Beam splitter benefits from topological antichiral edge states

Beam splitters play a crucial role in a wide range of optical systems.A typical beam splitter consists of several transport channels,and an input beam from one channel is split into multiple output beams coupled into other channels.For traditional beam splitters,their transportation channels(either in free space or waveguides)are reciprocal,being sensitive to various perturbations caused by defects and obstacles.

Design of a photonic crystal fiber polarization beam splitter with simple structure and ultra-wide bandwidth

A novel polarization beam splitter(PBS)based on dual-core photonic crystal fiber(DC-PCF)is proposed in this work.The proposed DC-PCF PBS contains two kinds of lattices and three kinds of air holes to form the asymmetrical elliptic dual-core structure.By using the full-vector finite element method,the propagation characteristics of the proposed DC-PCF PBS are investigated.The simulation results show that the bandwidth of the proposed DC-PCF PBS can reach to 340 nm,which covers the S+C+L+U communication bands,the shortest splitting length is 1.97 mm,and the maximum extinction ratio appears near wavelength 1550 nm.Moreover,the insertion loss of the proposed DC-PCF PBS is very low.It is believed that the proposed DC-PCF PBS has important applications in the field of all-optical communication and network.

An Ultra-Compact Broadband Polarizing Beam Splitter Utilizing Hybrid Plasmonic Waveguide

Polarizing beam splitter has rather significant applications in polarization diversity circuits and polarization multiplexing systems.In this paper,we present an asymmetric polarizing beam splitter utilizing hybrid plasmonic waveguide.The special hybrid structure with a hybrid waveguide and a dielectric waveguide can limit the energy of TE and TM modes to a different layer.Therefore,we can achieve beam splitting by adjusting the corresponding parameters of the two waveguides.First,we studied the influences of different structure parameters on the real part of the effective mode refractive index of the two waveguides,and obtained a set of parameters that satisfy the condition of strong coupling of TM mode and weak coupling of TE mode.Then,the performance of our proposed polarizing beam splitter is evaluated numerically.The length of the coupling section is only 4.1μm,and the propagation loss of TM and TE modes is 0.0025 d B/μm and 0.0031 d B/μm respectively.Additionally,the extinction ratios of TM and TE modes are 10.62 d B and 12.55 d B,respectively.Particularly,the proposed device has excellent wavelength insensitivity.Over the entire C-band,the fluctuation of the whole normalized output power is less than 0.03.In short,our proposed asymmetric polarizing beam splitter features ultra-compactness,low propagation loss,and broad bandwidth,which would provide promising applications in polarization multiplexing system and polarization diversity circuits relevant to optical interconnection.

取秧侧向零偏移的空间轨迹再生稻分插机构设计与试验

为了解决现有空间行星轮系式分插机构在再生稻宽窄行机械化种植取秧过程中出现侧向偏移量和侧向偏转角的技术难题,本文提出一种具有局部平面轨迹特性的空间轨迹不等速行星轮系机构,并开展基于取秧口和机构回转中心位置约束下的宽窄行分插机构综合研究。构建了基于关键位姿点(取秧起始点、取秧结束点、推秧点)的空间轮系机构运动综合模型,利用关键位姿点求解机构杆长参数与空间交错轴信息,并通过优选二杆相对角位移参数实现机构传动比分配。将不完全非圆齿轮副引入空间行星轮系机构,利用间歇机构锁止弧约束行星轴,实现机构取秧过程侧向零偏移量、侧向零偏转角的平面轨迹段。通过仿真分析与机构样机试验验证了机构实际作业性能与理论设计相一致,结果表明:分插机构取秧侧向零偏移量,取秧侧向零偏转角,推秧侧向总偏移量为50.24 mm、取秧角为5.18°、推秧角为71.56°、推秧侧向角为16.26°、插秧穴口宽度为22.43 mm、轨迹高度为289.76 mm,满足预期设计要求。最后通过田间试验验证,分插机构可实现等行距取秧口和既定机构回转中心下宽行(40 cm)与窄行(20 cm)间隔机插,满足再生稻宽窄行种植要求。

