的长周期波导光栅可调谐耦合器.该耦合器利用长周期光栅的独有特性将输入波导的导模经包层模耦合至输出波导导模.由于LiNbO_3的电光效应,波导光栅芯层与包层的有效折射率随外加电压变化,从而耦合器的谐振波长及耦合效率可由外加电压调谐.分析了光栅周期与耦合器的长度对耦合器带宽和耦合效率调谐范围的影响,以及波导尺寸对谐振波长调谐灵敏度的影响.结果表明光栅周期越短,耦合器长度越长,则耦合器的带宽越窄,耦合效率调谐范围也越大.此外,谐振波长调谐灵敏度随波导宽度的增加而减小,而波导厚度对谐振波长调谐灵敏度的影响可以忽略.对光栅周期为94μm、长度为3.52cm的耦合器进行仿真,结果表明,谐振波长灵敏度为26.2pm/V,3dB带宽可达4.5nm,当外加电压从0变化到200V时,谐振波长变化5.24nm,耦合效率可在1到0.15之间进行调谐.     

氮氧化硅/聚合物混合集成低功耗可变光衰减器

利用具有相反热光特性的氮氧化硅与聚合物材料,采用混合集成波导结构设计了一种低功耗S型可变光衰减器.该衰减器以聚合物为芯层材料,氮氧化硅为包层材料,在弯曲波导上方制作加热电极从而通过热光效应来实现可调谐的衰减功能.理论分析表明,对于1.55μm的工作波长,衰减器实现50dB的衰减仅需要3.6mW的功率.实验结果可实现0~40dB的衰减范围,相应的最大温度变化为70.4℃,器件插入损耗为5.4dB.     

基于铌酸锂薄膜波导的电光调谐光栅辅助定向耦合器研究

提出并实验研究了一种基于铌酸锂薄膜光波导的电光调谐的光栅辅助定向耦合器。该耦合器由单模与双模脊形波导及制作于双模波导侧壁的长周期光栅构成。长周期光栅的引入补偿了单模与双模波导中基模的相位失配,可在共振波长实现两波导中基模的高效耦合。进一步地,在双模脊形波导两侧制作调谐电极实现了高速、低驱动电压的电光调谐功能。优化了器件的制作工艺,并采用单次干法刻蚀将耦合器的光栅与波导同步制作于X切铌酸锂薄膜上。测试结果表明所制作的器件在1 595.3 nm波长处实现了14.8 dB的隔离度,其电光调谐效率为0.38 nm/V(1 595.3 nm～1 599.0 nm),热光调谐效率为0.14 nm/℃（25℃～50℃）。该器件可用于实现可调谐滤波、滤模、电光调制及高灵敏度温度传感等功能。     

光纤型热光可调光衰减器的设计及其衰减分析

提出了一种基于热光调节的可调光衰减器结构。该衰减器通过腐蚀光纤包层到一定厚度和长度后,在表面涂覆较大热光系数的聚合物材料得到。从模场变化角度分析了传输光束的衰减与涂覆材料折射率的关系,并从实验上测试了使用不同涂覆材料时的衰减。理论分析与实验结果均表明在涂覆材料折射率略大于原光纤包层材料折射率时,涂覆材料折射率微小的变化将引起传播光束衰减的大幅度变化,并且光纤被腐蚀的长度越长或包层材料剩余厚度越小,衰减越大。因此,由热光系数大、折射率略大于光纤包层的聚合物材料所组成的可调光纤衰减器,具有衰减调节范围大且功耗小、插入损耗小、成本低、低偏振特性、易于与其它光纤器件耦合或集成等特点。     

快速可调谐电光聚合物波导光栅

提出并设计了快速可调谐电光聚合物波导光栅.该波导光栅通过极化聚合物的线性电光效应 可实现谐振波长的纳秒级快速调谐，调谐灵敏度为61pm/V.研究了该波导光栅的反射谱和透 射谱特性与光栅周期,周期数,折射率调制函数及其调制大小的关系.讨论了波导光栅的材料 选择,制备工艺,快速可调谐性和偏振相关性.该波导光栅不仅克服了光纤光栅调谐速度慢和不利于大规模集成的不足，而且具有调谐灵敏度高,制备工艺与半导体工艺兼容和偏振无关 等优点. 关键词： 光通信器件 光波导 电光效应 聚合物 波导光栅 光纤光栅     

一种基于聚合物材料的延迟线阵列与热光开关集成器件的设计

设计了一种基于聚合物材料的延迟线阵列与热光开关的集成器件.利用Rsoft软件设计并模拟了多模干涉热光开关的性能,可实现输出光场强度随电极加热温度变化.设计了螺旋结构的延迟线阵列,利用BPM软件对螺旋结构波导进行数值模拟,综合考虑器件尺寸和损耗参量设计出螺旋结构的弯曲半径.将延迟线阵列结构与热光开关进行集成,能够实现热光控制的聚合物延迟线阵列,该器件可实现的最大延迟时间为399.4ps,延迟间隔为9.2ps.以SiO2为下包层,SU-8紫外固化光刻胶为波导芯层,聚甲基丙烯酸甲脂为上包层,采用旋涂、光刻、湿法腐蚀等工艺制备了1×4延迟线阵列与MMI热光开关的集成器件,测试得到了延迟线阵列的近红外输出光斑,插入损耗为15~19dB.     

