Coupling characteristics of laterally coupled gratings with slots

Laterally-coupled ridge-waveguide distributed feedback lasers fabricated without epitaxial regrowth steps have the advantages of process simplification and low cost. We present a laterally coupled grating with slots. The slots etched between the ridge and grating area are designed to suppress the lateral diffusion of carriers and to reduce the influence of the aspect-ratio-dependent-etching effect on the grating morphology in the etching process. Moreover, the grating height in this structure can be decreased to lower the aspect ratio significantly, which is advantageous over the conventional laterally coupled ridge waveguide gratings. The effects of five main structural parameters on the coupling characteristics of gratings are studied by MODE Solutions. It is found that varying the lateral width of the grating can be used as an effective way to tune the coupling strength; narrow slots (100 nm and 300 nm) and wide ridge (2 μm-4 μm) promote the stability of grating coupling coefficient and device performance. It is important to note that the grating bottom should be fabricated precisely. The comparative study of carrier distribution and mode field distribution shows that the introduction of narrow slots can strengthen the competitive advantage and stability of the fundamental mode.     

拉伸载荷作用下单边缺陷-边裂纹应力强度因子研究

利用杂交位移不连续法研究拉伸载荷作用下矩形板中单边缺陷-边裂纹(半圆孔裂纹和半方孔裂纹)问题,给出了这三种平面弹性裂纹问题的应力强度因子的详细数值解。通过半圆孔裂纹问题和半方孔裂纹问题与单边裂纹问题的应力强度因子的比较,发现半圆孔和半方孔对单边裂纹有屏蔽影响。此外,本文的研究结果表明,杂交位移不连续法用于分析平面弹性有限体中复杂裂纹问题的应力强度因子简单且又准确。     

微量Co修饰的碳载超细Pt纳米粒子的制备及其在燃料电池氧还原催化中的应用

质子交换膜燃料电池(PEMFC)具有清洁、高效等优点,是一种理想的汽车动力电源.然而,由于其阴极氧还原反应(ORR)速率缓慢,需要使用大量的Pt基催化剂,导致燃料电池成本居高不下,严重制约了PEMFC的商业化发展.将Pt与过渡金属Fe, Co, Ni等形成合金,对表面Pt原子的几何结构和电子结构进行调变,可以有效提高催化剂的活性,实现Pt用量和燃料电池成本的降低.但是目前合金催化剂多采用溶剂热、浸渍-高温退火等制备方法,使用有毒有害试剂和难清洗的表面活性剂,且过程复杂、能耗高,不利于大规模化生产.此外,合金中过渡金属占比高,在燃料电池工况下,大量过渡金属溶解,加速了膜的降解,导致实际PEMFC性能的降低.对此,我们探索了一种简便有效的方法制备高活性、高稳定性的碳载Pt-Co催化剂.在没有添加表面活性剂的情况下,采用硼氢化钠辅助乙二醇还原法合成了具有超小尺寸和均匀分布的Pt-Co纳米颗粒,后续酸刻蚀处理去除不稳定的Co原子,重组双金属纳米颗粒的表面结构形成富Pt壳层,进一步提高了催化剂的活性和稳定性.通过电感耦合等离子体、X射线粉末衍射、透射电子显微镜、高分辨透射电子显微镜、高角环形暗场-扫描透射-元素分布及光电子能谱等物理表征证实了微量Co改性的碳载超细铂合金纳米颗粒的组成和结构.进一步对催化剂进行旋转圆盘电极和单电池测试,结果表明, Pt_(36)Co/C具有明显高于商业化Pt/C的有效电化学活性面积和电池性能.此外,加速衰减测试和衰减前后的电镜图片表明, Pt_(36)Co/C催化剂的稳定性相较于Pt/C亦有所增强.分析Pt-Co/C催化性能提高的原因,主要归于以下三点:(1)催化剂纳米颗粒在载体上分布均匀,且具有超小的粒径尺寸,提供了大量的三相反应界面位点;(2)双金属配体和电子效应的协同作用,降低了氧化物质在催化表面的吸附能力,加速了ORR的电催化动力学;(3)酸蚀刻导致的不稳定Co的溶解及催化剂表面结构的重排,形成了富Pt壳层结构,有利于提高催化剂的稳定性.这种简单有效的合金制备方法可以在电催化领域推广使用.     

