A High-Sensitivity Refractive-Index Sensor Based on Plasmonic Waveguides Asymmetrically Coupled with a Nanodisk Resonator

A high-sensitivity plasmonic refractive-index sensor based on the asymmetrical coupling of two metal-insulator- metal waveguides with a nanodisk resonator is proposed and simulated in the finite-difference time domain. Both analytic and simulated results show that the resonance wavelengths of the sensor have an approximate linear relationship with the refractive index of the materials which are filled into the slit waveguides and the disk- shaped resonator. The working mechanism of this sensor is exactly due to the linear relationship, based on which tile refractive index of the materials unknown can be obtained from the detection of the resonance wavelength. The measurement sensitivity can reach as high as 6.45 × 10-7, which is nearly five times higher than the results reported in the recent literature [Opt. Commun. 300 （2013） 265]. With an optimum design, the sensing value can be further improved, and it can be widely applied into the biological sensing. Tile sensor working for temperature sensing is also analyzed.

Enhancing performance of GaN-based LDs by using GaN/InGaN asymmetric lower waveguide layers

The effects of Ga N/In Ga N asymmetric lower waveguide(LWG)layers on photoelectrical properties of In Ga N multiple quantum well laser diodes(LDs)with an emission wavelength of around 416 nm are theoretically investigated by tuning the thickness and the indium content of In Ga N insertion layer(In Ga N-IL)between the Ga N lower waveguide layer and the quantum wells,which is achieved with the Crosslight Device Simulation Software(PIC3D,Crosslight Software Inc.).The optimal thickness and the indium content of the In Ga N-IL in lower waveguide layers are found to be 300 nm and 4%,respectively.The thickness of In Ga N-IL predominantly affects the output power and the optical field distribution in comparison with the indium content,and the highest output power is achieved to be 1.25 times that of the reference structure(symmetric Ga N waveguide),which is attributed to the reduced optical absorption loss as well as the concentrated optical field nearby quantum wells.Furthermore,when the thickness and indium content of In Ga N-IL both reach a higher level,the performance of asymmetric quantum wells LDs will be weakened rapidly due to the obvious decrease of optical confinement factor(OCF)related to the concentrated optical field in the lower waveguide.

Optical Code Generating Device Using 1×N Asymmetric Hollow Waveguide Couplers

An optical code generating device for security access system application is presented. The code generating device constructed using asymmetric hollow optical waveguide coupler design provides a unique series of output light intensities which are successively used as an optical code. The design of the waveguide is made using two major components which are asymmetric Y-junction splitter and a linear taper. Waveguiding is done using a hollow waveguide structure. Construction of higher level 1×N hollow waveguide coupler is done utilizing a basic 1×2 asymmetric waveguide coupler design together with a cascaded design scheme. Non-sequential ray tracing of the asymmetric hollow optical waveguide couplers is performed to predict the optical transmission properties of the waveguide. A representation of the code combination that can be generated from the device is obtained using combinatory number theory.

Optical properties of the direct-coupled Y-branch filters by using photonic crystal slabs

We fabricated a new type of two-dimensional photonic crystal slab filter. The resonant cavities were directly put into the waveguide arms. The optical transmissions of the filters were measured and the results show that the optimized two-channel filters give good intensity distribution at the output ports of the waveguide. A minimum wavelength spacing of 5 nm of the filter outputs is realized by accurately controlling the size of the resonant cavities.

Oscillating Guided Modes in Graphene-Based Asymmetric Waveguides

We investigate the guided modes in monolayer graphene-based waveguides with asymmetric quantum well structure induced by unequal dc voltages. The dispersion relation for the guided modes is obtained analytically, the structures of the guided modes are discussed under three distinct cases. For the cases of the classical motion and the Klein tunneling, the asymmetric structure does not influence the mode structures dramatically compared with that in the symmetric waveguide. But for the mixing case of the former two, the mode structures and the motion characteristics for the electron and the hole exhibit different behaviors at same condition. The results may be helpful for the practical application of graphene-based quantum devices.