紫外固化型聚合物高阶布拉格波导光栅滤波器

利用紫外固化材料SU-82005与热交联聚合物甲基丙烯酸甲酯一甲基丙烯酸缩水甘油酯[P（MMA—GMA）]分别作为波导芯层和包层材料,通过直接光刻技术,成功实现了厚度为5μm,宽度为9μm,光栅高度为4μm的起伏型高阶布拉格波导光栅滤波器。对光栅器件的谐振波长,光透射率等重要参数进行了模拟设计。测得制备的聚合物高阶布拉格波导光栅滤波器的谐振波长为1550．4nm,消光比为23dB,3-dB带宽为2nm。     

基于等效折射率人工剪裁的宽带高效光栅耦合器

利用不同占空比的亚波长结构剪裁光栅槽的等效折射率来改变光栅的衍射特性实现衍射输出光束与单模光纤之间的模式匹配,通过优化埋氧化层厚度和集成底部金反射镜,可以改善光栅耦合器弱的方向性,从而设计出用于SOI波导与光纤之间高效率耦合的光栅耦合器。采用本征模展开方法,模拟了光栅耦合器随剪裁的光栅槽等效折射率变化的相关特性,在SOI波导和单模光纤之间对波长为1550nm的光获得了最高93.1%的耦合效率,3dB带宽为82nm。     

波导厚度变动、偏振变动以及折射率变动脱敏高分子宽带耦合器设计

针对高分子光波导在制造工艺中波导芯厚度难以控制、芯层和包层的折射率差变动时的随机性以及材料各向异性引起的偏振态依赖性等实际问题,提出了采用抗波导芯厚度误差、抗折射率差变动和抗偏振变动的宽带波导耦合器回路结构的解决方案,给出了设计的理论和方法。在实测数据的基础上,进行了带宽为120nm的3dB氟化聚酰亚胺波导耦合器设计。由该器件的三维BPM仿真结果表明,在上述带宽上,波导芯厚度的变动范围为7～8μm、相对折射率差变动范围为0 24%～0.30%,两个正交偏振态都具有(50±2.0)%功率输出比的良好特性。     

一种基于光学偏置的新型Math—Zehnder调制器结构设计

设计了一种基于光学偏置并以有机聚合物PMMA／DRI作为光波导材料的新型Mach-Zehdner调制器。利用有效折射率法（EIM）,分析了脊波导的有效折射率随脊波导结构参数变化情况,包括脊宽训、脊高b和芯层厚度d,以及上下包层厚度。采用微带线单电极调制方式结合脊波导的结构设计,实现了微波和光波的速率匹配。针对优化的结构参数,采用BPM方法进行光场和功率传输的模拟仿真,完成了非等臂Math—Zehnder调制器的结构设计,实现了两臂89．84。的初始相位差,消光比约为27dB。     

Simulation and optimization of a polymer directional coupler electro-optic switch with push-pull electrodes

Structural model and design technique are proposed for a polymer directional coupler electro-optic switch with rib waveguides and push-pull electrodes, of which the electric field distribution is analyzed by the conformal transforming method and image method. In order to get the minimum mode loss and the minimum switching voltage, the parameters of the waveguide and electrode are optimized, such as the core with, core thickness, buffer layer between the core and the electrode, coupling gap between the waveguides, electrode thickness, electrode width and electrode gap. Switching Characteristics are analyzed, which include the output power, insertion loss, and crosstalk. To realize normal switching function, the fabrication error, spectrum shift, and coupling loss between a single mode fiber (SMF) and the waveguide are discussed. Simulation results show that the coupling length is 3082 μm, push-pull switching voltage is 2.14 V, insertion loss is less than 1.17 dB, and crosstalk is less than −30 dB for the designed device.     

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.     

Hybrid vertical directional coupling between a long range surface plasmon polariton waveguide and a dielectric waveguide

To investigate light coupling between a long range surface plasmon polariton (LRSPP) waveguide and a conventional integrated optical component, a hybrid vertical directional coupler consisting of a LRSPP waveguides and a dielectric waveguide is investigated and fabricated. In the proposed coupler the dielectric waveguide and LRSPP waveguide are vertically configured for dense integration and strong coupling. The characteristics of the even and odd super-modes of the coupler are also analyzed to design the device. The fabricated device exhibits damped sinusoidal behavior along the coupling length due to propagation loss of the LRSPP waveguide. The maximum power transfer of 86% from the LRSPP waveguide to the dielectric waveguide is achieved at the coupling length of 600 μm. The measured characteristics of the device are in relatively good agreement with a theoretical analysis.     

