Analysis of Bragg reflection waveguides with finite cladding: An accurate matrix method formulation

Ideal Bragg reflection waveguides (BRWs) are assumed to have an infinitely extended periodic cladding whereas in practice, the cladding of BRWs is of a finite extent. Bloch theorem is widely used to analyze the propagation characteristics of the BRWs. Since Bloch theorem is ideally valid only for an infinitely extended periodic medium, its application to study such BRWs is an approximation. We present a matrix method for a more accurate analysis of finite-clad BRWs and estimate the extent of errors involved in the values of the propagation constant obtained by the Bloch wave formalism. The proposed method can be used to obtain the mode effective indices as well as the radiation loss of a finite-clad BRW without resorting to solving any complex transcendental equation. In addition, since the method does not inherently assume a periodic cladding, it can also be used to analyze symmetric multi-channel BRWs, chirped structures and directional couplers.     

Husimi Operator for Describing Probability Distribution of Electron States in Uniform Magnetic Field Studied by Virtue of Entangled State Representation

For the first time we introduce an operator Δ _h (γ,ε;κ) for studying Husimi distribution function in phase space (γ,ε) for electron’s states in uniform magnetic field, where κ is the Gaussian spatial width parameter. The marginal distributions of the Husimi function are Gaussian-broadened version of the Wigner marginal distributions. Using the Wigner operator in the entangled state 〈λ | representation we find that Δ _h (γ,ε;κ) is just a pure squeezed coherent state density operator | γ,ε〉 _{κ κ} 〈γ,ε |, which brings much convenience for studying Husimi distribution, so we name Δ _h (γ,ε;κ) the Husimi operator. We then derive Husimi operator’s normally ordered form that provides us with an operator version to examine various properties of the Husimi distribution. Work supported by the National Natural Science Foundation under the grant: 10775097.     

扶手椅型石墨烯介观环中的持续电流

在紧束缚近似下, 解析求解了扶手椅型边界石墨烯介观环的能量本征值问题, 计算和讨论了不同大小尺寸的介观环中持续电流随Aharonov-Bohm (A-B)磁通的变化, 并证明了能级和持续电流关于磁通变化的周期性和特殊对称性. 研究表明, 持续电流显著地依赖于介观环的几何结构; 零能量附近的能级可以承载较大的持续电流, 而远离零能量的其他能级对持续电流的贡献很小.     

Bounds on the Mass for the High Dimensional Gaussian Lattice Field between Two Hard Walls

We consider the d(≥3)-dimensional Gaussian lattice field confined between two hard walls. We show that the field becomes massive and identify the precise asymptotic behavior of the mass and the variance of the field as the height of the wall goes to infinity.     

结合NSDTCT和稀疏表示的遥感图像融合

为了提高全色图像与多光谱图像的融合质量,提出一种基于非下采样双树复轮廓波变换和稀疏表示的图像融合算法.对多光谱图像进行亮度-色度-饱和度变换,再对亮度分量和全色图像进行直方图匹配及亮度平滑滤波处理.利用非下采样双树复轮廓波变换处理亮度分量和全色图像,得到对应的高低频系数.对于低频系数,利用稀疏表示进行融合,采用空间频率和l1范数双指标取大的融合规则得到稀疏表示系数;对于高频系数,将改进的拉普拉斯能量和作为脉冲耦合神经网络的外部输入项,提出了改进的脉冲耦合神经网络的融合策略.最后进行非下采样双树复轮廓波逆变换和亮度-色度-饱和度逆变换得到融合结果.实验结果表明,该算法最大限度地保留光谱信息的同时可以提高空间分辨率,视觉效果及客观指标均优于经典的融合算法.     

Non‐centrosymmetric plasmonic crystals for second‐harmonic generation with controlled anisotropy and enhancement

Rectangular arrays of pyramidal recesses coated by silver film are investigated by means of polarization‐resolved nonlinear microscopy at 900 nm fundamental wavelength, demonstrating strong dependence of the dipole‐allowed SHG upon the lattice parameters. The plasmonic band gap causes nearly complete SHG suppression in arrays of 650 nm periodicity, whereas a sharp resonance at 550 nm periodicity is observed due to excitation of band edge Bloch states at fundamental frequency, accompanied by symmetry‐constrained interactions with similar modes at the second‐harmonic frequency. Additionally, coupling with modes at the bottom side of the silver film may lead to extraordinary optical transmission, opening a channel for SHG from the highly nonlinear GaAs substrate. Changing the lattice geometry enables SHG intensity modulation over three orders of magnitude, while the effective nonlinear anisotropy can be continuously switched between the two lattice directions, reaching values as high as ±0.96.

     

基于半监督稀疏多流形嵌入的高光谱影像分类

提出了一种半监督稀疏多流形嵌入方法,并应用于高光谱影像分类.该方法充分利用少量标记和大量无标记样本,采用稀疏表示方法得到样本的稀疏系数,并选取来自同一流形的点作为近邻点,然后构建相似图来表征多流形结构,得到样本在每个流形上低维鉴别特征,增加来自同一流形的数据点聚集性,进而提升分类性能.本文方法在PaviaU和Salinas两个高光谱数据集上的总体分类准确度分别达到84.91%和89.74%,相较于其他方法明显提高了地物分类性能.     

New two-mode intermediate momentum-coordinate representation with quantum entanglement and its application

We construct four linear composite operators for a two-particle system and give common eigenvectors of those operators. The technique of integration within an ordered product (IWOP) of operators is employed to prove that those common eigenvectors are complete and orthonormal. Therefore, a new two-mode intermediate momentum-coordinate representation which involves quantum entanglement for a two-particle system is proposed and applied to some two-body dynamic problems. Moreover, the pure-state density matrix | ξ ₁ ,ξ ₂ >_C,DC,D< ξ ₁ ,ξ ₂ | is a Radon transform of Wigner operator.