基于非对称辐射单元的毫米波全金属漏波天线

周期漏波天线具备后向端射-前向端射的连续波束扫描能力。全金属周期漏波天线在毫米波雷达等系统中具有明确的应用前景,但普通方案受制于开放阻带效应,边射性能差、扫描性能受限。目前抑制开放阻带效应的方法主要包括加载四分之一波长变换器或匹配短截线、不对等双辐射元、短路过孔匹配等,适合于全金属周期漏波天线的解决方案尚待发掘。文中提出了一种采用非对称辐射单元抑制开放阻带效应的方法,并结合等效电路模型进行机理分析和方法验证。采用非对称辐射单元设计了毫米波全金属波纹平行板波导周期漏波天线。该天线在26.5~36 GHz频带内具有-47.5°~8.5°的连续波束扫描能力,且辐射效率高于78%。仿真和实验结果表明,该非对称辐射单元能够很好地抑制开放阻带效应,适用于宽角频扫全金属周期漏波天线设计。

1060 nm锑化物应变补偿有源区激光二极管仿真及其性能研究

本文设计了GaAs基1060 nm高性能激光二极管的有源区结构,通过在有源区中引入锑化物的应变补偿结构GaAsP/InGaAs/GaAsSb/InGaAsSb/GaAsP,改变了有源区的能带结构,解决了禁带宽度对发光波长的限制,将弱Ⅱ型的量子阱能带结构变为Ⅰ型,增大了电子空穴的波函数重叠,提高了激光二极管跃迁概率和辐射复合概率及内量子效率,降低了非辐射复合,有效增强了器件输出功率和电光转换效率。同时,设计了非对称异质双窄波导结构,p侧采用导带差大、价带差小的AlGaAs作为内、外波导层,有利于价带空穴注入有源区且对导带中的电子形成良好的限制。n侧采用导带差小、价带差大的GaInAsP作为内、外波导层,有利于导带电子的注入且对价带中的空穴形成更高的势垒。电子注入势垒和空穴注入势垒分别由原先的218、172 meV降低到148、155 meV,提高了激光二极管的载流子注入效率;电子泄漏势垒和空穴泄漏势垒分别由252、287 meV上升到289、310 meV,增强了载流子限制能力。最后获得的激光二极管的输出功率和电光转换效率分别达到了6.27 W和85.39%,为制备高性能GaAs基1060 nm激光二极管提供了理论指导和数据支撑。

Asymmetric transmission of acoustic waves in a waveguide via gradient index metamaterials

We demonstrate that asymmetric acoustic wave transmission in a waveguide can be achieved via gradient index metamaterials(GIMs). We theoretically prove that the acoustic wave can be efficiently converted to surface waves(SWs) via GIMs. The GIMs in a waveguide can allow the transmission of acoustic waves in one direction but block them in the other direction. This theory is validated by experiments. Our findings may provide new applications in various scenarios such as high-efficiency acoustic couplers and noise control.

An asymmetric broad waveguide structure for a 0.98-μm high-conversion-efficiency diode laser

A novel asymmetric broad waveguide diode laser structure was designed for high power conversion efficiency（PCE）.The internal quantum efficiency,the series resistance,and the thermal resistance were theoretically optimized.The series resistance and the thermal resistance were greatly decreased by optimizing the thickness of the P-waveguide and the P-cladding layers.The internal quantum efficiency was increased by introducing a novel strain-compensated GaAs0.9P0.1/InGaAs quantum well.Experimentally,a single 1-cm bar with 20% fill factor and 900 μm cavity length was mounted P-side down on a microchannel-cooled heatsink,and a peak PCE of 60% is obtained at 26.3-W continuous wave output power.The results prove that this novel asymmetric waveguide structure design is an efficient approach to improve the PCE.

1.55μm脊波导大功率DFB激光器的研究

为了提高1.55μm波段DFB激光器的输出性能及高温特性,制作了两种不同结构的InAlGaAs/InP大光腔激光器。两种激光器芯片均在外延设计上采用非对称结构,能够有效减少器件内吸收损耗,从而提高输出功率。对两种芯片均进行了不同腔长、发散角及高温性能测试,可以观测到采用较厚n侧限制层的芯片的输出功率更大。

810-nm InGaAlAs/AlGaAs double quantum well semiconductor lasers with asymmetric waveguide structures

The 810-nm InGaAlAs/AlGaAs double quantum well （QW） semiconductor lasers with asymmetric waveguide structures, grown by molecular beam epitaxy, show high quantum efficiency and high-power conver- sion efficiency at continuous-wave （CW） power output. The threshold current density and slope efficiency of the device are 180 A/cm^2 and 1.3 W/A, respectively. The internal loss and the internal quantum efficiency are 1.7 cm^-1 and 93%, respectively. The 70% maximum power conversion efficiency is achieved with narrow far-field patterns.