分流叶片长度及周向偏移量对ORC向心透平性能的影响

利用分流叶片能有效改善叶片通道内的流动阻塞问题,降低流动损失。针对某带分流叶片的有机朗肯循环(ORC)向心透平,研究了不同分流叶片长度和周向偏移量对透平性能的影响,对不同叶片布置方案进行数值模拟,分析了内部流动状况、叶片载荷和损失分布。结果表明:分流叶片能有效削弱通道中的涡流,改善流动状况,使通道内部的压力分布合理;同时在一定程度上分担了主叶片的载荷。与分流叶片长度系数相比,周向偏移量对熵产率的影响较为明显;随着长度系数和周向偏移量的增加,高熵产率范围和总压损失系数均呈现先减后增的趋势,等熵效率的变化则相反,当l=0.5、d=0.5时等熵效率最大,为91.26%,而功率与叶片长度大体呈正相关;将长度系数和周向偏移量分别控制在0.5~0.6时,能保持较为理想的流动状况及叶片载荷分布,高熵产率范围较小,有利于透平性能的提升。

基于开口圆环结构的太赫兹分束器设计

提出了一种基于开口圆环结构的太赫兹分束器,其由两种单元结构组成,这两种结构的区别在于是否存在底层连续金属层,这两种结构的顶层金属图案由开口圆环组成,介质层为聚酰亚胺薄膜。通过改变开口圆环的开口大小和半径排列构成了8×8的相位梯度超表面。当太赫兹波分别沿-z轴方向和+z轴方向垂直入射时,电磁波会被分成沿x,y轴对称但能量分布不同的四束波,两种入射模式能够得到两种不同的分束比。在0.7 THz下,当太赫兹波分别沿-z轴方向和+z轴方向垂直入射时,其分束比分别为0.8∶1和1.9∶1,实现对分束比的调谐。此分束器具有体积小、成本低的优点,可应用于太赫兹通信、太赫兹成像和太赫兹隐身等领域。

隔板构型对超声速混合层流动及混合特性的影响研究

为进一步揭示超声速来流下混合层流场演化过程物理机制,采用高精度计算方法对超声速来流下混合层流动及生长特性开展数值研究。首先,采用经典算例深入验证了本文所发展计算程序在复杂流场预示方面的精度和可靠性。然后,对四种不同构型隔板下混合层流动及生长机制进行了深入分析。研究结果发现,在典型隔板构型中引入凹腔、楔形角及凸台结构后,整体流场结构变得更为复杂,且诱发了更为剧烈的混合层的涡卷起、配对、合并、旋转等流体物理现象。在典型隔板工况中混合层出现了再层流化现象,而引入凹腔、楔形角及凸台结构后能够有效抑制混合层出现再层流化现象。此外,所有隔板构型工况下湍流转捩区雷诺应力均出现了“多峰值”现象,但典型隔板工况的混合层附近的湍动能明显小于其余工况,同时,典型隔板工况的雷诺应力峰值与分布范围明显小于其余工况。就本文研究工况而言,在出口处楔形角隔板工况的混合效率最高,为0.050;同时其混合层厚度也最大,达到27.9 mm;但楔形角隔板工况的总压损失也最大,为0.22。

分流叶片对液力透平压力脉动的影响

为揭示分流叶片对低比转速液力透平性能的影响,以一台低比转速离心泵(n_(s)=33)反转作液力透平为例,设计出4种不同分流叶片数的叶轮(复合叶轮),通过CFX软件对原始叶轮和4种复合叶轮进行数值模拟并对比分析。结果表明,4种新模型在最优工况下效率和水头均有所提高,其中当分流叶片数Z=6+6时液力透平的性能最佳,在最优工况下效率、水头分别提高了2.23%、6.83%;叶轮内压力分布更加均匀;叶轮进口漩涡区域减弱;内部各个监测点压力系数、脉动幅值均小于原始模型,说明分流叶片可以降低液力透平内部的压力脉动、提升透平机组运行的稳定性。研究结果可为低比转速液力透平性能提升提供参考。

