Improved simulation of VCSEL distributed Bragg reflectors

In this paper, the Floquet-Bloch theory (FBT) has been applied to the accurate simulation of distributed Bragg reflectors in vertical cavity surface emitting lasers (VCSELs). A number of comparisons with other methods largely used in commercial CAD tools is presented. Performance predictions for long-wavelength GaInAsP VCSELs are derived.     

Optimization of III–V compound semiconductor heterostructures for distributed Bragg reflector applications in VCSELs

A selectively oxidized vertical cavity surface emitting laser (VCSEL) has been designed and fabricated for operation at a wavelength of 1.546 μm. The device structure was grown on an InP substrate using III–V quaternary semiconductor alloys for the two mirror stacks and unstrained multi-quantum wells for the active layer. A threshold current as low as 2.2 mA has been achieved. The influence of the intentional and growth-related compositional grading at the heterointerfaces on the mirror reflectivity and laser characteristics has been investigated, and key sensitivities to laser performance have been determined.     

新型反射腔在多频相对论返波振荡器中的粒子模拟研究

设计了两类新型同轴反射腔并成功地应用于多频高功率微波输出.反射腔采用非对称的同轴结构,置于同轴相对论返波振荡器(CRBWO)慢波系统的前端.文中利用2.5维CHIPIC粒子模拟软件进行粒子模拟研究.仿真结果表明,带有两类新型同轴反射腔的双频CRBWO都实现了X波段双频稳定输出,并且其工作的电压和磁场的稳定性要明显好于传统谐振腔双频返波管.采用第二类新型同轴反射腔,在强流电子束电压480 kV,电流7.5kA,磁场2.7T的条件下,得到了稳定的三频、四频输出,其注波转换效率分别为15.3％和13.9％,明显高于其他类型的多频高功率微波器件.     

Moderator Temperature Coefficient in BWR Core

Temperature dependences of infinite multiplication factor k∞ and neutron leakage from the core must be examined for estimation of moderator temperature coefficient. Temperature dependence on k∞ has been investigated by many researchers, however, the dependence on neutron leakage of a BWR with cruciformed control rods has hardly been done. Because there are difficulties and necessity on calculations of three space dimensional and multi-energy groups neutron distribution in a BWR core.

In this study, moderator temperature coefficients of JPDR-II (BWR) core were obtained by calculation with DIFFUSION-ACE, which is newly developed three-dimensional multi- group computer code. The results were compared with experimental data measured from 20 to 275°C of the moderator temperature and the good agreement was obtained between calculation and measurement.

In order to evaluate neutron leakage from the core, the other two calculations were carried out, adjusting criticality by uniform absorption rate and by material buckling. The former underestimated neutron leakage and the latter overestimated it. Discussion on the results shows that in order to estimate the temperature coefficient of BWR, neutron leakage must be evaluated precisely, therefore the calculation at actual pattern of control rods is necessary.     

Galileo卫星激光反射器的结构设计

卫星激光反射器的结构设计是激光反射器设计的重要内容,本文以Galileo卫星激光反射器为例,阐述了中高轨导航卫星激光反射器结构设计所需解决的问题和措施途径,包括结构总体布局、角反射器组件结构、材料设计、减振缓冲、静电防护、热控技术等;并针对航天环境载荷(结构装配、恒加速度、振动、冲击、热循环等),对激光反射器的机械和光学性能影响进行了分析、计算和讨论,以此验证结构设计的可行性;Galileo卫星实际测距效果理想进一步表明Galileo反射器结构设计的合理。     

一种基于波分复用的光控波束合成网络

提出了一种基于波分复用光控波束合成网络,其核心是采用了由波分复用器、可调衰减器和光反射镜构成的光延时模块,通过光反射镜的光程调节获得通道之间的延时。根据该方案制作了18 GHz工作频率下,波束指向为0°和-45°的两个16通道光延时模块。测试结果表明,模块的相位精度达到了±15°,幅度一致性优于±0.1 dB,仿真方向图显示了较高的波束指向精度。     

多外腔自混合干涉现象的理论与实验

考虑激光器外有多个反射体时所产生的自混合干涉现象，运用薄膜干涉理论，对弱光反馈条件下的多外腔自混合干涉理论进行了研究。基于复合腔激光器结构，建立了理论模型。理论分析构造了一个含有五个反射面的自混合干涉模型，模型是由三个外腔构成的多外腔自混合干涉。对模型进行了理论分析及数值仿真，得出在弱光反馈条件下，多外腔自混合干涉信号类似于传统的自混合干涉信号，为一类正弦波(外部反射率较小时)或类锯齿波(外部反射率较大时)。设计了实验系统，给出了实验结果并进行了验证。如果忽略多外腔的结构，理论所得结果与简单的三镜腔自混合干涉结构所得结果一致。     

The AlN based solidly mounted resonators consisted of the all-metal conductive acoustic Bragg reflectors

The AlN based solidly mounted resonators utilizing the all-metal conductive Bragg reflectors have been demonstrated. The devices with different reflectors of Mo/Ti, W/Ti and AlN/Mo pairs have been fabricated and the frequency responses have been compared. The bottom electrode is incorporated into the conductive Bragg reflector, thereby reducing the parasitic resistance and the damping of the acoustic energy. The experimental results reveal that Mo/Ti and W/Ti reflectors exhibit excellent properties of frequency selection and clamping the acoustic wave. The devices show the distinct resonant phenomenon near 2.4 GHz with the excellent suppression of the shear mode and the sidelobe mode. Compared to the conventional device consisted of AlN/Mo reflector, the devices consisted of the conductive reflectors demonstrate the higher resonance frequency and obviously improved performance.     

A novel approach of deposition for uniform diamond films on circular saw blades

Uniform diamond films are highly desirable for cutting industries,due to their high performance and long lifetime used on cutting tools.Nevertheless,they are difficult to obtain on cutting tools with complicated shapes,greatly limiting the applications of diamond films.In this study,a novel approach of deposition for uniform diamond films is proposed,on circular saw blades made of cemented carbide using reflectors of brass sheets.Diamond films are deposited using hot filament chemical vapor deposition (HFCVD).A novel concave structure of brass sheets is designed and fabricated,improving the distribution of temperature field,and overcoming the disadvantages of the conventional HFCVD systems.This increases the energy efficiency of use without changing the structure and increasing the cost of HFCVD.The grains are refined and the intensities of diamond peaks are strengthened obviously,which is confirmed by scanning electron microscopy and Raman spectra respectively.     

太阳能电池聚光器的模拟优化

设计了三种槽式太阳能电池聚光反射器模型：梯形、圆弧形和抛物线形,在光学软件Fred中建立模型,利用软件提供的光线跟踪方法,针对其有、无跟踪太阳两种情况进行优化,得出了在这两种情况下,不同几何聚集比（C=1．5,2,2．5,3,3．5）时的最佳形状参数（倾角θ或高底比Hd）,为实际生产加工过程提供了指导,最后对比了三种聚光反射结构的优缺点。