Simultaneous measurement of SO2 and NO2 concentration using an optical fiber-based LP-DOAS system

SO2 and NO2 are the most important pollution in atmosphere.An optimized long path(LP)differential optical absorption spectroscopy(DOAS)system of high light intensity at an ultraviolet(UV)wavelength is proposed and used to measure the concentration of SO2 and NO2 simultaneously.In contrast to the traditional DOAS,the system adopted a Y-type optical fiber structure instead of a combination of mirrors in the telescope.The UV light intensity test shows that the light intensity of UV can arrive to above 80% of the max measuring range when the light path reaches 135 m,and the integral time of the spectrograph is only 15 ms.The system is proved to be efficacious through laboratory calibration.The maximum error of SO2 calibration is 4.19%,and is 5.22% for NO2.The error of the SO2 and NO2 mixture calibration is within 10%.Field measurement is implemented in a wastewater treatment plant in winter.The measurement light path is 738 m.The concentration of SO2 varies from 6μg/m^3(2.26 ppb)to 20μg/m^3(7.52 ppb),and the concentration of NO2varies from 100μg/m^3(53.2 ppb)to 200μg/m^3(106.4 ppb)approximately.The results are in accordance with the data from a monitoring station nearby in magnitude order and variation tendency mostly.     

纳米羟基磷灰石的合成方法研究进展

羟基磷灰石(Hydroxyapatite,HAP)是一种重要的生物、医药、重金属污染土壤/水体修复材料,本文总结了HAP的结构、组成、发展历程及应用,并从干法、湿法两个大方面系统总结了羟基磷灰石的合成方法及各种方法的优劣,对HAP合成方法的改进方向及应用前景进行了展望.     

基于Metop-B/GOME-2的TG-2/MAI可见光通道交叉定标

2016年9月15日发射的TG-2空间实验室上搭载的MAI是我国首个在轨运行的多角度偏振成像仪，主要用于获取云和气溶胶等大气环境信息。星载遥感仪器的定标是观测资料定量应用的关键前提且贯穿仪器的整个寿命期。MAI发射前已经进行了实验室定标，且精度较高。为了监测MAI发射后的在轨运行情况，针对其未配置在轨定标装置的问题，利用Metop-B/GOME-2可见光波段的高光谱分辨率和较高探测精度的优势，提出了基于GOME-2对MAI 565，670以及763 nm通道进行在轨监测及交叉定标的方法。该方法首先通过时空匹配、视线几何匹配等获取MAI与GOME-2相近时刻、相近视线几何条件下的同目标观测数据，再将GOME-2反射率按照MAI可见光通道光谱响应函数进行卷积，得到各通道的参考反射率，与MAI反射率进行对比分析，从而实现对MAI的定标。利用不同反照率特性目标的匹配观测数据，该方法能够实现仪器的高、中、低端观测的全覆盖定标。定标过程主要包括： (1)对2016年12月到2017年2月期间TG-2和Metop-B的运行轨道进行预报，获取二者交叉观测的整轨数据；设置观测时间差为900 s，初步匹配得到8组MAI与GOME-2交叉观测样例，包含2 455组匹配像元；(2)对匹配像元空间位置进行检验，保留单个GOME-2像元覆盖的MAI像元数超过338的交叉样本，以确保单个GOME-2像元尽可能被MAI观测充满；(3)给定GOME-2观测天顶角小于30°的限制条件，同时设置视线几何检验条件为两仪器观测天顶角余弦的比值接近于1，且相差不超过0.05，并充分利用MAI的多角度观测优势，对每一个MAI像元采用最多14个方向的视线几何进行匹配，从而选择最优的视线匹配方向；(4)设置观测目标均匀性检验条件为一个GOME-2像元覆盖的全部MAI像元反射率的标准差和均值之比小于0.5，对匹配像元进行检验，得到469个匹配的GOME-2像元。(5)将以上GOME-2像元对应的各个波长的反射率按照MAI可见光通道的光谱响应函数进行积分，即可得到MAI各通道对应的GOME-2参考反射率。(6)利用GOME-2像元空间分辨率显著大于MAI分辨率的特征，对每个GOME-2像元覆盖的全部MAI像元反射率进行平均作为MAI反射率，显著降低了定标结果对观测目标均匀性的依赖程度。(7)将GOME-2参考反射率与MAI反射率进行回归分析，得到定标系数，实现对MAI的在轨交叉定标。为了分析各匹配条件对定标结果的影响，利用单一变量法对像元匹配过程中各检验条件阈值进行调整并开展了分析试验。结果表明，当进一步严格匹配筛选条件时，定标结果不会产生显著变化。基于该方法对MAI三个通道反射率和GOME-2参考反射率进行对比分析，结果表明二者之间存在显著地线性关系，且相关系数均优于0.97，对比差异的均值分别为1.6%，4.2%和2.3%，标准差分别为3.1%，4.1%和2.4%。总体来看，利用在轨交叉定标方法能够实现MAI可见光波段的在轨监测及定标，为MAI数据的定量应用奠定了基础。     