低偏振超宽光谱分色膜设计与制备

可见/红外超宽光谱分色片是星载中分辨率光谱成像仪Ⅲ型光学系统中的重要光学薄膜器件。利用诱导透射原理,采用金属-介质膜系结构加非对称等效导纳匹配层,实现了45°入射时0.4~1.05μm光谱高效透射,1.35~13μm波段光谱高效反射,从而将入射光束分配到不同的光路。同时通过消偏振控制设计,获得了可见近红外波段低偏振灵敏度(LPS)。所研制的分色片可见近红外波段平均透射率大于85%,LPS小于4%;短波及长波红外波段平均反射率大于90%。

Microstructures and properties of Al-45%Si alloy prepared by liquid-solid separation process and spray deposition

The microstructures and properties of A1-45%Si alloy prepared by liquid-solid separation （LSS） process and spray deposition （SD） were studied. The results show that the size, shape and distribution of the primary Si phase have different influence on the properties of alloys. Comparing with the Si particles with irregular shape, fine size and continuous distribution in SD alloy, the primary Si phase in LSS alloy is sphere-like, coarse and surrounded by the continuous AI matrix. The microstructure features of LSS alloy are beneficial to the higher thermal conductivity and lower thermal expansion coefficient at room temperature. The fine Si particle in SD alloy is advantageous to improving the mechanical properties. The increasing rates of thermal expansion coefficient with temperature are influenced by the distribution of the Si particles, where a lower rate is obtained in SD alloy with continuous Si particles. The agreement of thermal expansion coefficient with the model in LSS alloy differs from that in the SD alloy because of the different microstructure characteristics.

Microstructure evolution of Al-Ti liquid-solid interface

Al-Ti diffusion couples were made by embedded technology and treated at the temperature between the melting points of Al and Ti. The microstructure evolution and growth mechanism of the Al-Ti DRZ were investigated. The result shows that the DRZ, the mixture of TiAl3 and Al, grows layer by layer along their chemical equilibrium zone. In the course, the growth interface moves toward the aluminum side. TiAl3 is the only new phase which forms earliest in the course of heat-treatment. The growth mechanism of the DRZ changes after the phase transition of titanium. Before the phase transition of titanium, the growth of the DRZ is controlled by the dissolution speed of the titanium to the molten aluminum, while after the phase transition of titanium, the growth is controlled by the chemical reaction speed of Al and Ti atoms, and consequently, its growth rate is greatly increased.

Microstructure and properties of SiC_p/Al electronic packaging shell produced by liquid-solid separation

The electronic packaging shell of high silicon carbide （54%SiC, volume fraction） aluminum-based composites was produced by liquid-solid separation technique. The characteristics of distribution and morphology of SiC as well as the shell’s fracture surface were examined by optical microscopy and scanning electron microscopy, and the thermo-physical and mechanical properties of the shell were also tested. The results show that Al matrix has a net-like structure while SiC is uniformly distributed in the Al matrix. The SiCp/Al composites have a low density of 2.93 g/cm^3, and its relative density is 98.7%. Thermal conductivity of the composites is 175 W/（·K）, coefficient of thermal expansion （CTE） is 10.3×10^-6 K-1 （25-400 ℃）, compressive strength is 496 MPa, bending strength is 404.5 MPa, and the main fracture mode is brittle fracture of SiC particles accompanied by ductile fracture of Al matrix.Its thermal conductivity is higher than that of Si/Al alloy, and its CTE matches with that of the chip material.