多波导定向耦合器耦合特性

利用拉普拉斯变换,将多波导定向耦合器的耦合模方程组变换为三对角线性方程组,并采用追赶法求出了该方程组的通解;进一步,给定初始条件,进行拉普拉斯变换反演,即可严格地求出该耦合模方程组的解。采用该方法研究了5波导定向耦合器光从一个波导入射和等光强从5个波导入射时的耦合特性,求出了耦合模方程组解的解析表达式,给出了每个波导中光功率变化规律曲线。利用该方法,可很方便地求出任意有限数目波导组成的定向耦合器在任意入射条件下耦合模方程组的解,因此对于多波导定向耦合器结构的合理设计,具有非常重要的意义。     

Estimation of the performance of a 3-dB Y-junction optical coupler with a channel profile of proton-exchanged lithium niobate

A 3-dB optical coupler (power splitter) based on a Y-junction waveguide with a channel profile of proton-exchanged lithium niobate has been modeled. Finite difference beam propagation method has been used to investigate light wave propagation in axially varying waveguides. It is found that the structure splits the input power equally at the Y-junction with an efficiency of 99% and an average excess loss ?0.04 dB. The novelty of the coupling structure proposed is its capability to function as a wavelength-independent 3-dB coupler while maintaining very low-power imbalance for widespread optical communication wavelengths of 1.3 and 1.55 µm.     

Design and fabrication of wavelength tunable AWGs based on the thermo-optic effect

In this Letter, a 16 channel 200 GHz wavelength tunable arrayed waveguide grating(AWG) is designed and fabricated based on the silicon on insulator platform. Considering that the performance of the AWG, such as central wavelength and crosstalk, is sensitive to the dimension variation of waveguides, the error analysis of the AWG with width fluctuations is worked out using the transfer function method. A heater is designed to realize the wavelength tunability of the AWG based on the thermo-optic effect of silicon. The measured results show that the insertion loss of the AWG is about 6 d B, and the crosstalk is 7.5 d B. The wavelength tunability of 1.1 nm is achieved at 276 m W power consumption, and more wavelength shifts will gain at larger power consumption.     

跑道形玻璃波导谐振腔滤波器的研制

采用Ag+-Na+离子工艺,在K9玻璃上制备了跑道形波导谐振腔滤波器.测试得到该滤波器自由光谱范围为FSR=0.177 nm,对比对为Cr＝7.5 dB.同时分析得到耦合器的耦合系数为κ=0.916,耦合器和环形腔的损耗因子分别为δ=0.55,γ=0.48.耦合器的两波导几乎相连、条波导边缘不规则和一次离子交换波导表面缺陷是造成该波导滤波器具有较大损耗的主要原因.通过改进工艺技术降低波导损耗,该滤波器可以用于光通信、传感等领域,也可与其它波导结构相结合实现新的功能.     

Design of tunable asymmetric directional coupler filter using periodically segmented Ti:LiNbO3 waveguides

A tunable wavelength filter is designed using Ti:LiNbO₃ asymmetric directional coupler. One arm of the directional coupler is made of continuous waveguide while the other arm is periodic segmented. This segmentation reduces the lithographic steps and hence the fabrication cost required for such asymmetric coupler based filter. The propagation constant of periodical segmented and continuous waveguides are analysed using Effective-Index-based Matrix Method. The tunability is achieved using electro-optic property of LiNbO₃.     

Asymmetric plasmonic-dielectric coupler with short coupling length, high extinction ratio, and low insertion loss

Asymmetric directional coupling between a hybrid plasmonic waveguide with subwavelength field confinement and a conventional dielectric waveguide is investigated. The proposed hybrid coupler features short coupling length, high coupling efficiency, high extinction ratio, and low insertion loss; it can also be integrated into a silicon-based platform. This coupler can be potentially adopted for signal routing between plasmonic waveguides and dielectric waveguides in photonic integrated circuits. Furthermore, it can be exploited to efficiently excite hybrid plasmonic modes with conventional dielectric modes.     

A Cutoff Waveguide ICRF Coupler for Large Tokamaks

This paper proposes a cutoff waveguide Ion-Cyclotron Range of Frequencies (ICRF) coupler in heatings of fusion plasma for large tokamaks. Structures of tokamaks do not permit enough aperture areas for using cylindrical waveguides in the propagative region. However, if the power source to excite the coupler is located near its aperture, electromagnetic power is expected to pass through the cutoff region as a tunnel effect and radiate into the fusion plasma. We calculate characteristics of the normalized radiation power and the input impedance for this cutoff waveguide coupler, regarding its aperture as a slot. Numerical results show that the cutoff waveguide coupler has a few million watts handling power when the effective dielectric constant of the plasma is between 60 and 100. Experiments for a one-tenth model of actual size are performed using air and water instead of the fusion plasma. Measured input impedance showed a fine agreement with the theory for typical ones. Furthermore, experiments verify that its input impedance can be controlled by the location of a short-circuiting plunger. All these results suggest that the cutoff waveguide coupler is very attractive for ICRF heating.