Alignment and efficiency-monitoring method of high-power fiber-to-fiber coupling

High-power fiber-to-fiber coupling is extensively used in fiber laser applications,and its performance is determined by coupling efficiency.We demonstrate a novel method for alignment and monitoring efficiency by detecting backscattering power at the fiber end cap.The relationship between alignment error and backscattering power is determined by simulations and experiments.Through this method,a state-of-the-art kW-level fiberto-fiber optic switch is developed(transmission efficiency>97%).It performs well for longer than 60 min.To the best of our knowledge,it is the first time to establish the mathematical model based on this method.Our results can provide guidance in high-power fiber-to-fiber coupling.     

基于吸收互补有机半导体本体复合薄膜的高性能柔性光突触晶体管

采用光吸收互补的聚(3-己基噻吩)(P3HT)和引达省并二噻吩-苯并噻二唑共聚物(PIDT-BT), 通过溶液法制备了两者的本体复合异质结构有机半导体薄膜, 并研究了薄膜的表面结构和光电性质. 将PIDT-BT:P3HT复合薄膜作为一类新型光敏沟道层, 与聚电解质介电材料相结合, 制备了高性能柔性低电压光突触晶体管. 考察了不同光刺激条件对光突触晶体管性能的影响及半导体机制, 发现PIDT-BT:P3HT器件具有明显光突触特性, 并且相较于单纯PIDT-BT或P3HT器件具有更高响应的兴奋性突触后电流. 基于PIDT-BT:P3HT薄膜的光突触器件, 在绿红双色光刺激下的响应大于两种单色光分别刺激的响应之和, 表明附加光刺激可调控器件的记忆效率. 该研究为发展高性能光响应半导体薄膜及柔性低功耗光突触器件提供了新策略.     

GaAs基980 nm高功率半导体激光器的研究进展

GaAs基980 nm半导体激光器在材料加工、通信和医疗等领域有着重要应用。应变量子阱结构的出现提高了GaAs基半导体激光器的转换效率、输出功率和可靠性。本文综述了高功率GaAs基量子阱激光器历史发展,介绍了高功率半导体激光器的外延结构、芯片结构和封装结构设计,重点阐述了影响高功率GaAs基量子阱激光器光电性能、散热和实际应用的问题。针对以上问题讨论了相应解决方案及研究成果,并指出了各个方案的不足之处和改进方向。最后,总结了高功率半导体激光器的发展现状,对高功率半导体激光器发展方向进行了展望。     

Research progress of Pt and Pt-based cathode electrocatalysts for proton-exchange membrane fuel cells

Proton-exchange membrane fuel cells (PEMFCs) have been widely used commercially to solve the energy crisis and environmental pollution. The oxygen reduction reaction (ORR) at the cathode is the rate-determining step in PEMFCs. Platinum (Pt) catalysts are used to accelerate the ORR kinetics. Pt's scarcity, high cost, and instability in an acidic environment at high potentials seriously hinder the commercialization of PEMFCs. Therefore, studies should explore electrocatalysts with high catalytic activity, enhanced stability, and low-Pt loading. This review briefly introduces the research progress on Pt and Pt-based ORR electrocatalysts for PEMFCs, including anticorrosion catalyst supports, Pt, and Pt-based alloy electrocatalysts. Advanced preparation technology and material characterization of Pt-based ORR electrocatalysts are necessary to improve the performance and corresponding reaction mechanisms.