带分流叶片水泵水轮机甩负荷过渡过程中的压力脉动特征

为减轻水泵水轮机过渡过程中剧烈压力脉动对抽水蓄能电站安全产生的不利影响,需充分认识水泵水轮机的压力脉动特征。本文对某带分流叶片水泵水轮机甩负荷过渡过程中的实测压力脉动数据开展深入研究。首先从压力脉动的频域特性出发,提出了一种基于变分模态分解的时均压力和脉动压力提取方法。然后采用傅里叶变换和短时傅里叶变换分析水泵水轮机稳定运行和甩负荷过程中蜗壳进口、无叶区、顶盖和尾水锥管进口的脉动压力,揭示了带分流叶片水泵水轮机在稳定运行和甩负荷过渡过程中压力脉动的频率组成和时频变化特性的普遍规律。研究表明,带分流叶片水泵水轮机无叶区压力脉动的主频由叶片通过频率及其半次谐波共同主导,且叶片通过频率的半次谐波具有向上下游传播的特点。尾水锥管进口压力脉动频率主要由低频成分及叶片通过频率的半次谐波构成。甩负荷过渡过程中,无叶区叶片通过频率及其谐波的频率会随着时间的变化出现增大和减小现象,且变化规律与转轮转速的变化趋势一致。本文所提出的方法为压力脉动实测数据分析提供了一种新手段,为带分流叶片水泵水轮机压力脉动的特征研究提供了参考与借鉴,对结构异常振动溯源和保障机组安全运行具有重要意义。

星间通信系统高精度分光镜的研制

随着星间通信系统的迅速发展,数据传输的精度要求不断提高。分光镜作为系统的核心元件,其光谱特性和面形精度直接影响整个系统的传输精度。本文基于薄膜干涉理论,选取Ta_(2)O_(5)与SiO_(2)作为高低折射率膜层材料进行膜系设计,采用电子束蒸发的方式在石英基板上制备高精度分光镜。同时根据膜层应力补偿原理建立面形修正模型,修正分光镜面形。光谱分析仪检测结果显示,分光镜在入射角度为21.5°~23.5°内,1563 nm透过率大于98%,1540 nm反射率大于99%。激光干涉仪检测结果显示,分光镜反射面形精度RMS由λ/10修正至λ/90(λ=632.8 nm),透过面形精度RMS为λ/90。

基于硅基光电子芯片的低损耗动态偏振控制器

动态偏振控制器能够实现输入光场任意偏振态到输出光场任意偏振态的控制,可以动态补偿长距离单模光纤导致的双折射效应,是量子通信和相干通信系统中的重要器件.本文设计并实验验证了基于硅基光电子芯片的低损耗动态偏振控制器,芯片采用标准的绝缘体上硅工艺制作,器件整体尺寸为5.20 mm×0.12 mm×0.80 mm,整体损耗为5.7 dB,最大功耗为0.2W.基于可变步长.模拟退火算法、低噪声探测器和高静态消光比的器件,动态偏振消光比可锁定至30 dB以上.芯片采用热相移器对TE0光场的相位延迟量进行控制,整体为0°/45°/0°/45°结构,可实现无端偏振控制.基于Lumerical软件对核心部件偏振旋转分束结构进行了优化,该结构将以端面耦合方式进入波导中的TM0模式光场转化至另一波导中的TE0模式光场,而原单波导中TE0模式光场不发生转化,实验测得动态偏振控制器的静态偏振消光比可达40 dB以上.该器件具有小体积、低功耗和低成本的特点,可以广泛应用于量子通信和相干通信等领域,特别是需要考虑体积、功耗和成本的应用场合.

基于边缘优化设计的低损耗Si3N4光功率分束器

随着信息技术的发展,市场对于更小型化、更高效光器件的需求不断增加.采用互补金属氧化物半导体(complementary metal oxide semiconductor,CMOS)工艺,成功制备了Si_(3)N_(4)光功率分束器并对其进行测试.结果表明,在1550 nm波长下,边缘优化的1×8功率分束器的总损耗仅为1.30 dB,且其体积相较于传统设计可减小30%.本研究应用逆向优化算法,突破了传统设计仅能针对规则图形设计的限制,为实现小尺寸、低损耗的光功率分束器提供了一种可行途径.