非对称单巨原子腔阵列波导QED系统中的单光子散射

研究单巨原子腔阵列波导量子电动力学(quantum electrodynamics,QED)系统在不对称耦合情形下的单光子散射态.在实空间中推导出系统散射振幅的解析解,并据此分析巨原子通过2个耦合点与波导非对称耦合时,耦合的不对称度和耦合点间距等因素对单光子散射谱的影响.发现,如果巨原子2个耦合点非对称度较大,这时无论耦合点间距大小,系统的散射谱均与小原子类似;而如果非对称度较小且耦合点间距较大时,由于巨原子的非偶极效应的影响,散射谱会出现与小原子截然不同的线型.

Research of Asymmetric Y-Branching Total Internal Reflection All-Optical Switch

Y-branching TIR all-optical switch have been fabricated. When the switching optical intensity is 149.9W/mm2, the extinction ratio is 18dB. A theoretical model was also proposed which provided a good fit to the experimental data.

新型双极化波导缝隙天线研究

传统的双极化波导缝隙天线阵每种极化方式交叉极化都较差,极化端口隔离度不高,尤其是垂直极化波束在进行大角度扫描时,容易出现二次副瓣。针对上述情况,文中介绍了一种新型的双极化波导缝隙阵天线阵,水平极化天线采用非倾斜窄边缝波导缝隙天线阵,垂直极化天线采用非对称脊波导宽边开缝波导缝隙天线阵。通过对该新型双极化波导缝隙阵进行仿真分析和试验研究,发现该组阵方式较大改善了2种极化方式的交叉极化,有效提高了2种极化天线之间的隔离度,可实现宽角扫描,较大改善了整个阵面的性能,具有较好的工程实用性。

共面波导馈电超宽带天线研究

设计了一种刻蚀在单层覆铜介质基板上的共面波导馈电超宽带天线。所用介质基板由相对介电常数为2.65的聚四氟乙烯制成,尺寸为35.0 mm×35.0 mm×1.6 mm。利用仿真软件HFSS对该天线的参数进行了仿真和优化,并根据优化参数进行了实物天线的制作和性能测试。结果表明,通过在共面波导地面上刻蚀非对称结构的多边形槽,可使天线的频带宽度达到2.2-8.0 GHz（S11〈–10 dB）,相对带宽达到114%。该天线具有良好的方向图和增益性能,满足超宽带天线的性能要求。

双/三模基片集成波导和共面波导混合结构滤波器设计

针对微波带通滤波器小型化、高性能的应用需求,提出使用双/三模方形基片集成波导和共面波导混合结构设计带通滤波器.通过改变双模基片集成波导中TE_(102)和TE_(201)的谐振频率和外部耦合的强弱,可实现具有近似椭圆、非对称和无传输零点响应的双模滤波器;两个相同尺寸的共面波导作为谐振器蚀刻在基片集成波导表面,与TE_(102)和TE_(201)共同形成一个通带,设计具有多样性响应的四阶滤波器.在具有非对称响应四阶滤波器的基础上,使主模TE_(101)频率移动到该通带附近,设计更宽带宽的五阶滤波器.并对设计的滤波器进行加工和测试.测试结果与仿真结果吻合,表明了该混合结构设计高性能滤波器方法的可行性.

高功率、高效率808nm半导体激光器阵列

通过设计高效率808 nm非对称宽波导外延结构,减少P型波导层和包层的自由载流子光吸收,实现腔内光吸收损耗为0.63 cm^(-1).制备的808 nm半导体激光器阵列在室温25?C下,实现驱动电流135 A,工作电压1.76 V,连续输出功率大于150 W,斜率效率高达1.25 W/A,中心波长809.3 nm,器件最高电光转换效率为65.5%,这是目前国内报道的808 nm半导体激光器阵列的最高电光转换效率,达到国际同类器件最好水平.

不对称脊波导宽边中心裂缝天线的设计

介绍了 ２８ 单元不对称脊波导宽边中心裂缝阵列天线的设计过程和试验结果。

非对称异质波导半导体激光器结构

提出了一种非对称异质波导半导体激光器外延结构,即通过优化选择材料体系和结构厚度,对器件外延层的P侧限制结构和N侧限制结构分别设计,从而降低器件的电压损耗,使其满足高输出功率以及高的电光转换效率的要求.从载流子的输运和限制等微观机制出发,对器件的主要输出特性进行了理论分析和数值模拟,并以此为根据设计和制作了一种1060 nm In Ga As/Ga As单量子阱非对称异质波导结构半导体激光器,并对器件的主要输出特性进行了测试.实验结果表明,非对称异质结构是降低器件的电压降、增大限制结构对注入载流子的限制,提高半导体激光器电光转换效率的有效措施.