全光纤量子通信系统中的高速偏振控制方案

偏振控制在光通信中是至关重要的技术, 关系着通信系统的稳定性和误码率. 本文提出一种基于双向Sagnac环工作方式的全光纤高速偏振控制方案, 通过调节环中一个光纤电光相位调制器的相位差而精确控制光场偏振方向, 并且实现了单个端口输出各种偏振态, 无需后续耦合操作. 相位控制精度为10^-3 rad, 最大消光比可达30 dB, 工作速率可达2 GHz. 由于本方案的精度、调制速度和稳定性都很高, 并采用了器件简单、成本低廉的全光纤光路, 易于集成, 在量子保密通信等光通信领域中有很好的应用前景. 关键词： 光纤偏振控制器 Sagnac环 量子通信     

Self-Reinforced High-Density Polyethylene Prepared by Low Frequency Vibration-Assisted Injection Molding. II: Microstructure Investigation

Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and wide angle X-ray diffraction (WAXD) were employed to study the microstructure of self-reinforced high-density polyethylene (HDPE) prepared by conventional injection molding (CIM) and a low frequency vibration-assisted injection molding (VAIM). SEM micrographs following permanganic etching showed the self-reinforcement of HDPE is mainly due to the existence of shish-kebab morphology within the core region for VAIM-processed HDPE samples. Pronounced molecular alignment was identified by the WAXD data. An approximate 9% increase in the crystallinity was confirmed by DSC. Both preferred molecular orientation and increased crystallinity serve to yield stronger VAIM-processed injection moldings.     

Essential Work of Fracture Parameters of Injection-Molded Polypropylene/Polyolefin Elastomer Blends

The influence of polyolefin elastomer (POE) content on the fracture behavior of injection-molded polypropylene (PP)/POE blends was evaluated by means of the essential work of fracture (EWF) method. The results indicated that the EWF approach worked well for the PP/POE blends when POE content was 0～7.5 wt% of the blends. The specific essential work of fracture (w _e) increased with increasing POE content, and the dominant factor that affected w _e was the necking and subsequent fracture process. The specific nonessential work of fracture (βw _p) slightly decreased with increasing POE content, while the specific plastic work (w _p) showed an increasing trend with the decrease of the shape factor (β) of the specimen. Finally, it was shown that w _e could be predicted reasonably well via the COD values.     

Dynamic mechanical and morphological studies of homopolymer/block copolymer blends

A triblock copolymer of styrene-butadiene-styrene (SBS) was blended with a high and a low molecular weight polybutadiene [designated as PB(H) and PB(L), respectively]. Electron micrographs of these blends show that PB(L) was solubilized into the butadiene domains of the SBS, while PB(H) was present in a separate phase. Dynamic mechanical data of the SBS&PB(L) blends indicate the presence of an intermediate loss peak between those of the glass transitions of the styrene and butadiene blocks in SBS, which can be attributed to the slippage of untrapped entanglements of PB(L) chains. Similar data for blends containing PB(H) also show an intermediate loss peak, which is, however, due to crystallization and melting of the polycisbutadiene chains. The peak due to the primary glass transition of the butadiene phase was shifted to lower temperatures upon incorporation of PB(L) as a result of plasticization effect of PB(L). The same transition for PB(H) blends is split into a doublet because of the presence of the homopolymer in a separate phase. Dynamic mechanical data for cross-linked blends were also taken for comparison.     

ZnO nanowire array ultraviolet photodetectors with self-powered properties

A ZnO nanowire (NW) array ultraviolet photodetector (PD) with Pt Schottky contacts has been fabricated on a glass substrate. Under UV light illumination, this PD showed a high photo-to-dark current ratio of 892 at 30 V bias. Interestingly, it was also found that this PD had a high sensitivity of 475 without external bias. This phenomenon could be explained by the asymmetric Schottky barrier height (SBH) at the two ends causing different separation efficiency of photogenerated electron–hole pairs, which resulted in the formation of photocurrent. It is anticipated to have potential applications in self-powered UV detection field.     

广义流体动力学守恒方程组的弱解的存在性和唯一性问题

本文讨论了非定常广义流体动力学方程组在大尺度情况下平均流动参数所应满足的条件,提出了相应的假设,证明了大尺度平均流动参数弱解的存在性和唯一性。     

On the Volume of Unit Tangent Spheres in a Pinsler Manifold

Motivated by some issues which enter into the Gauss-Bonnet-Chern theorem in Finsler geometry, this paper studies the unit tangent sphere (or indicatrix) I_x M at each point x of a Pinsler manifold M. We demonstrate that the volume of I_mM, calculated with respect to a Riemannian metric induced naturally by the Finsler structure, is in general a function of x. This contrasts sharply with the situation in Riemannian geometry. We also express the derivative of such volume function in terms of the second curvature tensor of the Chern connection. In particular, we find that this function is constant on Landsberg spaces (though that constant need not be equal to the value taken by Riemannian manifolds).     

快速发光二极管的性能与分析

本文叙述了用于光通信快速、高辐射度GaAs/GaAlAs双异质结发光管的性能.其电带宽大于60MHz,光带宽在100MHz以上.在200mA辐射度为1017W/cm2·sr.尾纤输出超过160μw(NA=0.2).分析和讨论了影响辐射输出和调制能力的诸因素,并选取了最佳折衷方案.     

CaPtAs: A new noncentrosymmetric superconductor

We report the discovery of a new noncentrosymmetric superconductor CaPtAs.It crystallizes in a tetragonal structure(space group I41md,No.109),featuring three dimensional honeycomb networks of Pt-As and a much elongated c-axis(a=b=4.18?,and c=43.70?).The superconductivity of CaPtAs with Tc=1.47 K was characterized by means of electrical resistivity,specific heat,and ac magnetic susceptibility.The electronic specific heat Ce(T)/T shows evidence for a deviation from the behavior of a conventional BCS superconductor,and can be reasonably fitted by a p-wave model.The upper critical fieldμ0Hc2 of CaPtAs exhibits a moderate anisotropy,with an in-plane value of around 204 mT and an out-of-plane value of 148 mT.Density functional theory calculations indicate that the Pt-5 d and As-4 p orbitals mainly contribute to the density of states near the Fermi level,showing that the Pt-As honeycomb networks may significantly influence the superconducting properties.