掺铒聚合物光波导放大器的数值分析

针对掺铒聚合物光波导放大器(EDWA),提出了一种基于Douglas离散格式改进的有限差光束传播法(FD-BPM)的数值计算方法。对每一传输步长结合多能级速率方程计算出EDWA中光场传输强度分布,及掺铒光波导放大器的增益传输特性。设计并研究了掺铒聚合物通道波导和Y形分束器的放大增益特性。在掺铒聚合物直波导中,Er3 浓度为9.0×1025ions·m-3,输入信号和泵浦光功率分别为1μW和2mW,其增益为1.6dB/cm;在掺铒聚合物Y形分束器中,输出信号光分束比相等,并能实现无损耗分束。     

On the Boundary Control of a Hybrid System with Variable Coefficients

A model of the spacecraft control laboratory experiment with variable coefficients is considered. It is shown that the closed-loop system under boundary feedback damping has a sequence of generalized eigenfunctions, which form a Riesz basis for the state Hilbert space. The spectrum-determined growth condition, the exponential stability, and an asymptotic expression of the spectrum are obtained. Moreover, the exact controllability and exact observability of the system are also presented.     

Splitting of an edge dislocation by an optical vortex

In a linear medium an optical vortex induces the splitting of an edge dislocation into vortices of both topological charges. Their positions and number depend on which of the phase dislocations is shifted from the center of the host beam. Violations of the charge conservation law are discussed.     

Bandgap engineering of self-assembled InAs quantum dots with a thin AlAs barrier

We investigate the effects of a thin AlAs layer with different position and thickness on the optical properties of InAs quantum dots (QDs) by using transmission electron microscopy and photoluminescence (PL). The energy level shift of InAs QD samples is observed by introducing the thin AlAs layer without any significant loss of the QD qualities. The emission peak from InAs QDs directly grown on the 4 monolayer (ML) AlAs layer is blueshifted from that of reference sample by 219 meV with a little increase in FWHM from 42–47 meV for ground state. In contrast, InAs QDs grown under the 4 ML AlAs layer have PL peak a little redshifted to lower energy by 17 meV. This result is related to the interdiffusion of Al atom at the InAs QDs caused by the annealing effect during growing of InAs QDs on AlAs layer.     

Effect of Comatic Aberration on the Propagation Characteristics of Laguerre--Gaussian Beams

Seidel comatic aberration is an important cause of deformation for a Laguerre--Gaussian (LG) beam. In addition, mono-axial comatic aberration, whose phase modulation depends only on one transverse coordinate, is also an important cause of beam deformation. Deformation of an LG beam by such aberrations is analyzed through numerical simulation based on the angular spectrum method. It is also shown that for holographically generated LG beams quadratic spatial variation of grating pitch can produce seidel and mono-axial comatic aberrations. An example of an experimentally generated LG beam with mono-axial comatic aberration is reported.     

Second-Harmonic Generation in Domain-Inverted Grating Induced by Focused Ion Beam

The fabrication of a periodic domain inversion in LiTaO₃ and LiNbO₃ using direct ion-beam writing is presented. The polarization of these materials can be reversed at room temperature by irradiating Si²⁺ ions into +c faces. A first-order periodic domain inversion with a 50% duty cycle, a depth of 300μ, and an interaction length of 1 mm was realized in LiTaO₃. Using this structure, 300μW of blue light was generated for a conversion efficiency of 0.25%/W.     

Surface reconstructions and phase transitions on the GaAs(111)B surface

The (111)B surface of GaAs has been investigated using scanning tunneling microscopy (STM) and a number of different reconstructions have been found at different surface stoichiometries. In accordance with electron diffraction studies, we find the series (2 × 2), (1 × 1)_LT, ( ) and (1 × 1)_HT with increasing annealing temperature, corresponding to decreasing surface As concentration. The (1 × 1)_LT is of particular interest, since it only occurs in a narrow temperature window between the two more established reconstructions, the (2 × 2) and the ( ). We find the (1 × 1)_LT to take the form of a mixture of the local structures of both the (2 × 2) and ( ) phases, rather than having a distinct structure. This is behaviour consistent with a kinetically limited system, dominated by the supply of As adatoms to the surface, and may be an example of a continuous phase transition. Above the (1 × 1)_LT transition, atomic resolution images of the ( ) surface reveal only a three-fold symmetry of the hexagonal structural units, brought about by inequivalent surface bonding due to the 23.4° rotation of the surface unit cell relative to the substrate. This is responsible for the disorder found in the ( ) reconstruction, since the structure may form in one of two domains. At lower surface As concentration, the (1 × 1)_HT surface adopts a structure combining small domains of a 19.1° structure and random disorder. There is no apparent similarity between the (1 × 1)_LT and (1 × 1)_HT structures, which may be due to our measurements being conducted at room temperature and without an As flux to control the surface As concentration.     

Properties of GaAs single crystals grown by molecular beam epitaxy at low temperatures

Properties of GaAs single crystals grown at low temperatures by molecular beam epitaxy (LTMBE GaAs) have been studied. The results show that excessive arsenic atoms of about 10²⁰ cm⁻³ exist in LTMBE GaAs in the form of arsenic interstitial couples, and cause the dilation in lattice parameter of LTMBE GaAs. The arsenic interstitial couples will be decomposed, and the excessive arsenic atoms will precipitate during the annealing above 300°C. Arsenic precipitates accumulate in the junctions of epilayers with the increase in the temperature of annealing. The depletion regions caused by arsenic precipitates overlap each other in LTMBE GaAs, taking on the character of high resistivity, and the effects of backgating or sidegating are effectively restrained.     

空心楼板在吕梁体校训练馆的应用

从结构形式和经济比较方面，探讨了在框架结构中采用空心楼板代替井字梁的实用性和经济性。     

轴向受载铁木辛柯梁的弯曲研究

轴向受载的铁木辛柯梁的弯曲问题.在新近提出的一种铁木辛柯梁模型中,引入了一个反映变形过程中轴力方向的跃迁系数,基于此模型,解析地获得了多种边界条件下梁挠度的封闭形式的表达式.此外,采用数值计算验证当前结果的正确性,并探讨了跃迁系数对梁弯曲行为的影响.