一种基于功率合成器和功率分配器的2.45 GHz功率放大器

当前功率放大器在输出效率、输出功率以及线性度等方面不能很好地兼顾,针对这一问题,在三级级联放大方法的基础上,提出了一种基于功率合成器和功率分配器的AB类射频功率放大器。针对线性度和增益的问题,带通匹配和T型网络匹配技术对前置驱动级电路进行了优化设计;利用功率合成技术解决了末级放大器输出功率过大的问题,并且使功率放大器的稳定性和效率得到了保证。为防止功放的温度过高,对功率放大器腔体进行了热特性分析,最高温度为81℃,可以使功放得到良好的降温。在室温测试环境下,当中心频点为2.45 GHz时,射频功率放大器的输出功率为47 dBm,放大增益为42 dB,最大功率附加效率大于45%。测试结果与仿真结果相近,为后续放大器的研究与设计提供了一定的指导。

直流空气断路器高海拔环境下电弧重燃现象及其抑制措施

高海拔环境下直流空气断路器(DC ACB)在电弧开断过程中易发生重燃,导致开断失败的概率增加。为了抑制DC ACB高海拔开断时的电弧重燃,以轨道交通用车载DC ACB为研究对象,建立了二维磁流体动力学(MHD)仿真模型,分析了不同海拔下DC ACB中的电弧演变过程,通过增大横向磁场及设置“C”形栅片对其高海拔开断性能进行优化。结果表明增大横向磁场,2 km、3 km海拔下DC ACB不发生电弧重燃,但4 km、5 km海拔下发生电弧重燃。4 km、5 km海拔下,在增大横向磁场的基础上采用含“C”形栅片的改进灭弧室结构,能够使DC ACB在高海拔环境下成功开断。

分流板对圆柱绕流湍流结构演化影响的实验研究

采用粒子图像测速(Particle Image Velocimetry,PIV)技术实验研究了带分流板的圆柱绕流流动特性,分析了分流板对圆柱绕流湍流结构演化特性的影响。雷诺数为3.9×10^(3),分流板长度L与圆柱直径D之比L/D为0~2.50。实验结果表明,随着L/D从0增大至1.00,圆柱后方回流区长度和回流区面积显著增大;当L/D>1.00时,L/D对圆柱后方回流特性的影响较小。分流板影响圆柱绕流湍流结构的演化特性:当L/D<1.00时,分流板抑制尾涡脱落,斯特劳哈尔数Sr减小,L/D从0增大至1.00,Sr减小了26.34%。此外,圆柱尾涡在分流板后缘诱导形成旋转方向相反的二次涡,二次涡沿分流板向上游运动。1.00≤L/D<2.00时,分流板作用于圆柱尾涡,尾涡发生破碎,形成一些小尺度尾涡。L/D≥2.00时,尾涡附着于分流板上,二次涡主要分布于圆柱后方。随着L/D增大,分流板减小了圆柱后方的湍流脉动强度。

分离盘对Spar型浮式风力机涡激运动抑制特性的试验与数值研究

涡激运动是导致浮式结构系泊系统疲劳破坏的重要原因,该文利用模型试验和数值仿真方法,开展尾侧分离盘对Spar型浮式风力机主浮体结构涡激运动抑制机理的研究。主要探讨分离盘长度L/D对风力机涡激运动特性的影响规律。研究发现,分离盘长度L/D=0时,涡激响应随折合速度的增加呈现明显的上部分支、锁定区及去同步化分支3阶段,结构发生涡激共振问题;当分离盘长度L/D≥0.2时,风力机不再发生涡激共振现象,且当分离盘长度L/D≥0.4时其抑制效果达70%以上。同时发现分离盘结构能诱发Spar型浮式风力机的艏摇运动。结果表明,分离盘对Spar型浮式风力机的涡激运动响应有明显的抑制效果。